520-million-year-old animal fossils may not be animals at all

A species that lived about 520 million years ago and was thought to be the oldest known bryozoan is instead a type of colony-forming algae, a new study proposes.

Bryozoans are filter-feeding, tentacle-bearing animals that live in apartment complexes—such as colonies attached to rocks, shells, or other surfaces on the ocean floor or lake bottom. The trouble is, some other animals and algae live in the same type of modular construction. Whereas Protomellison Gatehouse First described in 1993, scientists didn’t classify it as a bryozoan until 2021.

Now, analysis of previously reported fossils suggests the species may not have been a bryozoan, says paleontologist Martin Smith of Durham University in England.

Where previous fossils only preserved the skeletal framework of the subspecies, the new fossils discovered in southern China also include the soft parts of the creature, Smith says. and rather than the tentacles found in immaculately preserved bryozoans, fossils have common leafy flange for some types of algaeHe and colleagues report on March 8 Nature,

If detected, the new discovery means that the oldest unicellular bryozoan fossils known are only about 480 million years old. They, Smith argues, are the only major group of bryozoan animals that did not first appear during the Cambrian period, an explosion of biological diversification that some scientists have referred to as “thebig bang of lifeand which ended about 488 million years ago (Sn: 4/24/19,

As a result, the Cambrian was not, as previously thought, a unique interval of innovation in evolutionary history during which all the blueprints for animal life were mapped, the researchers concluded.

“The question is, has evolution lost its ability to create new body plans?” Smith says. The team’s new finding suggests not, he says.

Not everyone agrees that the new fossils are not bryozoans. Paul Taylor, an invertebrate paleontologist at London’s Natural History Museum who was not involved in the study, says the leaf-like flanges described by Smith and his colleagues could easily be identified as body parts of individual animals in the bryozoan colony. can be explained.

Because the tentacles used by bryozoans to snatch prey from the water are soft tissue and usually not well preserved, their absence from the new fossils is not surprising, Taylor notes.

For Taylor, the new findings aren’t enough to dismiss P Gatehouse as Cambrian bryozoans, but they underscore the uncertainty inherent in identifying fossils with simple body plans. They say that more fossils preserving additional features, such as those preserving the early developmental stages of the organism, are needed to settle the question.