Irritator

Irritator is a genus of spinosaurid dinosaur that lived in what is now Brazil during the Albian stage of the Early Cretaceous Period, about 113 to 110 million years ago. It is known from a nearly complete skull found in the Romualdo Formation of the Araripe Basin. Fossil dealers had acquired this skull and sold it to the State Museum of Natural History Stuttgart. In 1996, the specimen became the holotype of the type species Irritator challengeri. The genus name comes from the word "irritation", reflecting the feelings of paleontologists who found the skull had been heavily damaged and altered by the collectors. The species name is a homage to the fictional character Professor Challenger from Arthur Conan Doyle's novels.

Some paleontologists regard Angaturama limai—known from a snout tip that was described later in 1996—as a potential junior synonym of Irritator. Both animals hail from the same stratigraphic units of the Araripe Basin. It was also previously proposed that Irritator and Angaturama's skull parts belonged to the same specimen. Although this has been cast into doubt, more overlapping fossil material is needed to confirm whether they are the same animal or not. Other spinosaurid skeletal material, some of which could belong to Irritator or Angaturama, was retrieved from the Romualdo Formation, allowing for a replica skeleton to be made and mounted for display at the National Museum of Rio de Janeiro in 2009.

Estimated at between 6 and 8 meters (20 and 26 ft) in length, Irritator weighed around 1 tonne (1.1 short tons), making it one of the smallest spinosaurids known. Its long, shallow and slender snout was lined with straight and unserrated conical teeth. Lengthwise atop the head ran a thin sagittal crest, to which powerful neck muscles were likely anchored. The nostrils were positioned far back from the tip of the snout, and a rigid secondary palate on the roof of the mouth would have strengthened the jaw when feeding. Belonging to a subadult, Irritator challengeri's holotype remains the most completely preserved spinosaurid skull yet found. The Angaturama snout tip expanded to the sides in a rosette-like shape, bearing long teeth and an unusually tall crest. One possible skeleton indicates it, like other spinosaurids, had enlarged first-finger claws and a sail running down its back.

Irritator had been mistaken initially for a pterosaur, and later a maniraptoran dinosaur. In 1996, the animal was identified as a spinosaurid theropod. The holotype skull was thoroughly prepared before being redescribed in 2002, confirming this classification. Both Irritator and Angaturama belong to the Spinosaurinae subfamily. A generalist diet—like that of today's crocodilians—has been suggested; Irritator might have preyed mainly on fish and any other small prey animals it could catch. Fossil evidence is known of an individual that ate a pterosaur, either from hunting or scavenging it. Irritator may have had semiaquatic habits, and inhabited the tropical environment of a coastal lagoon surrounded by dry regions. It coexisted with other carnivorous theropods as well as turtles, crocodyliforms, and a large number of pterosaur and fish species.

## History of research

The holotype of Irritator was excavated from a chalk concretion containing the rear of a large skull with lower jaws near the town of Santana do Cariri in northeastern Brazil. This fossil was acquired by dealers who sold it to Rupert Wild of the State Museum of Natural History Stuttgart, Germany. At the time it was assumed to be the skull of a giant basal pterosaur, or flying reptile, since the Chapada do Araripe region is famous for its copious pterosaur finds, and the German museum often bought such pieces. As it promised to be a unique discovery of singular importance, German and British pterosaur experts were contacted to study the exemplar. A paper describing it as a pterosaur had already been submitted for publication when the authors, German paleontologist Eberhard Frey and British paleontologist David Martill, were disabused of this notion by the peer reviewers, who suggested the fossil belonged to a theropod dinosaur.

The skull was flattened sideways somewhat and, as is common with fossils, was partly crushed. The right side was well preserved, while the left was extensively damaged during collection. Some of the skull's hindmost upper surface had eroded, and the lower jaw lacked its front end, both owing to breakage during fossilization. Parts of the specimen were also cracked due to being part of a septarian concretion. The tip of the upper jaw was also missing. Since there were no signs of erosion, it had most probably broken off during or after the fossil's collection. Evident corrosion on certain bones indicates acid preparation had been attempted. A vertical fracture was present across the middle of the skull, which had apparently been sealed with car body filler. In hopes of making it look more complete and valuable, the fossil traders had severely obscured the skull beneath plaster; a widespread practice among local collectors in the Chapada do Araripe, especially on fish fossils. The buyers were unaware of the modifications to the specimen until it was sent to universities in the United Kingdom for CT scan imaging. This revealed the collectors had tried to reconstruct the skull by grafting parts of the maxilla (main upper jaw bone) onto the front of the rostrum (snout). The skull (designated SMNS 58022) became the holotype specimen of the new genus and species Irritator challengeri in February 1996, when it was first scientifically described by paleontologists David M. Martill, Arthur R.I. Cruickshank, Eberhard Frey, Philip G. Small and Maria Clarke. In this paper, Martill and his team wrote that the generic name Irritator came "from irritation, the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated." The type species, Irritator challengeri, was named after Professor Challenger, a character in Arthur Conan Doyle's novels, specifically The Lost World. Two years earlier, Frey and Martill had named a new pterosaur species from the Crato Formation Arthurdactylus conandoylei, after the novelist himself.

When Martill and colleagues first described Irritator challengeri, the holotype was still extensively encased in calcareous rock matrix. Under the supervision of American paleontologist Hans-Dieter Sues, technician Diane M. Scott from the University of Toronto at Mississauga assumed the task of fully extracting the skull bones from the rock, allowing for a detailed redescription in 2002. Published by Sues, Frey, Martill, and Scott, this inspection of the now fully prepared specimen negated many of Martill and colleagues' original observations, which were based on misinterpretations of the damaged and largely concealed skull. The estimated length of the complete skull was 24 cm (9.4 in) shorter than previously proposed. What was originally thought to be a prominent head crest proved to be an unattached, indeterminate bone fragment. As in the previous study, Sues and colleagues regarded the African genus Spinosaurus as the most similar taxon to Irritator, because they shared many dental features, including mostly straight conical tooth crowns, thin enamel, well-defined edges with no serrations, and lengthwise fluting. Since little was known of Spinosaurus's skull at the time, these similarities were enough for the authors to suggest a possible junior synonymy of Irritator with Spinosaurus. Sues and colleagues noted that more overlapping skull material was needed for further diagnosis. As more of Spinosaurus's skull became known, later research maintained separation of the two taxa.

Although the site of discovery is uncertain, the specimen most probably stems from the Romualdo Formation (previously designated the Romualdo Member of the then Santana Formation). This assignment was confirmed by microfossils of the ostracod Pattersoncypris, and fish scales from the ichthyodectid Cladocyclus, both found in the Romualdo Formation. Questioning of local fossil dealers hinted at a locality near the village of Buxexé close to Santana Do Cariri at the flank of the Chapada do Araripe, at a height of approximately 650 meters (2,130 ft). Since the Romualdo Formation is indeed exposed there, and the matrix encasing the holotype has the same color and texture as those rocks, this locality can be regarded as the probable site of the discovery of the fossil. Irritator challengeri was the first dinosaur described from the Romualdo Formation, and its holotype specimen represents the most completely preserved spinosaurid skull known.

### Synonymy with Angaturama

Angaturama limai, another spinosaurid from the same time and place as Irritator challengeri, was described by the Brazilian paleontologists Alexander W. A. Kellner and Diogenes de Almeida Campos in February 1996. Kept today under specimen number USP GP/2T-5 at the University of São Paulo, the holotype specimen consists of an isolated snout tip from the Romualdo Formation. It was extracted from a calcareous nodule using a technique originally developed for pterosaur fossils. The generic name is in reference to Angaturama, a protective spirit in the aboriginal Tupi Indian culture of Brazil. The specific name honors the late Brazilian paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991.

In 1997, British paleontologists Alan J. Charig and Angela C. Milner considered Angaturama a likely junior synonym of Irritator, noting that both genera had retracted nostrils, long jaws, and characteristic spinosaurid dentition. Paul Sereno and colleagues in 1998 agreed with this possibility, and additionally observed that the holotype of Angaturama seems to complete that of Irritator (meaning that they could belong to the same specimen). Authors including Éric Buffetaut and Mohamed Ouaja in 2002, Cristiano Dal Sasso and colleagues in 2005, Tor G. Bertin in 2010, Darren Naish in 2013, and Madani Benyoucef and colleagues in 2015 supported this conclusion. In their redescription of Irritator, Sues and colleagues pointed out that both holotypes are equally as narrow, and share transversely round teeth with defined yet unserrated edges. They also noted that a sagittal crest on Angaturama's premaxillae may correspond with that of Irritator's nasal bones. Some objection has been raised to these assertions. Kellner and Campos in 2000 and Brazilian paleontologist Elaine B. Machado and Kellner in 2005 expressed the opinion that the fossils come from two different genera, and that the holotype of Angaturama limai was clearly more laterally flattened than that of Irritator challengeri.

A review of both fossils by the Brazilian paleontologists Marcos A. F. Sales and Cesar L. Schultz in 2017 noted that the specimens also differ in other aspects of their preservation: the Irritator specimen is brighter in color and is affected by a vertical crack, while the Angaturama specimen bears many cavities; the damage to the teeth of the Irritator challengeri holotype is also much less severe. Sales and Schultz also identified a possible point of overlap, the third left maxillary tooth, and observed that the skull of Angaturama could have been larger than that of Irritator based on the proportions of the closely related genus Baryonyx. They therefore concluded that the two specimens do not belong to the same individual, Sales and Schultz noted that synonymy at the genus level would need to be verified by more extensively overlapping remains. If Angaturama and Irritator are regarded as a member of the same genus, the latter would be the valid scientific name under rules of priority, since it was named almost a month earlier. The paleontologist Marco Schade and colleagues could not confirm the overlap in tooth positions in 2023 due to interpreting them differently, and could not provide information to resolve the issue.

