
The newly recognized Cretaceous Interval armored dinosaur Stegouros elengassen, whose fossilized stays had been found in Chile, is seen in an undated artist’s rendition. Courtesy of Mauricio Alvarez/Handout through REUTERS.
Greater than half a millennium in the past, Aztec warriors brandished a weapon referred to as a macuahuitl, a wood membership with jagged obsidian blades embedded on its sides, to inflict ugly wounds on enemies in shut fight.
A newly recognized armored dinosaur that inhabited the Patagonian area of Chile did a lot the identical factor to keep off predators about 74 million years in the past with a tail resembling a macuahuitl, scientists mentioned on Wednesday.
The four-legged plant-eating creature, named Stegouros elengassen, exemplifies the arms race that unfolded in the course of the age of dinosaurs to amass new traits to outlive in a dangerous world. It additionally sheds gentle on the evolution of a extremely profitable group of tank-like dinosaurs referred to as ankylosaurs.
Stegouros lived in what is now South America’s southernmost tip in the course of the Cretaceous Interval within the twilight of the dinosaur period. It was small relative to different armored dinosaurs, at about 7 ft (2 meters) lengthy. Stegouros possessed a beak-like mouth for cropping crops. Its again and sides had been studded with bony constructions referred to as osteoderms that served as a coat of armor.
Its tail is totally distinctive amongst dinosaurs. It’s comparatively brief with fewer vertebrae than different armored dinosaurs. The tail’s again half is roofed by a frond-like construction composed of seven pairs of flattened fused bony parts with craggy edges sticking outward.
“For now, we are able to solely think about how would possibly Stegouros have used this weapon – and tail-swinging facet to facet as self-defense mechanism is an effective guess,” mentioned vertebrate paleontologist Sergio Soto, a College of Chile doctoral scholar and lead creator of the research revealed within the journal Nature.
“The macuahuitl was an Aztec battle membership utilized in shut fight by Aztec warriors, in all probability in an identical approach to a sword, inflicting huge harm to the opponent. The tail weapon of Stegouros roughly resembles a macuahuitl,” research co-author and College of Chile vertebrate paleontologist Alexander Vargas added.
Stegouros was smaller than ankylosaurs from the northern hemisphere similar to Ankylosaurus, which reached 26 ft (8 meters) lengthy. Ankylosaurs, some possessing blunt bony golf equipment on the finish of their tails, are intently associated to an earlier group of armored dinosaurs referred to as stegosaurs whose tail weaponry got here within the type of a construction of paired spikes referred to as a thagomizer.
The tail of Stegouros differed from each.

Fossilized bones of the Stegouros elengassen, a newly recognized armored dinosaur, that inhabited the Chilean Patagonian space, are seen on this undated handout photograph taken in Santiago, Chile, and obtained by Reuters on November 30, 2021. Fundacion Azara/Handout through REUTERS
“Uncovering a brand new kind of tail weaponry in armored dinosaurs was an enormous shock for our workforce. Whenever you think about discovering a brand new kind of armored dinosaur, you don’t anticipate finding a morphology so dissimilar to these already identified,” Soto mentioned.
Stegouros lived alongside four-legged long-necked dinosaurs, two-legged carnivorous dinosaurs, turtles, frogs, and small mammals by the banks of meandering rivers.
The almost full and well-preserved fossil was excavated from a steep hill on inhospitable terrain close to Chile’s Torres del Paine nationwide park. Stegouros interprets to “roofed tail” whereas elengassen references a neighborhood native folks’s legendary armored monster.
Whereas northern hemisphere ankylosaurs are effectively understood based mostly on quite a few fossils, the anatomy of these from the southern hemisphere had remained mysterious owing to stays which are both fragmentary or not but totally studied.
Stegouros retained sure traits of the sooner stegosaurs, indicating that southern hemisphere ankylosaurs diverged from their northern cousins early within the ankylosaur lineage’s evolution, Soto mentioned. Soto referred to as Stegouros the “Rosetta Stone” of southern hemisphere ankylosaurs as a result of it has enabled scientists for the primary time to decipher their anatomy.
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