Nature & Environment

Newly Discovered Paddle Tracks Reveal How Ancient Reptiles Swam in the Sea

Catherine Griffin
First Posted: Jun 11, 2014 11:35 AM EDT

Millions of years ago, ancient marine reptiles propelled themselves through the water and across the seafloor. Now, trackways formed on an ancient seabed have shed some light on how these nothosaurs once moved.

About 252 to 66 million years ago during the Mesozoic, the seas were dominated by marine reptiles. One group of these reptiles was the nothosaurs, which were voracious, semi-aquatic hunters with long bodies and paddle-like limbs. About 245 years ago during the Triassic, these reptiles were the top predators along the coasts. Yet scientists have long wondered how these reptiles moved through the water.

Now, they may have their answer. Researchers studied trackways formed on an ancient seabed in southwest China. These tracks were formed by slots in the mud arranged in pairs, and in long series of ten to 50 that follow straight lines and sweeping curves.

It's very likely that these large reptiles moved over the seafloor by rowing their forelimbs in unison. It's likely that the large Nothosaurus and the small Lariosaurus were the trackmakers in this case.

"We interpret the tracks as foraging trails," said Qiyue Zhang, one of the researchers, in a news release. "The nothosaur was a predator, and this was a smart way to feed. As its paddles scooped out the soft mud, they probably disturbed fishes and shrimps, which it snapped up with needle-sharp teeth."

The findings reveal a bit more about these creatures and show how they lived millions of years ago. This, in turn, sheds some light on the conditions of the time.

"Here we see a detailed snapshot of how life was within 8 million years of the mass extinction," said Shixue Hu, one of the researchers, in a news release. "It took all that time for Earth to settle down from the cataclysm and the arrival of these large, complex marine predators shows us the ecosystems had finally rebuilt themselves, and life could be said to have recovered from the crisis."

The findings are published in the journal Nature Communications.

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