A new desert-dwelling dinosaur (Theropoda, Noasaurinae) from the Cretaceous of south Brazil

Abstract

Noasaurines form an enigmatic group of small-bodied predatory theropod dinosaurs known from the Late Cretaceous of Gondwana. They are relatively rare, with notable records in Argentina and Madagascar, and possible remains reported for Brazil, India, and continental Africa. In south-central Brazil, the deposits of the Bauru Basin have yielded a rich tetrapod fauna, which is concentrated in the Bauru Group. The mainly aeolian deposits of the Caiuá Group, on the contrary, bear a scarce fossil record composed only of lizards, turtles, and pterosaurs. Here, we describe the first dinosaur of the Caiuá Group, which also represents the best-preserved theropod of the entire Bauru Basin known to date. The recovered skeletal parts (vertebrae, girdles, limbs, and scarce cranial elements) show that the new taxon was just over 1 m long, with a unique anatomy among theropods. The shafts of its metatarsals II and IV are very lateromedially compressed, as are the blade-like ungual phalanges of the respective digits. This implies that the new taxon could have been functionally monodactyl, with a main central weight-bearing digit, flanked by neighbouring elements positioned very close to digit III or even held free of the ground. Such anatomical adaptation is formerly unrecorded among archosaurs, but has been previously inferred from footprints of the same stratigraphic unit that yielded the new dinosaur. A phylogenetic analysis nests the new taxon within the Noasaurinae clade, which is unresolved because of the multiple alternative positions that Noasaurus leali can acquire in the optimal trees. The exclusion of the latter form results in positioning the new dinosaur as the sister-taxon of the Argentinean Velocisaurus unicus .

Paleontological discoveries in the Chorrillo Formation (upper Campanian-lower Maastrichtian, Upper Cretaceous), Santa Cruz Province, Patagonia, Argentina

“…However, in the case for the phalanx here described the ventral projection proximally surpasses the level of the dorsal lip, contrasting with known noasaurids in which the projections are sub-equal in proximal extension (e.g., Laevisuchus, Noasaurus;Novas & Bandyopadhyay, 2001, Sampson et al, 2001Agnolin & Chiarelli, 2010;Brissón Egli et al, 2016). Noasaurids have been recorded in different Late Cretaceous localities of Gondwana, including India (Novas & Bandyopadhyay, 2001;, Africa (Sampson et al, 2001) and South America (Bonaparte & Powell, 1980;Bonaparte, 1991;Brissón Egli et al, 2016;Langer et al, 2019;Martinelli et al, 2019). Present specimen constitutes the southernmost record for this theropod family, and forms part of a small-sized theropod fauna also integrated by megaraptorids and unenlagiids (see below).…”

“…Comments. The pedal phalanx MPM 21547 resembles Noasauridae in being transversely narrow and dorsoventrally deep, a condition shared with Velocisaurus and Vespersaurus (Brissón Egli et al, 2016;Langer et al, 2019). Further, a well-developed, transversely thick, and posteriorly extended posterodorsal process is also shared with noasaurids, including Noasaurus, Ligabueino, Velocisaurus and Vespersaurus (Langer et al, 2019), constituting a synapomorphic feature of Noasauridae (Agnolin & Chiarelli, 2010).…”

“…The pedal phalanx MPM 21547 resembles Noasauridae in being transversely narrow and dorsoventrally deep, a condition shared with Velocisaurus and Vespersaurus (Brissón Egli et al, 2016;Langer et al, 2019). Further, a well-developed, transversely thick, and posteriorly extended posterodorsal process is also shared with noasaurids, including Noasaurus, Ligabueino, Velocisaurus and Vespersaurus (Langer et al, 2019), constituting a synapomorphic feature of Noasauridae (Agnolin & Chiarelli, 2010). However, in the case for the phalanx here described the ventral projection proximally surpasses the level of the dorsal lip, contrasting with known noasaurids in which the projections are sub-equal in proximal extension (e.g., Laevisuchus, Noasaurus;Novas & Bandyopadhyay, 2001, Sampson et al, 2001Agnolin & Chiarelli, 2010;Brissón Egli et al, 2016).…”

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

“…A similar morphology was observed in the mesial crown of Falcarius (UMNH 15097), which is also unserrated and D-shaped in cross-section. A D-shaped cross-section was also noted in: a mesial isolated tooth of the noasaurid Vespersaurus (Langer et al, 2019); the premaxillary teeth of the abelisaurids Rahiolisaurus (pm1 of ISIR 550; C.H. personal obs.)…”

A new toothless pterosaur (Pterodactyloidea) from Southern Brazil with insights into the paleoecology of a Cretaceous desert

“…the more numerous bones recovered so far belong to a small tapejarine pterosaur that was named Caiuajara dobruskii Manzig et al 2014. The previously identified dinosaur was recently named Vespersaurus paranaensis Langer et al 2019, also known by hundreds of isolated elements. An acrodont lizard, Gueragama sulamericana Simões et al 2015, which was described based on fragmentary material (Simões et al 2015), complete the known reptilian fauna from this site.…”