Busted and Broken Fossils Show How Dinosaurs Fought

Part of our enduring fascination with dinosaurs stems from how strange the ancient reptiles were. Sharp teeth with wicked serrations, enormous claws, splashes of horns and coats of armor make all of us—paleontologists and the public alike—wonder what all those amazing structures were for.

A century ago, experts thought these extraordinary dinosaur features were developed for interspecies attack and defense. The skull of Triceratops was a set of lances and a shield to defend against ravenous Tyrannosaurus, and the plates and spikes of Stegosaurus evolved to make Allosaurus think twice about taking a bite. But the story has changed since them. We now know that many of the strange anatomical quirks dinosaurs evolved were used to fight with members of their own species.

Here’s some of the most fascinating new evidence about dinosaur combat.

Ankylosaurs bashed each other with heavy tails

From nose to tail, Zuul was covered in bony armor. This 75-million-year-old ankylosaur was decked out with pointed spikes and, much like the classic Ankylosaurus itself, a heavy club at the end of its strong tail. While such structures could have been used to ward off the likes of Daspletosaurus, a carnivorous relative of the famous T. rex, a new study in Biology Letters found that Zuul must have fought each other. Though only one Zuul fossil specimen has yet been found, the armor along the dinosaur’s hip shows damage from a blunt object swung at the side—the tail of another Zuul would be a perfect fit.

Royal BC Museum paleontologist Victoria Arbour and colleagues also propose that ankylosaur species developed unique armor for communication and combat with fellow ankylosaurs. If defense against predators were the armor’s primary function, it would be very similar across different species. Over time, they would have developed a small range of optimal armor arrangements to guard against the hunting behaviors of carnivorous dinosaurs, which focus on big bites to vulnerable places. The vast array of different spike and plate arrangements among ankylosaur species indicates that the armor served a dual purpose as ornamentation and protection in Cretaceous sparring bouts.

Tyrannosaurs bit each other on the face

Paleontologists have spent more than a hundred years pondering how Tyrannosaurus rex used its jaws on its prey. But what happened when two T. rex faced off? Surely they didn’t arm wrestle. Instead, University of Wisconsin Oshkosh paleontologist Joseph Peterson and colleagues found, T. rex bit each other on the face.

The skull of the teenage T. rex “Jane” shows four partially healed bite marks. The punctures are consistent with the tooth shape of another T. rex about the same age. This fossil indicates not only that T. rex fought by biting each other on the snout, as some crocodile species do today, but also that this behavior started early in the life of the tyrant lizard. Other, older T. rex specimens have also been found with bite marks, reinforcing the notion that these iconic dinosaurs literally faced off.

Triceratops locked horns

Triceratops has always been an unusual dinosaur. The frill atop its skull was solid bone rather than having large openings called fenestrae in it, like all other horned dinosaurs. And its three horns actually represent a very low number compared to the dinosaur’s relatives. Rather than being used for defense against carnivores, however, this arrangement allowed Triceratops to settle disputes among themselves in a unique way—by locking horns.

Healed lesions on multiple Triceratops skulls, Raymond M. Alf Museum of Paleontology researcher Andrew Farke and colleagues found, are consistent with how two dueling Triceratops would have had to place their horns in combat. Other horned dinosaurs, by comparison, lack this damage and might have used display more than brute force to settle disputes. And paleontologists are still finding evidence that Triceratops horns evolved as a social aspect of the well-known species. A recent analysis of an unexpected hole in the frill of a Triceratops nicknamed “Big John” indicates that the opening is a combat wound, perhaps caused by a slipped horn during a fight.

Pachycephalosaurs used their heads as battering rams

What in the world were pachycephalosaurs doing with their domed heads? Paleontologists have tussled with this question for decades. The thick, spike-rimmed skull roofs of these dinosaurs look perfect for use as battering rams, leading to plenty of depictions of Pachycephalosaurus and similar dinosaurs smacking heads just like bighorn sheep. The reality is a little bit different.

Different groups of paleontologists have found evidence that some pachycephalosaur skulls have healed injuries caused by some sort of blunt-force trauma. Such injuries, as well as biomechanical studies of the forces the multi-inch layers of pachycephalosaur skulls could withstand, hint that these dinosaurs used their heads as weapons. But the skeletons of pachycephalosaurs—and even their dome-like skulls—seem ill-suited for butting heads like bighorn sheep do. These dinosaurs’ necks are not adapted to handling the forces butting heads would create, and the dinosaurs lack the airy sinuses of head-butting mammals that absorb impact forces and prevent bones from breaking.

Instead, pachycephalosaurs may have used their heads to butt each other along the flanks or hips as part of their combat. No one knows for sure. Even partial skeletons of pachycephalosaurs are very rare, making it difficult to test ideas about how these dinosaurs might have fought. Paleontologists are fairly certain some kind of head-butting was involved, but the details await some future discovery.

Allosaurus ate each other

The terrible teeth and claws of dinosaurs like Allosaurus are often envisioned as weapons used to catch, kill, dismember and eat herbivorous dinosaurs. But we also know that many predatory dinosaurs had no qualms about eating their own.

In western Colorado, the 150-million-year-old Mygatt-Moore quarry contains the remains of many dinosaurs, including the long-necked Apatosaurus and the early ankylosaur Mymoorapelta. Allosaurus is in the mix, too, and, University of Tennessee, Knoxville paleontologist Stephanie Drumheller-Horton and colleagues reported, some Allosaurus bones from this quarry have bite marks that might have been made by other Allosaurus. At present, scientists can’t tell whether these bite marks were made after death or if Allosaurus attacked each other during times of drought. The cannibalistic hypothesis remains an open possibility, bolstered by the fact that—like other dinosaurs—baby and juvenile Allosaurus are extremely rare in the fossil record. Juvenile dinosaurs were especially vulnerable to predators, and if Allosaurus would resort to cannibalism, then baby Allosaurus might have had plenty to fear from adults of their own species.

Some dinos used their tails as whips

Dinosaurs such as Apatosaurus and Diplodocus are sometimes depicted as gentle giants, nibbling at Jurassic conifers. The tails of these dinosaurs, however, hint that these enormous herbivores sometimes clashed with each other. A team of paleontologists had previously proposed that the thin, whip-like tails of dinosaurs like Apatosaurus might have been able to crack like actual whips and break the sound barrier. A new analysis found that those dino tails couldn’t quite reach supersonic speeds—instead topping out at about 74 miles per hour—but the authors of the new Scientific Reports study suggested that these powerful tail swings might have been used in combat between Diplodocus. Such fights might explain why sauropod tail bones are sometimes found with healed breaks and infections, and, as experts await further evidence, it’s still fun to envision what a potential “Brontosmash” might have looked like.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.