The Mesozoic radiation of dryolestoids in South America: dental and cranial evidence.

GUILLERMO W. ROUGIER; SEBASTIÁN APESTEGUÍA

Colorado

Congreso; 64 Annual Meeting of the Society of Vertebrate Paleontology; 2004

Society of Vertebrate Paleontology

Despite the relatively poor South American mammalian record, recent discoveries from the Jurassic, Cretaceous and Paleocene allow the reconstruction of some of the major events in the Mesozoic mammalian fauna. The core of the evidence comes from Pstagonia (Argentina) with minor extra-Patagonian additions. The Jurassic and Early Cretaceous record is restricted to triconodonts, tribosphenic australosphenidans and the nearly tribosphenic Vincelestes. The Late Cretaceous record is yet to provide a tribosphenic mammal and the faunas are dominated instead by non-tribosphenic cladotheres, dryolestoids in particular. The earliest South American dryolestoids are from the Cenomanian-Turonian Candeleros Formation where two closely related species are represented by jaw and skull malerial: both of them have single rooted molars and a low postcanine count. The Campanian record is more abundant with two localities in northern Patagonia: Los Alamitos and Cerro Tortuga. Several lineages arc represented, including probable true Dryolestidae,Quirogatheridae, Casamiquelidae, Mesungulatidae and Reigitheridae. All these taxa seem to have a relatively low number of molarifoms, probably 4. The molar size of the Campanian dryolestoids range in size from under one millimeter to almost one centimeter and their inferred diet would range from insectivory to fairly deicated herbivory. Non-dryolestoid components of these faunas (multituberculates, gondwanatherians. triconodonts?) are neither abundant nor diverse. A few dryolestoid molars are known from the Bolivian Late Cretaceous. The Maastrichtian dryolestoids are well represented in several localities of the central patagonian La Colonia Formation. Only reigitherids and large to mid-size mesungulatids havc been found. Despite the abundant collection, the diversity is poor. Multituberculates are prcsent but gundwanatherians have not yet been found. The latest record of a dryolestoid is represented by the large-sized Peligrotherium of the mid-Paleocene Salamanca Formation which seems to represent a very derived member of the Reigitheridae radiation that survived the K-T extinction.