La peculiar mano de un titanosaurio de Lo Hueco el XII Congreso de la EAVP

Turín es bien conocida por su equipo de fútbol, la fábrica de coches FIAT, el sudario santo, los museos Egipcio y del Cine, la Mole Antonelliana, su espectacular comida,… pero todo esto quedó relegado a segundo plano la semana del 24 al 28 de junio, ya que eran estas fechas en las que se celebraba la reunión anual de la European Association of Vertebrate Palaeontologists (¡ya la duodécima!). Ha sido una de las EAVP más concurridas, y se realizaron varios simposios dedicados a primates fósiles, cambios faunales, paleoherpetología, aves, y dinosaurios europeos. Y precisamente fue en este último simposio en el que nuestro equipo hizo acto de presencia, nada más y nada menos que presentando en una comunicación oral unos metacarpianos de titanosaurio encontrados en el yacimiento de “Lo Hueco” con una morfología cuánto menos peculiar… A continuación os detallamos el resumen, pero para las fotos ¡tendréis que esperar a la publicación!

A CASE OF EXTREME MANUS ELONGATION IN SAUROPODS FROM THE LATE CRETACEOUS OF “LO HUECO” (SPAIN) 

The manus of the titanosauriform sauropods shows a stressing evolutionary pattern, characterized by elongated and tubular disposed elements, which is highly related with the columnar morphology of their forelimbs. Basal titanosauriforms elongation of the metacarpals is also correlated with an elongation of the humerus relatively to the femur (Salgado et al., 1997). The metacarpal elongation, also present as a convergence in some basal eusauropods such as Turiasaurus or Atlasaurus, persists in some more derived titanosauriforms, including basal lithostrotians such as Rapetosaurus or Malawisaurus.

Herein, an isolated set of four metacarpals (I, II, III, and IV) from the same left manus is described, being the most complete sauropod manus recorded from the Iberoarmorican territory. The specimen was collected at the “Lo Hueco” site (Cuenca, Spain), dated as Campanian-Maastrichtian (Late Cretaceous). The metacarpals are markedly slender (maximum diameter in the center of the shaft / length in the metacarpal III= 12.06). Metacarpal III is the longest, as generally occurs in titanosauriforms (Upchurch et al., 2004), while the shorter – metacarpal I –, is only reduced to 80% of the length of the III. Metacarpals II, III, and IV have flat distal surfaces, probably associated with the loss of pedal phalanges as occurs in lithostrotians (Salgado et al., 1997). The proximal end of metacarpal I is not totally preserved, but seems to be transversely compressed as in other titanosauriforms (Apesteguía, 2005). The distal third of the diaphysis is slightly bowed – character usually referred to the presence of a short first phalanx and ungual –, and the distal articular surface does not extend onto the dorsal surface of the metacarpal – except for metacarpal I – and is undivided, features considered as synapomorphies of Titanosauriformes (D’Emic, 2012). Metacarpal III presents a proximal articular end with a triangular profile, as in most advanced titanosaurs (Apesteguía, 2005), but also present in basal titanosauriforms. When rearranged together, the manus present a tubular structure, with “U”-shaped profile in proximal view. Laterally and medially the metacarpals became significantly shorter compared with the metacarpal III.

The stratigraphic position, the faunal context, and the combination of characters allow considering this manus as belonging to indeterminate titanosauriform that probably corresponds to a titanosaur. However, it is considered that such delicate and slender metacarpals are unique for sauropods, even for basal titanosauriforms, and particularly for titanosaurs. These metacarpals are unusually slender even compared with those of the basal lithostrotian Rapetosaurus, and distinct from the more robust type present in saltasaurids (Apesteguía, 2005). This manus probably belongs to one of the still undescribed titanosaur taxa from “Lo Hueco” (Ortega et al., 2008), but at present it is not possible to relate it with any of them. So, its taxonomic assignment remains open pending of further analyses. The interpretation of the “Lo Hueco” titanosaurian faunas will allow understand the phylogenetic position of this extreme digitigrade sauropod.

P.D.: Un grazie mille a Massimo Delfino y al resto del Host Comittee por un congreso inolvidable.

P.D.2: ¡¡Nos vemos el año que viene en el EAVP en Polonia!!

Más información:

• Referencia: Díez Díaz, V., Mocho, P., Ortega, F., and Sanz, J.L. 2014. A case of extreme manus elongation in sauropods from the Late Cretaceous of “Lo Hueco” (Spain). p. 52. In: Delfino, M., Carnevale, G., and Pavia, M. (Eds.): Abstract Book and Field Trip Guide, XII Annual Meeting of the European Association of Vertebrate Palaeontologists. Museo Regionale di Scienze Naturali, Regione Piemonte, Torino, pp. 192.
• Imagen: Foto de grupo del XII EAVP. Cortesía de Fabio Marco Dalla Vecchia.