One less relative to be ashamed of: Scientists have ruled out the possibility that a 535-million-year-old microscopic fossil that looks like “angry minions” is our earliest known ancestor.
Previous studies have shown this Saccorhytus coronarius, tiny a bag-like creature with a large mouth and no anuswas one of the early members of the large group of animals called bivalves, which includes vertebrates, including humans.
Now researchers say they are sure of it Succorfit is not second-mouthed, but part of the same evolutionary group as arthropods, which includes insects and crustaceans.
“The paper suggested that Succorfit was an early member of our own evolutionary lineage, a group of animals known as suborders. But we had better-preserved samples, so we immediately knew the authors were wrong,” said Philip Donoghue, Professor University of Bristol and co-author of a new study published in Nature.
The team recently collected hundreds of additional specimens, which they used to create 3D digital models of the creature that revealed microscopic features in greater detail.
“Succorfit is only about a millimeter in size and looks like a tiny wrinkled ball with a bunch of spikes and a mouth with rings of teeth around it,” Donoghue said. “I like to describe it as an angry minion.”
The discovery was made when the team realized that the spines and holes around the fossil’s mouth were not respiratory organs, which had misled previous researchers.
“The preliminary conclusion was based in large part on the fact that Succorfit the fossils have a series of openings around the mouth, which they interpreted as primitive gills, a feature of the second-order. But now we know that those holes are just where the teeth chipped off,” Donoghue said. “Our analysis shows this Succorfit actually belongs to a group of arthropods and their relatives called ecdysozoa, although we can’t say exactly where it belongs.’
While deuterostome embryos develop an anus and then a second opening that becomes the mouth, Succorfit has only one opening that serves both.
“Succorfit it doesn’t have an anus, just a mouth-like structure from which it would happily regurgitate whatever it had eaten,” Donoghue said.
The search for our earliest ancestors continues, Donoghue said. “Our understanding of the deuterostome lineage is in complete disarray. We are sifting through early fossils to better understand our evolution,” he added.
The authors of the earlier study have been contacted for comment.