Family of ornithocheiran pterosaurs
 
Ornithocheiridae (or ornithocheirids, meaning "bird hands") is a group of pterosaurs within the suborder Pterodactyloidea. These pterosaurs were among the last to possess teeth. Members that belong to this group lived from the Early to Late Cretaceous periods (Valanginian to Turonian stages), around 140 to 90 million years ago.
Ornithocheirids are generally infamous for having an enormously controversial and very confusing taxonomy. Although agreements that these animals were related, and therefore similar to istiodactylids and pteranodontians, there is still no virtual consensus over the exact content and interrelationships of this group. Ornithocheirids were the most successful pterosaurs during their reign, and were also the largest pterosaurs before the appearance of the azhdarchids such as "Quetzalcoatlus". Ornithocheirids were excellent fish hunters, using various flight techniques to catch their prey, and were also capable of flying great distances without flapping constantly. Paleontologists suspect that ornithocheirids were the ancestors of the pteranodontians; this is due to many shared aspects, such as unique flying techniques, capability of long-distance flights, and most of their diet, which mainly consisted of fish.
History.
Naming.
The family Ornithocheiridae is without a doubt, one of the most well-known pterosaur groups, mostly due to their very controversial and convoluted taxonomic history. Most of the ornithocheirid fossil record consists of isolated teeth, as well as fragmentary bones, reaching hundreds or even thousands of remains in some localities. The first uncovered ornithocheirid remains were described in 1861 by British paleontologist Sir Richard Owen, who assigned the fossil remains to a new species of "Pterodactylus": "P. simus". In 1869, British paleontologist Harry Govier Seeley erected the new generic name "Ornithocheirus" (from Ancient Greek meaning "bird hand"), and assigned "P. simus" as its type species, therefore creating "Ornithocheirus simus". Later, in 1870, Seeley created the name Ornithocheirae to only contain "Ornithocheirus". However, in the same year, this was emended to Ornithocheiridae by Seeley himself following the article 11.7.1.3 of the ICZN.
In 1874, Owen had proposed two new genera for the Cretaceous British pterosaurs: "Coloborhynchus" (meaning "maimed beak") and "Criorhynchus" (meaning "ram beak") based on highly distinctive jaw fragments. Owen reassigned "P. simus" as the type species of "Criorhynchus", creating "Criorhynchus simus". He referred three species to "Coloborhynchus", including the addition of a new species called "C. clavirostris"; no type species was designated, however. In 1876, however, Seeley pointed out that "Criorhynchus" was a junior synonym of "Ornithocheirus", a concept that was followed by paleontologist Richard Lydekker in 1888. In the latter year, Lydekker acknowledged that "Ornithocheirus simus" was the type species of "Ornithocheirus", and also distinguished "O. simus" by its tall rostrum, while other species referred to "Ornithocheirus" had lanceolate jaw tips. Therefore, to avoid confusion, Lydekker preferred to use the name "Criorhynchus" for "O. simus", and "Ornithocheirus" for the species with lanceolate jaw tips, a concept later favored by paleontologist Reginald Walter Hooley in 1914. In his review of "Ornithocheirus", he divided the family Ornithocheiridae into two subfamilies: Ornithocheirinae and Criorhynchinae; the former consisted of "Ornithocheirus" and "Lonchodectes", while the latter consisted of "Amblydectes" and "Criorhynchus". In his review, Hooley also considered the species "Coloborhynchus clavirostris" as a synonym of "Criorhynchus simus". In 1967, paleontologist Oskar Kuhn placed "Criorhynchus" within the family Criorhynchidae (which is now considered synonymous to Ornithocheiridae), and recognized "Ornithocheirus" within the family Ornithocheiridae and subfamily Ornithocheirinae. He also designated the species "Coloborhynchus clavirostris" as the type species of "Coloborhynchus", but agreed with Hooley that it was synonymous with "Criorhynchus simus". In 1994, however, Yuong-Nam Lee revalidated the genus "Coloborhynchus" (with "C. clavirostris" as its type species), and regarded it as distinct from "Criorhynchus simus". Later, in 2001, paleontologist David Unwin revised the taxonomic history of the Cambridge Greensand pterosaurs, and divided Ornithocheiridae into three genera: "Ornithocheirus", "Coloborhynchus" and "Anhanguera". Unwin also designated "Ornithocheirus simus" as the type and only species of "Ornithocheirus".
