¿Qué ha pasado en Ornithomimosauria en 25 años?, en el XVI EJIP

Foto de Elena Cuesta con el poster presentado en el XVI EJIP

Seguimos con más trabajos presentados en el pasado XVI EJIP que tuvo lugar los días 11-14 de Abril en Zarautz. Esta vez, el trabajo presentado por el Elena Cuesta sobre los últimos descubrimientos en Ornithomimosauria. Hace 25 años que se descubrió el holotipo de Pelecanimimus polyodon, cuyos resultados de su análisis preliminar, publicado en 1994, aportan un gran avance en el estudio de este grupo. Sin embargo, el número de taxones hallados en este cuarto de siglo de Ornithomimosauria ha aumentado como la espuma, suponiendo un gran avance en el conocimiento de este grupo clave de celurosaurios. Por ejemplo, este grupo era previamente conocido en Asia Oriental y Norte América cuando Pelecanimimus, el primer especimen hallado en Europa, fue descrito, sin embargo, ahora se conocen taxones en muchas partes del mundo, incluyendo restos en lo que antes era Gondwana. Conocer todos estos descubrimientos son clave para el estudio actual que se está haciendo en Pelecanimimus, el cual aportará resultados para entender la historia evolutiva de este grupo.

Aquí dejamos el resumen en inglés de este trabajo:

INTRODUCTION

Ornithomimosauria is a Coelurosaurian clade, more derived than Tyrannosauroidea and the sister group of Maniraptora, being one of the most basal clades in Coelurosauria. Moreover, this is a clade of highly specialized theropod dinosaurs, whose functional behaviour has hitherto been subject of debate.

Ornithomimosaurs are widely distributed throughout the world, especially in Cretaceous beds of Asia and North America. The European record is poorly represented; with only some specimens from England, France, and Spain. The first known European ornithomimosaur was Pelecanimimus polyodon from Las Hoyas fossil site, a Konservat-lagerstätte from the Barremian (Early Cretaceous) of Cuenca (Spain). Thus, the holotype is well-preserved like other specimens from Las Hoyas. It is composed of the anterior half of the skeleton, including the complete skull. Moreover, Pelecanimimus also preserves integumentary impressions, such as an occipital crest and an angular pouch.

Over the last years, a vast number of new discoveries have increased the known diversity of the group. Based on these discoveries, several analyses have been performed to provide new looks at the Ornithomimosauria phylogeny in the last 25 years.

25 YEARS OF NEW DISCOVERIES IN ORNITHOMIMOSAURIA

When Pelecanimimus was published by Pérez-Moreno et al. (1994), Ornithomimosauria was a group composed of derived taxa (Ornithomimidae) from Asia, such as Gallimimus bullatus, Anserimimus planinychus, Archaeornithomimus asiaticus, and North America, like Ornithomimus edmontonicus and Struthiomimus altus. Yet the primitive Asian taxa (Basal Ornithomimosauria) Harpymimus okladnikovi and Garudimimus brevipes were was also known. Therefore, the discovery of Pelecanimimus implied the first unambiguous evidence of ornithomimosaurian theropods in Europe. The phylogenetic results by Pérez-Moreno et al. (1994) also indicated that Pelecanimimus was the most basal representative of the clade.

At present, the new discoveries indicate that the group is more widely distributed than was previously thought, occurring even in the Berriasian-Valanginian (Early Cretaceous) of Africa with the presence of Nqwebasaurus thwazi, which is currently the most basal taxa within the clade. The western European record has been enlarged with new discoveries such as the Hauterivian-Barremian Angeac bone bed material of France, not described in detail yet; and some fragmentary Early Cretaceous material from England like Valdoraptor, which has been considered as a nomen dubium.

The eastern Asian record has increased in the last years. The most basal Chinese ornithomimosaurian, discovered by Ji et al. (2003), is Shenzhousaurus orientalis from the Yixian Formation (Early Cretaceous). Moreover, another non-ornithomimid taxon was also described by Makovicky et al., 2009, Beishanlong grandis, from the Aptian-Albian (Early Cretaceous) of China. Furthermore, two new species of Ornithomimidae have been included in the eastern Asian record in the last years: Aepyornithomimus tugrikinensis from the Upper Cretaceous of Mongolia and Sinornithomimus dongi from the Lower Cretaceous of China, which includes several complete specimens that suggest a gregarious behaviour. Together with the discoveries in East Asia, there are also new records in Central Asia, due to the discovery of an almost complete ornithomimosaurian from the Bissekty Formation (Turonian, Late Cretaceous of Uzbekistan), of fragmentary material from the Lower Cenomanian (Late Cretaceous) of Kyrgyzstan, from the Coniacian–Lower Santonian (Late Cretaceous) of Tajikistan, and from the Santonian-Campanian (Late Cretaceous) of Kazakhstan. In Central Asia, the oldest known ornithomimosaurian, Lepidocheirosaurus natatilis, has been described by Alifanov and Saveliev (2015), from the Upper Jurassic of Transbaikalia, Russia.

In addition to the new discoveries of the last 25 years, a re-examination of classical Asian ornithomimosaurs has been also carried out, which has led to new phylogenetic hypotheses or to the support of the previous ones. For instance, the new information provided by Kobayashi and Barsbold (2004, 2005) supports that Ornithomimidae is a sister taxon to the clade composed of Beishalong+Garudimimus+Deinocheirus. It is worth mentioning the recent publication on new skeletal material of Deinocheirus mirificus that has revealed that this species unequivocally belongs to Ornithomimosauria, hypothesis that was previously casted doubt by Makovicky et al. (2004).

Finally, the North American record has also provided new material within Ornithomimosauria from the Lower Cretaceous beds of the United States (Ornithomimosaur indet: Brownstein, 2017) to the Upper Cretaceous beds of Mexico (Tototlmimus packardensis: Serrano-Brañas et al., 2016) and Canada (Ornithomimid indet: Longrich, 2008).

CONCLUSIONS: FUTURE PERSPECTIVES

Since the discovery of Pelecanimimus, the known diversity of the Ornithomimosauria has increased with new discoveries of fossil material throughout the world. The European localization of Pelecanimimus and its basal position within the clade implies that this taxon is key to understanding the palaeobiogeographical and phylogenetical hypotheses of Ornithomimosauria. Therefore, a review of the holotype and its integration with the new information of ornithomimosaurian known taxa collected in these last years would shed light on the evolutionary history of this theropod lineage.