Earth's Earliest Animals Were Strange Sea Creatures

Wednesday, August 22, 2018

The Cambrian fossil Stromatoveris proved an important link between earlier and later animal groups from the Ediacaran and Cambrian periods. Photo by Northwest University, China/J. Hoyal Cuthill

New fossil analysis suggests the planet's earliest known animals emerged at least 571 million years ago.

The new study -- published this month in the journal Paleontology -- proves members of the Ediacaran biota are indeed animals and were diversifying for several million years before the acceleration of speciation known as the Cambrian explosion.

Scientists recovered the first Stromatoveris psygmoglena fossil in the mid-20th century. The frond-like sea creature baffled paleontologists for decades.

Stromatoveris psygmoglena hails from the Cambrian period, but dozens of similar blob-like fossil imprints have been found among older strata -- rocks from the Ediacaran period, which lasted from 635 to 542 million years ago.

Until now, scientists have struggled to understand the relationship between Stromatoveris psygmoglena, Ediacaran biota and the animal forms that emerged during the Cambrian explosion.

Using a new computer analysis method, scientists were able to tease out important relations between Ediacaran biota and a range of other animal groups. The computer model helped scientists compare the anatomical characteristics of fossils from the Ediacaran and Cambrian periods.

"These methods are very frequently used in biology and palaeontology but had not previously been applied to test the wider relationships of these Ediacaran biota," Jennifer Hoyal Cuthill, visiting researcher in palaeobiology at the University of Cambridge, told UPI.

The unique frond-like forms of Ediacaran biota made it difficult for scientists to compare the ancient species to Cambrian animals.

"To help us to compare the Ediacaran biota to a wide range of other groups, from algae to complex animals, we used a popular online system called MorphoBank which allowed us to upload and compare photographs of the fossils," Cuthill said.

The computer analysis revealed previously unknown relationships between Ediacaran biota and a variety of Cambrian animal groups. According to the model, Stromatoveris psygmoglena was an important link between the early and later animal groups.

"Rather than first appearing in the Cambrian period as had once been thought, animals must have originated and begun to diversify by the Ediacaran period," Cuthill said. "Our analysis also showed that a biological group called the Petalonamae, which includes members of the Ediacaran biota and the Cambrian animal Stromatoveris, didn't go extinct at the end of the Ediacaran period as some had thought."

Scientists determined petalonamids persisted for some 53 million years, dominating the seafloor in Earth's ancient oceans. These early animals were more resilient than scientists previously thought.

This early evolutionary success, scientists determined, set the stage for more sophisticated adaptations.

"The common ancestor they shared with later animals was likely to have had a more complex, differentiated anatomy than sponges, for example, setting the stage for further evolutionary innovations among the complex animals," Cuthill said.

Because the research confirms the emergence of animals during the Ediacaran period, scientists need to reconsider the timeline of early animal evolution, said Cuthill. Evolutionary biologists and paleontologists should start looking for evidence of the first animals even earlier in the fossil record.

"Scientists from all over the world are searching for evidence of early animals," Cuthill said. "These palaeontologists are using a range of techniques, from chemical tests for the traces of life to the tried and tested method of simply looking for fossils out in the field."