A NEW ALLIGATOR FROM THE UPPER CRETACEOUS OF CANADA AND THE RELATIONSHIPS OF EARLY EUSUCHIANS

A new alligatorine eusuchian, Stangerochampsa mccabei gen. et sp. nov. , is described on the basis of a partial skeleton from the Horseshoe C anyon Formation (Early Maastrichtian) of southern Alberta. It is uniqu e in possessing an ectopterygoid/palatine contact, a ventrolateral pro cess of the quadrate, a groove-like recess for nerves and blood vessel s in the upper jaw, a rectangular palatine with a lateral process at i ts midpoint, and a basioccipital with a ventral exposure longer than t hat of the pterygoid. Several derived characters indicate a close rela tionship of S. mccabei with two Late Cretaceous alligatorines, Brachyc hampsa montana and Albertochampsa langstoni. A preliminary phylogeneti c analysis, based on 46 characters of selected taxa, leads to the hypo thesis that Leidyosuchus, rather than Hylaeochampsa, is the most primi tive eusuchian, supports the monophyly of the Alligatorinae (with the exclusion of Prodiplocynodon), and suggests that the Alligatorinae may consist of at least two distinct assemblages.