The bite stuff: an old jaw provides clues to ancient diversity, ecology, and geography

Natural History, May, 2002 by Scott D. Sampson

In 1995 during a paleontology field season in Madagascar, a large island off the east coast of Africa, my good friend and fellow expedition member Cathy Forster unearthed part of a strange fossil jaw. Even at first glance, the shape of the four-inch-long bone and the linear arrangement of tooth sockets told us that this was a dentary, or tooth-bearing portion of a lower jaw. Yet the socket for the missing frontmost tooth, instead of being directed upward, pointed forward, suggesting that this tooth had been oriented almost horizontally. The next few sockets on either side were also inclined forward, though at successively lesser angles. At the back of the jaw, the preserved teeth were bladelike and serrated, whereas the single preserved front tooth was long and conical, with a hooked tip. Thus, we knew from the start that the owner of the ancient jaw was an odd little beast with protruding teeth.

The fossil quarry that produced this specimen is one of the richest and most important in Madagascar. The sediments and bones are of Late Cretaceous age, about 70 million years old, from a time several million years before the demise of the dinosaurs. Because we were unsure what kind of animal the bone--which we affectionately called "weird jaw"--might belong to, we informally consulted colleagues after returning home. To our request for a "best guess," we received responses ranging from dinosaur to crocodile to bird to pterosaur, or flying reptile. Only after comparing the dentary with that of Majungatholus, a theropod (bipedal carnivorous dinosaur) found in the same deposits in Madagascar, were we convinced that the weird jaw, too, once formed part of the weaponry of a predatory dinosaur.

However, it was not until 1999 that we were able to bring the identity of this animal into sharper focus. While working at the same quarry, we found a concentration of small theropod fossils: vertebrae, various limb bones, and a few skull parts, including three more weird jaws. We uncovered multiple examples of many of the bones, which belonged to several individuals, all of the same buck-toothed species. By piecing together the fragile fossils, Cathy and I, together with our colleague Matt Carrano, reconstructed almost half of the total skeleton and were able to get a pretty good idea of the size and shape of this new species. Our Mesozoic meat eater was a lightweight, as dinosaurs go. It had a body length of five to six feet, most of which was neck and tail, and would have weighed approximately eighty pounds, roughly as much as a German shepherd. Now all we needed was a suitable name.

Paleontologists and biologists have the honor of giving a two-word name, or binomial, to any new species they formally describe in the scientific literature, and the rules for naming are relatively few. For the first part of the name, we combined the Malagasy word for "vicious," masiaka, and the Greek for "lizard" santos. Masiakasaurus seemed an appropriate moniker for a dinosaur with a putative dietary preference for flesh.

The second part of the name came about more through serendipity than science. Life in the field is rather spartan, so it's always a good idea to bring along a few comforts from home, including music. During our 1999 season, whenever we played the rock music of Mark Knopfler and his group Dire Straits, crew members seemed to uncover more Masiakasaurus bones. The converse appeared true also: no Dire Straits, no bones. So in a nonstandard but, we thought, fitting gesture, we followed Cathy's suggestion and named the carnivore after our musical talisman. The beast was officially dubbed Masiakasaurus knopfleri: the vicious dinosaur of Knopfler.

Our team, led by David Krause, of SUNY Stony Brook, has been working in Madagascar since 1993, and Masiakasaurus is not the only bizarre animal we've found. Others include Rahonavis, a bird with a raptorlike sickle claw; the previously mentioned Majungatholus, a large theropod with a dome atop its head; and Simosuchus, a pug-nosed, possibly vegetarian crocodile. So far, no other dinosaur from anywhere in the world exhibits specialized jaws and teeth like those of Masiakasaurus, which makes one wonder what this animal did for a living. A few species of modern mammals may provide an analogue. Some small mammals--various shrews, for example--possess a similar dental setup, with long, conical, forward-projecting teeth up front. In virtually all these mammals, the front teeth are used for grasping and piercing prey--mainly insects. Masiakasaurus may have employed the same kind of strategy, capturing and manipulating prey with its slanted front teeth. Prey candidates include insects, fish, lizards, snakes, and mammals. Following the initial attack, the bladelike rear teeth may have been used to tear and slice the victim into bite-sized chunks.

Both of the Malagasy theropods from our site are members of an enigmatic group called abelisauroids, known almost entirely from the Southern Hemisphere. Through our research, Matt, Cathy, and I have found that Masiakasaurus shares a number of specialized features with predatory dinosaurs from India and Argentina. This discovery indicates that toward the end of the dinosaurs' reign, small-bodied theropods were spreading throughout much of the Southern Hemisphere. This southern radiation parallels the spread of small theropods such as the dromaeosaurids, or "raptors," through the Northern Hemisphere during the same time period.