Damage to the spikes on the back of a fossil of a Zuul crurivastator suggest that these armoured dinosaurs didn’t use their tail clubs to fend off Tyrannosaurs but to fight each other
Zuul, destroyer of shins, was a living tank. This dinosaur’s spine and tail were covered in armoured plates studded with spikes, ending in a club previously thought to be used to fight off vicious predators like the Tyrannosaurus rex. But a rare fleshy fossil suggests these armoured herbivores probably used their tails less to fend off T. rex and more to dominate each other.
Zuul crurivastator’s name comes from the demonic Zuul from the 1984 film Ghostbusters, with crurivastator meaning “destroyer of shins”. Its fossil was discovered nearly a decade ago – during a dig in Montana to unearth a Gorgosaurus, an earlier cousin of T. rex – when excavators bumped into the dinosaur’s tail club. Years later, when researchers at the Royal Ontario Museum in Toronto were preparing the fossil for exhibition, they found that some of the fossil’s spikes were damaged. Many of these had smooth areas indicating the bone had reformed, and some had growths of keratin – both signs of healing, suggesting injuries on multiple occasions.
“The [damaged spikes] are just in this little range around the hips, and just on the sides of the body,” says Victoria Arbour at the Royal BC Museum in British Columbia. They’re not broken on the top of the body or up by the head, which is where you’d expect a predator like T. rex to attack, she says.
“Big, predatory dinosaurs can bite with enough force to leave scratches and puncture marks on bone,” says Arbour. But these marks are missing on this fossil.
Based on the damaged spikes being at different stages of healing, and in a location both easily reachable by another Z. crurivastator’s swinging tail and unlikely to be fatal, the researchers believe the dinosaurs used their tails to fight each other for social dominance. They suspect it was similar to the way modern animals use antlers or other body parts to stake claim to territory or mates. So, although the club-like tail may have come in handy for self-defence, its evolution was probably driven more by sexual selection than predation So, although the club-like tail may have come in handy for self-defence, its evolution was probably driven more by sexual selection than predation.
The idea of these dinosaurs using their tail clubs to fight off T. rex had “become something of a textbook stereotype”, says Stephan Lautenschlager at the University of Birmingham in the UK. He sees this study as a prime example of how a long-standing hypothesis can be upended with new evidence. “Now that palaeontologists know what to look for, the same damage in other, maybe yet-undiscovered, fossils could come to light,” he says.
Journal reference: Biology Letters, DOI: 10.1098/rsbl.2022.0404
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