The ?Rosetta Stone? for deciphering the anatomy of the stem turtle Condorchelys antiqua (Early-Middle Jurassic; Chubut, Argentina)

STERLI, J.; DE LA FUENTE, M.S.; ROUGIER, G. W.

Rio de Janeiro

Simposio; 5th Turtle Evolution Symposium; 2015

Museu Nacional Univerdidade Federal do Rio de Janeiro

Background. Condorchelys antiqua is a stem turtle previously described from the QuesoRallado Locality, Cañadón Asfalto Formation (Early-Middle Jurassic), Chubut, Argentina. In2014 a skull (MPEF-PV 10900) and an articulated shell with associated postcranial remains(MPEF-PV 10884) of C. antiqua were discovered in the mentioned locality.Methods. The new specimens have been prepared by L. Reiner (technician at the MuseoEgidio Feruglio) and then studied using the regular paleontological methodology (e.g., directobservations and under the microscope, photography, and drawings). The new data providedby these two specimens, plus some other isolated remains that were re-prepared, allowed us toscore a 25% more of the characters of C. antiqua in the most complete up to date matrix forMesozoic turtles. The matrix was build in Mesquite and analyzed under maximum parsimonyin TNT. We performed two rounds of Tree Bisection Reconnection and calculated a strictconsensus. Branch supports were provided using bootstrap, jackknife, and Bremer support.Results. We regard the specimen MPEF-PV 10900 as represented by the basicranium andsome previously unknown skull bones like the maxilla, frontal, parietal, and postorbital. Thisspecimen also shows that there were no teeth in the pterygoid of C. antiqua. On the otherhand, specimen MPEF-PV 10884 is an almost complete carapace and plastron with 4 thoracicvertebrae and ribs, scapular and pelvic girdles, humerus, left radius, femur, tibia, fibula, 2metatarsal/carpals, 2 phalanges, 1 ungual phalanx and 1 chevron bone. The preliminarycladistic analysis resulted in 750 most parsimonious trees of 893 steps. The result of theanalysis corroborates the position of C. antiqua as a stem turtle more derived than the Triassicand Australochelys africanus. Condorchelys antiqua is recovered in a polytomy together withother early-middle Jurassic turtles (e.g., Kayentachelys aprix and Indochelys spatulata) andthe clade formed by the remaining turtles.