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Researchers are now closer to uncovering the origins of one of nature's most impressive defensive tools.
Ankylosaurs, herbivorous dinosaurs covered in armor, first emerged approximately 156 to 152 million years ago and inhabited every continent except Africa. A specialized group called ankylosaurids evolved an additional protective feature: a massive club at the end of their tails. These clubs, weighing up to 45 pounds or more, could deliver devastating, potentially bone-crushing blows when swung.
A recent study, published in the Journal of Anatomy, suggests that the stiff tails of these dinosaurs evolved before the development of their powerful clubs. Co-author Victoria Arbour explains, 'For an ankylosaur to effectively wield a heavy club, its tail needed to be rigid, much like an axe handle. Without this stiffness, the force generated by the club could damage muscles or dislocate vertebrae.'
Which evolved first—the rigid tail or the massive club, or did they develop together? To explore these possibilities, Arbour and paleontologist Phillip J. Currie examined millions of years of ankylosaur evolution, analyzing species like China’s Gobisaurus and the club-less Lianoningosaurus.
Their findings revealed that stiff-tailed ankylosaurids emerged during the early Cretaceous Period (145 to 100 million years ago), while clubbed species appeared much later. Using Arbour’s “axe” analogy, the handle (stiff tail) came before the blade (club). She notes, 'While some species might have developed both features simultaneously, it’s more likely that the tail stiffened first to enhance its effectiveness as a weapon before the club evolved.'
Species without clubs relied on other defensive adaptations. For example, North America’s Sauropelta featured sharp shoulder spikes, while Gastonia had shark fin-like blades along its tail.
Ankylosaurs are often compared to tanks due to their nearly impenetrable armor of bony plates called osteoderms. With formidable predators like T. rex roaming the earth, such extreme defenses were essential for survival.
