A chroniosuchid from the Triassic of Kyrgyzstan and analysis of chroniosuchian relationships

Abstract

A nearly complete skull and associated osteoderms from the Middle/Upper Triassic Madygen Formation of Kyrgyzstan are referred to a new chroniosuchid genus and species. The new taxon is characterized by a parabolic skull outline, pustular ornamentation, tabular-squamosal contact, marked postparietal embayments, and the lack of an antorbital fontanelle. The palate is only preserved in part, showing broad palatines and ectopterygoids. Presence of a preorbital fenestra and characteristic osteoderm morphology are synapomorphies shared with all other chroniosuchids. According to the phylogenetic analysis performed, the new chroniosuchid nests with Chroniosaurus, with which it shares the wide, transversely extended osteoderms and pustular ornamentation. The chroniosuchians are robustly supported as a natural group, but their position within the reptiliomorph (stem-amniote) clade is not adequately understood. Whereas the parasphenoid is similar to that of anthracosaurs, most other characters support a higher nesting of chroniosuchians within the stem-amniotes. © 2010 The Linnean Society of London.