More Denton: unlikely transitions (Introduction)

by David Turell , Monday, February 20, 2023, 17:32 (433 days ago) @ David Turell

Tiktaalik revisited showing transition skeletal changes:

https://www.newscientist.com/article/2360024-spine-of-early-crawling-fish-was-becoming-...

"A CT scan of a fossil of Tiktaalik, one of the first fish to crawl on land, has revealed more features of its body that are intermediate between fish and land-dwelling animals. In particular, they show that its fins were becoming connected to its spine, a feature of limbs in land vertebrates, but not of fins in fish.

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"In land vertebrates, the hind legs are connected to the spine via the pelvis. In fish, the equivalent of the pelvis is positioned away from the spine with no direct connection to it. In Tiktaalik, the shape of the vertebrae and ribs suggest that the pelvis was closer to the spine and that there was a soft tissue connection between the pelvis and spine, says Stuart.

"Other features, such as the shape of Tiktaalik’s ribs, are also intermediate, says Stuart.

“'It is a very nice looking piece of research,” says Martin Brazeau at Imperial College London, who wasn’t part of the team. “A connection between the vertebral column and the pelvis is one of those things that’s neither explicitly expected or excluded based on where Tiktaalik sits in the evolutionary tree.'”

Comment: a valuable transitional form. we should expect to find more examples.