Stegosaur fossil discovery has ‘weird mix of features’
The ancient fossil belongs to a stegosaur, an herbivorous dinosaur with a tiny head and bony plates marching down its back, ending in a spiked tail. The specimen also had some unique characteristics that can’t be traced in other stegosaurs. It’s the oldest one recovered from Asia and may belong to one of the earliest stegosaurs ever found, according to new research.
Stegosauria is one of a larger group of armored dinosaurs known as thyreophorans that lived during parts of the Jurassic period as well as the early Cretaceous period, between 100.5 million and 201 million years ago. Their fossils, belonging to 14 different species, have been found nearly everywhere except for Antarctica and Australia.
Researchers uncovered dinosaur fossils in 2016 at a well-known site called the Shaximiao Formation in the Chongqing municipality of China. Part of this site dates to the Middle Jurassic period, which lasted between 163.5 million and 174.1 million years ago.
Located between layers of purplish-red mudstone and grayish-yellow sandstone were several armor plates and the shoulder, thigh, feet, back and rib bones of a stegosaur. But stegosaur fossils from the Middle Jurassic are rare, making this discovery unique since the dinosaur lived much earlier than most of its known relatives.
The researchers named the dinosaur Bashanosaurus primitivus, with “Bashan” in reference to the ancient name of Chongqing and “primitivus” signifying first in Latin, given the dinosaur’s age.
The fossil is helping scientists better understand how stegosaurs evolved — something of which they know precious little.
Rare early stegosaur
Some stegosaurs were known for having giant shoulder spines, while others had a long neck, but it’s been difficult for researchers to determine how they related to one another.
Bashanosaurus had smaller and less developed shoulder blades, thicker yet narrower bases for its armor plates and other eccentricities that make it stand out from other stegosaurs. It also shared similarities with some of the first armored dinosaurs that lived 20 million years earlier.
The newly discovered species is “a really weird mix of features,” usually seen in more primitive armored dinosaurs as well as hallmarks of stegosaurs, said study coauthor Susannah Maidment, a paleontologist at London’s Natural History Museum.
Some of the primitive features of Bashanosaurus include longer tail vertebrae and narrower shoulder blades that flared out. Unlike other known stegosaurs, the bases of its armor plates curved outward.
“It’s exciting because it helps us understand how stegosaurs gradually acquired the features of their iconic body plan,” Maidment said. “Bashanosaurus didn’t have the giant plates extending along its back like Stegosaurus had; instead it had much smaller, spine-like (armor), that arguably would have been more useful for defending itself against predators than the very thin but very flashy (armor) of Stegosaurus, which might have been more about display.”
“Adratiklit is roughly the same age, or perhaps a couple of million years younger…
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