The last marine reptiles over Patagonia: signs of southgondwanan distribution

GASPARINI, ZULMA; SALGADO, LEONARDO; FERNÁNDEZ, MARTA; CASADIO, SILVIO; CONCHEYRO, ANDREA; PARRAS, ANA; BALLENT, SARA

Mendoza

Congreso; Gondwana 12; 2005

Academia Nacional de Ciencias

The knowledge of the Late Maastrichtian marine reptiles of the Argentine Patagonia was very scarce up to the end of the XXth century. This situation changed since the systematic revision of plesiosaurs and new findings in central Río Negro province. Four elasmosaurid plesiosaurs and three mosasaurs were found in Salinas de Trapalcó, in the upper section of the Jagüel Formation, between 50 and 0.30 m below the K/P boundary (Gasparini et al., 2002; Concheyro et al., 2002). Plesiosaurs were referred to cf. Mauisaurus sp. and a new species ?Tuarangisaurus cabazai (Gasparini et al., 2003b). Mauisaurus has been recorded in the upper Maastrichtian of Chile, James Ross Is. (Antarctica) and New Zealand, while Tuarangisaurus is frequent in New Zealand. This southgondwanan distribution observed in the elasmosaurids of northern Patagonia is also seen in Aristonectes parvidens Cabrera (=Morturneria) from the upper Maastrichtian of central Patagonia, southern Chile and Seymour Is. (Antarctica) (Gasparini et al., 2003a). Preliminary studies of Patagonian mosasaurs do not suggest so clearly a southgondwanan distribution. Fernández et al. (2005) reported the presence of plioplatecarpines (Plioplatecarpus sp.) and two mosasaurines: a still indeterminate form and Mosasaurus sp., aff. M. hoffmanni. Both Mosasaurus and Plioplatecarpus are cosmopolitan genera, and Martin et al. (2002) recognized the presence of these and other genera frequent in the northern Hemisphere in the upper Maastrichtian of Vega, Seymour and James Ross islands. The specimen referred to Mosasaurus sp. aff. M. hoffmanni belongs to a different species from M. hoffmanni, thereby, at species level, not all the southgondwanan mosasaurs would have been cosmopolitan. Coincidentally, a tylosaurine (Lakumasaurus antarcticus) was found also in James Ross Is. is closely related to other from New Zealand, suggesting at least in this case, southgondwanan relationships (Novas et al. 2002). The presence of reptiles with southgondwanan distribution agrees with some molluscan groups (Casadío et al., in press), cytheroid ostracods and Rostrocytherida (Ballent and Whatley, this Congress), and calcareous nannofossils as Cribrosphaerella daniae, Nephrolithus frequens and Prediscosphaera stoveri, all species distributed in Neuquén and Austral Basins, Patagonia,  as well as in the Austral Ocean and Seymour Island.