Extinct genus of dinosaurs
Pararhabdodon (meaning "near fluted tooth" in reference to "Rhabdodon") is a genus of tsintaosaurin hadrosaurid dinosaur, from the Maastrichtian-age Upper Cretaceous Tremp Group of Spain. The first remains were discovered from the Sant Romà d’Abella fossil locality and assigned to the genus "Rhabdodon", and later named as the distinct species Pararhabdodon isonensis in 1993. Known material includes assorted postcranial remains, mostly vertebrae, as well as ;dfn id="" ;maxillae ;/dfn ; from the skull. Specimens from other sites, including remains from France, a maxilla previously considered the distinct taxon "Koutalisaurus kohlerorum", an additional maxilla from another locality, the material assigned to the genera "Blasisaurus" and "Arenysaurus", and the extensive Basturs Poble bonebed have been considered at different times to belong to the species, but all of these assignments have more recently been questioned. It was one of the last non-avian dinosaurs known from the fossil record that went extinct during the Cretaceous-Paleogene extinction event.
Initially, the material was thought to belong to a rhabdodontid dinosaur, or some other similar type of primitive iguanodontian. Later discoveries of additional material revealed its true nature as a hadrosaur. Its placement within the group remained controversial - in 1999 it was proposed it belonged to the subfamily Lambeosaurinae, making it the first known from the continent of Europe. Later studies questioned this, instead classifying it as a more primitive hadrosauroid. In 2009 evidence was put forward that it was indeed a lambeosaurine, and more specifically a close relative of "Tsintaosaurus", a genus from China. This position has been repeatedly found since, and the group containing them was later named Tsintaosaurini. A different position, related to other European lambeosaurs in the group Arenysaurini, was proposed in 2020.
History and assigned material.
Sant Romà d’Abella material.
Excavation of specimens that would later be used to erect "Pararhabdodon" began in Spring 1985, at the Sant Romà d’Abella (SRA) locality (in the Pyrenees near Isona, Lleida, Spain) of the Talarn Formation in the Tremp Group. In 1987, Casanovas-Cladellas "et al." described remains of an ornithopod from Catalonia, including a cervical vertebra, some partial dorsals, a humerus, and a fragmentary scapula, as "Rhabdodon" sp. New remains from this site, excavated in 1990, brought about a reconsideration of the material, and Casanovas-Cladellas and colleagues named it as the new genus and species "Pararhabdodon isonense" in 1993. At the time, it was still considered to be a rhabdodont-like basal iguanodont, hence the name; "isonense" was in reference to Isona.
Additional material from the type locality was collected in 1994 - including two maxillae, two dorsal vertebrae, a complete sacrum, two fragmentary ribs, and a partial ischium. The species name was corrected to "isonensis" in 1997 by Laurent "et al.". The new material, most importantly cranial and mandibular elements (those from the skull) led to Casanovas-Cladellas' team re-classifying it as a hadrosaurid as opposed to a basal iguanodont. In 1999 it was more specifically identified as a lambeosaurine hadrosaur, in a paper again by Casanovas-Cladellas "et al.". This made it the first member of the subfamily from the continent, and the second valid hadrosaur, preceded by "Telmatosaurus" and the dubious "Orthomerus".
In total, known material from the type locality includes: a left and a right maxilla; five cervical, five dorsal, and one caudal vertebra; a sacrum; fragmentary rib bones; one end of the right ;dfn id="" ;ischium ;/dfn ;; a fragment of the left ;dfn id="" ;scapula ;/dfn ;, an ;dfn id="" ;ulna ;/dfn ; and a ;dfn id="" ;humerus ;/dfn ;. All of this material was excavated from a by surface, and it is thought to have belonged to a single individual. The holotype is a nearly complete caudally located cervical vertebra (a cervical vertebra located near the base of the neck), specimen number IPS SRA-1. Another cervical, a humerus, and an ulna were designated the paratype specimens. In 2020, Jesús F. Serrano and colleagues described new hindlimb material from the site, found in 2018. These are thought to belong to the holotype individual. This includes a ;dfn id="" ;femur ;/dfn ;, a partial ;dfn id="" ;tibia ;/dfn ;, a complete ;dfn id="" ;fibula ;/dfn ;, and a ;dfn id="" ;haemal arch ;/dfn ;.
