Thereuodon(Theria, Symmetrodonta) from the Lower Cretaceous of North Africa and Europe, and a brief review of symmetrodonts

Abstract

Until now the Symmetrodonta were known in the Purbeck fauna of southern England by only one genus,Spalacotherium-Peralestes. Five isolated teeth found during recent work in this formation reveal the presence of another taxon, close to one previously described from the Early Cretaceous fauna of Morocco,Thereuodon dahmani(which is considered here as representing a new family, the Thereuodontidae); the Purbeck form is described asT. taraktessp. nov. A brief historical review of all genera and species of symmetrodonts is given, followed by a presentation of the distribution of 25 dental characters in these taxa. The similarities noted betweenThereuodonand a Campanian therian from Argentina,Barberenia, could suggest either a common ancestry before the isolation of that part of South America or, more likely, a case of parallelism. Finally, a new interpretation of the wear facets on molars of Symmetrodonta is presented; this leads us to question the homology between those of early therians and of tribosphenic therians, and underlines the early individualization of the latter.