Swimming Behaviors Of Triassic Sea Creatures Identified Based On Paddle Print Fossils
April Flowers for redOrbit.com – Your Universe Online
Earth is full of evidence that dinosaurs once walked our planet. From fossil fuels to fossils themselves, the dinosaurs left their mark. These prehistoric creatures also left their footprints. Footprints can be found from Texas to China, tantalizing the imagination of the public and researchers alike.
Such tracks have been found in an ancient seabed in China that, according to an international research team from the University of Bristol and the Chengdu Center of China Geological Survey, shed light on how nothosaurs moved. Their results were published in a recent issue of Nature Communications.
A wide variety of marine reptiles ruled the seas during the Mesozoic era, 252-66 million years ago. Nothosaurs, voracious semi-aquatic hunters, were one of the earliest groups. With their elongated bodies and paddle-like limbs, the nothosaurs were the top predators of the Triassic coasts around 245 million years ago.
Scientists have debated how nothosaurs swam for a long time. One theory is the reptiles used their paddle-like feet to row with a back-and-forth motion. A second theory has the dinosaurs sweeping their forepaddles in a figure-eight motion, much like a modern penguin. This motion would allow them to “fly” through the water.
The research team studied recently-discovered trackways formed on an ancient seabed in Yunnan, in the southwest region of China. In straight lines and sweeping curves of ten to fifty, the tracks are slots in the mud, arranged in pairs.
Size and spacing of the paired markings allowed the scientists to identify them as being created by the forelimbs of nothosaurs. The animals were between three and nine feet long.
The researchers say their results reveal how the rowing theory of locomotion is correct. The animals propelled themselves by rowing their forelimbs in unison. The results represent the first direct evidence of nothosaur propulsion.
The scientists believe the markings are from two types of nothosuars, the large Nothosaurus and the diminutive Lariosaurus, known from complete fossil skeletons from the Triassic of southern China.
Professor Qiyue Zhang from Chengdu Center of China Geological Survey, said, “We interpret the tracks as foraging trails. 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 tracks analyzed for this study were found at sites around Luoping in Yunnan. Luoping is known for exceptionally well-preserved fossils and had yielded thousands of exquisite fossils of sea creatures, and occasional plants and small terrestrial animals blown in from the nearby islands.
Professor Michael Benton from the University of Bristol, said, “When I first saw the site, I couldn’t believe the amazing quality of the fossils. It’s quite unusual to find skeletons of marine reptiles such as the nothosaurs so close to evidence of their tracks.”
Fossil sites like Luoping and others in South China are illuminating the recovery of life after the Permo-Triassic mass extinction event. This event wiped out nearly 90 percent of all life on Earth. Marine reptiles such as the nothosaur were part of the emerging ecosystem as it recovered.
Professor Shixue Hu, also from Chengdu Center of China Geological Survey, said, “Here we see a detailed snapshot of how life was within 8 million years of the mass extinction. It took all that time for the 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.”
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