Humans genetically similar to 555-million-year-old animals, study reveals

RIVERSIDE, Calif. —  Genes from some of the Earth’s earliest ocean animals are similar to those of modern-day animals and humans, according to a recent study. These creatures, which existed 555 million years ago, lacked skeletal systems and appendages, however, fossil records indicate a number of shared genes between us and them. 

“None of them had heads or skeletons. Many of them probably looked like three-dimensional bathmats on the seafloor, round discs that stuck up,” explains Mary Droser, a geology professor at the University of California, Riverside and the study’s first author, in a statement. “These animals are so weird and so different, it’s difficult to assign them to modern categories of living organisms just by looking at them, and it’s not like we can extract their DNA — we can’t.”

The physical appearance of these animals, as well as their possible behaviors, were compared to modern-day animals via fossil records that are well-preserved. Droser and Scott Evans, a recent doctoral graduate of UCR, linked these characteristics to certain genes within today’s living organisms. 

Paleontologist Scott Evans
Paleontologist Scott Evans studying fossils in the Australian outback. (Credit: Droser Lab/UCR)

Although there are over 40 species discovered from the Ediacaran period, the researchers chose four representative creatures to analyze, ranging from one or two millimeters in size to almost a meter long. 

One of the chosen species was Kimberella, an animal that was shaped like a teardrop with an elongated “foot” used to gather food off of the seafloor. The foot was also used for movement, similar to modern-day snails and clams. Dickinsonia, another species of the study, was shaped like an oval and had a ribbed surface. 

The species Tribrachidium and Ikaria were also analyzed. Tribrachidium were spiral-shaped, sessile organisms that lived on the seafloor. The newly discovered Ikaria fossils are similar to the modern-day worm, however, were only about 2mm long. 

Scientists say Ikaria were possibly the first of the bilateral animals, evolving a gut system that connected a head or front region to a back region. According to Evans, the species likely ate as they moved over the seafloor, indicating they had mouths that aren’t shown in fossil records.

All representative species in the study were multicellular, and most exhibited bilateral symmetry. Their nervous systems, although not as robust as a humans, spanned their entire body similar to modern-day animals. Also, they had muscular systems akin to today’s animals, with muscles developed into most areas of the body.

The study also reveals that these species could repair their body via apoptosis, the same event that occurs in the human body to destroy infected cells. According to scientists, this indicates a similarity in genes between these ancient species and humans. “The fact that we can say these genes were operating in something that’s been extinct for half a billion years is fascinating to me,” says Evans.

To understand how these animals and other species after them have evolved, researchers plan to study the development of their musculature, as well as how each species functioned. “Our work is a way to put these animals on the tree of life, in some respects,” Droser adds. “And show they’re genetically linked to modern animals, and to us.”

These findings are published in the journal Proceedings of the Royal Society B.