Re-analysis of a fossil finds it’s from the earliest vertebrate branch
NotSanguine writes:
Ars Technica is reporting on a paper published on 7 July 2022 in the journal Science, where researchers believe they've identified one of the first vertebrates.
From the article:
A group of organisms called yunnanozoans had gills, precursor to jaws.
Because we're a member of the group, it's easy to see vertebrates as the pinnacle of evolution, a group capable of producing bats, birds, and giant whales in addition to ourselves. But when they first evolved, vertebrates were anything but a sure thing. They branched off from a group that lived in the mud and didn't need to tell its top from its bottom or its left from its right, and so ended up losing an organized nerve cord. Our closest non-vertebrate relatives re-established a nerve cord (on the wrong side of the body, naturally) but couldn't be bothered with niceties like a skeleton.
How exactly vertebrates came out of this hasn't been clear, and the probable lack of a skeleton in our immediate ancestors has helped ensure that we don't have a lot of fossils to help clarify matters.
But in Thursday's issue of Science, researchers have re-evaluated some enigmatic fossils that date back to the Cambrian period and settled several arguments about exactly what features the yunnanozoans had. The answers include cartilaginous structures that supported gills and a possible ancestor to what became our lower jaw. In the process, they show that yunnanozoans are likely the earliest branch of the vertebrate tree.
[...]
You can get a sense of what a yunnanozoan looks like from the image above. The soft tissue down its flanks was divided into segments, a feature in both our closest living non-vertebrate relatives (the amphioxus or lancelet) and is present in vertebrate embryos but generally gets lost as they proceed through development into adults. Near the animal's head-and it does have a clear head and mouth-there's also an array of arched structures that look a lot like the similarly located gill arches found near the head of modern fish.
Journal Reference:
Qingyi Tian, Fangchen Zhao, Han Zeng, et al., Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans, Science, 377, 6602, 2022. DOI: 10.1126/science.abm2708
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