Evolution: water to land limb changes studied (Evolution)

by David Turell , Friday, January 22, 2021, 23:16 (1399 days ago) @ David Turell

It took much research, but there are still huge gaps:

https://phys.org/news/2021-01-forelimb-function-vertebrates-limbs.html

"The earliest tetrapods originated from their fish ancestors in the Devonian period and are more than twice as old as the oldest dinosaur fossils. They resembled a cross between a giant salamander and a crocodile and were about 1-2 meters long, had gills, webbed feet and tail fins, and were still heavily tied to water. Their short arms and legs had up to eight digits on each hand and foot and they were probably ambush predators, lurking in shallow water waiting for prey to come near.

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"The research led by Julia Molnar, Assistant Professor at New York Institute of Technology College of Osteopathic Medicine and Stephanie Pierce, Thomas D. Cabot Associate Professor of Organismic and Evolutionary Biology at Harvard University, discovered three distinct functional stages in the transition from fins to limbs, and that these early tetrapods had a very distinct pattern of muscle leverage that didn't look like a fish fin or modern tetrapod limbs.

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"To determine how the fins and limbs worked, the researchers used computational software originally developed to study human locomotion. This technique had been used recently to study locomotion in the ancestors of humans and also dinosaurs like T. rex, but never in something as old as an early tetrapod.

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"The fin from Eusthenopteron had a pattern that was reminiscent of the lungfish, which is one of the closest living relatives of tetrapods," said Pierce. "But the early tetrapod limbs showed more similarities to each other than either fish or modern tetrapods."

"That was perhaps the most surprising," said Molnar. "I thought Pederpes, and possibly Acanthostega, would fall pretty well within the range of modern tetrapods. But they formed their own distinct cluster that didn't look like a modern tetrapod limb or a fish fin. They were not smack dab in the middle but had their own collection of characteristics that probably reflected their unique environment and behaviors."

"The results showed that early tetrapod limbs were more adapted for propulsion rather than weight bearing. In the water, animals use their limbs for propulsion to move themselves forward or backward allowing the water to support their body weight. Moving on land, however, requires the animal act against gravity and push downward with their limbs to support their body mass.

"This doesn't mean that early tetrapods were incapable of moving on land, but rather they didn't move like a modern-day living tetrapod. Their means of locomotion was probably unique to these animals that were still very much tied to the water, but were also venturing onto land, where there were many opportunities for vertebrate animals but little competition or fear from predators."

Comment: I did not cover the lengthy description of the methodology, but the results are a mazing. The problem is the changes jump ahead as new functions appear and no tiny alterations are ever found. Back to Gould's gaps. I've had courses in comparative anatomy in pre-med. Muscles and bones can be compared and similarities always seen. For example, we know the horse hoof and leg are exactly equivalent to a single human toe and nail. So we know similarities don't help us with the gaps in form and function. The gaps tell us speciation is not due to simple step-by-step adaptations. You may ask for transitional forms, and they exist with huge gaps. From my viewpoint, the gaps tell us design is real.