THE LARGEST THICK SHELLED GIANT TORTOISE (TESTUDINES: TESTUDINIDAE) FROM SOUTH AMERICA

ZACARIAS, G.; DE LA FUENTE, M. S; ZURITA, A. E.; IRIONDO, M

San Juan

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

The thickened shelled ?giant? tortoises is a land turtle morphotype recognized by Pritchard and Trebbau (1984) to include ?a large array of widely distributed tortoises with maximum carapace length of about 120 cm, found on most continents (except Australia and Antarctica) and many continental islands?. This parataxonomic category of tortoises is characterized by thickened dorsal carapace and unreduced plastron, and it is regarded as an entirely extinct group. In this contribution, the largest specimen referred to this morphotype is reported. This specimen (MHRSP 177) was exhumed in 1952 from Urundel Formation (upper Pleistocene; ca. 36-8.5 ka; Iriondo, 1993, 2010) at La Matanza locality, Quitilipi Department, Chaco Province, Argentina. Its generic assignation to Chelonoidis Fitzinger is based on the absence of cervical scale and an undivided supracaudal scale. The peripheral bones I, II, and III anteriorly projected, absence of pleural gibes, and a great development of vertebral gibes suggest that this specimen would belong to a new species. In addition, the dorsal profile is more clearly convex than that observed in other thickened shelled species of this genus. The carapace length of MHRSP 177 is 140 cm, the carapace height is 77 cm and the thickest peripheral bones ranges between 10 and 15 cm. These measurements suggest that La Matanza specimen is the largest known South American tortoise.