Redescription of <i>Cearadactylus atrox</i> (Pterosauria, Pterodactyloidea) from the Early Cretaceous Romualdo Formation (Santana Group) of the Araripe Basin, Brazil

<div><p>ABSTRACT</p><p>Based on one of the first cranial pterosaur specimens unearthed from the Romualdo Formation (Araripe Basin), <i>Cearadactylus atrox</i> has caused disagreement among paleontologists regarding its relationships. Ranging from an ornithocheirid, an indeterminated pterodactyloid, to a ctenochasmatid, some authors even regarded this species as representing a distinct suprageneric clade. Further preparation of the holotype that was transferred to the collections of the Museu Nacional/UFRJ (MN 7019-V) revealed several new features allowing a redescription and reevaluation of the phylogenetic position of this species. Among the new observations, it is clear that the rostral end of this specimen had been glued to the skull, rendering previous anatomical interpretations incorrect. There is no rostral gap, and the expanded rostral end of the premaxillae is larger than the dentary, rather than smaller. <i>Cearadactylus atrox</i> is here considered a valid taxon that can be diagnosed by a dentary groove that bifurcates at the rostral end, orbit and naris in a high position relative to the nasoantorbital fenestra, and a comparatively small number of teeth (32–36 maxillary, 22–26 mandibular), decreasing in size towards the posterior end. Phylogeneticaly, it is placed as the sister group of the Anhangueridae, forming a large clade of Brazilian forms (<i>Tropeognathus</i> and <i>Anhanguera</i>), which has a European taxon (‘<i>Ornithocheirus</i>’ <i>compressirostris</i>) as its sister group.</p> <p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="http://www.tandfonline.com/UJVP" target="_blank">www.tandfonline.com/UJVP</a></p> </div

Histological characteristics of the Rib.

<p>(A) View of the cortex exhibiting parallel-fibred bone embedded with osteocyte lacunae and a deposition of spongy tissue highlighted by erosion rooms (ER). Five simple lines of arrested growth—LAGs (marked by lines) can be observed in the cortex. (B) View of the complete transect. Black boxes indicates respectively, were the related images were taken. (C) Detail of the outer cortex showing the intense remodeling process and the presence of few secondary osteons (black arrows) and an isolated simple vascular canal (red arrow).</p

Simplified cladistic hypotheses for Neosuchia and the phylogenetic positioning of <i>Susisuchus anatoceps</i>.

<p>(A) Hypothesis of Fortier & Schultz (2009) shows susisuchids as an "advanced neosuchian" and the sister-taxon of Eusuchia. (B) Hypothesis of Turner & Pritchard (2015) displays a more basal positioning for <i>S</i>. <i>anatoceps</i> along with the Australian species <i>I</i>. <i>duncani</i>.</p

Histological characteristics of the Ulna.

<p>(A) View of the cross section. Black boxes indicate where the related images were taken. (B) View of the cortex exhibiting vascular canals parallel-fibered bone embedded with osteocyte lacunae. Seventeen simple lines of arrested growth—LAGs (partially covered by lines) can be observed from the inner cortex (endosteal region) to the outer surface (periosteal region) and seven annulus (marked by A), the white arrows indicate erosion rooms. (C) Detail of the primary bone tissue, showing the few scattered simple and anastomosed vascular canals composesing the vascular network.</p

Sampled bones of MPSC R1136 with respective thin sections.

<p>(A) General view of the specimen. Red (marked B) and green (marked C) arrows (corresponding to rib and ulna respectively) indicate where the cut were made for the sample collection. (B) View of the cross section of the ulna. (C) View of the cross section of the rib. Scale bar 50 mm in A; 5 mm in B; C.</p

Schematic representation of resting postures of <i>Susisuchus anatoceps</i> based in extant crocodylomorphs.

<p>(A) Resting in shallow water with both body and tail contacting the bottom. (B) In shallow water when it is not able to touch the ground the hind limbs and half of the tail helping to support the animal. (C) When resting in deep water the limbs are held out nearly horizontally from the body, with fore and hind limbs extended to controls its position in buoyancy.</p

Comparative size of <i>Susisuchus anatoceps</i> to other Brazilian Cretaceous Crocodylomorphs.

<p>Comparative size diagram of Brazilian fossil crocodylomorphs, showing the dwarfism of <i>Susisuchus anatoceps</i> with 70 cm of maximum length. Ilustration by Aline M. Ghilard.</p