Ankylosaurs were squat and thick four-legged dinosaurs with club tails and tough body armor. In other words, invincible Pokémon. A new fossil discovery, however, has revealed that the earliest ankylosaurs were several orders of magnitude more badass than their descendants.
In a study published today in the journal Nature, researchers describe the partial skeleton of a Spicomellus, a genus of early ankylosaurs, unearthed in Morocco and dating to around 165 million years ago. The finding includes six ribs with spikes, a pelvic shield with long and short spikes, a bony collar with plates and two pairs of spikes—one of them is almost complete and is 34 inches (87 centimeters) long. Oh, did we mention spikes?
The fossils indicate that the earliest known ankylosaurs had unique armored features, unparalleled among vertebrates as well as their own ankylosaurian descendants.
Unveiling fossil mysteries
“The armoured ankylosaurian dinosaurs are best known from Late Cretaceous Northern Hemisphere ecosystems, but their early evolution in the Early–Middle Jurassic is shrouded in mystery due to a poor fossil record,” the researchers wrote in the study. The Jurassic Period lasted from around 201 million years ago to 145 million years ago and was followed by the Cretaceous Period, which ended around 66 million years ago with the infamous dinosaur-killing asteroid.
Researchers had previously suggested that a single partial rib also dating to the Middle Jurassic and found in Morocco’s Atlas Mountains, belonging to a Spicomellus afer, represented the world’s oldest known ankylosaur. If you’re thinking a bone fragment isn’t much to go on, you’re not wrong. That’s why the recent discovery is so exciting—it consists of a larger quantity of Spicomellus remains, providing fresh insights into these early ankylosaurs. Now we can imagine a giant snapping turtle-porcupine mix with a thick, spiky tail.
Calling paleontological theories into question
“Here we describe a new, much more complete specimen that confirms the ankylosaurian affinities of Spicomellus, and demonstrates that it has uniquely elaborate dermal armour unlike that of any other vertebrate, extant or extinct,” the researchers explained. The remains suggest that Spicomellus had a nasty tail weapon, challenging previously held theories that ankylosaurs’ tail clubs had only evolved in the Early Cretaceous.
The flashy armor “may have functioned for display as well as defence,” with later species in the Late Cretaceous featuring simpler plating with fewer elaborate bumps. This could mean the armor’s role shifted “towards a primarily defensive function,” the team added.
Arms race in action
Extreme defenses like those seen in ankylosaurs shouldn’t come as a surprise—they were the product of a relentless evolutionary arms race. These tank-like herbivores had to protect themselves from some of the most ferocious hypercarnivores to ever walk the Earth, including Allosaurus in the Late Jurassic and carcharodontosaurs and tyrannosaurs in the Cretaceous.
As these predators got bigger, badder, and stronger, prey animals had to keep up with their own evolutionary solutions. In the case of Spicomellus, this led to the birth of one of the strangest armored dinosaurs scientists have ever discovered.