Plesiosaurios de Castilla-La Mancha en las XXIX Jornadas de la SEP

Como ya se ha indicado, en las XXIX Jornadas de la Sociedad Española de Paleontología, celebradas hace unos días en Córdoba, se defendieron varios trabajos centrados en el registro de algunos reptiles fósiles. Hemos hablado de algunas investigaciones allí defendidas referentes al registro de quelonios (y seguiremos haciéndolo en los próximos días), pero los plesiosaurios también estuvieron representados. Además de la recopilación y análisis de las referencias a Plesiosauria del registro ibérico, Bardet y colaboradores refieren el hallazgo de material de este grupo en Guadalajara y, más concretamente, en niveles tanto jurásicos como cretácicos. Os dejamos aquí su resumen:

The Iberian plesiosaur fossil record: state of the art

The Iberian Mesozoic marine reptile fossil record is rather scarce, both quantitatively and qualitatively, compared to other European countries. However, though most of the discoveries correspond to isolated and fragmentary specimens, this fossil record is of surprisingly long duration, from the Middle Triassic to the latest Cretaceous, and also desplays high-level taxonomical diversity, with most of the major clades of Mesozoic marine reptiles being represented. As far as Sauropterygians are concerned, they represent the best known clade of marine reptiles of the Iberian Peninsula and are known by Triassic pachypleurosaurs, placodonts, nothosaurs and pistosaurs, as well as by Jurassic and Cretaceous plesiosaurs.

Historically, the first Mesozoic marine reptile specimen - a partial skeleton now lost - found in the Iberian Peninsula was probably a plesiosaur. It was briefly described in the mid-19th century and was found in the Pliensbachian of Asturias, Northern Spain. At the end of the 19th century, new plesiosaur specimens from Portugal were described, among them a Plesiosaurus sp. partial skull from the Toarcian of Coimbra, reassigned recently to the new plesiosaurid genus and species Lusonectes sauvagei. Since that time, no reviews or new discoveries were made until the end of the 20th century.

Twelve outcrops have yielded plesiosaur specimens in the Iberian Peninsula. Up to now, all the corresponding Jurassic outcrops are located on the Atlantic coast, both in Spain (Hettangian/Sinemurian, Pliensbachian and Kimmeridgian of Asturias) and Portugal (Toarcian of Coimbra, Kimmeridgian/Tithonian of Lisboa). In contrast, most of the Cretaceous ones are located in the northeastern part of Spain (Barremian and Albian/Cenomanian of Teruel, and Aptian of Castellón). Other Cretaceous records are from central and southern Portugal (Middle Cretaceous of Lisboa and Cenomanian of Faro) and from northern Iberian Peninsula (Maastrichtian of Treviño County).

With regards to the systematical record, currently, the only valid plesiosaur taxon from the Iberian Peninsula is Lusonectes from the Toarcian of Portugal, which represents moreover the only cranial specimen known. The most complete specimen is a juvenile partial postcranial skeleton of a Plesiosauroidea indet. from the Pliensabachian of Asturias. The other specimens, all isolated teeth and vertebrae, are of indeterminate attribution. It should be noted that most are referred to Plesiosauroidea (including Elasmosauridae) whereas Pliosauroidea remain extremely scarce.

New Plesiosaur specimens from the Guadalajara Province

Recently, two new plesiosaur specimens have been discovered in the North of Guadalajara Province, Castilla-La Mancha, central Spain. Though very fragmentary, these two specimens are the first ones found in this region.

The first specimen comes from the Lias of Maranchón, located NE of the city of Guadalajara. It has been found by one of us (LMCF) in two blocks of dolomitic limestone used for the construction of a field wall. The provenance of this material is most probably very local and corresponds to a bioclastic limestone of the Baharona Formation (Pliensbachian). The material consists of 12 dorsal vertebrae preserved mostly in close natural articulation, plus ribs and some indeterminate fragments. Because the specimen exhibits almost rounded centra which are slightly higher/wider than long (H = W > L) and blade-like dorsal neural spines, it can be referred to a Plesiosauroidea. Unfortunately, plesiosaur dorsal vertebrae are not very diagnostic so that more precise identification is not possible.

The second specimen comes from the early part of the Late Cretaceous of Algora, located also NE of the city of Gusdalajara, not far from Maranchón. The sandy coastal deposits of the upper part of the Arenas de Utrillas Formation (Cenomanian) have already yielded, in this locality, a rich vertebrate fauna including fishes, turtles, crocodyliformes and dinosaurs. The recently discovered plesiosaur specimen consists of several elements of a single individual: both incomplete ischions, a caudal vertebra and other flat fragments, under preparation, that could be additional parts of the pelvis. The shortness of the ischions permits to reference of this specimen to a Plesiosauroidea and most probably to an elasmosaurid.