Tuesday, 5 March 2013

A Predator To Match The Dinosaurs

It is often said that dinosaurs dominated the Earth during the Mesozoic era. Tyrannosaurus rex, the tyrant king of the lizards, was the deadliest carnivore on the face of Pangaea. Raptors terrorized entire herds of herbivorous dinosaurs. Even though Baryonyx was a fish feeder, with its giant sickle claws, it was more than a match for any creature it encountered. Yet an even older lineage of reptiles whose members still lurk in the rivers and swamp lands of Africa and Florida were equally fierce if a little cumbersome on land: the crocodilians. Creatures such as Deinosuchus were longer than the tyrannosaurids and had a far stronger bite force.
An artist's impression of Deinosuchus, the largest
crocodile to have ever walked the Earth.

Such creatures began to evolve towards the end of the Cretaceous period when the empire of the marine reptiles was slowly crumbling. They were the top predators in their environments, feeding on fish, turtles and dinosaurs, including large carnivores.

New fossil evidence has shown that it was not only the large dinosaurs who suffered at the jaws of their aquatic cousins. A number of bone fragments were uncovered at the Grand Staircase Escalante - National Monument in southern Utah. They were taken to the South Dakota School of Mines and Technology for analysis. The research team, led by Dr Clint Boyd, found that many of the bones, including a relatively complete femur and partial skull, belonged to a new species of dinosaur.

While the name and identity of this newcomer has not yet been released (a paper is due soon) what made these specimens particularly interesting was that many of them displayed bite marks from what were potentially fatal skirmishes with a predator. The marks were associated with the joints in particular which is the modus operandi of the crocodilians.
The femur and associated crocodilian tooth from the
Grand Staircase Escalante National Monument.

In the water, these giant reptiles grasp onto their prey and perform what is known as a death roll designed to tear flesh from the victim. On land, while they do not roll over they still shake their heads in a vice-like grip. From their relatively low vantage point, just a few inches off the ground, legs are an easy and obvious target, as well as the dual effect of preventing the prey from escaping. Even if the animal did manage to break free, the leg would have been left behind, making the creature easy to recapture.

The clinching piece of evidence, however, was a crocodilian tooth embedded in the femur. Until now, there was only evidence of interaction between large dinosaurs and the crocodilians. This adds a new dimension to the Cretaceous Earth, showing that these predators targeted smaller and easier meals. Indeed, a study of the bones showed that they came from dinosaurs which would have been no more than two metres in length.

'A lot of times you find material in close association or you can find some feeding marks or traces on the outside of the bone and you can hypothesize that maybe it was a certain animal doing this, but this was only the second time we have really good definitive evidence of a crocodyliform feeding on a prey animal and in this case an ornithischian dinosaur,' said Boyd. It's an interesting note that as the dinosaurs slowly declined, the crocodiles began to rise.

The number of species which existed towards the end of the Cretaceous was staggering and while they suffered a decline during the K-T boundary extinction event, they survived while the dinosaurs did not. Indeed, had the asteroid never struck the Earth, it is still possible that dinosaurs might have gone extinct, out-competed by the hardy crocodilians, while the smaller ecological niches were overrun by the mammals and the birds. The world may well have been very different.