New Species of Ankylosaur Unearthed in Chile Had a Flat, Weapon-Like Tail

Buried under the fine sediments of Chile’s arid Patagonia region, researchers were astonished to find a nearly complete fossilized dinosaur skeleton with an unusual club-like tail. The tail had seven pairs of flat, blade-like bony scales fused together—not seen before in any other dinosaur, reports Michael Greshko for National Geographic. 

After further analysis, researchers revealed that the skeleton belongs to a new kind of armored dinosaur dubbed Stegouros elengassen, a species of ankylosaur that roamed the Earth about 72 to 75 million years ago. Details of the animal’s skeleton and its unique tail may reveal an early evolutionary split in ankylosaurs, according to a study published this week in Nature.

Ankylosaurs were herbivores that lived during the Late Cretaceous period. They had distinct plates of bone riddling their bodies and heads called osteoderms for defense against other carnivorous dinosaurs, reports Chen Ly for New Scientist. Various species of ankylosaurs sport club-like tails and barbed skulls, but researchers have never seen a tail like the one found on S. elengassen. The dinosaur also had less body armor, and its limbs were more slender than others of the same species. 

The dinosaur sports features from both ankylosaurs and stegosaurs. It walked on all fours, stood less than two feet tall and measured less than seven feet from head to tail, National Geographic reports. The pelvis of S. elengassen even looks nearly identical to that of a stegosaur. However, the jawbones confirmed that the skeleton did in fact belong to an ankylosaur, New Scientist reports. 

“This is our first good look at a South American armoured dinosaur, and it is not like any armoured dinosaur you’ve ever seen before,” study author Alexander Vargas, a paleontologist at the University of Chile, tells New Scientist. “It has a tail weapon that is a new category – all we knew [before] was tail spikes and tail clubs, now we have this weird frond-like thing.”

Ankylosaur fossils from the northern portion of what used to make up the supercontinent Pangea have been well-researched, per New Scientist. However, few ankylosaur fossils have been dug up in the Southern Hemisphere, but those found may be the earliest species of the group and may even represent an early evolutionary branch of armored dinosaurs from the mid-Jurassic era, reports Carolyn Gramling for Science News. 

Early ankylosaurs found in the northern hemisphere do not sport tail clubs, and later specimens developed tails made of stiffened vertebrae that formed a blunt hammer shape, reports Asher Elbein for the New York Times. However, S. elengassen’s fused, spiked tail may have been encased in razor-sharp sheets of keratin, says James Kirkland, a state paleontologist at the Utah Geological Survey who was not involved in the study, to the New York Times. 

Researchers suspect the split in the lineage occurred when Laurasia and Gondwana drifted apart during the late Jurassic. The researchers also suggest that because of the division, there may be an entire lineage of ankylosaurs yet to be discovered in what used to be Gondwana, per the New York Times.

"We don’t quite understand what the evolutionary driving forces are for these ankylosaurians to remain morphologically more ancestral compared to the ankylosaurian dinosaurs from the northern hemisphere,” says Jelle Wiersma, a geoscience expert at James Cook University who was not involved with the study, to New Scientist. “But this study certainly highlights that there is still a lot to learn about this particular group of dinosaurs.”

On December 1, S. elengassen’s fossilized remains were presented to the world at the Central House of the University of Chile by the researchers of the study, per a statement.

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.