### Postcranial material and additional finds

Besides the skull, the snout fragment, and some isolated teeth, the Romualdo Formation has also yielded postcranial remains that may belong to spinosaurids, many of which are hitherto undescribed, and all of them pertaining to the Spinosaurinae subfamily. In 2004, parts of a spinal column (MN 4743-V) were unearthed at the formation. Brazilian paleontologist Jonathas Bittencourt and Kellner assigned these, due to their structure, to the Spinosauridae. It is uncertain whether this specimen can be referred to Irritator or Angaturama, given that both are based only on skull material. In 2007, Machado and Kellner tentatively referred a rib fragment (MN 7021-V) to the Spinosauridae. However, the most complete spinosaur specimen retrieved from the Romualdo Formation is MN 4819-V, a partial skeleton lacking the skull. First reported in 1991, the specimen was referred by Kellner to the Spinosauridae in 2001 because of its tall sacral neural spines and the enlarged condition of the hand claw. The skeleton was fully described in 2010 in an as-of-yet unpublished master's thesis by Machado. An incomplete hind limb (MPSC R-2089) mentioned in 2013 might also pertain to the Spinosauridae. In 2018, Tito Aureliano and his team described LPP-PV-0042, part of a left tibia from a particularly large individual. As is common with fossils from the Araripe Basin, the majority of spinosaurid material from the Romualdo Formation was collected under uncontrolled circumstances for use in the illegal fossil trade. As such, many specimens are partly damaged and without precise geological field data.

Some of the Romualdo Formation postcrania were used as the basis for the creation of a replica Angaturama skeleton, later mounted at the Federal University-owned Museu Nacional do Rio de Janeiro (National Museum of Rio de Janeiro). The skeleton depicted the animal carrying an anhanguerid pterosaur in its jaws. It was the centerpiece of the Dinossauros no Sertão (Dinosaurs of Sertão) exhibit, which opened to the public in March 2009, becoming the first large carnivorous Brazilian dinosaur to be put on display. Some of the original postcranial elements (including the fossil pelvis and sacral vertebrae) were presented alongside the mount. In press releases of the exhibit's opening, Kellner informally implied MN 4819-V as belonging to Angaturama. This is also reflected in the specimen's inclusion in the skeletal mount. In 2011, a third Brazilian spinosaur, Oxalaia quilombensis, was named and described from the Alcântara Formation of the Itapecuru Group, part of the São Luís Basin. This larger species, known only from an isolated snout tip and upper jaw fragment, lived during the Cenomanian stage, around six to nine million years after Irritator and Angaturama. Oxalaia quilombensis is differentiated from Angaturama limai by its broader, more rounded snout and lack of a sagittal crest on the premaxillae. In September 2018, a fire broke out at the palace housing the Museu Nacional, largely destroying the fossil collections and possibly the exhibited Angaturama skeleton and fossil elements. The holotype of Oxalaia quilombensis, which was stored in the same building, may also have been destroyed.

## Description

Even by maximal size estimates, Irritator was smaller than other known spinosaurids. Gregory S. Paul calculated its length at 7.5 meters (25 ft) and weight at 1 tonne (1.1 short tons). Thomas R. Holtz Jr. published a higher estimate of 8 meters (26 ft), with a weight between 0.9 to 3.6 tonnes (0.99 to 3.97 short tons). Estimates by Dougal Dixon were lower at 6 meters (20 ft) long and 2 meters (6.6 ft) high. When scaled by Aureliano and colleagues, the reconstructions from the study by Sales and Schultz provided a length of 6.5 meters (21 ft) for the Irritator challengeri holotype, and 8.3 meters (27 ft) for the Angaturama limai holotype. Some of the skull bones of the former holotype had not yet fully co-ossified (fused), indicating that the specimen belonged to a subadult. The partial spinosaurine skeleton MN 4819-V represented a moderately sized individual, estimated by Machado at 5 to 6 meters (16 to 20 ft) in length. Many elements from this specimen were incorporated into the skeletal mount in the National Museum of Rio de Janeiro, which had a length of 6 meters (20 ft) and a height of 2 meters (6.6 ft). However, spinosaurids from the Romualdo Formation possibly attained greater sizes. Although LPP-PV-0042 is represented only by a tibia fragment, Aureliano and colleagues estimated its length at roughly 10 meters (33 ft). Bone histology indicates that this individual was a subadult, so the mature animal may have been larger.

### Anatomy of the Irritator challengeri holotype

The holotype skull of Irritator challengeri, although heavily damaged in certain places, is largely complete; missing only the tip of the snout and the front of the mandible. The preserved skull is 16.5 cm (6.5 in) tall and 10 cm (3.9 in) wide, its full length has been estimated at 60 cm (24 in), based on comparisons with Baryonyx. Irritator's skull was long, narrow, and somewhat triangular in cross section. The braincase was inclined backwards, and deeper than it was long. Extending from it was an elongate and low snout, with both sides relatively flat and slightly angled towards the skull midline. Only the rear ends of the paired premaxillae (frontmost snout bones) remain intact, forming the front upper and lower borders of the external nares (bony nostrils). As in all spinosaurids, the maxillae (main upper jaw bones) extended below and past the nostrils in a long, low branch that formed the lower border of this opening, consequently separating the premaxillae and nasal bones in that location. Irritator's maxillary sinuses (located in the body of the maxillae) bore a large oval opening, as in Allosaurus. The nostril openings were oval and, as in all spinosaurids, positioned farther back on the skull than in typical theropods. Irritator's nostrils were both proportionately and absolutely smaller than in Suchomimus and Baryonyx, but larger than those of Spinosaurus. The opening behind the orbit (eye socket), the lateral temporal fenestra, was very large, while the antorbital fenestra, in front of the eyes, was long and elliptical. The orbit itself was deep and wider at the top (where the eyeball was placed) than the bottom. The lacrimal bone separated the orbit from the antorbital fenestra, forming the upper and lower rear margins of the latter with two processes that enclosed a 40-degree angle; similar to Baryonyx, where it enclosed 35 degrees. Unlike in Baryonyx, Irritator's lacrimal did not form a bony horn core. The prefrontal bones were large and sturdy, while the thinner frontal bones, situated behind them, were smooth and concave on top; both of these bones formed the upper rim of the orbit.

A thin sagittal crest, constructed from the elongate nasal bones, extended along the skull midline before stopping just above the eye in a slightly flattened bulge. Although the complete shape and height of this structure is unknown in Irritator, these head crests were commonplace in spinosaurids, having possibly served a display function when the animal was alive. The preserved part of Irritator's crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of Spinosaurus. Like others in its family, Irritator possessed a long and bony structure on the roof of its mouth called a secondary palate, separating the oral from the nasal cavity. This is a feature observed in extant crocodilians, but absent in most theropod dinosaurs. Also like its relatives, Irritator had two additional openings on the skull roof (called the postnasal fenestrae) as well as long and only partially diverging basipterygoid processes (bony extensions connecting the braincase with the palate). The back of the lower jaw was deep, its rear upper surface consisting mainly of the large surangular bone, which articulated with the shallower angular bone below it. The mandibular fenestra, a sideways-facing opening in the lower jaw, was oval and comparatively large. The dentary (tooth-bearing bone of the mandible) is unknown in Irritator, save for a possible remnant at the front of the surangular. Irritator challengeri's holotype is unique in that it is one of the few non-avian (or non-bird) dinosaur fossils found with a preserved stapes.

Irritator had straight or only faintly recurved conical teeth, bearing sharply defined but unserrated edges. Flutes (lengthwise ridges) were present on its tooth crowns, a common dental trait among spinosaurids. Both sides of Irritator's teeth were fluted, as in Spinosaurus, whereas Baryonyx exhibited them only on the lingual (inward facing) side of its teeth. Irritator's teeth were circular in cross section, as opposed to the laterally flattened condition of most theropod teeth. The enamel (first layer of the teeth) was thin, with a finely wrinkled texture also observed in Baryonyx. Both of Irritator's maxillae preserve nine teeth, although the left maxilla's tooth crowns are more intact, and there are traces of a tenth tooth in the rock matrix. The teeth were deeply inserted into the jaw and widely spaced towards the front of the maxilla. The first and second preserved maxillary teeth were the largest, at 32 mm (1.3 in) and 40 mm (1.6 in) in crown length. The seven remaining teeth became progressively smaller towards the rear, one of the last ones measuring 6 mm (0.24 in) in estimated crown length. CT scans performed on the specimen revealed replacement teeth on both sides of the upper jaw. Their roots ran deep into the maxillae and converged close to the midline, nearly reaching the top of the skull. Based on comparisons with Irritator's relatives, the maxillae were probably lined with a total of 11 teeth each, similar to the number of 12 teeth in MSNM V4047, an upper jaw fossil referred to Spinosaurus. The hindmost tooth of the Irritator specimen's left maxilla was not yet fully erupted, and only the tip of it was visible.

