Armored dinosaurs like Stegosaurus and Ankylosaurus were mostly big, bulky animals that walked on four legs, but paleontologists have now discovered a bizarre relative the size of a dog that strutted around on two legs.
One of the largest and most striking groups of dinosaurs were the thyreophora, herbivores that all sported thick plates and armor to protect them from predators. The most famous members of the group would be the stegosaur family, which had big plates along their backs and spiked tails, and the ankylosaurs, which were built like tanks and often had heavy clubs of bone on their tails.
But while this group were usually giants and almost exclusively quadrupedal, paleontologists have now found one that bucks the trend. The new species, named Jakapil kaniukura, had similar bony plates running up its back, neck and tail, except it was just 1.5 m (4.9 ft) long and only weighed between 4 and 7 kg (8.8 and 15.4 lb). Weirder still, it ran around on two legs, and had tiny little chicken-wing arms.
“The neck armor of this dinosaur is unique and it protected that delicate area from predator attacks,” said Sebastián Apesteguía, an author of the study. “The bones that are preserved from the arms show us that they were tiny, something that does not occur in the rest of the thyreophorans, the vast majority of which are quadrupeds.”
Despite its possibly fearsome appearance, Jakapil was still a herbivore. Its teeth were found to be leaf-shaped with a large face for grinding up plant matter, in a similar layout to its relatives. It also had a unique mandible that was relatively short and had a large ridge underneath.
But maybe the strangest part of all is where Jakapil fits in the family tree. It seems to be somewhat of a missing link from early thyreophoran dinosaurs to the diverse groups of later stegosaurs and ankylosaurs, which became quadrupedal as they got more armored and much heavier. The only other bipedal family member is Scutellosaurus, which lived in the early Jurassic period, some 196 million years ago, in what is now the US.
But Jakapil lived in Patagonia about 100 million years later. The team says this makes it a member of an ancient basal thyreophoran lineage that survived well into the Cretaceous – long after relatives like Stegosaurus evolved and died out. And being the first of its kind to be found in South America shows that this group was more widespread than previously thought.
The research was published in the journal Scientific Reports.