Dinosaur ancestor of long-necked Diplodocus ran swiftly on two legs

The big and gradual sauropod dinosaurs like Diplodocus had small two-legged ancestors – and one, Thecodontosaurus, was fast and nimble

Thecodontosaurus antiquus

Stocktrek Photos, Inc. / Alamy

An early ancestor of enormous, long-necked, four-legged dinosaurs like Brachiosaurus and Diplodocus was a fast, nimble biped that in all probability used its forelimbs to know its meals, which included leaves, branches – and meat.

Thecodontosaurus antiquus, a 30-centimetre-high dinosaur that lived greater than 200 million years in the past through the late Triassic, was a ‘sauropodomorph’ – which suggests it belonged to the identical group as the big herbivorous sauropods that lived later, within the Jurassic and Cretaceous.

T. antiquus had muscle mass in its again legs that favoured pace over power, whereas its forelimb muscle mass would have been extra apt for greedy than weight-bearing. By the early Jurassic about 20 million years later, nonetheless, its descendants had shifted into slow-moving quadrupeds with muscle mass able to supporting far more weight, says Antonio Ballell on the College of Bristol, UK.

Ballell and his colleagues examined the muscle insertion factors, grooves, protrusions, crests, and scars associated to muscle morphology in limb and physique bones of T. antiquus– one of many first dinosaurs ever studied and the primary Triassic dinosaur species to be named. The fossils, which come from an historic fissure within the Triassic land floor of what's now southwest England, are exceptionally well-preserved.

“This isn't quite common,” says Ballell. “Often the surfaces of the bone are weathered away so you possibly can’t see the fantastic element.” The researchers in contrast the fossil bone surfaces with the surfaces of recent crocodile and fowl bones, wanting particularly at websites on the bones the place muscle and different tender tissues had been as soon as hooked up. In addition they checked out bones from modern-day lizards and examined knowledge beforehand acquired about four-legged sauropodomorphs from the Triassic and Jurassic.

They discovered that T. antiquus’s hindlimb muscle mass would have contracted shortly, thus permitting for quick, agile motion, Ballell says. “There’s a trade-off [because] muscle mass that generates lots of power contract slowly, and muscle mass that contract quick normally produce much less power,” he says. “So the place and orientation of the muscle mass of T. antiquus point out that it was in direction of the quick facet of the spectrum, which means that it may transfer quicker … and possibly do quick turns.”

Against this, the large Jurassic sauropodomorphs had been “megaherbivores”, which suggests they wanted 4 pillar-like legs to assist maintain their “large digestive tracts” mandatory for digesting all of the plant matter they had been consuming, Ballell says.

As for the forelimbs of T. antiquus, a “deep and scarred” groove and different marks within the elbow bone and shoulder blade suggests they'd nice elbow flexibility and extension. The lengthy, slender form of the arm and shoulder bones hints at smaller muscle mass and fewer shoulder extension, making them unlikely to function weight-bearing limbs. The hip bones additionally mirror the presence of muscle mass that may have allowed the dinosaur – which the researchers say was probably omnivorous – to face up and stroll on its two hindlimbs.

“They had been in all probability utilizing their palms – which had been very well-developed with a claw within the [thumb] – to chop branches and assist them procure meals,” Ballell says.

The findings contribute to a greater understanding of how and when dinosaurs – and the sauropodomorph line particularly – developed from strolling on two legs to strolling on all fours, says Ballell. “The evolution of posture in dinosaurs is kind of sophisticated,” he says.

Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.211356