The highly unusual skull of the dryolestoid mammals: Keys from the southern part of the Atlantic

APESTEGUÍA, S., GAETANO L. & ROUGIER, G

Marrakech, Marruecos

Congreso; 1er Congrès International sur la Paléontologie des Vertébrés du Nord de l’Afrique; 2009

Université Cadi Ayyad UCAM - Marrakech - Societé Marrocaine d'Herpetologie

Dryolestoids are relatively small mammals mainly known from Upper Jurassic-Lower Cretaceous rocks of the northern hemisphere, represented mostly by relatively abundant isolated teeth and occasional fragmentary lower jaws or partial skeletons. In the southern continents, dryolestoids are important in the Early Cretaceous of Morocco and latest Cretaceous and Early Paleocene strata of South America. The Campanian-Maastrichtian mammalian fauna from Patagonian is dryolestoid-dominated, with in addition ferugliotheriids, and gondwanatherians. The abundant Laurasian and Gondwanan dental record is in sharp contrast with the poor skull and postcranial knowledge. Recently, the early Late Cretaceous fluvial rocks of La Buitrera (Candeleros Fm, Cenomanian-Coniacian), Argentina, have provided a rich assemblage of small to mid-sized tetrapods including dinosaurs, crocodiles, turtles, sphenodontians, lizards, limbed snakes and mammals. Among the latter, dryolestoids are the most abundant, particularly a long snouted taxon with a rounded palate, surprisingly similar to zalambdalestid eutherians, or the living elephant shrew in superficial traits. Additionally, this taxon presents impressive miniature saber-tooth canines suggesting it was a very specialized mammal, for which no other similar model exists. It is probably part of a Gondwanan dryolestoid lineage that ulteriorly originated the latest Cretaceous and Paleocene South American forms. This new form is represented by several specimens including four partial skulls that retain a generalized plesiomorphic pattern of braincase organization. The new well preserved specimens will play a key role in the further understanding of dryolestoid diversity, evolution and paleobiogeography.