75 to 72 million years ago, in what is now Chilean Patagonia, the carcass of a squat-tailed dinosaur ended up buried in a river delta, where fine sediments exquisitely preserved the bones as they fossilized.
Judging by dinosaur standards, this creature wasn’t huge. Walking on all fours, it was less than two feet long and was less than two meters long from muzzle to tail. But he was a cruel little animal in a world of giants. This dinosaur had skin covered in armor to defend itself – and a unique weapon at the rear.
The end of this creature’s tail is unlike anything scientists have found so far: a mass of molten bone resembling a toothed cricket bat. “It’s completely unprecedented,” says Alexandre Vargas, a paleontologist at the University of Chile.
Fossil skeleton, which was revealed in the journal temper nature, belongs to a newly discovered type of armored dinosaur called Stegouros lengassen. The name owes to its peculiar “tiled tail” (stegoros) and an armored creature from the legends of the Aónik’enk people in Patagonia (Langasin).
In addition to the unique tail, the stegoros It also fills an evolutionary gap. According to University of Maryland paleontologist Tom Holtz, who was not involved in the study, very few armored dinosaurs have been found in the lands that once formed Gondwana, the ancient giant continent that split to form South America, Africa, Antarctica, Australia, and the subcontinent. Indian. and the Arabian Peninsula.
before stegoros Only two armored dinosaurs were found in the southern region of Gondwana, and these animals are incomplete or partially studied fossils. the sample stegoros About 80% complete – and her skeleton is a strange anatomical mosaic. The dinosaur’s skull, teeth, and rolled, stick-shaped tail appear to have belonged to Ankylosaurus and other, later, armored dinosaurs. However, the bones of the thin limbs and pelvis of dinosaurs are similar to those of Stegosaurus, which at the time were stegoros It became extinct tens of millions of years ago.
“If you showed me this aquarium and asked what animal it belonged to, I would be 100% sure it was a stegosaurus,” says Susanna Maidment, a paleontologist at the Natural History Museum in London, who was not involved in the study. “This specimen totally blew me away…it changed everything I thought I knew.”
Bones in the mountains of Patagonia
NS stegoros It was discovered in the Dorotea Formation, an area with layers of rock scattered across Chile and Argentina, where researchers from around the world frequently search for dinosaur fossils and other signs of ancient life.
In 2017, a group from the University of Texas visited a site in the Rio de las Chinas Valley in Chile, a place known for its fossilsAnd spotted some attractive-looking bones. In February 2018, the University of Chile sent a team to investigate the University of Texas group’s report led by colleagues Alexander Vargas, Sergio Soto Acuña, and Jonathan Kaluza.
Investigators found the first traces of bone on top of a steep cliff and began digging around the fossil. The team recovered the remains in a massive stone block covered in gypsum for transport to the lab, but removing the uninfected fossil was a major challenge. Scientists had to contend with freezing temperatures, the risk of hypothermia and sprained ankles.
At first, the team was only able to see the dinosaur’s slender limb bones, leading researchers to believe that this specimen might belong to Ornithopods – a type of herbivorous two-legged dinosaur. But when the fossil became available in the lab, careful cleaning of the rock exposed the animal’s tail.
“I was in shock the rest of the day,” Alexander Vargas says.
war tail
Fully armed tails are a rarity among animals, but those that have been carved by evolution in very efficient ways. Among the dinosaurs, Stegosaurus had two pairs of spines on the ends of their tails. Some ankylosaurs, such as AnkylosaurusTails long and solid with bony mace in the shape of a hammer.
The so-called war tails have already appeared in groups of animals that are very distantly related. Gliptodons, the extinct giant armadillo that lived up to 10,000 years ago, evolved a tail similar to that of Ankylosaurus, for example.
However, the tail stegoros Unique. Flatter and more like a knife than the war tails of its peers, this anatomical structure was named macuahuitl by the research team, in honor of the wooden stick with an obsidian blade that was used by the Aztecs.
Armored dinosaurs may have used their warlike tails to fight. One of a kind animals, perhaps in a regulations dispute. There is also evidence that these dinosaurs, when threatened, used their tails to defend themselves from predators. Tom Holtz says that some bones of Jurassic predators had lesions from puncture wounds that may have occurred in encounters with stegosaurus. In fact, Canada’s Royal Ontario Museum contains a fossil of a dinosaur with a broken reed – possibly an injury caused by an ankylosaurus wagging its tail.
It is still not known exactly how stegoros He used his tail, but Tom Holtz speculates that the tyrannosaurus may have used it as a kind of cutting weapon. On the other hand, the potential predators of stegoros They are known. The largest predatory dinosaurs of that time and place were mysterious animals called megaraptorids, which Alexander Vargas described as “things very large and bad-looking, like allosaurs with long, coiled arms.”
Looking for more clues
When the Chilean team managed to observe the complete skeleton of stegorosSergio Soto Acuña and Alexander Vargas carefully compare the anatomy of the animal with that of other armored dinosaurs. When the researchers analyzed the data to identify potential family trees, they found that the ancestors of stegoros It branched off from the rest of Ankylosaurus about 165 million years ago, forming a hitherto unknown lineage.
The closest cousins of this Chilean dinosaur are the other two ankylosaurus recorded in southern Gondwana. One of them, the Australian ankylosaurus Conparasaurus, known primarily for its skull. the other, AntarcticaOnly a few bone fragments are known from the Antarctic sediments.
NS stegoros It can help scientists better understand their misunderstood relatives. Some isolated bones of the sample Antarctica It has striking similarities with the fused tail bones. macuahuitl Act stegoros. Alexander Vargas and his colleagues believe that this combination may mean that Antarctica – which was twice the file size stegoros – It had a similar war tail.
Susanna Maidment of the Natural History Museum in London, one of the world’s leading experts on stegosaurs, adds that the curious combination of characteristics stegoros It can cause some “shaking” in the armored dinosaur family tree. The classification of stegosaurus is based mainly on the fact that these dinosaurs had three main anatomical features – one of which is the exact type of pelvis found in stegoros, which is not a stegosaurus, although the name is similar. Therefore, Susanna Maidment says that some of the segmented dinosaurs currently classified as Stegosaurus may not even be Stegosaurus.
The formation of Dorotea and other parts of Patagonia has revealed unusual fossils for decades, and the area may have more fossil evidence hidden in the rocks. Future missions in Chile or Argentina may encounter other armored dinosaurs with sticks coated in place of a tail.
Meanwhile, Alexandre Vargas and his colleagues are already searching for other fossils of stegoros. We found other areas stegoros – It seems to be common,” says Alexander Vargas. “We hope to find more.”
This article was published in English on Location nationalgeographic.com
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