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Dickinsonia. Credit: Scott Evans

Yes, we really share genes with headless sea creatures from half a billion years ago

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Mar 12, 2021, 7:42 PM EST (Updated)

Humans (and every other creature on Earth) didn’t materialize out of nothing. Some of our origins are strange, and strange is an understatement.

Life-forms that existed and evolved during the Ediacaran period were slowly creeping their way up towards what would eventually turn into the Cambrian explosion that gave rise to so many species. Some creatures were especially peculiar. What was once a vast ocean has now yielded 555-million-year-old fossils of things that looked like everything from bath mats to teardrops with a proboscis. They are unrecognizable when compared to anything extant, never mind that there was no DNA left to extract for scientists to see what they could possibly be related to.

Some of the fauna that emerged during the Ediacaran had no heads, no brains, no skeletons, no complex organ systems, but are still thought to share genes with humans. Paleobiologist Scott Evans unearthed some of these weird creatures. Despite being so primitive, they apparently passed on their DNA to whatever would evolve later.

“Based on the results coming out of modern developmental biology, there is a certain amount of complexity of interactions between genes needed to produce things like a head,” Evans, who co-authored a study recently published in PNAS, told SYFY WIRE. “The Ediacaran Period represents such an early stage in the evolution of animals that this level of complexity had not yet been achieved.”

Evans and his team figured that out by studying what they did have, which meant the fossils themselves, along with DNA data from both extant and extinct species. Every structure in a living thing is the way it is because it was genetically coded to form like that. Observing physical structures visible in the fossils can reveal a surprising amount about the kinds of genes an animal had based on what shows up. The researchers then matched them to genetic mechanisms that are behind similar types of structures in animals with more familiar genetic profiles, which could at least give the researchers an idea of what kinds of genes created animals that have only left behind impressions on rock that used to be an ancient seafloor.

Dickinsonia, a primitive Ediacaran creature that probably had more DNA than its looks might betray. Credit: Scott Evans

Maybe the most bizarre of these species was Kimberella. This was the giant teardrop whose body is thought to have been much like a muscular foot. It is thought to have gotten around with a frill, much like that of a cuttlefish, and would feed by sticking its long proboscis into mats of bacteria below. Scratch marks on fossilized bacterial mats are thought to be evidence of its eating habits. Ikaria were tiny elliptical organisms that could have been mistaken for sea maggots, but they are the oldest known bilaterians, which have a front, back, and a gut that connected openings at both ends. Dickinsonia is (at least as Evans calls it) the bath mat.

“We determined likely genetic elements based on their conserved role in producing the same characters we find in these ancient impressions in a variety of animals today,” he said. “Species like Dickinsonia had the genetic tools to produce symmetry, muscles, and a nervous system but not yet the [complex] interactions for those more advanced traits like a head or skeleton.”

For something that doesn’t seem too fancy, Dickinsonia must have had more genetic equipment than would be expected out of a headless blob. Symmetry in animals that have a front and back, or a top and bottom, or both, is the result of specific gene groups that determine which end is which. Because the morphology of both Ikaria and Dickinsonia was pretty symmetrical, Evans and his team were able to attribute it to those genetic groups. It is also possible that Dickinsonia was capable of apoptosis, since there is what looks to be fossilized evidence of it regenerating some of its own body, much like starfish or sea urchins can. The problem is, since something with no skeleton is mostly soft tissue, it’s almost inevitably going to disintegrate over millions of years.

Think about it. Many of the genetic groups these freaky animals were determined to have also exist in humans. We are bilateral, symmetrical, and have muscles and nerves. That might not be the end of the similarities. It is also possible that any of these species had a mouth, or an unknown appendage, or some sort of rudimentary smelling mechanism. Ikaria is thought to have plowed through the sand much like an earthworm passes through dirt, digesting nutrients and leaving sediment in its wake. The fossils that have already been studied may not have all the answers. There are more still waiting in what is now a dry and silent sea.

“I think that there are more genes and regulatory tools that can be identified in these fossils,” Evans said. “So the hope is that by comparing patterns of muscle development in living things with what Ediacaran fossils we find will give us a better idea of the total complement of genes used by these organisms.”