Chubutemys copelloi, GAFFNEY & RICH & VICKERS-RICH & CONSTANTINE & VACCA & KOOL, 2007

GAFFNEY, EUGENE S., RICH, THOMAS H., VICKERS-RICH, PATRICIA, CONSTANTINE, ANDREW, VACCA, RAUL & KOOL, LESLEY, 2007, Chubutemys, a New Eucryptodiran Turtle from the Early Cretaceous of Argentina, and the Relationships of the Meiolaniidae, American Museum Novitates 3599, pp. 1-36 : 4-7

Chubutemys copelloi , new species

TYPE SPECIMEN: MPEF-PV1236 , a partial skull lacking much of the bone from its dorsal surface, but with an internal mold of it present, ventral surfaces preserved intact with stapes in situ, atlas elements disarticulated, and a piece of presumed hyoid in right temporal fossa .

TYPE LOCALITY: ‘‘ Turtle Town’ ’, 43 ° 36 9 S, 68 ° 55 9 W (figs. 1–3; Rich et al., 1998: fig. 1), Chubut Province, Argentina .

HORIZON: Cerro Castaño Member (fig. 3), Cerro Barcino Formation, Chubut Group, Aptian ( Codignotto et al., 1978; Rich et al., 1998; Rauhut et al., 2003) based on the work of two of the authors, T. Rich and A. Constantine.

DIAGNOSIS: as for genus.

ETYMOLOGY: For Maria Copello, who discovered the holotype.

REFERRED MATERIAL: The locality that yielded the skull of Chubutemys also coughed up enough turtle remains to cause its giddy discoverers to call it ‘‘Turtle Town’’ (figs. 1–3; Rich et al., 1998: fig. 1). The fossils from the site consist of shell and postcranial fragments of cryptodires and pleurodires, as well as the skull described here. No shell or postcranial material was found directly associated with the type skull of Chubutemys . However, there are postcranial elements that probably belong to Chubutemys . The cryptodire material is identifiable because it consists of a partial carapace with anterior thoracic centra and an articulated eighth cervical, as well as peripherals, including bridge peripherals, that are very similar to the ‘‘sinemydid/macrobaenid’’ postcrania described for Dracochelys , Ordosemys, Hangaiemys , Judithemys , and Otwayemys . The shell fragment with an eighth cervical, MPEF PV1940, is identified as a cryptodire on the basis of the widely spaced zygapophyses and the close agreement of this cervical with those of Ordosemys and Dracochelys (see below). Three sets of peripherals are also identified as cryptodire and probably belong to Chubutemys . These are MPEF PV1941, PV1942, and PV1943. They are very similar to peripherals figured by Brinkman (2001) for Dracochelys . They are relatively flat, show extensive costo-peripheral fontanelles, and have dorsally concave guttering as in Dracochelys .

There is at least one other species of turtle at this locality, a chelid pleurodire much smaller than Chubutemys . Most of these chelid bones differ from the cryptodire in being at least half the size and in having a very differently shaped shell with fused pelvis, no costo-peripheral fontanelles, and finely incised sulci.

DISCUSSION: Discovery of a definitive, skull-based eucryptodire in the Early Cretaceous of Argentina prompts reexamination of the published record, which has generally referred nonmarine turtles to the Pleurodira or Meiolaniidae (Broin and Fuente, 1993) . Much of this material is too fragmentary to reassess with confidence, but two specimens previously identified as pleurodires are probably cryptodires. These were originally identified as ‘‘grand Chelidae primitif indetérmine´’’ ( Broin and Fuente, 1993b: fig. 5, 18–19) from the Los Alamitos, Rio Negro, Late Cretaceous. Both specimens are in the Museo Argentino de Ciencias Naturales and have been examined by the senior author (E.S.G.). MACN 907 was identified as a fifth cervical, but it is very similar to the undoubted eighth cervical of MPEF PV1940. Both are biconvex with a narrowed centrum and a wide, midway positioned transverse process, distinct from any described chelid. MACN 907 lacks the neural arch as well as the zygapophyses. The principal difference between them is that the anterior central articulation of MPEF PV1940 is slightly larger than the posterior one, whereas in MACN 907 they are closer in size. The other specimen, MACN 908, identified as an eighth cervical (Broin and Fuente, 1993), probably is an eighth; it agrees closely with MACN 907 but lacks transverse processes and a neural arch and only shows a biconvex centrum, so its identity must remain ambiguous. Nonetheless, it is very likely that MACN 908 is also a eucryptodire, along with MACN 907.