### Anatomy of the Angaturama limai holotype

The holotype of Angaturama limai consists only of the front part of the upper jaw, comprising the tips of the paired premaxillae and the frontmost ends of the maxillae. The specimen measures 19.2 cm (7.6 in) in height and 11 cm (4.3 in) in length, with the width of the palatal region being 4 to 5 mm (0.16 to 0.20 in). The suture between the maxilla and premaxilla was jagged at the front and straightened out towards the rear. The lower margin of the premaxillae was concave, with the concavity reaching its apex at the sixth premaxillary tooth. The front of the snout was expanded, forming the spoon-shaped terminal rosette characteristic of spinosaurids. This concave underside of the premaxillae would have complemented a convex and enlarged mandible tip. The premaxillae connected with each other on the bottom to form Angaturama's secondary palate, which was also partially contributed to by two processes extending from the maxillae. The snout was strongly compressed laterally, and the premaxillae gently tapered towards the top to form a tall sagittal crest 1 to 2 mm (0.039 to 0.079 in) in thickness. This crest was larger and extended farther forwards on the snout than in other known spinosaurids. The frontmost upper border of the premaxilla had a small bulge that overhung the base of the crest. This bulge was apparently damaged on its upper surface, indicating that the top of the crest may have extended even farther over and forwards from that point. The front of Angaturama's snout hence had a vertically straight or concave margin, atypical from the more smoothly sloping snouts of other spinosaurs.

In the premaxilla, a broken-off tooth with partial tooth crown was recovered. The strongly extended and straight teeth with unserrated conical crowns, which measured 6 to 40 mm (0.24 to 1.57 in) in length, were singly embedded. This indicates continuous tooth replacement where new teeth were pushed up between the old ones. Judging by the alveoli (tooth sockets), the premaxilla had seven teeth altogether, the third tooth being the largest. The frontmost three teeth of the maxilla were also preserved. The premaxillary teeth increased in size from the first to third, shrank from the third to the sixth, and enlarged again from the sixth premaxillary to third maxillary positions. A 16 cm (6.3 in) diastema (gap in tooth row) was present between the last premaxillary and first maxillary tooth.

### Postcrania

Though no skeletal remains were discovered with the original Angaturama snout tip, one partial skeleton (MN 4819-V) from a different location may belong to the genus. But since there is no overlapping material between the two specimens, direct comparisons cannot be made. MN 4819-V comprises a largely intact pelvis, some dorsal (back) and caudal (tail) vertebrae, five sacral (hip) vertebrae, a partial right tibia and fibula (shin and calf bones), most of the right femur (thigh bone), and part of an ulna (forearm bone). It also has the most complete hand known from a spinosaurid, including metacarpals, phalanges, one carpals, and one claw. Like in all spinosaurids, the claw of the first finger (the "thumb") was enlarged.

The pelvic bones are well preserved, with the right side better articulated than the left. The fused sacral vertebrae are still attached to the pelvis, which lacks the distal ends of both of its pubic bones and ischia (lower and rearmost hip bones). The ilium (main hip bone) is 55.3 cm (21.8 in) long. The preacetabular ala (front expansion) of the ilium was curved on the bottom and was somewhat shorter and deeper than the postacetabular ala (rear expansion). The preacetabular ala were somewhat enlarged at the front, in contrast to the more slender condition of the postacetabular ala. The brevis fossa (groove at the bottom of the postacetabular ala) was concave, as was the rear margin of the ischium. The pubis bore a relatively large and almost closed obturator notch, an indentation in the lower margin of the rear part of the bone that allowed for the passage of the obturator nerve. The upwards projecting neural spines of the sacrum were elongated, as is typical in spinosaurs. In life, these would have been covered in skin, forming a "sail" down the animal's back. MN 4819-V is distinguished from Suchomimus due to its longer and shallower ilium with a less curved upper margin, and from Baryonyx by having a more developed obturator process, a blade-like structure on the bottom of the ischium.

## Classification

Martill and his team originally classified Irritator as a maniraptoran dinosaur in the clade Bullatosauria (a group no longer considered monophyletic), as a close relative to the feathered ornithomimosaurs and troodontids. Given that its dental morphology, particularly long snout, and assumed fin-shaped crest were features unknown in "other" maniraptorans, the researchers erected the new family Irritatoridae within the clade. They recognized Irritator's affinities with Spinosaurus, in that they both had similarly shaped and unserrated teeth, but noted that the latter's mandible would not conform with the front of Irritator's upper jaw, and that other non-avian dinosaurs like Compsognathus and Ornitholestes also bore no serrations on some or all of their teeth. Some of these claims were questioned in 1996 by Kellner who found that Irritator's skull lacked the one autapomorphy (distinguishing feature) diagnosed in maniraptorans at the time, which was having its jugal (cheek) bone forming part of the antorbital fenestra. He also pointed out that since Irritator challengeri's holotype lacked the tip of its snout, it would not be possible to know if Spinosaurus's dentary could complement it or not. Based on comparisons with Spinosaurus, Kellner resolved Irritator as a spinosaurid and synonymized Irritatoridae with that family. Irritator was then assigned to the Baryonychidae along with Angaturama, Baryonyx, Suchomimus, and Spinosaurus by Oliver W.M. Rauhut in 2003. Thomas Holtz and colleagues in 2004 considered the Baryonychidae synonymous with Spinosauridae, and moved these genera to the latter family. Most later revisions have upheld these classifications. As spinosaurids, Irritator and Angaturama are placed within the superfamily Megalosauroidea, with Spinosauridae being a possible sister taxon to the Megalosauridae.

In 1998, Sereno and colleagues defined two subfamilies within the Spinosauridae based on craniodental (skull and tooth) characteristics. They were Spinosaurinae, where they placed Spinosaurus and Irritator; and Baryonychinae, to which they assigned Baryonyx, Suchomimus, and Cristatusaurus. Spinosaurines were distinguished by their unserrated, straighter, and more widely spaced teeth, as well as smaller first teeth of the premaxilla. In 2005, Dal Sasso and colleagues assumed Irritator's nostrils as being located above the middle of the maxillary tooth row; more posteriorly than in baryonychines, but less so than in Spinosaurus. Sales and Schultz in 2017 found that Irritator's nostrils were in fact positioned closer to the front of the jaw, as in Baryonyx and Suchomimus; this more forward nostril placement was typically considered characteristic of baryonychines. Nevertheless, Irritator also bore unserrated teeth, a trait associated with spinosaurines. Sales and Schultz thus noted that the Araripe Basin spinosaurids Irritator and Angaturama might represent intermediate forms between the earlier baryonychines and later spinosaurines, and that further research may eventually render the former a paraphyletic (unnatural) group.

Irritator is further distinguished from Baryonyx, Suchomimus, and Cristatusaurus by having slightly over half as many teeth in the maxilla, and from Spinosaurus due to its comparatively larger and more forwardly positioned nostril openings, which, unlike in Spinosaurus, are also formed by the premaxilla. The narrow sagittal crest, which ends in a knob-like process above the frontals, is another autapomorphy separating Irritator from other spinosaurids. Although Angaturama limai's snout is generally narrower than in other spinosaurids, this might be due to damage sustained by the fossil; the holotype appears partly crushed and broken on its lower margin, with some of the preserved teeth having been sectioned off along their length. Therefore, Angaturama's only valid autapomorphy is its sagittal crest, which extends farther forwards on the rostrum and is more exaggerated than in other known spinosaurid skulls.

Topology A: Benson and colleagues (2009)

Topology B: Sales and Schultz (2017)

## Paleobiology

### Diet and feeding

In 1996, Martill and colleagues theorized that Irritator challengeri, with its elongated snout and unserrated conical teeth, likely had at least a partly piscivorous (fish-eating) diet. Although much of the holotype's morphology turned out to be greatly different than they thought, later studies supported these observations. Spinosaurids had very narrow and elongated jaws with relatively homogeneous pointed teeth, an arrangement found particularly in animals like the Indian gharial—the most piscivorous extant crocodilian. The long conical teeth, which in spinosaurines did not possess serrated edges, were suitable for grabbing and holding prey. They differed from teeth of other theropods, which seemed geared towards tearing or cutting off seized body parts.

Irritator shared with crocodilians a stiff secondary palate and reduced antorbital fenestrae. In 2007, a finite-element analysis study by British paleontologist Emily J. Rayfield and colleagues found that these attributes, present in other spinosaurids as well, made the skull more resistant to torsion from prey item loads when feeding. The authors pointed out that in contrast, most theropods lacked secondary palates and had large antorbital fenestrae, exchanging strength for lighter skull builds. The nostrils of Irritator were shifted far back from the snout tip; this, along with the secondary palate, which separated the animal's nasal passages from the inside of its mouth, made respiration possible even if most of the jaw was underwater or held prey. In particular, the sagittal crest of Irritator is an indication for pronounced neck musculature, which would have been necessary to close the jaws quickly against water resistance and withdraw the head rapidly. In 2015, German paleontologist Serjoscha W. Evers and colleagues found evidence for similar adaptations in the African spinosaur Sigilmassasaurus. The neck vertebrae of this genus have a heavily furrowed undersurface. This is consistent with the attachment of powerful neck muscles for use in fishing or rapidly snatching small prey, a trait also observed in extant crocodilians and birds. Sales and Schultz in 2017 found that Irritator and baryonychines might have relied more on their sense of smell for hunting than Spinosaurus did, since they had larger, less retracted nostrils and more room in their skulls for the nasal cavity. Spinosaurus itself probably made heavier use of senses like vision or the mechanoreceptors on the tip of its snout, like those used by crocodilians to sense prey moving in the water.