In 2003, Unwin defined the family Ornithocheiridae as "Haopterus gracilis", "Ornithocheirus simus", their most recent common ancestor, and all its descendants. He included the genera "Anhanguera", "Brasileodactylus", "Coloborhynchus", "Haopterus", "Ludodactylus" and "Ornithocheirus" within the family, and also concluded that "Araripesaurus", "Arthurdactylus" and "Santanadactylus" may belong to this family as well. However, their taxonomic status and precise relationships with other ornithocheirids are uncertain. In 2019, upon the description of the pterosaur "Mimodactylus", "Haopterus", which was assigned to this family by Unwin, and recovered as a basal eupterodactyloid by Brian Andres and colleagues, was reassigned by Alexander Kellner and colleagues as the sister taxon of the former.
In 2014, Andres and colleagues defined the Ornithocheiridae with a different definition: the most inclusive clade containing "Ornithocheirus simus" but not "Anhanguera blittersdorffi". They placed the genera "Coloborhynchus", "Ornithocheirus" and "Tropeognathus" within the Ornithocheiridae, while placing "Anhanguera" within the separate family Anhangueridae. However, back in 2001, Unwin considered the name Anhangueridae a junior synonym of Ornithocheiridae, a concept that was later followed by several paleontologists such as Mark Witton in 2013. Some phylogenetic analyses, however, contradict this name synonymy, with Ornithocheiridae and Anhangueridae classified as different families, therefore following the 2014 analysis by Andres and colleagues instead. Other studies such as the ones by Kellner and colleagues in 2019 have used a different concept, classifying "Coloborhynchus", "Tropeognathus", as well as several other close relatives such as "Ludodactylus" and "Caulkicephalus" within the Anhangueridae, which, along with the family Hamipteridae, forms the larger group Anhangueria. They assigned "Ornithocheirus" outside the Anhangueria due to being undiagnosable. Most recent studies have since followed this concept.
Description.
Among toothed pterodactyloids, ornithocheirids were the largest; they were also among the most successful and widely distributed pterosaurs. Ornithocheirids were characterized by long jaws with spike-like teeth. Ornithocheirid wingspans varied in size, with smaller species having wingspans of approximately , while giant morphs reached wingspans of up to or more. Specimen NHMUK R481, a specimen that belongs to the species "Coloborhynchus capito", the largest toothed pterosaur, had a wingspan that may have reached . However, in 2013, a specimen referred to the genus "Tropeognathus" (MN 6594-V), a possible ornithocheirid (as it may be an anhanguerid), was calculated to have had a normal wingspan of , with another calculated maximum wingspan reached , indicating that the wingspans of toothed pterosaurs could exceed .
Skull.
Ornithocheirids had elongated jaws with rounded sagittal crests on both tips, as well as robust fang-like teeth. The sagittal crest of the species "Ornithocheirus simus" and "Tropeognathus mesembrinus" extended to the anterior end of the rostrum, a feature that is also seen in the ornithocheirid (or alternately anhanguerid) species "Siroccopteryx moroccensis"; further synapomorphies between these three species were also found, including the premaxilla having a tall and narrow shape in anterior aspect, the anterolateral margins of the premaxilla being convex in both anterior and lateral view, a feature that resulted in a bluntly rounded outline of the tip of the rostrum. The rostrum in "S. moroccensis" lacks a constriction that is posterior to the anterior rosette, a feature also shared by "O. simus" and "T. mesembrinus", therefore another synapomorphy supported by these three species. Yet another feature shared by these three species is that the teeth are short, straight, and relatively uniform in size, something that is not present in other ornithocheirans such as "Coloborhynchus" and "Anhanguera". In "Coloborhynchus", the teeth were found to have been heterodont, elongated, recurved and caniniform, which is similar to those seen in another ornithocheirid (though also recovered as an anhanguerid) called "Caulkicephalus". The genus "Caulkicephalus", though having similarities with other ornithocheirids, including the anterior end of the rostrum being transversely expanded, or having a low, bony sagittal crest that includes a smooth dorsal margin on the rostrum, still possesses some unique features. The most distinct characteristic of "Caulkicephalus" is that it bores a frontoparietal crest, a feature that is only seen in pteranodontians such as "Pteranodon", and in "Ludodactylus", a pterosaur once assigned to the Ornithocheiridae, but some recent analysis have placed it within the more inclusive group Anhangueria, outside the Ornithocheiridae. Other studies, however, have recovered it within the Anhangueridae instead.
Postcranial skeleton.
