Very particular 'fossils' may have been preserved in human DNA: the genetic remains of the first animals to appear on the planet, multicellular organisms with bizarre shapes that lived over 500 million years ago on the ocean floor.
Uncovering their unsuspected similarities to modern animals (including humans) is a study by the Natural History Museum of Washington and the University of California at Riverside, published in the journal Proceedings of the Royal Society B.
The researchers focused in particular on four representative animals of the over 40 species identified among those that lived in the Ediacaran period, between 570 and 539 million years ago, ranging from a few millimeters to even one meter: they are the ancestor of the Kimberella molluscs, drop-shaped, capable of moving like a snail and eating with a small trunk;
the Dickinsonia, flat and oval with raised stripes on the back;
the Tribrachid, with a hemispherical shape;
finally Ikaria, an animal as small as a grain of rice and the first to have a front and a rear part, with two orifices connected by the digestive system.
"None of these living things had a head or a skeleton," explains paleobiologist Mary Droser of the University of California.
"Probably a lot of them looked like 3D non-slip mats on the seabed, simple, rounded, fixed discs."
"These animals - continues Droser - were so strange and different that it is difficult to assign them to the modern categories of living beings only on the basis of appearance, and moreover we cannot extract their DNA".
By studying their fossils, however, the researchers tried to infer how they moved, how they fed and, more generally, how they lived on the seabed.
All four animals were composed of different types of cells, had a symmetry between the right and left side of the body, were equipped with musculature and a non-centralized nervous system.
They were also able to repair damaged parts of the body through the mechanism of programmed cell death (apoptosis), still crucial for our immune system against viruses and tumors today.
They probably already had the genetic instructions to build the head and sense organs, but the interaction between the various genes had not yet been refined.
"This analysis - the researchers write - shows that the genetic circuits for multicellularity, axial polarity, musculature and nervous system were probably already present in some of these primordial animals".