Another trait spinosaurs shared with gharials was an enlarged snout tip that wielded a rosette-shaped array of interlocking teeth, adept for impaling and catching fish. Although to a lesser degree than most known spinosaurs, this feature was also present in the Angaturama limai holotype. In 2002, Sues and colleagues pointed out, however, that there would be no reason to assume that the Spinosauridae specialized completely in fishing. They stressed rather that this head morphology indicates a generalistic feeding, particularly on small prey animals. In fact, portions of a young Iguanodon, a terrestrial herbivore, were found inside the fossil skeleton of one Baryonyx. Naish and colleagues in 2004 supported the theory that Irritator hunted both aquatic and terrestrial animals as a generalist within the coastal area and in addition probably searched for carrion. A tooth belonging to Irritator was discovered still inserted into the fossil neck vertebral column of an ornithocheirid pterosaur, likely with a wingspan of 3.3 m (11 ft). This indicates that Irritator ate pterosaurs as well, although it is not known if it actively hunted these animals or simply scavenged the remains. In 2018, Aureliano and colleagues presented a possible scenario for the food web of the Romualdo Formation. The researchers proposed that spinosaurines from the formation may have also preyed on terrestrial and aquatic crocodyliforms, juveniles of their own species, turtles, and small to medium-sized dinosaurs. This would have made spinosaurines apex predators within this particular ecosystem.

Examinations and digital reconstructions of Irritator published in 2023 by Schade, Rauhut et al., suggests that the lower jaws of this spinosaurid could rotate and open laterally, with a gape similar to that of modern pelicans; this would have allowed the theropod to swallow very large prey items. It was also discovered to have a very weak but rapid bite as a result of this analysis. The study also reaffirms that Irritator likely possessed binocular vision and would have held its snout at an inclined orientation. Additionally, the examinations reaffirmed classification of spinosaurids as megalosauroids and that megalosauroids and allosauroidea were part of a monophyletic Carnosauria, with Monolophosaurus standing as a sister taxon to spinosauridae.

### Aquatic habits

Many spinosaurs likely had semiaquatic habits, as has been shown in studies using techniques like isotope analysis and bone histology. It has been found that they probably took advantage of aquatic prey and environments (usually marginal and coastal habitats) to occupy a distinct ecological niche, therefore avoiding competition with more terrestrial theropods. Spinosaurines appear to have been more adapted for such lifestyles than baryonychines. A 2018 study by British paleontologist Thomas M. S. Arden and colleagues examined the morphology of spinosaurine skull bones for possible aquatic traits. They found that the frontal bones of Irritator, Spinosaurus, and Sigilmassasaurus were similar in being arched, concave on top, and narrowed at the front; features that would have resulted in the eyes being positioned further up on the head than in other theropods. In particular, the broad lower jaw and narrowed frontals of Irritator resulted in the orbits facing at a steep incline towards the midline of the skull, whereas most theropods had laterally facing orbits. These traits would have permitted the animal to see above the waterline when submerged.

In 2018, Aureliano and colleagues conducted an analysis on the Romualdo Formation tibia fragment. CT scanning of the specimen in the University of São Carlos revealed the presence of osteosclerosis (high bone density). This condition had previously only been observed in Spinosaurus aegyptiacus, as a possible way of facilitating submersion in water by making its bones heavier. The presence of this condition on the Brazilian leg fragment showed that compact bones had already evolved in spinosaurines at least 10 million years before the appearance of Spinosaurus in Morocco. According to phylogenetic bracketing—a method used to infer unknown traits in organisms by comparison with their relatives—osteosclerosis therefore might have been the norm in the Spinosaurinae. The significance of these traits was questioned in a later 2018 publication, where Canadian paleobiologist Donald Henderson argued that osteosclerosis would not have changed a theropod's buoyancy to a significant extent.

### Neuroanatomy and senses

In 2020, German paleontologist Marco Schade and colleagues analyzed the anatomy of the holotype skull braincase through CT scans, revealing numerous details about behavioral capabilities of Irritator. With the scans, they created a 3D model of the skull and braincase, discovering that Irritator had elongated olfactory tracts and a relatively large floccular recesses (area that pierces through the semicircular canals and connects the brain with the inner ear). The flocculus, itself, is an important element in the coordination and control of head and ocular movements during gaze stabilization (visual ability during head movement), by being involved in the coordination of the vestibulo-ocular (VOR) and vestibulo-collic (VCR) reflexes. The flocculus appears to be enlarged in taxa that rely on quick movements of the head body. In addition, the vestibular part of the endosseous labyrinth has a large anterior semicircular canal with a lateral oriented semicircular canal.

Both floccular recesses and semicircular canal suggest that Irritator could coordinate fast head movements and had a downward inclined snout posture, enabling an unobstructed, stereoscopic forward vision, which is important for distance perception and therefore precise snatching movements of the snout. These inferences seem to be an agreement with a piscivore life-style. They also noted that the relatively well-developed cochlear duct may have enable an average hearing frequency of 1,950 Hz with a frequency band width of 3,196 Hz. However, they considered these ranges as rough estimates and established an overall frequency range of 350–3,550 Hz, making Irritator to be placed under bird hearing but above crocodiles.

## Paleoenvironment and paleobiogeography

Irritator and Angaturama are known from the Romualdo Formation, whose rocks are dated to the Albian stage of the Early Cretaceous Period, about 110 million years ago. During this time, the Southern Atlantic Ocean was opening, forming the series of circum-Atlantic basins of southern Brazil and southwestern Africa, but the northeastern part of Brazil and West Africa were still connected. The Romualdo Formation is part of the Santana Group and, at the time Irritator was described, was thought to be a member of what was then considered the Santana Formation. The Romualdo Formation is a Lagerstätte (a sedimentary deposit that preserves fossils in excellent condition) consisting of limestone concretions embedded in shales, and overlies the Crato Formation. It is well known for preserving fossils three-dimensionally in limestone concretions, including many pterosaur fossils. In addition to muscle fibres of pterosaurs and dinosaurs, fish, preserving gills, digestive tracts, and hearts, have been found there. The formation is interpreted as a coastal lagoon with irregular freshwater influence that contended with cycles of transgressing and regressing sea levels. The climate of the formation was tropical and largely corresponded to today's Brazilian climate. The regions surrounding the formation were arid to semi-arid, with most of the local flora being xerophytic (adapted to dry environments). Cycadales and the extinct conifer Brachyphyllum were the most widespread plants.

This environment was dominated by pterosaurs, including: Anhanguera, Araripedactylus, Araripesaurus, Brasileodactylus, Cearadactylus, Coloborhynchus, Santanadactylus, Tapejara, Thalassodromeus, Tupuxuara, Barbosania, Maaradactylus, Tropeognathus, and Unwindia. The known dinosaur fauna besides Irritator was represented by other theropods like the tyrannosauroid Santanaraptor, the compsognathid Mirischia, an indeterminate unenlagiine dromaeosaurid, and a megaraptoran. The crocodyliforms Araripesuchus and Caririsuchus, as well as the turtles Brasilemys, Cearachelys, Araripemys, Euraxemys, and Santanachelys, are known from the deposits. There were also clam shrimps, sea urchins, ostracods, and molluscs. Various well-preserved fish fossils record the presence of: hybodont sharks, guitarfish, gars, amiids, ophiopsids, oshuniids, pycnodontids, aspidorhynchids, cladocyclids, bonefishes, chanids, mawsoniids and some uncertain forms. According to Naish and colleagues, the lack of herbivorous dinosaurs could mean that the local vegetation was scant and thus incapable of sustaining a large population of them. The abundant carnivorous theropods would have then likely turned to the lush aquatic life as a primary food source. They also hypothesized that following storm events, pterosaur and fish carcasses might have washed up on the shoreline, providing theropods with plenty of carrion. Multiple piscivorous animals were present in the formation, which might in theory have led to high competition. Aureliano and colleagues stated there must have, therefore, been some degree of niche partitioning, where different animals would have fed on prey of varied sizes and locations within the lagoon.

Similarities between the fauna of the Romualdo and Crato Formations to that of Middle Cretaceous Africa suggest that the Araripe Basin was connected to the Tethys Sea, though this link was likely sporadic, because the lack of marine invertebrates indicates the basin had a non-marine depositional setting. Spinosaurids had already achieved a cosmopolitan distribution during the Early Cretaceous. Sereno and colleagues in 1998 suggested that with the opening of the Tethys Sea, spinosaurines would have evolved in the south (Africa, in Gondwana) and baryonychines in the north (Europe, in Laurasia). In following, Machado and Kellner theorized in 2005 that spinosaurines would have then spread to South America from Africa. Sereno and colleagues postulated that divergent evolution between spinosaurines in South America and Africa likely occurred as a consequence of the Atlantic Ocean, whose opening gradually separated the continents and contributed to differences between taxa. A similar scenario was suggested in 2014 by Brazilian paleontologist Manuel A. Medeiros and colleagues for the fauna of the Alcântara Formation, where Oxalaia has been found. But the paleobiogeography of spinosaurids remains highly theoretical and uncertain, with discoveries in Asia and Australia indicating that it may have been complex.

### Taphonomy

The taphonomy (changes between death and fossilization) of the Irritator challengeri holotype specimen has been discussed by some researchers. The skull was found lying on its side. Preceding fossilization, several bones from the back of the braincase, as well as the dentary, splenial, coronoid, and right angular bones from the lower jaw, were lost. Other bones, mostly from the skull rear, had become disarticulated and displaced towards alternate regions of the head before burial. Naish and colleagues in 2004 asserted that the Romualdo Formation dinosaur fauna is represented by animals that died near shorelines or rivers before being carried out to sea, where their floating remains were eventually fossilized. In 2018, Aureliano and colleagues argued against this scenario, stating that the Irritator challengeri holotype's mandible was preserved in articulation with the rest of the skull, whereas it would have likely detached had the carcass been floating at sea. They also noted that the corpse would have quickly sunk due to the osteosclerosis of the skeleton. The researchers, therefore, concluded that fossils from the Santana Group represent organisms that were buried in their natural habitat, instead of having been deposited allochthonously (other than at their present position).

