Monday, 19 March 2012

Kelmayisaurus petrolicus reconsidered.

Kelmayisaurus petrolicus was described in 1973 by ZM Dong in 1973, based upon a single fragmentary pair of jaws from the Early Cretaceous Junggar Basin in Xinjiang Province. It appears to have been a large theropod dinosaur, similar in size to Allosaurus, though the remains are to limited for any real estimate of scale to be attempted.

Map showing the location of the Junggar Basin. Han et al. (2009).

Since this time our understanding of Cretaceous Therapods has increased spectacularly, with completely novel groups being discovered, and the biology of others being revised completely, so that we now have a picture of a far more diverse group of animals than was the case in the early 1970s.

In a paper in the March 2012 edition of the journal Acta Palaeontologica Polonica, Stephen Brusatte of the Division of Paleontology at the American Museum of Natural History, Roger Benson of the Department of Earth Sciences at University College London and Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, re-examine Kelmayisaurus petrolicus to determine whether it can genuinely be considered a separate species (which has been disputed), and what its taxonomic position is.

(A) Left maxilla (upper jaw) of Kelmayisaurus petrolicus in (A₁) lateral, (A₂) medial and (A₃) ventral view. (m1) first maxillary tooth, (m6) sixth maxillary tooth. Scale bar 5 mm. (B) Left Dentary of Kelmayisaurus petrolicus in (B₁) lateral, (B₂) medial and (B₃) dorsal view. (d15) fifteenth dentary tooth, (d2) second dentary tooth. Scale bar 5 mm. Brusatte et al. (2012).

Brusatte et al. concluded that although the remains of Kelmayisaurus petrolicus are extremely fragmentary, they are sufficient for taxonomic analysis, with enough material preserved to exclude K. petrolicus from any other described species, and attempt to place it on the Therapod family tree. They conclude K. petrolicus is an early Carcharodontosaurid, a member of a group of dinosaurs previously thought to be exclusively Gondwanan in distribution (i.e. restricted to Gondwanaland, a Late Mesozoic super-continent comprised of the modern continents of South America, Africa, Madagascar, India, Australia, New Zealand and Antarctica), but which have recently been found at several locations in Eurasia. K. petrolicus could potentially be the oldest Eurasian member of the group, though it is not very precisely dated, probably being somewhere between 140 and 99.6 million years old, so unless further material comes to light this cannot be determined.

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