When Tyrannosaurus rex had for breakfast… another Tyrannosaurus rex

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(This was first published at The Urban Times)

In a study published in the online journal PLoS ONE yesterday, researchers show evidence for cannibalistic behaviour in Tyrannosaurus rex. Indeed, the king of the dinosaurs not only fed on other dinos but also on fellow T. rex, say the researchers after identifying bite marks on giants’ bones.

Tyrannosaurus rex was a quite amazing being: 42 ft in length, 13 ft tall at the hips and up to 7 tones in weight, with his two small but strong forelimbs and a running speed of 18km/h. It lived during the Late Cretaceous (which is between 67 and 65 millions of years ago), prior to the extension event. It was one of the few carnivorous species and is believed to have been preying upon hadrosaurs and ceratopsians; some experts have suggested it was primarily a scavenger.

The debate on T. rex feeding strategies is old: in the beginning of the 20th century, Lambe compared it to Gorgosaurus (a close relative) and suggested that both were scavengers because the fossil teeth showed no wear. But this argument was not taken seriously any longer given that these dinos replaced their teeth frequently. Thus, most scientists have speculated that T. rex was a predator and could also scavenge or steal another predator’s prey.

Jack Horner, a hadrosaur expert, is the major advocate of the idea T. rex was exclusively scavenger and did not therefore hunt actively. This is supported by several arguments such as large olfactory bulbs and nerves (relative to the brain size) which suggests a well developed sense of smell helping to sniff out carcasses over great distances. Moreover, Tyrannosaur could crush bone, therefore extract as much food (bone marrow) as possible from the carcasses.

However, these arguments can be countered. Indeed, T. rex teeth were not as well adapted to chewing bone as hyenas’ are to extract bone marrow. Even if T. rex was not the fastest animal (it walked rather running), it could have been fast enough to prey on large hadrosaurs and ceratopsians. Furthermore, the position of its eyes was giving it a binocular vision which is evaluated to be slightly better than that of modern hawks. In modern animals, binocular vision is found majorly in predators. For these and other reasons, most paleontologists accept T. rex was both a scavenger and an active hunter.

The study by Nicholas Longrich and colleagues is thus a landmark in this debate. What they reported is that his insatiable desire for meat pushed T. rex to feed on his cousins. As described in the study, 17 dino specimens were examined as bearing tooth marks made by T. rex. Four out of the 17 dinos represent T. rex. When having a closer look to the T. rex bones (three foot bones and one arm bone, inset), the gouges are deep, U- and V-shaped. This kind of marks could have been made by any big carnivore, but T. rex was the only big carnivore in the area at that time.

Tyrannosaurus rex bones bearing tooth marks made by Tyrannosaurus rex.
Tyrannosaurus rex bones bearing tooth marks made by Tyrannosaurus rex. Adapted from Longrich et al., PLoS ONE 2010

Longrich and colleagues discuss the possibility these marks are made by Crocodylians and reject it because of the small size of the latter and their different teeth order and shape. Furthermore, insects can modify bone, but the scars found here do not look like any traces made by insects and known to day. Finally, the gouges on the T. rex bones “do not represent tool marks made during excavation, because tools could not penetrate deeply into the fossil without shattering the brittle bone”.

Researchers argue therefore that these scars result from one T. rex feeding on a cousin rather than intraspecific combat. They define it as “an indiscriminate and opportunistic feeder”: what is better than having a dinner from the enemy. These gouges seem to have been made “after most of the flesh and meat had been removed from the carcass”, write the authors.

T. rex becomes the second dino species to be shown being engaged in cannibalism (along with Majungatholus). It is an additional argument favouring the idea that cannibalism was widespread in dinosaurs. This would not be that astonishing given that cannibalism is common in nature and in particular among large carnivores (bears, hyenas, large felids, etc.).

Longrich, N., Horner, J., Erickson, G., & Currie, P. (2010). Cannibalism in Tyrannosaurus rex PLoS ONE, 5 (10) DOI: 10.1371/journal.pone.0013419

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