Dientes de terópodo del Jurásico Medio de Niger en el 73rd Annual Meeting de la SVP

Y para ir cerrando el capítulo de la SVP en Los Ángeles, era primordial hacer más referencia al grupo al que pertenece nuestra sufrida mascota: los terópodos. En este trabajo se han descrito algunos dientes aislados de terópodo hallados en Niger, asociados a nuestro conocido Spinophorosaurus nigerensis. Y para tratar de conocer mejor la identidad de nuestro “mellado” amigo se usaron métodos morfométricos y comparación directa con material ya descrito.

Los resultados indican que algunos de los vecinos de Spinophorosaurus fueron allosauridos. Pero la sorpresa nos la da una de las piezas, de corona subcircular, esmalte ornamentado en forma de micropliegues y con gran cantidad de dentículos. Esta pieza presenta una serie de caracteres comunes a los tetanuros basales y a los espinosaurios, lo que arroja algo de luz sobre la evolución de este extraño grupo de dinosaurios.

El resumen es el siguiente:

Isolated theropod teeth are common fossils in the continental Mesozoic deposits. Three well-preserved crowns were found associated with the holotype skeleton of Spinophorosaurus nigerensis from the “Argiles de l’Irhazer” (Middle Jurassic: ?Bathonian) in Niger.

These specimens can be divided into two morphotypes. The first morphotype includes two teeth that do not show any distinct diagnostic character. Therefore, morphometric analyses had to be performed to help identify them. The results of the DFA and of a scatter plot of the first and second canonical functions generated by the discriminant analysis suggested that they are from an allosaurid. The second morphotype includes a peculiar tooth that shows “spinosaurid-like” characters, viz. subconical with textured enamel and many minute denticles. However, it is not as conical as typical spinosaurid teeth, and it does not bear any apicobasal ridges. Its position on the scatter plot is ambiguous, between basal tetanurans and spinosaurids. The mosaic characters and the scatter plot may make sense if this tooth pertained to a basal spinosaurid, which would show a transition between the archetypal theropod dental morphology and the apomorphic spinosaurid teeth. No Middle Jurassic spinosaurid is known so far, but the age of the specimen is not in conflict with this identification as stratigraphically calibrated phylogenies of tetanuran theropods show.

If confirmed, the presence of the earliest known spinosaurid in the Middle Jurassic of Niger would support an African origin for the clade.

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