The forelimbs of ornithocheirids were proportionally enormous, around five times longer than their legs. Substantial anchorage on the body is required given the mighty arms, and accordingly, ornithocheirids have robust scapulocoracoids, and stout, deeply keeled sterna, which served the purpose of housing their substantial forelimb muscles. The shoulder or pectoral girdle in ornithocheirids is set at a perpendicular angle to the spine, with the coracoids being much longer than the scapulae. The shoulder girdle is also of typical construction for ornithocheiroids. Over 60 percent of the wing length is occupied by the wing fingers, making them among the longest possessed by any pterodactyloids.
In adult ornithocheirids, the sacrum develops a supraneural plate above its neural spines. The tails of ornithocheirids are poorly known, though they appear to be composed of at least eleven short vertebrae, and become relatively circular in cross section toward the end of the series. Like the related istiodactylids, the slender femora of ornithocheirids have femoral heads that project almost in line with the femoral shaft, but seem to lack prominent processes that anchor their hindlimb muscles. Ornithocheirid shinbones (or tibiae) are similarly developed and of equal length to the femora. Although the feet in ornithocheirids are poorly known, they seem to be relatively small and gracile, with undeveloped claws and a hook-like fifth metatarsal.
Classification.
The family Ornithocheiridae has had a controversial and very confusing taxonomic history; paleontologists who have studied this group seem to have had a different opinion on the composition of ornithocheirid taxonomy. A term called Anhangueridae was coined by Diogenes de Almeida Campos and Kellner in 1985 to refer to pterosaurs that belong in this family. In 2001, however, Unwin argued that the name Ornithocheiridae refers to an identical group, and should have nomenclatural priority. He therefore considered Anhangueridae a junior synonym of Ornithocheiridae in his study of pterosaur phylogeny in 2003. However, in many recent studies, Anhangueridae is recovered as a separate and distinct family from Ornithocheiridae, each containing different genera. The original term Ornithocheirae by Seeley had been redefined as the least inclusive clade containing "Anhanguera blittersdorffi" and "Ornithocheirus simus", therefore it is recovered as a larger group comprising the families Anhangueridae and Ornithocheiridae in recent analysis.
Formerly assigned genera.
In the past, many pterosaur genera were assigned to the Ornithocheiridae; however, following recent studies, these supposed ornithocheirids had been reclassified to other groups or families. The pterosaur "Boreopterus" for example, was initially classified within the Ornithocheiridae; however, later analysis had found it in a different family called Boreopteridae, with "Boreopterus" being the sister taxon of "Zhenyuanopterus"; both pterosaurs were recovered as basal members of the Lanceodontia in several recent studies such as the ones by Rodrigo Pêgas and colleagues, and Adele Pentland and colleagues, both studies of which are from 2019.
"Aetodactylus" is another pterosaur that was initially classified within the Ornithocheiridae; later analysis have found it outside the Ornithocheiridae: Timothy Myers in 2015 and Nicholas Longrich and colleagues in 2018 for example, are two studies that found "Aetodactylus" as sister taxon to the two species of "Cimoliopterus" ("C. cuvieri" and "C. dunni"). In 2019, Pêgas and colleagues have found "Aetodactylus", along with two other pterosaurs ("Camposipterus" and "Cimoliopterus"), within the clade Targaryendraconia, more specifically placed within the family Cimoliopteridae in a polytomy.
The genus "Haopterus" was used to define the Ornithocheiridae in Unwin's 2003 study; however, Andres and Myers in 2013 argued that "Haopterus" had not been previously referred to the Ornithocheiridae besides a note added in proof to Unwin in 2001 that stated that "Haopterus" appeared to be a small ornithocheirid. Phylogenetic analyses since then have found "Haopterus" as a rogue taxon either within the Pterodactyloidea, the Ornithocheiroidea, the Pteranodontoidea, or the Istiodactylidae. In the phylogenetic analysis by Andres and Myers, "Haopterus" was recovered as a stable sister taxon to the group Ornithocheiroidea. Some later analyses have also recovered this concept, with both "Haopterus" and the Ornithocheiroidea placed within the larger group Eupterodactyloidea. Another study in 2019 recovered "Haopterus" within a different group called Mimodactylidae.
Phylogeny.
Different phylogenetic analysis have found Ornithocheiridae to comprise different genera, the most typical ones being "Tropeognathus", "Coloborhynchus" and "Ornithocheirus". In 2014, Andres and colleagues created the subfamily Ornithocheirinae to contain "Coloborhynchus" and "Ornithocheirus", as a sister taxon to "Tropeognathus", and altogether formed the family Ornithocheiridae. In 2018, Longrich and colleagues had included the genus "Siroccopteryx" in their phylogenetic analysis, specifically as a member of the ornithocheirine subfamily, sister taxon to "Coloborhynchus". In 2019,