Histology and pneumaticity of Aoniraptor libertatem (Dinosauria, Theropoda), an enigmatic mid‐sized megaraptoran from Patagonia

Abstract

Aoniraptor libertatem is a mid‐sized megaraptoran that comes from the Late Cretaceous (Turonian) Huincul Formation at Río Negro province, Patagonia, Argentina. In this study, we conducted a detailed analysis of pneumaticity of the sacrum and tail of Aoniraptor. This shows a complex structure within these vertebrae, being composed by small diverticulae surrounding large pneumatic canals and a central chamber that opens outside through pleurocoels or pneumatic canals. Further, we carried out a histologic analysis which confirms the pneumatic nature of these anatomical features. Both analyses found that chevrons in Aoniraptor were invaded by pneumaticity, a feature that appears to be unique to this taxon. In addition, a comparative analysis between Aoniraptor and other theropods (e.g. Gualicho and other megaraptorans) was carried out. This resulted in the modification of previous schemes about the evolution of pneumaticity through Theropoda, the finding of some evolutionary pneumatic traits through Megaraptora, and the usefulness of pneumatic traits as a taxonomic tool.

A large Megaraptoridae (Theropoda: Coelurosauria) from Upper Cretaceous (Maastrichtian) of Patagonia, Argentina

“…Aoniraptor is resolved as a megaraptoran of uncertain affinities (Fig. 15 A), as has been observed in other works 13 , 32 . The enigmatic theropod Gualicho 18 , which in some analyses 63 has been considered as a possible synonym of Aoniraptor , here is deeply nested within Tyrannosauroidea, but far from Aoniraptor (Fig.…”

“…In sum, following Aranciaga Rolando et al . 13 , we conclude that both taxa are not closely related.…”

“…Their articular surfaces are ovoid and face dorsomedially. The PRSF is deep and transversely narrow, and within this fossa there is a subtriangular pneumatopore as occurs in Aoniraptor 13 . The left process is completely preserved and becomes dorsoventrally thicker towards its tip.…”

“…Argentine Patagonia has the richest megaraptorid record of the continent. The oldest Patagonian records consist of an indeterminate megaraptorid coming from Bajo Barreal Formation (Cenomanian-Turonian 20 ) and Aoniraptor libertatem found in beds of the Huincul Formation (Cenomanian-Turonian 13 , 32 ). The following records are, from oldest to youngest, Megaraptor namunhuaiquii from the Portezuelo Formation (Coniacian 6 , 10 , 17 ), Murusraptor barrosaensis from the Sierra Barrosa Formation (Coniacian 33 ), Aerosteon riocoloradensis from the Anacleto Formation (Santonian 34 ), Tratayenia rosalesi from the Bajo de la Carpa Formation (Santonian 19 ), Orkoraptor burkei from the Cerro Fortaleza Formation (Campanian 35 ), and some indeterminate megaraptoran remains from two Maastrichtian units: Lago Colhué Huapi 36 , 37 and Chorrillo formations 3 .…”

Reconstruction of the pectoral girdle and forelimb musculature of Megaraptora (Dinosauria: Theropoda)

“…Early branching megaraptorans are known from the Early and middle Cretaceous of Thailand (Phuwiangvenator yaemniyomi and Vayuraptor nongbualamphuensis; Samathi et al, 2019Samathi et al, , 2022, Japan (Fukuiraptor kitadaniensis; Azuma & Currie, 2000;Currie & Azuma, 2006), and probably Australia (Aranciaga Rolando et al, 2022;Benson et al, 2012) and South America (e.g., Aoniraptor libertatem; Aranciaga Rolando et al, 2018Rolando et al, , 2020Motta et al, 2016). More derived megaraptorans-that is, members of Megaraptoridae-have been found in the mid-Cretaceous of Australia (Australovenator wintonensis, "Rapator ornitholestoides," Megaraptoridae cf.…”