When were fossils of the Pararhabdodon first found?
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Pararhabdodon (meaning "near fluted tooth" in reference to "Rhabdodon") is a genus of tsintaosaurin hadrosaurid dinosaur, from the Maastrichtian-age Upper Cretaceous Tremp Formation 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 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.
Pararhabdodon
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"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 speciemens 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 of its vertebrae, as the cranial remains had not yet been found. In 1994 these cranial remains would be found - two maxilla - and these would be used by the original authors to establish it as a species of hadrosaur.
Pararhabdodon
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The same 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 earlier "gray unit" of the Tremp Formation. 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 couldn't 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.
Pararhabdodon
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Near the village Abella de la Conca, in the 1990s, palaeontologist Marc Boada discovered a new site in the Tremp 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, and the dentary's location was corrected to the LL locality, away from and below the SRA locality.
Pararhabdodon
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Marc Boada discovered, in the late 1990s, a new fossil-bearing locality from the village of Basturs. As the village already lent its name to a locality where dinosaur eggs had been found, it was named the Basturs Poble (BP) locality, "poble" derived from the word for village. The locality belongs to the Conques Formation of the Tremp Group, dated to the late-Early Maastrictian. Over ten years, from 2001 through 2011, field work was done at this site, and a massive bonebed - consisting of some one thousand skeletal elements - was discovered. The discovery was first reported in the literature in an abstract at the "55th Symposium for Vertebrate Palaeontology and Comparative Anatomy and the 16th meeting of the Symposium for Palaeontological Preparation and Conservation" conference in 2007. The authors, then, approached the bonebed under the hypothesis of a single species being present at the site. It was reported that all ontogenetic stages were present. Later, a poster presentation and abstract at another conference suggested the specimens may have belonged to "Koutalisaurus kohlororum", but they cautioned an adult dentary from the bonebed would need to be discovered to test the hypothesis. This was later rejected, as "Koutalisaurus" was found to be an invalid "nomen dubium". In 2018, the material was instead noted as possibly referrable to "Pararhabdodon isonensis".
Pararhabdodon
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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 innaccuracies, 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.
Pararhabdodon
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Fondevilla "et al." (2018) compared to the material from Basturs Poble to recognized species of lambeosaurine from geographically and temporally similar locations in the Pyrenees. The jugals from the sample were found to be distinct from those known from "Blasisaurus" and "Arenysaurus" (possible synonyms of "Pararhabdodon"), and the frontals were also distinguishable from the latter. Identity as specimens as either of those taxa was therefore ruled out. Overlapping taxonomically informative material with "Pararhabdodon" was not found from the bonebed, excepting a maxilla too fragmentary for use in referral. However, both the type locality of SRA and the locality of the referred maxilla MCD 4919 are close to the area the bonebed was found. As such, it was considered most likely the Basturs Poble hadrosaurs are members of the species "P. isonensis", but the poor state of preservation of the only comparable material in the bonebed prevented a secure referral. Later, a 2019 study by Prieto-Márquez "et al." described a new genus and species of Spanish lambeosaurine, "Adynomosaurus arcanus". They compared the material of their species to that of the bonebed, and though similarities were found, their tooth crowns and ilia had different shapes, and the from the site lacked the distinct shallow nature that characterizes "A. arcanus". Accordingly, they considered it unlikely the bonebed belonged to their species. Additionally, they commented on the lack of tsintaosaurin synapomorphies in the bonebed material and so kept a referral as indeterminate lambeosaurines rather than considering it to represent "Pararhabdodon".
Pararhabdodon
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In their 1997 paper, Laurent and colleagues referred additional remains (jaw material, vertebrae, and limb bones of multiple individuals of different ages) 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, though noting they had not examined the material themselves. They concluded all of the specimens, excepting one fragmentary humerus, were too poorly preserved to allow proper comparison with the Spanish "Pararhabdodon" material, and so disagreed with the referral. Of the humerus, they found it was distinguishable from "P. isonensis", and so also not referable to the species. A group composed of some of the same authors as the 2006 study, including Prieto-Márquez, investigated the material first hand for a 2013 re-evaluation of all European lambeosaurine material, and supported their previous conclusions. Laurent had, in a 2003 dissertation, referred more French lambeosaurine material to "Pararhabdodon"; in this case, material held at the Musée des Dinosaures d’Espéraza. The referral was made as the genus was, at that point, the only lambeosaurine named from the continent. Prieto-Márquez "et al." (2013) used this material to establish their new taxon, "Canardia garonnensis".
Pararhabdodon
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In 2013, a maxilla, specimen designation MCD 4919, was referred to "P. isonensis". It possessed synapomorphies of the tsintaosaurin tribe to which "Pararhabdodon" was by that point assigned to, and was referable to "Pararhabdodon" in particular due to rostrocaudally broad rostrocaudal region of the maxilla, a trait unique to "P. isonensis" relative to "Tsintaosaurus", the other named tsintaosaurin taxon. The specimen was discovered at the Serrat del Rostiar 1 locality, part of the "lower red unit" of the Tremp formation just like the type locality, SRA, but in a lower section of the strata, making it older. This extended the range of species further within the upper Maastrichtian. The Serrat del Rostiar 1 locality is near the village of Basturns. In 2019, the new genus and species "Adynomosaurus arcanus" was described, and in the paper describing the referral of MCD 4919 to "P. isonensis" was questioned. The specimen was found to have a differing to the maxilla of the SRA "Pararhabdodon", which would conflict with their identity as 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".
Pararhabdodon
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The stratigraphic layer where the bonebed was found is in thickness. Around 95% of all remains from the site belong to dinosaurs; nearly all identified specimens from this sample belong to hadrosaurs. Of prepared material, 270 skeletal elements can confidently be identified as belonging to hadrosauroids. The number of hadrosaur specimens from the site in total could number over 500, and possibly as much as 900. In addition to the large numbers of fossils of the animals themselves, the BP locality is one of many sites from the Tremp Syncline where hadrosaurs tracks have been found. At least one track is preserved at the site, in a sandstone block from a stratigraphic level similar to that of the bonebed. It is the richest hadrosaur bonebed ever found in Europe, and the largest ever found in one palaeoinsular locale; as such, it is the most important hadrosauroid site of the eastern Tremp Syncline.
Pararhabdodon