Simosuchus

Abstract: Here, we describe a new species of Azendohsaurus from the Middle–Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle–Late Triassic (or even later), ‘leaf-shaped’ teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occurs in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.

Abstract: The pug-nosed crocodyliform Simosuchus clarki is known from several specimens that collectively preserve, in addition to the skull and postcranial endoskeletal elements, a complete complement of osteoderms covering every major body region. This comprehensive sample of osteoderms facilitates the reconstruction, from multiple sources, of the entire postcranial dermal skeleton of this crocodyliform. In this contribution, I describe the anatomy, arrangement, and histology of the osteoderms of S. clarki, and provide comments on the phylogenetic and functional importance of these structures. As in other crocodyliforms, the osteoderms of Simosuchus were organized into discrete ‘shields’ covering the dorsal and ventral regions of the trunk and tail. Simosuchus also exhibited extensive osteodermal coverage of the limbs, a feature that characterizes very few crocodyliforms. The osteoderms from different shields possess distinctive morphological features, allowing isolated osteoderms to be assigned accurate...

Abstract: The notosuchian crocodyliform Simosuchus clarki from the Late Cretaceous of Madagascar, originally known from a single specimen preserving primarily the skull, lower jaw, and anterior postcranial skeleton, is now known from three additional partial skeletons that collectively preserve nearly the entire appendicular skeleton. Although typically crocodyliform in overall morphology, the appendicular skeleton of Simosuchus preserves a number of derived features of phylogenetic and functional significance. Notable features of the pectoral girdle and forelimb include an anteroposteriorly broad, tripartite scapular blade; a laterally directed scapular prominence; a proximally expanded humerus with a shallow deltopectoral crest; a distinct, semi-ellipsoidal glenohumeral condyle; a tightly articulating radius and ulna; and a relatively foreshortened manus with robust distal unguals. Notable features of the pelvic girdle and hind limb include a distinct, spur-like projection of the anterior process of the ...

Abstract: Simosuchus clarki Buckley, Brochu, Krause, and Pol, 2000, a small, pug-nosed notosuchian crocodyliform from the Late Cretaceous of Madagascar, was described a decade ago in a preliminary report based on a single specimen that included the skull, lower jaw, and anterior portions of the postcranial skeleton; details of the preserved cervical and anterior dorsal vertebrae and ribs were not described With the subsequent collection of several additional specimens, which collectively also preserve the posterior dorsal, sacral, and caudal regions of the vertebral column, the postcranial axial skeleton of S clarki is now one of the most completely known of any basal mesoeucrocodylian This report includes a detailed description of the vertebral and costal morphology of this bizarre notosuchian and an assessment of its functional and phylogenetic significance Simosuchus had eight cervical, at least 15 dorsal, two sacral, and probably fewer than 20 caudal vertebrae Most aspects of the vertebral morphol