Spinosaurid theropod dinosaur genus from the Early Cretaceous Period

Early Cretaceous dinosaurs of South America


Spinning Around

"Spinning Around" is a song by Australian singer Kylie Minogue for her seventh studio album, Light Years (2000). Written by Ira Shickman, Osborne Bingham, Kara DioGuardi and Paula Abdul, the song was initially meant to be recorded by Abdul for her own album, but was given to Minogue after the plan never came to fruition. Produced by Mike Spencer, the disco-influenced dance-pop song was then released in the UK as the lead single from Light Years on 19 June 2000, through Mushroom Records and Parlophone. Lyrically, the song addresses the theme of reinvention, with Minogue claiming that she has changed as a person and learned from the past.

Upon its release, "Spinning Around" received favourable reviews from music critics, who singled it out as one of the highlights from the album and praised Minogue for returning to her signature musical style. Commercially, the single was a success and became Minogue's "comeback" single following the critical and commercial disappointment of her previous album Impossible Princess (1997). It entered the Australian Singles Chart at number one, becoming Minogue's first chart-topper since "Confide in Me" in 1994. The single also debuted at number one in the United Kingdom, where it became her first single to peak atop the chart since "Tears on My Pillow" in 1990. Elsewhere, it reached the top five in several countries, including Croatia, Czech Republic, Ireland, New Zealand and Russia. "Spinning Around" was certified platinum and gold in Australia and the United Kingdom, respectively. The song won the 2000 ARIA Music Award for "Best Pop Release".

The accompanying music video for "Spinning Around", directed by Dawn Shadforth, features Minogue dancing and enjoying herself at a nightclub. It became popular for the gold hotpants she sported in most of the scenes and led to her bottom gaining extensive coverage from the media. The hotpants are considered to be "iconic" and have been displayed in exhibitions of Minogue's fashion. "Spinning Around" has been performed by Minogue during all of her tours, with the exception of the Anti Tour. In 2003, Q magazine ranked "Spinning Around" at number 90 in their list of the "1001 Best Songs Ever".

## Background and recording

In 1997, Minogue released her sixth studio album, Impossible Princess. The album represented a drastic change in the singer's musical direction, shifting from her signature dance-pop styles to incorporate elements of electronica and pop rock. It was her second album to be released on British record label Deconstruction and became a success in her native Australia, peaking at number four on the ARIA Albums Chart. In the United Kingdom Impossible Princess was less successful than Minogue's previous albums and peaked at number ten on the UK Albums Chart. The album also suffered from poor reviews in the UK as commentators criticised its different musical approach; many also considered that Minogue's career was over. Despite embarking on a successful promotional tour, Minogue was dropped by Deconstruction in 1999. Minogue then signed to Parlophone, another British record label.

After various discussions, Minogue decided to do what she did "best" and record a simple pop album inspired by disco and Europop, entitled Light Years. "Spinning Around" was included as the opening track of the album and was written by Ira Shickman, Osborne Bingham, Kara DioGuardi and Paula Abdul, and produced by Mike Spencer. Abdul had based the song on her divorce from clothing designer Brad Beckerman and had originally intended to record it for her own studio album, but it was given to Minogue after the album failed to materialise. The song was the first major songwriting project for DioGuardi, who had not been offered any notable projects previously. In an interview discussing the development of Light Years, Minogue revealed that the song had initially been found as a demo in New York by her A&R executive Jamie Nelson, who believed it would be "perfect" for the singer. After listening to the demo, Minogue agreed to record it and felt the song had the potential to be a hit. "Spinning Around" was then released as the lead single from the album on 19 June 2000 in both Australia and the United Kingdom.

## Composition

Similar to most of the songs from Light Years, "Spinning Around" is a "string-laden" dance-pop track with prominent influences from disco music. According to the sheet music of the song published by BMG Rights Management at Musicnotes.com, it is composed in the key of F minor and features a moderate tempo of 120 beats per minute. Minogue's vocal range spans from the low note of F3 to the high note of C5. Addressing the theme of reinvention, the lyrics declare that Minogue has changed and learned from her past mistakes; it contains lines like "I'm spinning around/Move out of my way ... I'm not the same" and "Mistakes that I made have given me the strength to really believe." In an analysis of the lyrics of the song, Pom Avoledo from Blogcritics wrote that Minogue demands attention in the chorus towards the changes in her personality and asserts that people appreciate them, in the line "I know you're feelin[g] me [be]cause you like it like this." The first verse deals with Minogue ridding herself of items and symbols from her past and starting afresh, evidenced in lines like "Threw away my old clothes, got myself a better wardrobe." The critic felt that in the second verse Minogue faces her mistakes and accepts herself as she is. The bridge of the song features the repetition of the hook "You know you like it like this," with Minogue's voice being vocoded. Chris True from AllMusic felt that through the lyrics, Minogue was admitting that releasing Impossible Princess in 1997 was not the best decision.

## Critical reaction

"Spinning Around" received favourable reviews from music critics. Chris True from AllMusic selected it as a highlight from the album and said it was a "fun and string-laden declaration that she may have made a mistake back in 1997." Pom Avoledo praised Minogue for returning to her signature dance-pop style and complimented her for giving "Spinning Around" an "air of elegance and sensuality which was lacking in her early material." A very positive review came from Siobhan Grogan of NME, who favoured the chorus of the song and commended Minogue for coming back to "what she knows best." The critic felt the song would become a hit in gay clubs and commented that "[Spinning Around] is made of the same fizzing, giddy disco-pop that made Kylie famous in the first place." Gary Crossing from Yahoo! Music, who gave Light Years a mixed review, felt that "Spinning Around" was one of the better tracks from the album and called it a "slinky little number." Olive Pometsey from GQ deemed it one of Minogue's most "iconic" tracks, concluding that "from the funky bass to those gold shorts, our pop queen did not return to the charts to play; she came to reign".

In his review of Minogue's 2004 greatest hits album Ultimate Kylie, Jason Shawahn from About.com praised the inclusion of songs like "Spinning Around" and other tracks from Light Years, calling them "a blessing for domestic music consumers, since that disc has never found its way onto official US release, though with any collection of Minogue hits, one simply has to look at what they have in their collection versus what they don't." At the 14th ARIA Music Awards ceremony in 2000, "Spinning Around" won the award for "Best Pop Release". Billboard's Jason Lipshutz wrote the track found the singer "returning to straightforward pop after 1997's ambitious Impossible Princess and corralling some disco thump to create an especially giddy effect"; calling it one of Minogue's "most effortless hits to date". Louis Vartel from the LGBT oriented website NewNownext, called it her "coolest, most liberated dance opus". He placed it at number seven of his list of the singer's 48 greatest songs, in honor of her 48th birthday. Writing for the Herald Sun, Cameron Adams ranked it at number 42 on his list of the singer's best songs, in honor of her 50th birthday and said: "Remember at the time many thought Kylie was washed-up, so a 70s-soaked disco pop tune was the ideal way to recalibrate the good ship Minogue. It worked, with a little help from some very little hungry gold hotpants", the last part being a reference to the song's music video.

## Chart performance

The song was a commercial success. In Australia it was certified gold by the Australian Recording Industry Association (ARIA) prior to its release on the strength of pre-orders. On the chart date of 2 July 2000, it debuted at number one on the ARIA Singles Chart. The following week, it dropped to number five and it stayed in the top ten for four consecutive weeks in total. It was Minogue's first number-one single in the country since "Confide in Me", which was released six years earlier. "Spinning Around" charted for a total of 12 weeks and was later certified platinum by the ARIA for shipments of 70,000 units. The song also performed well in New Zealand, entering the RIANZ Singles Chart at number eight and peaking at number two. It spent a total of 17 weeks on the chart and was certified gold by the Recording Industry Association of New Zealand (RIANZ) for sales of 7,500 units.

With first-week sales of over 82,000 units, "Spinning Around" debuted atop the UK Singles Chart on the chart date of 1 July 2000, becoming Minogue's first number-one single in a decade. Her previous chart-topping single was "Tears on My Pillow" from her second studio album Enjoy Yourself (1989). "Spinning Around" was Minogue's fifth number-one single in the United Kingdom. Minogue became one of only two artists to have a number one single in three consecutive decades, achieving this in the 1980s, 1990s, and 2000s. The other artist to hold this distinction is Madonna, whose song "American Pie" topped the UK singles chart in March 2000. "Spinning Around" charted inside the top ten for two weeks and inside the top forty for eight weeks. The British Phonographic Industry (BPI) certified the song gold for shipments of 400,000 units. As of March 2014, the single has sold 300,000 units in the country according to the Official Charts Company. "Spinning Around" was deemed a successful "comeback" single for Minogue and, along with parent album Light Years, helped relaunch her career.

## Music video

### Development and synopsis

The accompanying music video for "Spinning Around" was directed by Dawn Shadforth. As the song was meant to be Minogue's "comeback" single and mark a "decisive return" to pop music following Impossible Princess, the video did not contain any dark themes and put the "emphasis firmly upon dance, fun, and freedom." The video begins with a shot of Minogue's feet as she enters a disco-like setting. She is then shown dancing on the floor with a man, whom she later flirts with on a sofa. Scenes of her performing a dance routine on and in front of a bar and lying on neon blue and gold lights are interspersed throughout the video. Most of the shots are focused on Minogue's body and various scenes feature her wearing gold lamé hotpants.

