To beat back supersized predators, many herbivorous dinosaurs have been biologically armed to the tooth. Some had skulls studded with horns, whereas others had tails bristling with spikes. However few matched the arsenal of ankylosaurs, a gaggle of herbivores that peaked in range throughout the Cretaceous interval. Many of the ankylosaur’s physique was encased in bony plates that jutted out into jagged factors, and a few lugged round a sledgehammer-like tail membership able to delivering a bone-cracking blow.
Due to their seemingly indestructible nature, paleoartists and researchers alike have spent many years hypothetically pitting these plant-powered tanks towards tyrannosaurs and different apex carnivores. Nevertheless, predators might not have been the one creatures absorbing their batterings.
In a examine revealed Wednesday within the Royal Society Open Science, researchers analyzed the anatomy of one of many world’s most full ankylosaur skeletons. They found a number of damaged and healed armor plates concentrated across the creature’s hips that lacked any clear indicators of illness or predation. As an alternative, the armor appeared to have been splintered by one other ankylosaur’s membership.
“The accidents are proper the place you’d count on two battling ankylosaurs would break issues,” mentioned Victoria Arbour, a paleontologist on the Royal BC Museum in British Columbia and an creator of the examine.
The exquisitely preserved ankylosaur skeleton, which sports activities a full go well with of armor plates referred to as osteoderms, was by chance unearthed in 2014 by business fossil hunters excavating a close-by tyrannosaur in Montana’s Judith River Formation. When the Royal Ontario Museum in Toronto acquired it, the majority of the creature’s skeleton was nonetheless entombed in a 35,000-pound slab of sandstone, leaving simply its cranium and tail free.
Based mostly on the ankylosaur’s cranium and its membership on the finish of a thorny tail, it was clear the animal was a novel species. The dinosaur’s horn-encrusted head reminded Dr. Arbour, then a postdoctoral researcher on the Ontario museum, of the gnarly mug of Zuul, the fear canine from the movie “Ghostbusters.” In 2017, she and her colleagues christened the brand new species Zuul crurivastator, or “Zuul, the destroyer of shins.”
The remainder of Zuul’s physique remained trapped within the stone for greater than a yr as fossil preparators painstakingly chipped away on the rock. They finally uncovered fossilized pores and skin dotted with osteoderms. As they labored their method towards Zuul’s bottom, they found that some spikes alongside the animal’s hips have been lacking their suggestions and that the bony sheaths encasing these osteoderms had damaged and healed into blunt factors.
As a result of the broken plates have been clustered round Zuul’s hips, Dr. Arbour and her colleagues started to query whether or not they have been defensive scars from a failed assault. Bipedal hunters like Gorgosaurus, a lanky cousin of the Tyrannosaurus rex, would have attacked Zuul from above as an alternative of smashing into its flank. And few spots have been as unappetizing as Zuul’s spike-covered haunches, which have been inside placing distance of its membership.
As an alternative, Dr. Arbour and her crew concluded that the position of the battered plates, together with an absence of chunk marks, have been in step with a crack from one other Zuul’s tail membership. As a result of the broken osteoderms have been at completely different phases of therapeutic, it was doubtless that this ankylosaur took its justifiable share of thumpings 76 million years in the past.
The authors proposed that the accidents occurred throughout fight between Zuul and its brawny brethren. Like immediately’s head-butting bighorn sheep or neck-swinging giraffes, competing ankylosaurs might have established dominance by touchdown armor-shattering physique blows with their tail golf equipment.
The brand new proof is crucial for learning the habits of those traditional, but enigmatic, dinosaurs. “Ankylosaurs left no residing descendants, so now we have no residing analogues to study what historic ankylosaurs did,” mentioned Jordan Mallon, a paleontologist on the Canadian Museum of Nature in Ottawa, who was not concerned within the examine. “That is the primary instance the place we’ve been in a position to marshal some proof to assist that this stuff have been truly utilizing their tail golf equipment to smash into each other in a ritualistic method.”
And this observe might need pushed the evolution of gnarlier tail golf equipment, very like how trendy elk make use of their elaborate antlers not solely to tussle with each other but in addition to impress potential mates. “The rationale that they’ve a tail membership might be not pushed by predation, however extra for intraspecific fight,” Dr. Arbour mentioned. “It’s extra sexual choice than pure choice.”
Whereas these golf equipment might have developed to assist ankylosaurs bash one another, they have been nonetheless able to delivering a debilitating blow beneath a tyrannosaur’s knee. “The destroyer of shins continues to be fairly apt,” Dr. Arbour mentioned.