The uppermost Cretaceous continental deposits at the southern end of Patagonia, the Chorrillo Formation case study (Austral-Magallanes Basin): Sedimentology, fossil content and regional implications

A large Megaraptoridae (Theropoda: Coelurosauria) from Upper Cretaceous (Maastrichtian) of Patagonia, Argentina

“…MPM-PV-22864 and MPM-PV-22865 are almost identical in morphology differing, as expected, in those traits that vary within the anterior and posterior parts of the jaw (such as the symmetry or not of the tooth crowns). Conversely, one tooth (MACN-Pv 19,066) differs from the rest in having a high density of distal denticles (5 per mm vs 3 per mm in all other megaraptorids 3 , 39 ). It should be noted that MACN-Pv 19,066 was collected in the area in 1980 but lacks specific stratigraphic and geographic provenances 3 .…”

“…In sum, Maip macrothorax is the first megaraptorid taxon to be named for the Maastrichtian of southern Patagonia, representing the biggest among currently known megaraptorids (Lamanna et al 20 and Supplementary Information II ), and one of the youngest records (alongside with those from Lago Colhué Huapi Formation) for the entire clade 39 .…”

“…Maip , from the Chorillo Formation, is not the only record of Megaraptoridae from the uppermost Cretaceous, although it is currently the most complete. In addition to Maip, the Chorrillo Formation has yielded at least four additional megaraptorid specimens: an isolated dorsal centrum (MPM 21,546); an isolated tooth (MACN-Pv 19,066); and two sets of associated teeth (MPM-PV-22864–5 3 , 39 ). It must be said, however, that comparisons of the isolated dorsal centrum (MPM 21,546) with unenlagiids, such as Unenlagia, better suggests that this bone might pertain to Unenlagiidae rather than to Megaraptoridae.…”

“…3 ), La Anita Farm, 30 km SW of El Calafate city, Santa Cruz Province, Argentina. Chorrillo Formation (Maastrichtian 3 , 38 , 39 ).…”

“…The articular surface of the process is rounded in contour, slightly concave and ventrolaterally facing. The process shows a rugose anterior surface that probably constitutes the insertion of the ligaments that attach the rib to the vertebra 39 . Posteriorly, the transverse process shows at least three pneumatic foramina closer to its tip.…”