From what little we know of them, they seem so different. Mysterious creatures that lived in the ocean half a billion years ago – headless, limbless things, seemingly alien to us in all respects.
Except they weren't, new research suggests. In fact, the Ediacaran biota – a collection of ancient oceanic life-forms that dwelled on Earth between 570 to 539 million years ago – would have shared a number of genetic similarities with modern metazoans (multicellular animals) including humans, scientists say.
Not that the resemblances border on the uncanny, or anything.
"None of them had heads or skeletons," explains palaeobiologist Mary Droser from the University of California, Riverside.
"Many of them probably looked like three-dimensional bathmats on the sea floor, round discs that stuck up."
Droser has something of a speciality in investigating eerie organisms from Earth's distant past.
A year ago, she helmed a study that identified one such Ediacaran: Ikaria wariootia, a strange, sluggish blob about the size of a grain of rice, which may have been the earliest ancestor of all animals with bilaterally symmetrical bodies.
Not all Ediacarans necessarily have such close ties to animals today, however.
There are over 40 recognised species from the period – including the most famous, the ovoid Dickinsonia, and another named after President Obama – and determining where their fossilised forms ought to sit in the tree of life isn't always easy.
"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," Droser says. "And it's not like we can extract their DNA – we can't."
Without being able to analyse these creatures' genetic data first-hand, researchers have to make do by inferring what they can from the trace fossils these organisms left behind. Thankfully, those ancient imprints can reveal quite a bit.
In a new study co-authored by Droser and led by first author and palaeontologist Scott Evans from the Smithsonian National Museum of Natural History, researchers looked at four representatives from the Ediacaran biota: Dickinsonia, Ikaria, the slug-like Kimberella, and the hemispherical blob Tribrachidium.
Based on observations of the fossils and what we can deduce about how these creatures may have moved their bodies, sustained themselves, and generally lived their lives on the ancient seabed, the researchers propose the animals most likely contained a rudimentary form of nervous system, supported and regulated by the same kinds of genetic regulatory elements still used by living animals today, including humans.
"This analysis demonstrates that the genetic pathways for multicellularity, axial polarity, musculature, and a nervous system were likely present in some of these early animals," the authors write.
"Together these traits help to better constrain the phylogenetic position of several key Ediacara taxa and inform our views of early metazoan evolution."
Specifically, in the new study the team outlines a broad range of genes that may have influenced multicellularity, immunity, nerves, apoptosis (programmed cell death), axial patterning (that differentiates the sides of a body, like front or back and left or right), and more.
While there's still much to learn about these truly ancient creatures, the biology that unites us across millions of years shows they are perhaps not so strange as they seem.
"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," Evans says.
The findings are reported in Proceedings of the Royal Society B.