Stegosaurus is one of the most popular and well-known dinosaurs, identifiable by the diamond-shaped plates marching down its back from the base of its neck to the end of its spiky tail. A new specimen unearthed in the mountains of Morocco shows that the prehistoric species is much older and more geographically wide-ranging than paleontologists previously believed.
The specimen, which is thought to represent a new species and genus of stegosaurs, was identified by a team led by Susannah Maidment of the Natural History Museum in London, reports the Press Association. The fossils found in Morocco’s Middle Atlas Mountains only include a few vertebrae and an upper arm bone, but it was enough to identify the bones as belonging to one individual stegosaur. The team has named the species Adratiklit boulahfa, which means “mountain lizard” in the Berber language. The paper appears in the journal Gondwana Research.
While the small number of bones means we don’t know much about what the new species looked like or how it behaved, the find is important because it suggests the class of dinos is older and more widespread than previously believed.
“The discovery of Adratiklit boulahfa is particularly exciting as we have dated it to the middle Jurassic [168 million years ago],” Maidment says in a press release. “Most known stegosaurs date from far later in the Jurassic period, making this the oldest definite stegosaur described and helping to increase our understanding of the evolution of this group of dinosaurs.”
But determining the age of non-marine Mesozoic rocks, like the ones where the new stegosaurus fossil was found, is difficult unless they include volcanic material that can be dated radiometrically, explains paleobiologist Hans Sues of Smithsonian’s National Museum of Natural history.
“The age determinations in Morocco are still a bit problematic,” Sues tells Smithsonian magazine. “The new find might be slightly older than the previously oldest known stegosaur fossils from England and France.”
Still, where it was found is hugely significant. Modern-day Morocco is located where the southern supercontinent Gondwana would have been at the time the stegosaur was alive. However, to so-called “mountain lizard” seems to a relative of northern-dwelling stegosaurs not species from the south. “It is of interest because it is closely related to stegosaurs from England, France, and Portugal,” says Sues.
Anthropologist Tom Raven of London’s Natural History Museum suggests the new stegosaur is more closely related to fossils found in Europe than to those in the genera Kentrosaurus and Paranthodon, which were previously found in southern Africa.
Its location in the Atlas mountain range may mean stegosaur species roamed a much larger area of the Earth during the Jurassic than previously thought. During that time period, two supercontinents, Laurasia in the north and Gondwana in the south, dominated the planet. So far, the vast majority of stegosaurs have come from the northern continent, which was made up of present day Europe, Asia, and North America.
“Most stegosaurs we know of… have been found in Laurasian rock formations,” Maidment says in the release. “However, this may not mean that stegosaurs were uncommon in Gondwana. It may be due to the fact that Gondwana rock formations have been subject to far fewer excavations and detailed studies. What is exciting about this is that there could be many more armored dinosaurs to find in places that until now have not been excavated.”
There's still more to find out about the spiky species. In recent years, London’s Natural History Museum has become a hub of stegosaur research. In 2014, the institution put Sophie the Stegosaurus on display, the most complete stegosaurus fossil anywhere in the world. Found in 2003 in Wyoming, she is 85 percent complete with 360 individual bones. Not only is Sophie pretty awe-inspiring to look at, but digitized models of her remains are helping researchers solve big questions about the armored dinosaurs.
For instance, the creatures have pretty feeble teeth, which is a sign of herbivory, but paleontologists aren’t sure exactly what types of plants they could eat to maintain their massive body weight. Research on Sophie's skull found that despite their tiny teeth, stegosaurs had incredibly strong jaws. That bite strength pretty much gave them a free pass to munch on any plant of their choosing.
The biggest mystery is what, exactly, those big, spiky plates were for. “The function of the plates is quite controversial,” Paul Barrett, dinosaur researcher at London’s Natural History Museum, told the Press Association in 2014. “An early idea was that they were a form of armor but most people don’t believe that any more, because they were quite thin. It’s possible they provided a kind of passive defense because they would have made the dinosaur look a lot bigger from a distance.”
Because large blood vessels crisscrossed the plates, it’s also possible that they were used to radiate heat and cool down the massive beasts. Another theory is that the plates were used to attract mates, similar to peacock feathers. That wouldn’t be a crazy idea. Recent research suggest that many of the elaborate horns and frills found on ceratopsian dinos from the later Cretaceous period were likely ornaments that evolved to attract mates—not primarily for defense as previously believed.