Devonian fossils show sharks may have evolved from bony ancestors. Paleontology


Paleontologists have found fossilized remains in Mongolia Minginia TurgensisA new genus and species of placoderm fish that lived 410 million years ago (Early Devonian era). They have examined a partial braincase and skull roof Minginia Turgensis And found extensive endocondral bone, hard bone that forms our skeleton after birth. This finding suggests that the shark’s mild skeletons may have evolved from bony ancestors rather than other methods around them.

Virtual 3d model of braincase Minginia Turgensis Resulting from CT scan. The inset shows raw scan data inside the spongy endocondral bone. Picture Sincerely: Brazeau and others, doi: 10.1038 / s41559-020-01290-2.

There are skeletons made of shark’s cartilage, which is about half the density of bone.

Cartilaginous skeletons are known to have evolved before the bony, but it was thought that sharks had previously separated from other animals on the evolutionary tree, keeping their cartilaginous skeletons with other fish, and eventually we, the bone. Moved to develop.

Minginia Turgensis Belongs to a broad group of fish called placoderms, from which sharks and all other jaws develop vertebrates – spinal animals and mobile jaws.

Prior to this, no placoderm was found with endocondral bone, but skull fragments of ancient fish species were wall-to-wall endochondral.

This could suggest the shark’s ancestors first developed bone and then lost it again rather than keeping their initial cartilaginous state for over 400 million years.

“This was a very unexpected discovery,” said Dr Martin Martin, a researcher at the Department of Life Sciences at Imperial College London and the Department of Earth Sciences at the Natural History Museum, London.

“Conventional wisdom says that a bony internal skeleton was a unique innovation of the lineage that diverged from the ancestor of the shark more than 400 million years ago, but there is clear evidence of a bony internal skeleton in both the shark and the cousin of the two , After all, us. ”

“If the shark had bony skeletons and lost it, it could be an evolutionary adaptation,” he said.

“Sharks do not have swim bladders, which later evolved into bony fish, but a lighter skeleton would have helped them become more mobile in the water and swim at different depths.”

“This may be the one that helped the shark to be one of the first global fish species, which spread to the oceans around the world 400 million years ago.”

The study was published online today in the journal Nature Ecology and Development.

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Md brazeau and others. Endocondral bone in an early Devonian ‘placeoderm’ of Mongolia. Nat Ecol Evol, Online 7 September, 2020; doi: 10.1038 / s41559-020-01290-2