Ancient Fish Fossil Reveals How Elongate Animals Like Eels and Snakes May Have Evolved

Snake and eels have long bodies, their flexible vertebrae allowing them to move through their environment. This particular body plan has evolved many times independently in the more than 500 million years of vertebrate animals' history. Now, though, scientists have discovered a previously unknown mechanism for this body elongation in the evolution of early fishes by unearthing a fossil.

Before this finding, researchers believed that the extreme elongation of the body access occurred in one of two ways. It's possible that there was an elongation of the individual vertebrae of the vertebral column, which thus became longer, or there was a development of addition vertebrae and associated muscle segments. This latest finding, though, reveals a third mechanism.

The new fossil is of a creature known as Saurichthys curionii. Unlike other known fish with elongate bodies, the vertebral column of this fish does not have one vertebral arch per myomeric segement, but two. This resulted in an elongation of the body and gave it an overall elongate appearance.

"This evolutionary pattern for body elongation is new," said Erin Maxwell, one of the researchers, in a news release. "Previously, we only knew about an increase in the number of vertebrae and muscle segments or the elongation of the individual vertebrae."

The fossil itself revealed surprising details. Not only were the skeletal parts of the fish preserved, but its tendons and tendon attachments surrounding the muscles also survived. This not only allowed the researchers to draw conclusions about the evolution of the fish, but also allowed them to learn exactly how this creature might have moved through the water.

In fact, the fish was nowhere near as flexible as today's eels. Unlike modern oceanic fishes such as tuna, it was also probably unable to swim for long distances at high speed. It was probably comparable to the garfish or needlefish that exist today.

The findings reveal a little bit more about this ancient species and also tell scientists a little bit more about this body plan in general. This could help them understand this evolutionary process a bit better.

The findings are published in the journal Nature Communications