### Legacy

Following its release, the music video became popular for the gold hotpants Minogue sported. It resulted in a media sensation regarding her bottom. British national broadsheet newspaper The Sunday Times deemed her bottom a "wonder of nature" and The Sun sponsored a campaign to "have Kylie Minogue's rear-end heritage-listed, preserved for "posteriority" on the grounds that it's an Area of Outstanding Natural Beauty." Readers were requested by the tabloid newspaper to persuade the government to make sure "[Minogue's] bum remains in safe hands - by turning it into a national institution." Rumours and speculations claiming Minogue had undergone plastic surgery to make her bottom look more appealing also began to arise during this time. In the same year, English broadcaster and journalist Johnny Vaughan commented "if an alien landed on Earth he would think Kylie's arse is the world's leader." Minogue's stylist and close friend William Baker explained his decision to "showcase" her bottom in the video, saying "Kylie's bottom is like a peach - sex sells and her best asset is her bum." The singer's response to the attention regarding her bottom was "dry," claiming "You never know what the future holds. It could become a pear." It was reported that Minogue had her bottom insured for five million dollars.

The hotpants were deemed "iconic" and were said to be the reason behind "Spinning Around" becoming a "musical and visual anthem in 2000." According to the catalogue entry for the hotpants at the Performing Arts Collection at the Arts Centre, Melbourne, British artist and photographer Katerina Jebb bought them for fifty pence from a flea market and they were only selected for use in the video the night before the shoot, though Minogue had worn them previously for a website photoshoot. She was surprised by the attention they attracted, commenting "I never imagined what impact a 50p pair of hotpants would have." She also said that the revealing nature of the hotpants made her feel insecure during the shooting, saying "I actually wasn't confident [in them], that's the crazy thing. I remember feeling quite self-conscious and kept wrapping a robe around me on set and would discard [it] right before the take." The garment is often referred to as "those hotpants," and have become a symbol for the singer's vitality and youthfulness. Considered to be one of her trademark looks, the attire she wore in the music video was put on display at Kylie: The Exhibition, an exhibition that featured "costumes and memorabilia collected over Kylie's career", held at the Victoria and Albert Museum in London, England, and at Kylie: An Exhibition, a similar exhibition held at the Powerhouse Museum in Sydney, Australia. It was also included in Minogue's official fashion photography book Kylie / Fashion, which was released on 19 November 2012 by Thames and Hudson to celebrate Minogue's completion of 25 years in music. In February 2014, Minogue donated the hotpants to the Performing Arts Collection museum at the Arts Centre in her hometown of Melbourne.

## Live performances

On 30 June 2000, Minogue performed "Spinning Around" on British music chart television programme Top of the Pops. She performed the song for the second time on the programme on 7 July. On 18 October 2000, Minogue performed the song on the 2000 Summer Paralympics Opening Ceremony. On 2 August 2001, Minogue performed "Spinning Around" at the BBC Radio 1 One Big Sunday show held at Leicester, in the United Kingdom, along with "Can't Get You Out of My Head"; for the performance, she wore a black trilby hat, sleeveless T-shirt (with a picture of Marilyn Monroe printed on it), knee length black boots, and trousers with open zips placed on both the thighs. "Spinning Around" was included on the "On Yer Bike" act of Minogue's one-off concert show Money Can't Buy, which was held on 15 November 2003. On 4 June 2012, she sang "Spinning Around" at the Diamond Jubilee Concert in front of the Buckingham Palace, held in honour of Elizabeth II. Minogue's wardrobe consisted of a pearl-studded black jacket and hat. Dance troupe Flawless, finalists of British television talent show Britain's Got Talent, served as Minogue's backing dancers. To promote her 2012 album The Abbey Road Sessions, Minogue headlined at Proms in the Park event in Hyde Park, London. This version of the song was exclusively performed at the event, as it was not included on the track list of the album.

Since its release, "Spinning Around" has been included in the set list of each of Minogue's concert tours, except the 2012 Anti Tour. It was the final performance of the encore segment of the On a Night Like This tour, which was launched to promote Light Years in 2001. Minogue and her back-up dancers dressed in mid 1980s-inspired outfits while performing the song. The song was performed during the "Droogie Nights" act of the KylieFever2002 tour. In 2005, she performed the song on her Showgirl: The Greatest Hits Tour. This version of the song featured the piano riff of "Finally", a 1991 song by American recording artist CeCe Peniston. Minogue was unable to complete the tour as she was diagnosed with early breast cancer and had to cancel the Australian leg of the tour. After undergoing treatment and recovery, she resumed the concert tour in the form of Showgirl: The Homecoming Tour in 2007, and performed "Spinning Around" with combined elements of her previous singles "Shocked" and "What Do I Have to Do". The song was performed as part of the "Beach Party" act of the KylieX2008 tour, during which Minogue was dressed as a "sequinned sailor."

A medley of "Spinning Around", "Shocked", "What Do I Have to Do" and "Step Back in Time" was performed during the For You, for Me tour in 2009, Minogue's first North American tour. Dressed in a top hat and a black crinoline, Minogue performed "Spinning Around" during her Aphrodite: Les Folies Tour in 2011. Minogue performed "Spinning Around" as part of her seven-song set at the closing ceremony of the 2014 Commonwealth Games. The song was performed on Minogue's Kiss Me Once and Summer Tours, in 2014 and 2015 respectively, following a performance of "Step Back in Time", where Minogue wore a sparkly corset and jacket paired with a tie and thigh-high boots. For 2018-19's Golden Tour, "Spinning Around" was presented in a Studio 54 setting and found Minogue, dressed in a sparkly golden dress, surrounded by dancers. Writing for The Guardian, Alexandra Spring felt that during the performance, the singer seemed "happy to give that famous bottom a moment in the spotlight". The song was then included on Minogue's 2019 summer tour: it was remixed with Cheryl Lynn's "Got to Be Real" (1978) and performed as one of the closing numbers. The performance featured rainbow-colored confetti being blasted into the crowd and was praised by NME's Dan Stubbs as "an all-out celebration".

## Track listing and formats

- Australian, New Zealand, and UK CD1

1. "Spinning Around" – 3:27
2. "Spinning Around" (Sharp vocal mix) – 7:06
3. "Spinning Around" (7th Spinnin' Dizzy dub) – 5:20
4. "Spinning Around" (video)

- Australian, New Zealand, and UK CD2

1. "Spinning Around" – 3:28
2. "Cover Me with Kisses" – 3:08
3. "Paper Dolls" – 3:34

- New Zealand cassette single

1. "Spinning Around" – 3:27
2. "Spinning Around" (Sharp vocal mix) – 7:06

- UK cassette single

1. "Spinning Around" – 3:28
2. "Spinning Around" (Sharp Double Dub mix) – 7:08

- French CD single

1. "Spinning Around" – 3:28
2. "Cover Me with Kisses" – 3:06

- European maxi-CD single

1. "Spinning Around" – 3:27
2. "Cover Me with Kisses" – 3:07
3. "Paper Dolls" – 3:35
4. "Spinning Around" (Sharp vocal mix) – 7:04
5. "Spinning Around" (video)

- Digital download

1. "Spinning Around" (7th Spinnin' Dizzy dub) – 5:27
2. "Spinning Around" (live at Manchester Arena, 4 May 2002) – 4:15
3. "Spinning Around" (Sharp Double dub) – 7:08

## Charts

### Weekly charts

### Year-end charts

## Certifications and sales

## See also

- List of number-one singles of 2000 (Australia)
- List of UK Singles Chart number ones of the 2000s

2000 single by Kylie Minogue


Porpoise

Porpoises (/ˈpɔːrpəsɪz/) are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals and belugas than to the true dolphins. There are eight extant species of porpoise, all among the smallest of the toothed whales. Porpoises are distinguished from dolphins by their flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and lack of a pronounced beak, although some dolphins (e.g. Hector's dolphin) also lack a pronounced beak. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates.

Porpoises range in size from the vaquita, at 1.4 metres (4 feet 7 inches) in length and 54 kilograms (119 pounds) in weight, to the Dall's porpoise, at 2.3 m (7 ft 7 in) and 220 kg (490 lb). Several species exhibit sexual dimorphism in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Porpoises use echolocation as their primary sensory system. Some species are well adapted for diving to great depths. As all cetaceans, they have a layer of fat, or blubber, under the skin to keep them warm in cold water.

Porpoises are abundant and found in a multitude of environments, including rivers (finless porpoise), coastal and shelf waters (harbour porpoise, vaquita) and open ocean (Dall's porpoise and spectacled porpoise), covering all water temperatures from tropical (Sea of Cortez, vaquita) to polar (Greenland, harbour porpoise). Porpoises feed largely on fish and squid, much like the rest of the odontocetes. Little is known about reproductive behaviour. Females may have one calf every year under favourable conditions. Calves are typically born in the spring and summer months and remain dependent on the female until the following spring. Porpoises produce ultrasonic clicks, which are used for both navigation (echolocation) and social communication. In contrast to many dolphin species, porpoises do not form large social groups.

