Evolution: transitional fish, Tiktaalik new findings (Evolution)

by David Turell , Sunday, April 07, 2024, 15:42 (228 days ago) @ David Turell

New technique:

https://www.sciencedaily.com/releases/2024/04/240405231833.htm

"Before the evolution of legs from fins, the axial skeleton -- including the bones of the head, neck, back and ribs -- was already going through changes that would eventually help our ancestors support their bodies to walk on land. A research team including a Penn State biologist completed a new reconstruction of the skeleton of Tiktaalik, the 375-million-year-old fossil fish that is one of the closest relatives to limbed vertebrates. The new reconstruction shows that the fish's ribs likely attached to its pelvis, an innovation thought to be crucial to supporting the body and for the eventual evolution of walking.

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"The pelvic fins of fish are evolutionarily related to hind limbs in tetrapods -- four-limbed vertebrates, including humans. In fish, the pelvic fins and bones of the pelvic girdle are relatively small and float freely in the body. For the evolution of walking, the researchers explained, the hind limbs and pelvis became much larger and formed a connection to the vertebral column as a way of bracing the forces related to supporting the body.

"'Tiktaalik is remarkable because it gives us glimpses into this major evolutionary transition," Stewart said. "Across its whole skeleton, we see a combination of traits that are typical of fish and life in water as well as traits that are seen in land-dwelling animals."

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"'This reconstruction shows, for the first-time, how it all fit together and gives us clues about how walking might have first evolved."

"The researchers explained that, unlike our own hips where our bones fit tightly together, the connection between the pelvis and axial skeleton of Tiktaalik was likely a soft-tissue connection made of ligaments.

""Tiktaalik had specialized ribs that would have connected to the pelvis by a ligament," Stewart said. "It's astonishing really. This creature has so many traits -- large pair of hind appendages, large pelvis, and connection between the pelvis and axial skeleton -- that were key to the origin of walking. And while Tiktaalik probably wasn't walking across land, it was definitely doing something new. This was a fish that could likely prop itself up and push with its hind fin.'"

Comment: the authors of this article see the purpose in evolution as they describe the advances related to walking