Cartoonishly tiny arms? Check. Massive, bone-crunching jaws? Huge check. How about bloodthirsty cannibalistic impulses? For certain enormous Tyrannosaurs dinosaurs—including T. rex—apparently that's a big check, too.
A pair of paleontologists has just of a fascinating forensic report on a badly thrashed Tyrannosaur fossil—it comes from one of T. rex's marginally smaller cousins, Daspletosaurus. According to Dave Hone at the University of London, who led the investigation, team discovered not only healed wounds from vicious face-to-face, intra-species fights for dominance, but also the evidence of opportunistic cannibalism to boot.
"We're inferring these fights [for dominance] from nasty but healed bite marks on the fossil, which are only found around the skull," Hone says. The local of the bite marks say a lot. Tyrannosaur's fleeing prey often show brutal bite marks on their legs and tail, but usually not the head.
"There's also lots of evidence here of [cannibalistic] feeding traces on the fossil from other Tyrannosaurs," he says, including a bitten and partially missing lower-jaw. "On one hand this is something we've already seen in another fossil from a tyrannosaur, but keep in mind we still think this is probably a pretty rare occurrence." Because these big carnivores must have lived with a limited food supply, "it's unlikely that they're coming across one another often enough to scavenge like this."
Just like in police doing forensic work, paleontologists can distinguish between the severity of different injuries and scars on a fossil. One of biggest clues left behind on a battle-wound isn't just its size and shape, but whether or not it's healed. Healed injuries tell scientists about a dinosaur's daily life, not just how they died. And unlike bones that are broken and scraped during or after death, "the shape and texture of healed bones are totally different," Hone says.
Although it's difficult to identify how and why healed wounds were originally caused, his Daspletosaurus has quite a few fairly obvious scars that are from brutal head-on competition between two members of the same (or similar) species, Hone says. "For example, if you think about what could have caused this big, tyrannosaur tooth-sized hole at the back of this thing's skull… (laughs) we're fairly confident we can say it didn't just fall over and get hurt."
And based on the severity of these healed injuries, Hone discovered that these Tyrannosaurs were doing some bloody, lasting damage to one another while fighting—unlike say, head-butting rams today.
As for the cannibalism, Hone's evidence comes from unhealed tooth marks and tracks found across the fossil, many of which appear to be caused by teeth and jaws so large only a tyrannosaur could have made them. To paleontologists, this cutthroat finding isn't all that shocking; back in 2010 scientists found similar evidence on the most famous of all Tyrannosaurs: T. rex.
Curiously, the battle-scarred fossil that Hone and his partner—Darren Tanke at Royal Tyrrell Museum of Paleontology in Alberta, Canada—scoured for evidence is by no means a new discovery. First found more than two decades ago in Alberta, Canada, the odd fossil has been collecting dust since 1994. But this type of bone scarring is "only obvious if you're looking for it. If you're not looking for it, it's easy to overlook," says Nick Longrich, a paleontologist at the University of Bath, UK who was not involved in the study.
Longrich says these wounds offer rare evidence-based insight into the daily lives of these ancient beasts. "We can speculate endlessly about [how] an animal might have [behaved]," he says, "but tooth marks and injuries provide actual evidence of how the animal lived and died, and the interactions between animals."