Noblemen diminished: Late Cretaceous dwarf carcharodontosaurids in Patagonia

SEBASTIÁN APESTEGUÍA; ROBERTO DOS ANJOS CANDEIRO

La Plata

Jornada; XX Jornadas Argentinas de Paleontologia de Vertebrados; 2004

Museo de La Plata

Carcharodontosaurids are a group of gigantic Gondwanan theropod dinosaurs that constituted the top Patagonian predators from Aptian to Coniacian times, when they became geographically restricted, perhaps in relation to the spread of other tetanurans and later abelisauroids. No records of carcharodontosaurids have been found after Coniacian times in Patagonia, because of which they were considered extinct by several authors. However, they survived as a modest relict in Brazil (Marilia Formation, Late Maastrichtian). Reexamination of the theropod teeth from the Los Alamitos Formation at the MACN and MLP allowed us to recognize the presence of carcharodontosaurids in the latest Cretaceous of Patagonia. Differing from their earlier relatives, these late Campanian carcharodontosaurids attained only modest sizes. The teeth crowns are about 29.2 mm in length and, extrapolated  to carcharodontosaurid proportions, their body size would have ranged to about 3 meters long. Teeth show the typical denticle density of about 2 per mm, a furrowed enamel with well marked wrinkles, deep blood grooves and a straight crown, thus differing from all other known Late Cretaceous lineages (e.g. dromaeosaurids, abelisaurs). Los Alamitos carcharodontosaurid teeth are intensely worn, perhaps as result of tough food (including bones?), a delayed replacement mechanism, or the ingestion of prey contaminated with sand. The sudden appearance of carcharodontosaurids in Late Campanian outcrops of Patagonia suggest that they remained present during the whole Late Cretaceous in low preservation refuge areas, perhaps highlands or, on the contrary, they represent a late re-colonization arrived from other areas (Brazil?) after their original extinction in Patagonia.