Masiakasaurus Gets a Few Touch-Ups

Masiakasaurus was a weird-looking dinosaur. The paper that first described it was titled "A bizarre predatory dinosaur from the Late Cretaceous of Madagascar." What made it so strange were its teeth. At the front of its lower jaw, this six-foot theropod had forward-tilted teeth much different from those of its larger cousin Majungasaurus, which lived alongside it.

When Masiakasaurus was first described, by paleontologists Scott Sampson, Matthew Carrano and Catherine Forster in 2001, not much of Masiakasaurus was known. The hindlimbs, portions of the neck, back and tail, part of the hip, the upper arm bones, a portion of the upper jaw and most of the lower jaw were all that had been found. Still, this was enough to identify this dinosaur as a unique, small member of a group of predatory dinosaurs called abelisauroids found in what is now South America, Europe, Africa and India. It most closely resembled a small member of this group from Argentina called Noasaurus.

A more detailed 2002 study by the same authors provided a more comprehensive view of this dinosaur, including the assessment that this dinosaur probably seized prey with its front teeth and shredded prey with its back teeth. But a significant portion of this animal's anatomy remained missing. Thanks to additional specimens found during the past nine years, however, paleontologists Carrano, Mark Loewen and Joseph Sertich have filled in some of those gaps. They have reported their findings in a new Smithsonian Contributions to Paleobiology monograph.

With the exception of part of the skull, the bones of the lower arm and a few other pieces, almost the entire skeleton of Masiakasaurus has now been found. These did not come from a single find, but multiple specimens from thirty localities in northwestern Madagascar. Among the most important of the new finds is the premaxilla, or the frontmost part of the upper jaw. Much like the front of the lower jaw, the front of the upper jaw housed forward-oriented, recurved teeth, creating that impression that Masiakasaurus could have benefited from some braces.

Also noteworthy is that, in accord with similar studies of Noasaurus, bones thought to belong to the foot of Masiakasaurus were found to actually belong to the hand. On the surface this sounds a bit mundane, but this misidentification caused some paleontologists to propose that Noasaurus and its close relatives had a hyper-extendable sickle claw on their second toes, like those of very distantly related dinosaurs such as Deinonychus and Troodon. A study published in 2009 by Federico Agnolin and Pablo Chiarelli corrected this for Noasaurus, and the new Smithsonian monograph has corrected it for Masiakasaurus.

Within a decade of its initial description, Masiakasaurus has become the best-known dinosaur of its kind found anywhere in the world. Frustratingly, however, its closest relatives are known from such fragmentary material that we still don't have a solid idea of what they looked like or how they differed from each other. The dinosaurs Noasaurus, Genusaurus and Velocisaurus were likely relatively lanky and narrow-headed, but we can't know that for sure until paleontologists find more of them. As much as we have learned about Masiakasaurus, much remains unknown about its relatives and evolutionary history.

References

Agnolin, F., & Chiarelli, P. (2009). The position of the claws in Noasauridae (Dinosauria: Abelisauroidea) and its implications for abelisauroid manus evolution Paläontologische Zeitschrift, 84 (2), 293-300 DOI: 10.1007/s12542-009-0044-2

Carrano, M.T., Loewen, M.A., and Sertich, J.J.W. (2011). New Materials of Masiakasaurus knopfleri Sampson, Carrano, and Forster, 2001, and Implications for the Morphology of the Noasauridae (Theropoda: Ceratosauria) Smithsonian Contributions to Paleobiology, 95, 1-54

CARRANO, M., SAMPSON, S., & FORSTER, C. (2002). THE OSTEOLOGY OF MASIAKASAURUS KNOPFLERI, A SMALL ABELISAUROID (DINOSAURIA: THEROPODA) FROM THE LATE CRETACEOUS OF MADAGASCAR Journal of Vertebrate Paleontology, 22 (3), 510-534 DOI: 10.1671/0272-4634(2002)0222.0.CO;2

Sampson, S., Carrano, M., & Forster, C. (2001). A bizarre predatory dinosaur from the Late Cretaceous of Madagascar Nature, 409 (6819), 504-506 DOI: 10.1038/35054046

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.