Porpoises were, and still are, hunted by some countries by means of drive hunting. Larger threats to porpoises include extensive bycatch in gill nets, competition for food from fisheries, and marine pollution, in particular heavy metals and organochlorides. The vaquita is nearly extinct due to bycatch in gill nets, with a predicted population of fewer than a dozen individuals. Since the extinction of the baiji, the vaquita is considered the most endangered cetacean. Some species of porpoises have been and are kept in captivity and trained for research, education and public display.

## Taxonomy and evolution

Porpoises, along with whales and dolphins, are descendants of land-living ungulates (hoofed animals) that first entered the oceans around 50 million years ago (Mya). During the Miocene (23 to 5 Mya), mammals were fairly modern, meaning they seldom changed physiologically from the time. The cetaceans diversified, and fossil evidence suggests porpoises and dolphins diverged from their last common ancestor around 15 Mya. The oldest fossils are known from the shallow seas around the North Pacific, with animals spreading to the European coasts and Southern Hemisphere only much later, during the Pliocene.

- ORDER Artiodactyla
  - Infraorder Cetacea
    - Parvorder Odontoceti toothed whales
      - Superfamily Delphinoidea
        - Family Phocoenidae – porpoises
          - Genus †Haborophocoena
            - H. toyoshimai
          - Genus Neophocaena
            - N. phocaeniodes – Indo-Pacific finless porpoise
            - N. sunameri – East Asian finless porpoise
            - N. asiaeorientalis – Yangtze finless porpoise
          - Genus †Numataphocoena
            - N. yamashitai
          - Genus Phocoena
            - P. phocoena – harbour porpoise
            - P. sinus – vaquita
            - P. dioptrica – spectacled porpoise
            - P. spinipinnis – Burmeister's porpoise
          - Genus Phocoenoides
            - P. dalli – Dall's porpoise
          - Genus †Semirostrum
            - S.ceruttii
          - Genus †Septemtriocetus
            - S. bosselaersii
          - Genus †Piscolithax
            - P. aenigmaticus
            - P. longirostris
            - P. boreios
            - P. tedfordi

Recently discovered hybrids between male harbour porpoises and female Dall's porpoises indicate the two species may actually be members of the same genus.

## Biology

### Anatomy

Porpoises have a bulbous head, no external ear flaps, a non-flexible neck, a torpedo shaped body, limbs modified into flippers, and a tail fin. Their skull has small eye orbits, small, blunt snouts, and eyes placed on the sides of the head. Porpoises range in size from the 1.4 m (4 ft 7 in) and 54 kg (119 lb) Vaquita to the 2.3 m (7 ft 7 in) and 220 kg (490 lb) Dall's porpoise. Overall, they tend to be dwarfed by other cetaceans. Almost all species have female-biased sexual dimorphism, with the females being larger than the males, although those physical differences are generally small; one exception is Dall's porpoise.

Odontocetes possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Porpoises have a three-chambered stomach, including a fore-stomach and fundic and pyloric chambers. Porpoises, like other odontocetes, possess only one blowhole. Breathing involves expelling stale air from the blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs. All porpoises have a thick layer of blubber. This blubber can help with insulation from the harsh underwater climate, protection to some extent as predators would have a hard time getting through a thick layer of fat, and energy for leaner times. Calves are born with only a thin layer of blubber, but rapidly gain a thick layer from the milk, which has a very high fat content.

### Locomotion

Porpoises have two flippers on the front and a tail fin. Their flippers contain four digits. Although porpoises do not possess fully developed hind limbs, they possess discrete rudimentary appendages, which may contain feet and digits. Porpoises are fast swimmers in comparison to seals, which typically cruise at 9–28 km/h (5–15 kn). The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, making it impossible for them to turn their head. When swimming, they move their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Flipper movement is continuous. Some species log out of the water, which may allow them to travel faster, and sometimes they porpoise out of the water, meaning jump out of the water. Their skeletal anatomy allows them to be fast swimmers. They have a very well defined and triangular dorsal fin, allowing them to steer better in the water. Unlike their dolphin counterparts, they are adapted for coastal shores, bays, and estuaries.

### Senses

The porpoise ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance equaliser between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, porpoises receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The porpoise ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. Odontocetes send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. The large bulge on top of the porpoises head is caused by the melon.

The porpoise eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a porpoise are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When porpoises surface, their lens and cornea correct the nearsightedness that results from the refraction of light; their eyes contain both rod and cone cells, meaning they can see in both dim and bright light. Porpoises do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals. Most porpoises have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, they are able to form a very clear image of the surrounding area.

The olfactory lobes are absent in porpoises, suggesting that they have no sense of smell.

Porpoises are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some have preferences between different kinds of fish, indicating some sort of attachment to taste.

### Sleep

Unlike most animals, porpoises are conscious breathers. All mammals sleep, but porpoises cannot afford to become unconscious for long because they may drown. While knowledge of sleep in wild cetaceans is limited, porpoises in captivity have been recorded to sleep with one side of their brain at a time, so that they may swim, breathe consciously, and avoid both predators and social contact during their period of rest.

This means that the brain hemispheres take turns alternating between slow wave sleep and being awake. While one hemisphere displays slow waves, the other displays wake patterns on an electroencephalogram. It has been suggested that the brainstem controls this activity. All the while, porpoises also employ a minimal amount of suppressed REM sleep while swimming.

The same neural systems that regulate sleep in bihemispheric mammals are used in harbor porpoises. Cetaceans use many of the same neurotransmitters that other mammals use, although they have a significantly higher number. Although the way porpoises sleep is different from other mammals, they use the same neural mechanisms and pathways. One key difference is that porpoises seem to inhibit REM sleep more than most mammals, likely to prevent losing muscle tone and thus decreasing the risk of drowning or suffering from hypothermia. Porpoises differ from other mammals in terms of the neurons that regulate their sleep-wake cycle, however, the sleep-wake cycle overall is surprisingly similar to other mammals. This shows that despite differences in sleeping patterns, the sleep wake mechanism is conserved across species. The anatomy of the cetacean brain varies slightly from that of other mammals, with the area governing sleep-wake cycles (caudal to the posterior commissures) being significantly larger.

It is difficult to use traditional methods to determine whether a porpoise is sleeping, since half of the brain is awake at any given time. Parabolic dives have been shown to potentially be correlated to sleeping periods in porpoises, with decreased bioacoustics being transmitted during these periods. This means that during parabolic dives, porpoises generally do not employ echolocation clicks (about fifty percent of the time). This may be related to the side of the brain that is asleep. For instance, the left hemisphere signals to the right side of the brain, which controls the production of echolocation clicks. Thus, when the left side of the brain is asleep, echolocation cannot be produced.

Along with using less bioacoustics, porpoises roll less, use a lower vertical descent rate, and are overall less active while performing parabolic dives. Parabolic dives have shown to be of shallow depth and use a low amount of energy. These are different behaviors than the those displayed during foraging dives. Moreover, these behaviors are consistent with stereotypical sleeping behavior.

Interestingly, parabolic dives are more common during the daytime than during the nighttime and only take up a small amount of a wild porpoise's total time, as opposed to the time spent sleeping in other mammals. Meanwhile, captive cetaceans have been shown to spend up to fifty percent of their time sleeping and up to sixty-six percent of their time resting. A thought that deserves further consideration is that wild porpoises spend a significant fraction of their time near the surface of the water, and it is difficult to determine if this time is being spent resting or sleeping.

## Behaviour

### Life cycle

Porpoises are fully aquatic creatures. Females deliver a single calf after a gestation period lasting about a year. Calving takes place entirely under water, with the foetus positioned for tail-first delivery to help prevent drowning. Females have mammary glands, but the shape of a newborn calf's mouth does not allow it to obtain a seal around the nipple— instead of the calf sucking milk, the mother squirts milk into the calf's mouth. This milk contains high amounts of fat, which aids in the development of blubber; it contains so much fat that it has the consistency of toothpaste. The calves are weaned at about 11 months of age. Males play no part in rearing calves. The calf is dependent for one to two years, and maturity occurs after seven to ten years, all varying between species. This mode of reproduction produces few offspring, but increases the probability of each one surviving.

### Diet

Porpoises eat a wide variety of creatures. The stomach contents of harbour porpoises suggests that they mainly feed on benthic fish, and sometimes pelagic fish. They may also eat benthic invertebrates. In rare cases, algae, such as Ulva lactuca, is consumed. Atlantic porpoises are thought to follow the seasonal migration of bait fish, like herring, and their diet varies between seasons. The stomach contents of Dall's porpoises reveal that they mainly feed on cephalopods and bait fish, like capelin and sardines. Their stomachs also contained some deep-sea benthic organisms.

The finless porpoise is known to also follow seasonal migrations. It is known that populations in the mouth of the Indus River migrate to the sea from April through October to feed on the annual spawning of prawns. In Japan, sightings of small pods of them herding sand lance onto shore are common year-round.

Little is known about the diets of other species of porpoises. A dissection of three Burmeister's porpoises shows that they consume shrimp and euphausiids (krill). A dissection of a beached Vaquita showed remains of squid and grunts. Nothing is known about the diet of the spectacled porpoise.

## Interactions with humans

### Research history

In Aristotle's time, the 4th century BCE, porpoises were regarded as fish due to their superficial similarity. Aristotle, however, could already see many physiological and anatomical similarities with the terrestrial vertebrates, such as blood (circulation), lungs, uterus and fin anatomy. His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his "Natural history". In the art of this and subsequent periods, porpoises are portrayed with a long snout (typical of dolphins) and a high-arched head. The harbour porpoise was one of the most accessible species for early cetologists, because it could be seen very close to land, inhabiting shallow coastal areas of Europe. Much of the findings that apply to all cetaceans were first discovered in porpoises. One of the first anatomical descriptions of the airways of the whales on the basis of a harbor porpoise dates from 1671 by John Ray. It nevertheless referred to the porpoise as a fish, most likely not in the modern-day sense, where it refers to a zoological group, but the older reference as simply a creature of the sea (cf. for example star-fish, cuttle-fish, jelly-fish and whale-fish).

