The phylum echinodermata (‘echino’ meaning spiny and ‘derm’ meaning skin) are key to the study of evolution, as they are located at a junction where invertebrates and vertebrate diverged. Photo: Dr. Omri Bronstein / Tel Aviv University

An international study involving Tel Aviv University researchers suggests that types of marine animals including starfish and sea cucumbers lived in oceans about 50 million years earlier than previously thought.

The findings of the study, published in the peer-reviewed journal eLife, shed new light on dating the evolutionary development of echinoids — marine animals that live on the seabed, including sea urchins, starfish, sea cucumbers and their “spiny-skinned relatives.”

“Our work shows that modern echinoids emerged approximately 300 million years ago, and many of them survived the Permo-Triassic mass extinction event that occurred about 252 million years ago — the most severe biodiversity crisis in Earth’s history — and rapidly diversified in its aftermath,” stated Dr. Omri Bronstein of Tel Aviv University’s School of Zoology, one of authors of the study. “Our findings have great significance for the study of evolution in general, not just for that of sea urchins. They suggest that even when we have an abundance of fossils and very extensive research on a group, as in the case of sea urchins, estimates are likely to err by tens of millions of years.”

The Permo-Triassic mass extinction wiped out over 80% of the species on earth, more than 150 million years before the event that wiped out the dinosaurs.

“This is another reminder that there is still more that is unknown than known in the fascinating study of evolution,” Bronstein added.

Researchers from top institutes in the United States, England, Chile and Austria combined a phylogenetic analysis of the genomes of 54 different species, including 18 that have not yet been mapped, with paleontological dating of sea urchin fossils from around the world. They then integrated the genetic findings with fossil-based dating, in order to map the evolutionary history of the echinoids as accurately as possible.

“The findings were very surprising, as they indicate significant errors in the conventional dating of the divergence times (species differentiation points) on the evolutionary tree,” the researchers said.

There are about 1,000 living species of echinoids, including sea urchins, heart urchins, sand dollars and starfish, which live across different ocean environments. The phylum is particularly important in the study of evolution, Bronstein explained, because their place on the evolutionary tree appears where invertebrates and vertebrate diverged.

“Today we are also in the midst of a widespread extinction event, only this time human activity seems to be the main driver,” Bronstein noted. “An in-depth study of past extinction events, the reasons that led to their occurrence, and the species that managed to survive them, may help us deal with the current extinction.”