Referred material from other localities.
In their 1997 paper, Laurent and colleagues referred remains from the Le Bexen site of the uppermost Cretaceous of Aude, southern France, to the genus. Prieto-Márquez and colleagues commented on this referral in a 2006 paper, although noted they had not examined the material themselves. They concluded all the specimens, excepting one fragmentary humerus, were too poorly preserved to allow proper comparison with the holotype material. As such, they disagreed with the referral. Of the humerus, they found it distinguishable from that of the SRA material, and so also not referable to the species. First hand study for a 2013 re-evaluation of European lambeosaurine material supported these conclusions. Laurent had, in a 2003 dissertation, referred more French lambeosaurine material to "Pararhabdodon", held at the Musée des Dinosaures d’Espéraza; the referral was made as the genus was at that point the only named lambeosaurine from the continent. Prieto-Márquez "et al." (2013) used this material to establish a new taxon, "Canardia garonnensis".
A maxilla, specimen MCD 4919, was referred to "P. isonensis" in 2013. It possessed traits of the tsintaosaurin tribe which "Pararhabdodon" was by that point assigned to. It was referable to "Pararhabdodon" in particular because of the rostrocaudally broad rostrocaudal region of the maxilla, a trait unique to "P. isonensis" among the tribe. The specimen was discovered at the Serrat del Rostiar 1 locality, part of the Conques Formation; this is part of the Tremp Group just like the type locality, but in a lower section of the strata, making it older. The referral to "Pararhabdodon" thus extended the range of the genus further within the upper Maastrichtian. A 2019 paper questioned the referral of MCD 4919 to "P. isonensis". The specimen was found to have a differing ;dfn id="" ;ectopterygoid shelf ;/dfn ; compared to the maxilla of the holotype, which would conflict with belonging to the same species. As the specimen was still recognized as having tsintaosaurin characteristics, the authors still considered it to likely belong to a close relative of "P. isonensis".
The same 2013 study also evaluated "Blasisaurus canudoi", from the Blasi 1 locality of the underlying Arén Formation, and "Arenysaurus ardevoli", from the Blasi 3 locality of the La Posa Formation, another part of the Tremp Group. Previously claimed diagnostic traits of the two taxa were shown to be found in other hadrosaurs. This left the former with two unique characteristics - both in the jugal - and a unique combination of other characteristics, and the latter with only one unique characteristic - in the frontal. As overlapping fossils were not known for the relevant areas, it could not be ruled out that they were indeed synonymous, representatives of a single species. The same re-evaluation could not rule out that this single species or either of the separated species were synonyms of "Pararhabdodon isonensis", as no taxonomically informative areas of the skeleton are known from both "Pararhabdodon" and the other two taxa. The authors refrained from considering any of them representatives of one species pending data from more material. The "Pararhabdodon" himdlimb described in 2020 allowed for synonymy with "Arenysaurus" to be ruled out, as the femurs of the two taxa were anatomically distinct.
A hadrosaur mega-bonebed, later termed the Basturs Poble bonebed, was discovered in outcrops of the Conques Formation during the late 1990s. The taxonomic status of this bonebed has fluctuated over time. It has been debated whether the material represents a singular species or a combination of two distinct ones; but today a single, variable species is considered most likely. It was suggested the material likely belong to "Koutalisaurus", based on geographic proximity, but this reassignment was abandoned when that genus was recognized as indeterminate. Since then, it has instead been tentatively assigned to the genus "Pararhabdodon". However, due to the lack of any suitable material for comparison and the lack of tsintaosaurin characteristics in the bonebed material, it has been more recently suggested that it should instead be considered indeterminate lambeosaur material. The 2020 hindlimb description allowed for distinction between "Pararhabdodon" and the Basturs Poble material to be solidified, with the bonebed material showing inconsistent femoral anatomy with the genus.
