Because we are members of the group, it is easy to view vertebrates as the pinnacle of evolution, a group capable of producing bats, birds, and giant whales apart from themselves. But when they first evolved, vertebrates were anything but a certain thing. They broke away from a group that lived in the mud and did not need to tell from its bottom to the top or from its right side to the left, and thus lost an organized nerve cord. Our closest non-vertebrate relatives rewired a nerve cord (on the wrong side of the body, naturally), but couldn’t be bothered by such nuances as the skeleton.
How vertebrates came out of this is unclear, and the possible lack of skeletons in our immediate ancestors has helped ensure that we don’t have too many fossils to help clarify matters.
But in Thursday’s issue of Science, researchers reevaluate some enigmatic fossils that date to the Cambrian period and settle many arguments about what the features really are. yunnanzoans was. The answer includes the cartilaginous structures that supported the gills and a possible ancestor that became our lower jaw. In the process, they show that yunnanzoans Probably the earliest branch of the vertebrate tree.
you can understand what Yunnanzoan Looks like from above image. The soft tissue beneath its edges was divided into segments, a feature in both our closest living non-vertebrate relatives (amphioxus or lanceolate) and present in vertebrate embryos, but usually lost as they occur in adults. move forward through development. Near the animal’s head—and it has a pronounced head and mouth—there are also an array of arched structures that look like the similarly positioned gill arches found near modern fish heads.
If that interpretation is correct, it would mean yunnanzoans They look like an amphioxus, but have a characteristic that is otherwise only found in modern vertebrates. This would mean that it preserves features important to understanding the origin of vertebrates.
But the “if” starting from the previous paragraph is bigger. Many people in the area disagreed with this interpretation and put yunnanzoans elsewhere. Or rather in many other places, depending on who was actually arguing. Some put them in the same group as amphibians. Others further distanced them from vertebrates and placed them with a group of mud dwellers whose two body axes are not found in vertebrates. Still, others suggested that they were the ancestors of a vast group of organisms that includes things like sea urchins.
A small team from China has now tried to settle these arguments. It does this in part by imaging more than 100 new fossils of the species. But a big part is that they used some of the most sophisticated imaging techniques available. It involves three-dimensional X-ray imaging, electron microscopy, and a technique that bombards microscopic areas of a sample with electrons, then uses the emitted light to determine which elements are present.
I am showing one of the pictures in the paper below to give a sense of the details that these imaging techniques provide.