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Two views of the skull of Tapuiasaurus. From Zaher et al, 2011.

Sauropod skulls are rare. As big as impressive as these long-necked giants were, they often lost their heads after death. There were decades of confusion over what the skull of Apatosaurus looked like. This makes the discovery of any complete sauropod skull cause for celebration, and I was delighted to hear that an international team of paleontologists has just described the noggin of a previously unknown sauropod from Brazil.

Described in PLoS One, the new dinosaur is named Tapuiasaurus macedoi. A member of the sauropod subgroup called titanosaurs, its bones were discovered in the 125- to 112-million-year-old strata of Brazil. Vertebrae, parts of the shoulder, the radius, and a femur from this dinosaur were found, but the most significant discovery was a complete skull. In overall form the skull resembles those of titanosaurs from other places—such as Rapetosaurus from Madagascar and Nemegtosaurus from Mongolia—in having an elongated snout, a nasal opening at the level of the eyes, and narrow tooth crowns.

But Tapuiasaurus lived long before these dinosaurs. Even though Rapetosaurus and Nemegtosaurus were found to be the closest known relatives of the new dinosaur, they lived about 30 million years after Tapuiasaurus. In terms of evolutionary history, this means that the skull shape of the Late Cretaceous titanosaurs evolved much earlier than was previously thought, and there are probably many other related dinosaurs yet to be found in the gap between Tapuiasaurus and its later cousins. With any luck, more skulls will turn up to fill out the evolutionary history of these dinosaurs.

References:

Zaher, H., Pol, D., Carvalho, A., Nascimento, P., Riccomini, C., Larson, P., Juarez-Valieri, R., Pires-Domingues, R., da Silva, N., & de Almeida Campos, D. (2011). A Complete Skull of an Early Cretaceous Sauropod and the Evolution of Advanced Titanosaurians PLoS ONE, 6 (2) DOI: 10.1371/journal.pone.0016663