Ten years digging up dinosaurs in Patagonia: the Ibero-Patagonian connection in the Mesozoic

CANUDO, JOSÉ I.; SALGADO, LEONARDO; CARBALLIDO JOSE L.; GARRIDO, ALBERTO

Salas de los Infantes

Jornada; VI Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno; 2013

Th e Salas congress serves as a meeting point where researchers from diff erent parts of the world can devise projects in common. A good example of this is the series of joint research projects that we have been undertaking for more than ten years now. It started when two of us coincided at the 2001 Salas congress, where we raised a number of palaeobiogeographial questions that called for research into the vertebrates of Patagonia and Iberia (Canudo and Salgado, 2003). Researchers from the University of Zaragoza and various Argentinean institutions (Museo Olsacher de Zapala, Museo de Rincón de los Sauces, Museo Egidio Feruglio de Trelew, Universidad de Comahue, Universidad of Río Negro, Universidad de La Plata, Conicet) have taken part in these research projects. Th ey have been pursued for more than ten years, fi nanced mainly by the National Research Plan of the Government of Spain, but also supported by private enterprises such as Repsol and Petrobras, museums such as the Museo of Rincón de los Sauces and of Zapala, and institutions such as the Mining Offi ce of Neuquén and Endemás of Cipolletti. Th e fundamental idea was to use terrestrial vertebrates ? especially dinosaurs ? to infer the palaeobiogeographical relationships that existed between Iberia and Patagonia during the Cretaceous. South America and Africa were joined for most of the Lower Cretaceous, and there were also connections with Europe (Canudo et al., 2009). Standard models locate the fi nal separation of Africa and South America at the end of the Lower Cretaceous or at the beginning of the Upper Cretaceous, with the complete opening of the South Atlantic. One of the objectives of the project is precisely to pinpoint this defi nitive isolation. Th e presence in the Campanian- Maastrichtian of Europe of derived taxa of titanosaurian sauropods that are close to Argentinean taxa makes the scenario more complicated, since South America had apparently been isolated since the beginning of the Upper Cretaceous. In this communication we shall focus only on the work carried out in the region of Patagonia in Argentina. Th e phylogenetic proximity of taxa that are now separated by geographical barriers (such as oceans separating distinct continents) is one of the criteria that are commonly used as proof of geographical connections in the past. If we fi nd the same species on both sides of the barrier constituted by the ocean, the conclusion is immediate: when these two organisms were alive, the barrier did not exist. However, this is an ideal situation; in many cases it is representatives of the same supra-specifi c group that are found, but these may have undergone vicariant evolution within the two landmasses. Clarifying just such questions is one of the main lines of the project: distinguishing endemic taxa (both in Europe and in South America) from those taxa that exist in a close phylogenetic relation and that may have played a role in the dispersals from Gondwana to Laurasia or vice versa. From the outset this project has focused on a search for new specimens, above all in critical periods such as the upper part of the Lower Cretaceous and the lower part of the Upper Cretaceous. Prospection and excavation fi eld campaigns (generally one a year) have been undertaken in the provinces of Neuquén and Río Negro. Th e fi eld projects have generally been carried out in new areas and with little prior information. Th e 20 VI Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno. Salas de los Infantes, Burgos fi rst projects were undertaken in the Upper Cretaceous of the areas of El Anfi teatro (Río Negro) and Rincón de los Sauces (Neuquén). In El Anfi teatro a great quantity of fragmentary vertebrate material was found, shedding light on the palaeobiodiversity of the area (Salgado et al., 2009). In Rincón de los Sauces the remains of various titanosaurian sauropods have been excavated, one of which was described as Petrobrasaurus puestohernandezi from the Coniacian-Santonian of the Plottier Formation (Filippi et al., 2011). Th is period is particularly interesting as this was when the defi nitive separation of Africa and South America took place. Petrobrasaurus is a form that is related to other Argentinean titanosaurs and unrelated to the European ones. A group of special interest to the palaeobiogeographical debate is the rebbachisaurids. Th ese are basal diplodocimorphs represented in South America, Africa and Iberian Peninsula. A particularly interesting area is the west of the province of Neuquén with large outcrops from the Lower Cretaceous ? Upper Cretaceous boundary. A revision has been undertaken of the type area and material of Rayososaurus agrioensis from the Candeleros Formation (lower Cenomanian), initially considered to date to the Lower Cretaceous (Carballido et al., 2010). Furthermore, the new taxon Comahuesaurus windhauseni has been described on the basis of postcranial material from the Aptian-Albian of the Lohan Cura Formation (Carballido et al., 2012). Th ese rebbachisaurids seem to form part of an exclusively South American group. In the course of our fi eld work, we have for the fi rst time discovered sauropod remains in the Rayoso Formation. Th ese belong to a semi-articulated individual, including cranial elements, and two juvenile individuals (Salgado et al., 2012). Th is material is currently under preparation, but has been initially assigned to cf. Zapalasaurus. Th is taxon is of palaeobiogeographical interest because in phylogenetic proposals it is grouped in the same clade as Nigersaurus (Africa) and Demandasaurus (Spain).