Scientists claim to have found the earliest example of sex - between organisms living 565 million years ago.
Researchers have found organisms, known as rangeomorphs, could have been the first to reproduce sexually.
Rangeomorphs, which lived 2km under the sea, were some of the earliest complex organisms on Earth and have been considered to be some of the first animals.
They thrived in the oceans between 580 and 541 million years ago, and could reach up to two metres in length, although most were around ten centimetres long.
Looking like trees or ferns, fossils reveal they did not appear to have mouths, organs, or means of moving, and probably absorbed nutrients from the water around them.
Researchers led by Cambridge University observed that larger 'grandparent' rangeomorphs, of a type known as Fractofusus, were randomly distributed in their environment, and surrounded by distinct patterns of smaller 'parents' and 'children'.
They say these patterns strongly resemble biological clustering in modern plants, and suggest a dual mode of reproduction.
Like many life forms from that time rangeomorphs mysteriously disappeared at the start of the Cambrian period, which began about 540 million years ago.
Researchers used high-resolution GPS, spatial statistics and modelling to examine the fossils in Canada.