Sorry, sponges. The earliest animals were jellies

April 12, 2017, 4:06 p.m.
comb jellyfish
Photo: Kondratuk Aleksei/Shutterstock

For about a decade, zoologists have been hotly debating what creatures deserve the title of oldest branch of the animal family tree. Most believed it was the sponge due to the animal's simplicity. Others believed that the delicate marine predator the comb jelly evolved first.

A team of evolutionary biologists from Vanderbilt University and the University of Wisconsin-Madison used genetic analysis to settle the issue and concluded that comb jellies (aka ctenophores) were the earliest members of the animal kingdom. The results could impact how scientists determine the nervous system, digestive tract, and other organs in modern animals evolved, the researchers said.

Their study was published in the journal Nature Ecology & Evolution.

For nearly a century, scientists organized the animal family tree based largely on the complexity of individual animals. Because sponges were so simple compared to other animals, they were considered to be the first animals. But these beliefs began to shift as evolutionary biologists began to learn more about the DNA of more species.

In 2008, a study pinpointed comb jellies as the earliest members of the animal kingdom instead of sponges. A new field called phylogenomics was created to further study the evolutionary tree. This triggered a controversy, as several papers were published with conflicting results.

In this new study, researchers compared individual genes to see which gave more support for being the first in the family tree. They concluded that the jellies had more genes that supported the "first to diverge" status.

"We believe that our approach can help resolve many of these long-standing controversies and raise the game of phylogenetic reconstruction to a new level," said study senior researcher Antonis Rokas, a professor of biological sciences at Vanderbilt University.

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