New postcranial elements of the Thalassodrominae (Pterodactyloidea, Tapejaridae) from the Romualdo Formation (Aptian–Albian), Santana Group, Araripe Basin, Brazil

Abstract

Tapejarids are edentate pterosaurs recovered mainly from Early Cretaceous deposits. They are diagnosed by five synapomorphies, among which only one is postcranial: a broad and well‐developed tubercle at the ventroposterior margin of the coracoid. Regarding the clade Thalassodrominae, most phylogenetic studies are based on cranial elements, as postcranial skeletons of these pterosaurs are rare. Here, new postcranial material from the Romualdo Formation (Aptian–Albian) from the Araripe Basin is described. The material comprises the three posteriormost cervical vertebrae, the first seven dorsal vertebrae (fused into a notarium), both scapulocoracoids, a fragment of a sternum, a partial right humerus, a small fragment of a 4th phalanx of the wing finger, a distal extremity of the right femur and the proximal portions of both tibia and fibula. Comparisons with other specimens and morphological features examined in a phylogenetic context, such as the presence of three foramina lateral and dorsal to the neural canal of the cervical vertebrae, the presence of a notarium and a pneumatic foramen on the ventral side of the proximal portion of the humerus, allow the assignment of this specimen as Thalassodrominae indet. Regarding palaeobiogeographical aspects, to date, this clade is exclusively found in the Romualdo Formation. It is the most complete postcranial material assigned to the Thalassodrominae described so far.

A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants

“…An azhdarchoid identification is most likely for element A, with the unwarped deltopectoral crest, parallel-sided and straight shaft, and slender bone walls being typical of humeri in these large-headed, toothless pterosaurs [28,30,44,47]. The lack of diaphyseal expansion in element A corresponds particularly well with the humeri of several neoazhdarchian azhdarchoids (Thalassodromidae + Azhdarchidae, sensu Unwin [28]) such as the ‘Wessex’ humerus [30], the ‘Glen Rose’ humerus [48]; Azhdarcho lancicollis [49] and Quetzalcoatlus northropi [50].…”

Cretornis hlavaci Frič, 1881 from the Upper Cretaceous of Czech Republic (Pterosauria, Azhdarchoidea)

“…In Dsungaripteridae this character is variable, the foramen may be present (IVPP V4059) or absent (IVPP V4062). In "Tapejaridae," which is likely paraphyletic, the pneumatic foramen on posterior side of proximal humerus is present in Tapejara (Eck et al, 2011: fig.7: pl.1D) but absent in Tupuxuara (Aires et al, 2014: fig.6A, D). This foramen is absent in Cretornis hlavaci which suggest its placement in the clade Neoazhdarchia (Tupuxuara þ Azhdarchidae).…”

“…The humeral head in Cretornis hlavaci is saddle-shaped which is consistent with its attribution to Azhdarchoidea. The dorsal ridge of humeral head is prominent, but not hypertrophied as in Thalassodrominae (Aires et al, 2014: fig.6). …”

“…The crest is considerably displaced distally from the proximal end in Nyctosauridae (Williston, 1903: pl.42, fig.7) and to a somewhat less extent in Azhdarchidae (Godfrey and Currie, 2005: fig.16.6C, D;Averianov, 2010: fig.23) and non-azhdarchid azhdarchoids (Witton et al, 2009: figs 3D, E, 4D, E, 6D, E, 7D, E) including USNM 11925, the holotype of Bennettazhia oregonensis from the Albian of Oregon, USA (personal observation by AA). In Dsungaripteridae (IVPP V4059, V4062) and "Tapejaridae" (Eck et al, 2011: fig.7, pl.1;Aires et al, 2014: fig.6) the deltopectoral crest has the primitive proximal position. The distal displacement of deltopectoral crest in Nyctosauridae and non-tapejarid azhdarchoids was likely derived in parallel.…”

“…It is saddle-shaped, convex in anteroposterior section and concave in dorsoventral section in Pteranodontidae (Bennett, 2001a: fig.70), Nyctosauridae (Williston, 1903: pl.42, fig.7), Dsungaripteridae (IVPP V4059, V4062), "Tapejaridae" (Eck et al, 2011: fig.7, pl.1;Aires et al, 2014: fig.6), non-azhdarchid azhdarchoids (Witton et al, 2009: figs 3, 4, 6, 7), and Azhdarchidae (Averianov, 2010: fig.23). This difference in the shape of humeral head apparently reflects specialization of the flight mechanism in Ornithocheiroidea sensu stricto (excluding Pteranodontidae and Nyctosauridae, which evidently do not belong to that group; Hazlehurst and Rayner, 1992).…”