Jakapil kaniukura bipedal armored dinosaur with short arms

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The land before time introduced a generation of children to a few well-known dinosaurs – and a pterosaur – when it hit theaters in 1988. Littlefoot, Cera, Ducky, Petrie and Spike represented many of the major groups, representing sauropods, ceratopsians , hadrosaurs, pterosaurs, and stegosaurs, respectively. Then, of course, there was Sharptooth, a member of the Tyrannosaur family.

Over the next three and a half decades, paleontologists discovered countless new species, adding diversity to existing families and revealing brand new ones. For the most part, they fall into easily recognizable categories that it would be easy for a dinosaur-loving child or adult to place among the dinosaurs they already know. Every once in a while, however, we find something that breaks the rules and requires a new and more interesting understanding of dinosaur evolution. Whether The land before time were made today, we may need to add an additional player to the cast of characters.

Starting in 2012, paleontologists digging into the Candeleros Formation in Argentina began uncovering pieces of a previously unknown species called Jakapil kaniukura. The partially preserved skeleton reveals an animal related to other thyreophores – the group to which stegosaurs and ankylosaurs belong – but with strikingly different characteristics. Facundo Riguetti of the Felix de Azara Natural History Foundation and colleagues describe the species in a new paper published in the journal Scientific reports.

“Jakapil is found in all phylogenetic analyzes to be closely related to Scelidosaurus from the Lower Jurassic of the UK. These forms are outside the larger group that includes stegosaurs and ankylosaurs, and are commonly referred to as basal thyreophores,” said Riguetti at SYFY WIRE.

This means that while J. kaniukura is related to stegosaurs and other armored dinosaurs, its closest known relative existed around 200 million years ago in the Jurassic period. Therefore, it has an unusual morphology that sets it apart from other thyreophores of its time. Dating back to the mid-Cretaceous around 100 million years ago, J. kaniukura is a dinosaur you might be tempted to hug, weighing between 9 and 15 pounds and standing between 1.5 and 2 meters tall. You read that right… stand up.

“Most armored dinosaurs are large and quadrupedal. However, the primitive condition was bipedal. Early ornithischians of the Jurassic period, including early thyreophores like scutellosaurids, were bipedal forms. Jakapil is related to these early forms but was nearly 100 million years younger,” Riguetti said.

Finding new armored dinosaurs isn’t entirely unusual, not too long ago a new species was discovered in Chile, wielding a flattened tailed weapon that resembled an Aztec battle axe. However, finding one that breaks the mold so completely is unusual and reinforces the importance of highlighting the work done in the southern hemisphere.

“For several decades, the fossils of thyreophores and many other vertebrates have been studied in the northern continents, and all that we know is largely biased in favor of these species. However, several important discoveries have recently been made in the continents from the efforts of local researchers like our team at the Azara Foundation. In the near future, new species and groups from the southern continents will fill diversity gaps and shed light on evolutionary and ecological issues in fossil vertebrates,” said Riguetti. .

Alongside the partial skeleton, the researchers found a dozen leaf-shaped tooth fragments reminiscent of modern iguanas. The teeth suggest that J. kaniukura was herbivorous despite a body plan that seems more consistent with carnivorous theropods. Indeed, this relatively small armored dinosaur looks surprisingly like an armored T. rex, with short, stubby arms. At present, the function of their arms is unclear, but it is likely that they served a different purpose than those of T. rex.

“Unfortunately, the function of these tiny weapons in Jakapil is currently unknown, mainly because they are very fragmentary. New vestiges will help us solve this problem. Since the two species [J. kaniukura and T. rex] lived in different environments and filled a different ecological niche, the evolutionary pressures acting in the arms were likely different,” Riguetti said.

Thyrophore dinosaurs first appeared around 200 million years ago and their bipedal form was long thought to have been largely lost to the heavy four-legged chariots made famous by the stegosaurs. The existence of J. kaniukura proves that this is not the case. Instead, at least one lineage entered the Cretaceous while retaining the most primitive body plan. The time that has elapsed between this discovery and its Jurassic two-legged ancestors suggests a significant gap in the fossil record waiting to be filled.

“Between Jakapil and their relatives nearly 100 million years ago. We are very pleased to find a rich fossil record between them. Several recent discoveries in southern continents, mainly in South America and Africa, suggest rich wildlife in the southern hemisphere waiting to be discovered,” said Riguetti.

That J. kaniukura had such light weapons and that he is extinct is truly tragic. We bet it would give good hugs. It’s proof that you can’t judge a book about dinosaurs by its cover, that there’s still a lot of books to write and that you don’t know what you’ll find on the next page.

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