Evolution: an aquatic dinosaur (Evolution)

by David Turell , Saturday, December 03, 2022, 00:24 (720 days ago) @ David Turell
edited by David Turell, Saturday, December 03, 2022, 01:13

Land and water with early stage flippers:

https://www.livescience.com/diving-dinosaur-swimming-hunter-many-teeth?utm_term=C3CFD69...

"Noodle-necked swimming dinosaur may have been a diving predator like a penguin

"Scientists recently discovered the first non-avian theropod dinosaur with a streamlined body similar to that of penguins, auks and other modern diving birds

"A dinosaur with an undulating noodle neck and a streamlined body like those of modern diving birds may have plunged through the depths of a Cretaceous sea about 71 million to 72 million years ago, in what is now Mongolia. This predator belonged to a different lineage of theropods — bipedal and mostly meat-eating dinosaurs — than the one that produced modern birds, but its body shape and limbs hint that it swam and dove as a penguin does, scientists recently discovered.

"The skeleton was in exceptional condition with a near-complete skull. It was excavated from the Baruungoyot (also spelled Barun Goyot) Formation, a location in the southern part of Mongolia's Gobi Desert dating to the Cretaceous period (145 million to 66 million years ago). In life, it would have been about the size of a mallard duck, and researchers noted that its gooselike neck, flipperlike forelimbs and proportions of its digits resembled those of the Mongolian theropod genus Halszkaraptor, which is thought to be aquatic.

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"The newfound fossil is more complete than any of the known Halszkaraptor fossils; the skeleton is "mostly articulated" with ribs that are oriented toward the tail, as they are in aquatic diving birds, according to a study published Dec. 1 in the journal Communications Biology(opens in new tab). This offered scientists the first evidence of a nonavian theropod with a body that was optimized for reducing drag in aquatic environments.

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"N. polydontus probably wasn't able to soar through the air with its short, flattened forelimbs, though it may have used them to paddle through water. But one of the most compelling clues about its aquatic habits was its ribs — specifically, the direction in which they were pointing. In land-based theropods, the dorsal ribs extended from the spine in a mostly horizontal arc. But in N. polydontus, these ribs curved back toward its tail. Such backward-oriented ribs lower the height of the rib cage, and are a feature in diving birds, Lee told Live Science in an email. This suggests that N. polydontus had a streamlined body, "which would be advantageous because a streamlined body reduces drag in the water and allows efficient swimming," Lee said."

Comment: interesting in that it was only partially adapted to aquatic life. It may have evolved by trying to dive for food. But only if starving on land. More likely a God design. It walked on hind legs with forelimbs moderately flipperoid:

https://phys.org/news/2022-12-mongolian-fossil-species-non-avian-theropod.html