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POL Diego

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Título:

The skull of the titanosaur Tapuiasaurus macedoi: new insights into titanosaur feeding behavior

Autor/es:

WILSON, J.A.; CARVALHO, A.; POL, D.; ZAHER, H.

Lugar:

Mendoza

Reunión:

Congreso; 4th International Paleontological Congress; 2014

Resumen:

The recent discovery of a partial skeleton of the sauropod dinosaur Tapuiasaurus macedoi by Zaher and colleagues offers the first glimpse at the skull of a titanosaur from South America, where the greatest diversity of that group has accumulated since the late 19th Century. Surprisingly, although Titanosauria is the most diverse and late-surviving sauropod lineage, cranial elements are known for just over 20 of its 50+ genera?the vast majority of which are fairly fragmentary and restricted to the Late Cretaceous. Only four complete titanosaur skulls have been described to date; three of these are from the latest Cretaceous (Nemegtosaurus, Rapetosaurus, Quaesitosaurus), and the fourth, Tapuiasaurus, is from the Early Cretaceous (Aptian). Despite the ca. 70 Ma interval separating these Early and latest Cretaceous titanosaurs with complete skulls, phylogenetic analyses have recovered them as a monophyletic group called Nemegtosauridae. The hypothesis that Tapuiasaurus is more closely related to other nemegtosaurids than to other titanosaur genera is supported by features of the postcranial skeleton and cranial elements that are more commonly preserved (e.g., braincase); it implies a lengthy ghost lineage and that the peculiar morphology of the nemegtosaurid skull evolved early in the Cretaceous but is not primitive for Titanosauria. Here, we present further investigation of the skull anatomy of Tapuiasaurus macedoi, which improves its diagnosis and allows the interpretation of its feeding adaptations. The skull of Tapuiasaurus is approximately half a meter long and nearly half as tall. The dentigerous portion of the skull in Tapuiasaurus represents 28% its total length, which is slightly greater than in Diplodocus (17.5%) or Nemegtosaurus (20%). The values for these narrow-crowned forms differ significantly from those of broad-crowned forms (e.g., Camarasaurus = 50%), which have a comparable number of broad teeth, and from those of basal sauropodomorphs (e.g., Plateosaurus = 60%), which have a large number of medium-breadth teeth. Other similarities, which are independently derived, include the overall shape of the skull (braincase rotated posteriorly relative to the snout), elevated tooth replacement rates, and prominent vascular grooves on the dentigerous snout. Our study provides insights into the herbivorous adaptations that are shared by these narrow-crowned forms (diplocodoids, titanosaurs) and those that are unique to at least nemegtosaurid titanosaurs. We present a new hypothesis for titanosaur feeding, which supports modified version of the ?guillotine? hypothesis for titanosaur feeding forwarded a decade ago.

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