### In captivity

Harbour porpoises have historically been kept in captivity, under the assumption that they would fare better than their dolphin counterparts due to their smaller size and shallow-water habitats. Up until the 1980s, they were consistently short-lived. Harbour porpoises have a very long captive history, with poorly documented attempts as early as the 15th century, and better documented starting in the 1860s and 1870s in London Zoo, the now-closed Brighton Aquarium & Dolphinarium, and a zoo in Germany. At least 150 harbour porpoises have been kept worldwide, but only about 20 were actively caught for captivity. The captive history is best documented from Denmark where about 100 harbour porpoises have been kept, most in the 1960s and 1970s. All but two were incidental catches in fishing nets or strandings. Nearly half of these died within a month of diseases caught before they were captured or from damage sustained during capture. Up until 1984, none lived for more than 14 months. Attempts to rehabilitate seven rescued individuals in 1986 only resulted in three that could be released 6 months later. Very few have been brought into captivity later, but they have lived considerably longer. In recent decades, the only place keeping the species in Denmark is the Fjord & Bælt Centre, where three rescues have been kept, along with their offspring. Among the three rescues, one (father of world's first harbour porpoise born in captivity) lived for 20 years in captivity and another 15 years, while the third (mother of first born in captivity) is the world's oldest known harbour porpoise, being 28 years old in 2023. The typical age reached in the wild is 14 years or less. Very few harbour porpoises have been born in captivity. Historically, harbour porpoises were often kept singly and those who were together often were not mature or of the same sex. Disregarding one born more than 100 years ago that was the result of a pregnant female being brought into captivity, the world's first full captive breeding was in 2007 in the Fjord & Bælt Centre, followed by another in 2009 in the Dolfinarium Harderwijk, the Netherlands. In addition to the few kept in Europe, harbour porpoise were displayed at the Vancouver Aquarium (Canada) until recently. This was a female that had beached herself onto Horseshoe Bay in 2008 and a male that had done the same in 2011. They died in 2017 and 2016 respectively.

Finless porpoises have commonly been kept in Japan, as well as China and Indonesia. As of 1984, ninety-four in total had been in captivity in Japan, eleven in China, and at least two in Indonesia. As of 1986, three establishments in Japan had bred them, and there had been five recorded births. Three calves died moments after their birth, but two survived for several years. This breeding success, combined with the results with harbour porpoise in Denmark and the Netherlands, proved that porpoises can be successfully bred in captivity, and this could open up new conservation options. The reopened Miyajima Public Aquarium (Japan) houses three finless porpoises. As part of an attempt of saving the narrow-ridged (or Yangtze) finless porpoise, several are kept in the Baiji Dolphinarium in China. After having been kept in captivity for 9 years, the first breeding happened in 2005.

Small numbers of Dall's porpoises have been kept in captivity in both the United States and Japan, with the most recent being in the 1980s. The first recorded instance of a Dall's taken for an aquarium was in 1956 captured off Catalina Island in southern California. Dall's porpoises consistently failed to thrive in captivity. These animals often repeatedly ran into the walls of their enclosures, refused food, and exhibited skin sloughing. Almost all Dall's porpoises introduced to aquaria died shortly after, typically within days. Only two have lived for more than 60 days: a male reached 15 months at Marineland of the Pacific and another 21 months at a United States Navy facility.

As part of last-ditch effort of saving the extremely rare vaquita (the tiny remaining population is rapidly declining because of bycatch in gillnets), there have been attempts of transferring some to captivity. The first and only caught for captivity were two females in 2017. Both became distressed and were rapidly released, but one of them died in the process. Soon after the project was abandoned.

Only a single Burmeister's porpoise and a single spectacled porpoise have been kept in captivity. Both were stranded individuals that only survived a few days after their rescue.

### Threats

#### Hunting

Porpoises and other smaller cetaceans have traditionally been hunted in many areas, at least in Asia, Europe and North America, for their meat and blubber. A dominant hunting technique is drive hunting, where a pod of animals is driven together with boats and usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. This type of fishery for harbour porpoises is best documented from the Danish Straits, where it occurred until the end of the 19th century (it was banned in 1899), and again during the shortages in World War I and World War II. The Inuit in the Arctic hunt harbour porpoises by shooting and drive hunt for Dall's porpoise still takes place in Japan. The number of individuals taken each year is in the thousands, although a quota of around 17,000 per year is in effect today making it the largest direct hunt of any cetacean species in the world and the sustainability of the hunt has been questioned.

#### Fishing

Porpoises are highly affected by bycatch. Many porpoises, mainly the vaquita, are subject to great mortality due to gillnetting. Although it is the world's most endangered marine cetacean, the vaquita continues to be caught in small-mesh gillnet fisheries throughout much of its range. Incidental mortality caused by the fleet of El Golfo de Santa Clara was estimated to be at around 39 vaquitas per year, which is over 17% of the population size. Harbour porpoises also suffer drowning by gillnetting, but on a less threatening scale due to their high population; their mortality rate per year increases a mere 5% due to this.

The fishing market, historically has always had a porpoise bycatch. Today, the Marine Mammal Protection Act of 1972 has enforced the use of safer fishing equipment to reduce bycatch.

#### Environmental hazards

Porpoises are very sensitive to anthropogenic disturbances, and are keystone species, which can indicate the overall health of the marine environment. Populations of harbor porpoises in the North and Baltic Seas are under increasing pressure from anthropogenic causes such as offshore construction, ship traffic, fishing, and military exercises. Increasing pollution is a serious problem for marine mammals. Heavy metals and plastic waste are not biodegradable, and sometimes cetaceans consume these hazardous materials, mistaking them for food items. As a result, the animals are more susceptible to diseases and have fewer offspring. Harbour porpoises from the English Channel were found to have accumulated heavy metals.

The military and geologists employ strong sonar and produce an increases in noise in the oceans. Marine mammals that make use of biosonar for orientation and communication are not only hindered by the extra noise, but may race to the surface in panic. This may lead to a bubbling out of blood gases, and the animal then dies because the blood vessels become blocked, so-called decompression sickness. This effect, of course, only occurs in porpoises that dive to great depths, such as Dall's porpoise.

Additionally, civilian vessels produce sonar waves to measure the depth of the body of water in which they are. Similar to the navy, some boats produce waves that attract porpoises, while others may repel them. The problem with the waves that attract is that the animal may be injured or even killed by being hit by the vessel or its propeller.

### Conservation

The harbour porpoise, spectacled porpoise, Burmeister's porpoise, and Dall's porpoise are all listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). In addition, the Harbour porpoise is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS) and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia. Their conservation statuses are either at least concern or data deficient.

As of 2014, only 505 Yangtze finless porpoises remained in the main section of the Yangtze, with an alarming population density in Ezhou and Zhenjiang. While many threatened species decline rate slows after their classification, population decline rates of the porpoise are actually accelerating. While population decline tracked from 1994 to 2008 has been pegged at a rate of 6.06% annually, from 2006 to 2012, the porpoise population decreased by more than half. Finless porpoise population decrease of 69.8% in just a 22-year span from 1976 to 2000. 5.3%. A majority of factors of this population decline are being driven by the massive growth in Chinese industry since 1990 which caused increased shipping and pollution and ultimately environmental degradation. Some of these can be seen in damming of the river as well as illegal fishing activity. To protect the species, China's Ministry of Agriculture classified the species as being National First Grade Key Protected Wild Animal, the strictest classification by law, meaning it is illegal to bring harm to a porpoise. Protective measures in the Tian-e-Zhou Oxbow Nature Reserve has increased its population of porpoises from five to forty in 25 years. The Chinese Academy of Science's Wuhan Institute of Hydrobiology has been working with the World Wildlife Fund to ensure the future for this subspecies, and have placed five porpoises in another well-protected area, the He-wang-miao oxbow. Five protected natural reserves have been established in areas of the highest population density and mortality rates with measures being taken to ban patrolling and harmful fishing gear in those areas. There have also been efforts to study porpoise biology to help specialize conservation through captivation breeding. The Baiji Dolphinarium, was established in 1992 at the Institute of Hydrobiology of the Chinese Academy of Sciences in Wuhan which allowing the study of behavioral and biological factors affecting the finless porpoise, specifically breeding biology like seasonal changes in reproductive hormones and breeding behavior.

Because vaquitas are indigenous to the Gulf of California, Mexico is leading conservation efforts with the creation of the International Committee for the Recovery of the Vaquita (CIRVA), which has tried to prevent the accidental deaths of vaquitas by outlawing the use of fishing nets within the vaquita's habitat. CIRVA has worked together with the CITES, the Endangered Species Act, and the Marine Mammal Protection Act (MMPA) to nurse the vaquita population back to a point at which they can sustain themselves. CIRVA concluded in 2000 that between 39 and 84 individuals are killed each year by such gillnets. To try to prevent extinction, the Mexican government has created a nature reserve covering the upper part of the Gulf of California and the Colorado River delta. They have also placed a temporary ban on fishing, with compensation to those affected, that may pose a threat to the vaquita.

## See also

- List of individual cetaceans

Small cetacean of the family Phocoenidae