Relationship with "Koutalisaurus".
Near the village Abella de la Conca, in the 1990s, palaeontologist Marc Boada discovered a new site in the Talarn Formation, bearing dinosaur fossils. From this site, later named Les Llaus (LL), a right dentary, specimen designation IPS SRA 27, was excavated. In 1997, Casanovas-Cladellas and colleagues stated this dentary was discovered from SRA, the site where the original "Pararhabdodon" remains were found. The following year, they described the specimen and referred it to "P. isonensis", and again stated it was from the same stratigraphic level. In 2006, the stratigraphy of the region was re-evaluated by Albert Prieto-Márquez and colleagues, and the dentary's location was corrected to the LL locality, away from and below the SRA locality. They noted that no dentary had been found at the SRA locality to compare to the LL specimen, and so they restricted "P. isonensis" to material known from its original locality. Additionally, they named a genus and species for IPS SRA 27, "Koutalisaurus kohlerorum". One autapomorphy (unique trait) was used to diagnose the taxon as a new species: a very elongated edentulous section on the dentary, which was medially (inwardly) extended. The authors noted the possibility that future discoveries could lead to synonymization of their taxon with "P. isonensis"
Evidence for this synonymy would later come in a 2009 study, from Prieto-Márquez alongside Jonathan R. Wagner. Material from "Pararhabdodon", the holotype of "Koutalisaurus", and material of the Chinese species "Tsintaosaurus spinorhinus" were examined and compared, and the edentulous slope previously thought unique to "Koutalisaurus" was found to be nearly identical in "T. spinorhinus". No material had, as yet, been discovered from the SRA locality permitting comparison with "Pararhabdodon". However, traits uniting "P. isonensis" with "T. spinorhinus" were found. As both taxa from the Talarn Formation uniquely shared traits with the Asian genus, the authors decided to treat the two as one species, as maintaining them as provisionally separate would in their eyes be misleading to non-specialists, who would likely not distinguish that the two taxa were being kept separate to be conservative and not due to strong evidence for two hadrosaurs in the area.
Prieto-Márquez returned again to the dentary in 2013, in a study alongside colleagues providing a review and investigation of hadrosaurs from all over Europe. Further preparation of the specimen in the time since his last study regarding it revealed the uniqueness of the dentary had been exaggerated significantly by reconstruction of the specimen when it was first prepared in the 1990s. The "Tsintaosaurus" specimens showing the similar condition were found to have been distorted from a similar process. Correcting for the inaccuracies, the Los Llaus dentary is indistinguishable from that of multiple lambeosaurines, and shares no particular connection to "Tsintaosaurus". With this, their reasoning for assignment of the specimen to "Pararhabdodon" was voided, and the specimen is now considered a completely indeterminate lambeosaurine dentary.
Description.
"Pararhabdodon" would have been a bipedal-quadrupedal herbivore. The holotype specimen is estimated to have been around long. Histological analysis indicates the individual was not fully grown, and so the species likely reached similar sizes to North American and Asian relatives such as "Corythosaurus" and "Tsintaosaurus" (around long). This is despite "Pararhabdodon" living on an island, something generally associated with insular dwarfism, a phenomenon exhibited in other European hadrosaurs; "Adynomosaurus" was cited as a similar example, being around the same size.
Classification.
"Pararhabdodon" has been classified in a number of different positions within Iguanodontia since its remains were first discovered in the mid-1980s. When the first specimens were originally discovered and described by Casanovas-Cladellas and colleagues, they were not thought to belong a new taxon at all, but merely to belong to the genus "Rhabdodon", and of an uncertain species. Not long after, they would be recognized of those of a unique species, and in 1993 they were given their modern name. At this point it was still thought to be a rhabdodontid or some other type of primitive iguanodont closely related to them. This was based on the characteristics