Anatomy and relationships of the basal Crocodylomorphs Junggarsuchus sloani and Dibothrosuchus elaphros

The holotype of Junggarsuchus sloani, from the early Late Jurassic of
Xinjiang, China, consists of a nearly complete skull and the anterior half
of an articulated skeleton, including the pectoral girdles, nearly
complete forelimbs, vertebral column, and ribs. Here we describe its
anatomy and compare it to other basal crocodylomorphs, based in part on CT
scans of its skull and that of Dibothrosuchus elaphros from the Early
Jurassic of China. Junggarsuchus shares many features with a cursorial
group of crocodylomorphs, informally known as ‘sphenosuchians,’ whose
relationships are poorly understood. However, it also displays several
derived crocodyliform features that are not found among most members of
this group. A phylogenetic analysis corroborates the hypothesis that
Junggarsuchus is closer to Crocodyliformes, including living crocodylians,
than are Dibothrosuchus and Sphenosuchus, but not as close to
crocodyliforms as Almadasuchus and Macelognathus, and that the
“Sphenosuchia” are a paraphyletic assemblage. Dibothrosuchus elaphros and
Sphenosuchus acutus are hypothesized to be more closely related to
Crocodyliformes than are the remaining ‘Sphenosuchia,’ which form several
smaller groups but are largely unresolved.