29.9.16

Muslitos de titanosaurio de Lo Hueco en las VII Jornadas de Salas de los Infantes


Seguimos con la Crónica de unas Jornadas, en Salas de los Infantes. Entre los trabajos presentados, vuelve el turno de los saurópodos. Una de las comunicaciones orales dedicó unos minutos a tratar la variabilidad intrasepecífica en los elementos del esqueleto apendicular de los titanosaurios del yacimiento de Lo Hueco, Cuenca. Entre los numerosos restos de titanosaurios, una gran cantidad son elementos desarticulados de las extremidades, con cierta variabilidad entre ellos y los problemas de clasificación que conlleva. En estas jornadas se expuso la metodología empleada para identificar a qué taxón de los hallados en el yacimiento pertenecerían algunos de los fémures de la muestra y explorar cambios como los que se producen durante el crecimiento del titanosaurio.

Sauropod dinosaur present a very conservative bauplan along the phylogeny, especially in their limbs. While axial skeleton usually brings enough information to diagnose at genus or species level, appendicular bones tend to retain more general morphology common between upper clades (see Otero et al., 2008, Otero, 2010).
Multiple specimen association with scattered appendicular elements or even isolated appendicular bones from titanosaur sauropods have been reported from the Upper Cretaceous of Europe (Le Loeuff, 2005, Vila et al., 2012). While some have been attributed to known genus such as Ampelosaurus, Lirainosaurus or Magyarosaurus albeit having some variability within the sample. However, it has been also considered that some specimens have morphologies that differ enough of the forms already known as to consider that correspond to taxa still undescribed (Vila et al., 2012). This results in a possible very high diversity of titanosaur species in the Late Cretaceous of the Iberoarmorican domain when combining the described genus and the morphotypes attributable to different and unknown species.
The Upper Cretaceous fossil site of Lo Hueco was found during the construction of the AVE (Spanish high speed railroad) Madrid-Levante in 2007. In this site, thousands of dinosaur remains have been recovered, in which it is highlighted the high abundance of bones attributable to titanosaur sauropods. Several articulated partial skeletons and a sample of hundreds of scattered appendicular bones among them (Ortega et al., 2015). It is possible to identify, at least, two titanosaur morphotypes based on two types of cranial morphologies, appendicular elements, and teeth (Ortega et al. 2015). Two main appendicular morphotypes of femora and humeri have been also assessed in previous studies based on geometric morphometrics studies (Paramo et al. 2015).
In this study, a sample of femora are compared with those of other Iberoarmorican titanosaur taxa, such Lirainosaurus astibiae, and others of Gondwanan titanosaur belonging to several clades mostly of the Upper Cretaceous. Taxa with multiple specimen are selected in order to attempt to capture the variability of some characters, especially those having systematic relevance such as the variation in the presence of a linea cranialis intermuscularis and other muscular insertions (Vila et al. 2012).
Differences between both morphotypes from Lo Hueco could be attributed with some confidence to two different taxa. However, the variability in several features should be only attributed to intraspecific or ontogenetic variation. The extension of structures such as the trochanteric shelf (Paramo et al. 2015) or the variation in the presence of insertions like accessory trochanters of the fourth trochanter are discussed as possible intraspecific variation. Also, some other structures related with condylar rugosities, similar to those described for Ampelosaurus atacis (Vila et al. 2012) may be related with possible growth patterns, as they are present in bigger forms and less developed or absent in smaller specimens of Lo Hueco and other titanosaurs.
This instraspecific variation may affect previous estimations of Iberian diversity during Late Cretaceous as some undiagnostical elements may pertain to the same undescribed forms or attributable to already known taxa.

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