Liang Long ancestors "ran" with two legs

The early ancestors of large, long-necked, four-legged dinosaurs such as Brachiosaurus and Diplodocus, were agile bipedals that used their forelimbs to grab food, including leaves, branches, and flesh. The study was recently published in the Royal Society – Open Science.

Archaurus was a 30 cm tall dinosaur that lived more than 200 million years ago in the Late Triassic period and was a sauropod. This means that it belongs to the same tax group as the giant sauropods that lived in the later Jurassic and Cretaceous periods.

The use of the hind leg muscles of the ancient grooved tooth dragon is more inclined to speed than strength, and the forelimb muscles are more suitable for grasping than weight bearing. "However, in the early Jurassic period, about 20 million years later, its descendants have transformed into slow-moving quadrupeds whose muscles are able to support greater weight." Antonio Ballell of the University of Bristol in the United Kingdom said.

Ballell and colleagues examined muscle insertion points, grooves, protrusions, crests, and scars associated with muscle morphology in the limbs and body bones of The Ancient Groover. Archaic slothosaurs were one of the first dinosaurs to be studied and the first Triassic dinosaur species to be named. These fossils from an ancient crack in the triassic land surface in southwest England are remarkably well preserved.

"It's not common." Ballell says, "Usually the surface of the bone gets weathered off, so you can't see the details. The researchers compared the fossil's skeletal surface to that of modern crocodile and bird skeletons, especially those on the bones that once had muscles and other soft tissues attached. They also studied the skeletons of modern lizards and analyzed previous data on quadruped sauropods obtained from the Triassic and Jurassic periods.

They found that the hind limb muscles of The Ancient Grooved Tooth Dragon contracted very quickly, so they were able to perform rapid, agile movements. "It's a compromise because muscles that produce a lot of force contract slowly, while muscles that contract quickly usually produce less force." Ballell said, "The position and orientation of the ancient slotted dragon muscles suggests that it can move faster and may turn quickly. ”

"In contrast, Jurassic sauropods were 'giant plant-eaters,' meaning they needed four columnar legs to support the 'huge digestive tract.'" Ballell said.

"Deeply scarred" grooves and other marks on the elbow and shoulder blades of the forelimbs of Archaurus suggest that their elbows were highly flexible and stretchable. The elongated shape of the front paws and shoulder bones suggests that they have smaller muscles and less shoulder extension, making them less likely to act as weight-bearing limbs. The hip bones also reflect the presence of dinosaur muscles that may have allowed the dinosaur — which researchers say may have been omnivorous — to stand and walk on two hind legs.

"They are likely to grasp the branches with their front paws to obtain food." Ballell says the front paws develop well.

"The evolution of dinosaur postures is quite complex." Ballell said the findings helped to better understand how and when dinosaurs — particularly sauropods — evolved from bipedal to quadruped. (Li Muzi)

Related paper information:

https://doi.org/10.1098/rsos.211356

Source: China Science Daily