New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana

Abstract

The fossil record of basal paravians in Gondwana is still poorly known, being limited to the Cretaceous unenlagiids from South America and the problematic Rahonavis from Madagascar. Here we report on a new paravian from the Cenomanian-Turonian (Late Cretaceous) of Río Negro province, NW Patagonia, Argentina. The new taxon exhibits a derived bird-like morphology of the forelimbs (e.g., robust ulna with prominent, anteriorly oriented, and proximally saddle-shaped radial cotyle and wide medial flange on metacarpal I) and a plesiomorphic foot with a raptorial pedal digit II. Phylogenetic analysis recovers the new taxon in a monophyletic clade with Rahonavis, being the sister group of the remaining Avialae and more derived than other non-avian dinosaurs. Both exhibit derived forelimb traits in opposition with their plesiomorphic hind limbs. The position of the new taxon and Rahonavis as stem avialans indicates that Gondwanan basal paravians are represented by two different clades, at least. The new taxon probably constitutes a previously unknown grade in the avian-line theropods in which some flight-related adaptations of the forelimbs are present in cursorial taxa. The present discovery sheds light on the acquisition of flight-related traits in nonavian dinosaurs and on the still poorly known paravian radiation in Gondwana.

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

“…The Violante Farm Locality houses a large variety of carnivorous theropods such as the mid‐sized abelisaurid Tralkasaurus (Cerroni et al ., 2020), large‐sized carcharodontosaurid Taurovenator (Motta et al ., 2016), mid‐sized megaraptoran Aoniraptor (Motta et al ., 2016) and a small‐sized paravian (Motta et al, 2020), as well as the enigmatic Gualicho (Apesteguía et al ., 2016). In the original description, Apesteguía and collaborators placed Gualicho at the base of Coelurosauria, very close to Megaraptora.…”

Comments on the Morphology of Basal Paravian Shoulder Girdle: New Data Based on Unenlagiid Theropods and Paleognath Birds

“…We follow the phylogenetic framework proposed by Agnolín and Novas (2013); (see also Agnolín and Novas, 2011;Agnolín et al, 2019;Motta et al, 2020) in which Deinonychosauria is interpreted as a non-monophyletic group, and Dromaeosauridae is formed by Velociraptor, Dromaeosaurus, Deinonychus, and taxa more closely related to them than to Microraptor, Unenlagia, Rahonavis or Archaeopteryx. Microraptoria and Unenlagiidae are interpreted to form successively closer relatives of the clade Avialae (Figure 1).…”

“…We use the form Unenlagiidae Novas, 2011, 2013;Motta et al, 2020) instead of the form Unenlagiinae that has been employed by several authors (Makovicky et al, 2005;Turner et al, 2007, Turner et al, 2012Brusatte et al, 2015;Cau et al, 2017;Rauhut et al, 2018;Pei et al, 2020). The name Dromaeosauridae is instead restricted to the paravian Laurasian clade including Dromaeosaurus but not Passer and Troodon (see Agnolín et al, 2019).…”

“…The name Dromaeosauridae is instead restricted to the paravian Laurasian clade including Dromaeosaurus but not Passer and Troodon (see Agnolín et al, 2019). The Late Cretaceous Malagasy taxon Rahonavis ostromi (Forster et al, 1998) is here considered outside of Dromaeosauridae, following recent interpretations (e.g., O'Connor et al, 2011;Agnolín and Novas, 2013;Godefroit et al, 2013;Lefèvre et al, 2017;Novas et al, 2018;Motta et al, 2020).…”

Osteology ofUnenlagia comahuensis(Theropoda, Paraves, Unenlagiidae) from the Late Cretaceous of Patagonia

“…In its original description, Unenlagia was considered as a coelurosaurian theropod showing features more derived than Deinonychus, thus being phylogenetically closer to birds. These characters prompted Novas and Puerta (1997) to consider Unenlagia as the basalmost avialan theropod, a phylogenetic arrangement that was Unenlagia represents, alongside the unenlagiids Austroraptor, Neuquenraptor, Pamparaptor and Buitreraptor, and the enigmatic Overoraptor (Motta et al, 2020), one of the few basal paravians recorded in South America, and since its original description it was regarded as an important taxon that has the potential to help in the understanding of paravian phylogeny. However, except for a detailed account of the morphological features of the ilium (Novas, 2004), currently available studies on this taxon (e.g., Gianechini & Apesteguía, 2011;Novas & Puerta, 1997;Turner et al, 2012) consist on brief comments on general morphological aspects.…”