This ancient crocodile relative grew up on four legs then walked on two

A newly described poodle-sized reptile from the age of dinosaurs reveals a rare life-stage shift from four legs to two, challenging established views of ancient locomotion. | Contesto: cronaca

Punti chiave

• This ancient crocodile relative grew up on four legs then walked on two

Contesto

The fossilized remains of a bizarre, poodle-sized reptile that lived over 200 million years ago have revealed a startling life history: the animal, named *Sonselasuchus cedrus*, appears to have walked on all fours as a juvenile before transitioning to a two-legged posture as an adult. The discovery, detailed in a new study, comes from fossil-rich Triassic-period deposits in what is now Portugal. This rare and dramatic shift in locomotion during an individual's lifetime is a phenomenon scarcely documented in the fossil record and is forcing paleontologists to reconsider long-held assumptions about how ancient reptiles moved and developed. The significance of *Sonselasuchus cedrus* lies not just in its unusual growth pattern but in its place on the evolutionary tree. The creature is not a direct ancestor of modern crocodiles but a close relative within the broader group known as pseudosuchian archosaurs, which includes alligators, crocodiles, and their extinct kin. During the Triassic period, this group was phenomenally diverse, experimenting with body plans that would later be associated with dinosaurs and mammals. *Sonselasuchus* adds a new, unexpected layer to that diversity, demonstrating that some lineages explored developmental pathways where an animal's fundamental mode of movement was not fixed from birth. Analyzing the fossil material, researchers noted stark differences in the proportions and robustness of the forelimbs and hindlimbs between smaller, presumed juvenile specimens and larger adults. In the juveniles, the forelimbs were sturdy and well-formed, suggesting they bore significant weight. In mature individuals, however, the hind limbs became massively enlarged and dominant, while the forelimbs remained comparatively gracile. This anatomical shift points conclusively to a change in posture and gait. The creature likely spent its early life as a quadruped, foraging close to the ground, before becoming an agile, bipedal runner or walker in adulthood, a transformation more commonly associated with certain metamorphosing amphibians than with reptiles. This discovery challenges a foundational principle in paleontology: that an animal's posture is a...

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Categoria: cronaca