Tail Whips and Face Bites

Yesterday I wrote about Andrew Farke’s new paper on dinosaur combat. There’s still much to study and discover, but, as Farke makes clear, there’s a decent smattering of evidence that at least some dinosaurs in the Ornithischia subgroup – from spiky stegosaurs to dome-headed pachycephalosaurs – beat up on each other. Ornithischians weren’t the only dinosaurs, though. Some of the most famous dinosaurs of all, including celebrities such as Apatosaurus and Tyrannosaurus,  belonged to a second dinosaur subgroup called the Saurischia. How did these dinosaurs fight?

Saurischian dinosaurs come in two flavors. There’s the sauropodomorphs – long-necked, hefty dinosaurs such as Brachiosaurus and their archaic predecessors – and the theropods, a group best known because of predators like Allosaurus but which also includes birds. As they diverged from their common ancestor, the sauropodomorphs and theropods evolved into strikingly different forms that necessitated very different fighting styles.

Among the oldest possible evidence for combat on the sauropodomorph side is a messy glob of 200 million year old bone. Described by Richard Butler and colleagues a year ago, the fossil testifies to what must have been an extremely painful event wherein an unlucky Massospondylus lost the end of its tail. Exactly what happened is a mystery. The dinosaur might have been attacked by a predator, trampled by a member of its own species, or had some sort of accident. Finding out what happened is beyond our reach, yet the traumatized tail is still a potential sign of a dinosaur scuffle.

Later relatives of that poor Massospondylus suffered tail injuries, too. Paleontologists have found multiple cases of healed, inflamed vertebrae near the end of some sauropod tails, often in Late Jurassic dinosaurs such as Apatosaurus and Diplodocus. Researchers previously attributed these injuries to sneaky carnivores nibbling at the tips of sauropod tails or the painful price of trying to mate, but the whip-like anatomy of these tails tips brings up another possibility. Perhaps sauropods with these long, delicate strings of tail bones – belonging to a group appropriately-named the Flagellicaudata – really did swing their tails like whips, occasionally breaking their own bones in the process.

Sadly, we can’t watch sauropods in action to see whether or not they really used their tails this way. Modeling what sauropods could have done may be the closest we can get. A 1997 biomechanics study by Nathan Myhrvold and paleontologist Philip Currie suggested that Apatosaurus and other sauropods really could crack their tails like whips. But rather than being a weapon to strike with, the authors proposed, the tail whips would have been better for making loud cracking sounds. Still, this would be just one sort of weapon in the sauropod arsenal. Other sauropods, such as Shunosaurus, had tail clubs that they could have come in handy for predator defense, fights with each other, or as a flag for species recognition.

If sauropods used their tails for self-defense, they probably swung them at the carnivorous theropods that nipped at their flanks. Not all theropods were dedicated carnivores – many appear to have evolved omniovorous or even herbivorous lifestyles – but the best evidence for combat comes from the dagger-toothed members of the group. These predators often fought with their mouths.

Lesions and healed wounds on Mesozoic skulls show that allosaurs, tyrannosaurs, and other theropods shared a common mode of attack. They bit each other on the face. Paleontologists Darren Tanke and Philip Currie noted at least four tyrannosaurs and one specimen of the allosaur Sinraptor with such injuries on their skulls, and the juvenile Tyrannosaurus “Jane” was recently found to have pathologies on her snout that match the bite of a similar-sized rival.

There may even be evidence of a fatal tyrannosaur duel. In 2010 Phil Bell and Philip Currie described a piece of tyrannosaur jaw bone with part of another tyrannosaur’s tooth lodged in the bone. The jaw shows no sign of healing, meaning it happened around the time of death or afterward. This could have been a case of scavenging, or, as Bell and Currie point out, it might be a rare example of a fatal fight between two tyrannosaurs.

Potential signs of theropod fights aren’t restricted to the big bruisers alone, though. The quarry that inspired Jurassic Park‘s pack-hunting raptors may instead be a sign of deadly aggression among the human-sized, switchblade-clawed Deinonychus.

The number of shed teeth and partial Deinonychus skeletons found in a single Montana quarry led paleontologist John Ostrom to speculate that these dinosaurs might have been hunting their prey – a dinosaur named Tenontosaurus found in the same place – as a group. But a 2007 reassessment of the site by researchers Brian Roach and Daniel Brinkman forwarded an alternative scenario. Instead of working together, perhaps Deinonychus fought each other as they competed for access to meat. With a skeptical eye towards proposals of cooperative theropods, Roach and Brinkman hypothesized that “nonavian theropod behavior was more agonistic, cannibalistic, and diapsid-like than has been widely believed.”

The case of the Deinonychus boneyard isn’t closed just yet, nor are many of the other possibilities I’ve mentioned in this post. As Farke pointed out in his paper on ornithischian tussles, there’s only so far the available evidence can take us. Comparisons with modern animals, biomechanical studies, and pathologies are useful guideposts for following dinosaur behavior, but each method of approach has limitations. Still, the fact that we have such records to scrutinize at all is a fortuitous turn in nature, and paleontologists will continue to test old ideas and propose new ones as they try to understand the lives that fossil bones represent.