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

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The gigantic and dilatory sauropod dinosaurs similar Diplodocus had tiny two-legged ancestors – and one, Thecodontosaurus, was speedy and nimble

19 January 2022

By Christa Lesté-Lasserre

Thecodontosaurus antiquus, Late Triassic of The United Kingdom. Illustration.

An aboriginal ancestor of large, long-necked, four-legged dinosaurs similar Brachiosaurus and Diplodocus was a quick, nimble biped that astir apt utilized its forelimbs to grasp its food, which included leaves, branches – and meat.

Thecodontosaurus antiquus, a 30-centimetre-high dinosaur that lived much than 200 cardinal years agone during the precocious Triassic, was a ‘sauropodomorph’ – which means it belonged to the aforesaid radical arsenic the gigantic herbivorous sauropods that lived later, successful the Jurassic and Cretaceous.

T. antiquus had muscles successful its backmost legs that favoured velocity implicit force, whereas its forelimb muscles would person been much apt for grasping than weight-bearing. By the aboriginal Jurassic astir 20 cardinal years later, however, its descendants had shifted into slow-moving quadrupeds with muscles susceptible of supporting overmuch much weight, says Antonio Ballell astatine the University of Bristol, UK.

Ballell and his colleagues examined the musculus insertion points, grooves, protrusions, crests, and scars related to musculus morphology successful limb and assemblage bones of T. antiquus – one of the archetypal dinosaurs ever studied and the archetypal Triassic dinosaur taxon to beryllium named. The fossils, which travel from an past fissure successful the Triassic onshore aboveground of what is present southwest England, are exceptionally well-preserved.

“This is not precise common,” says Ballell. “Usually the surfaces of the bony are weathered distant truthful you can’t spot the good detail.” The researchers compared the fossil bony surfaces with the surfaces of modern crocodile and vertebrate bones, looking successful peculiar astatine sites connected the bones wherever musculus and different brushed tissues were erstwhile attached. They besides looked astatine bones from modern-day lizards and examined information antecedently acquired astir four-legged sauropodomorphs from the Triassic and Jurassic.

They recovered that T. antiquus’s hindlimb muscles would person contracted quickly, frankincense allowing for fast, agile movement, Ballell says. “There’s a trade-off [because] muscles that generates a batch of unit declaration slowly, and muscles that declaration accelerated usually nutrient little force,” helium says. “So the presumption and predisposition of the muscles of T. antiquus bespeak that it was towards the accelerated broadside of the spectrum, meaning that it could determination faster … and astir apt bash accelerated turns.”

By contrast, the elephantine Jurassic sauropodomorphs were “megaherbivores”, which means they needed 4 pillar-like legs to assistance clasp their “huge digestive tracts” indispensable for digesting each the works substance they were consuming, Ballell says.

As for the forelimbs of T. antiquus, a “deep and scarred” groove and different marks successful the elbow bony and enarthrosis leaf suggests they had large elbow flexibility and extension. The long, slender signifier of the limb and enarthrosis bones hints astatine smaller muscles and little enarthrosis extension, making them improbable to service arsenic weight-bearing limbs. The hep bones besides bespeak the beingness of muscles that would person allowed the dinosaur – which the researchers accidental was apt omnivorous – to basal up and locomotion connected its 2 hindlimbs.

“They were astir apt utilizing their hands – which were precise well-developed with a claw successful the [thumb] – to chopped branches and assistance them procure food,” Ballell says.

The findings lend to a amended knowing of however and erstwhile dinosaurs – and the sauropodomorph enactment successful peculiar – evolved from walking connected 2 legs to walking connected each fours, says Ballell. “The improvement of posture successful dinosaurs is rather complicated,” helium says.

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