Trackways formed on an ancient seabed have shed new light on how nothosaurs, ancient marine reptiles that lived during the age of the dinosaurs, propelled themselves through water. The evidence is described by a team from Bristol and China in Nature Communications today.
During the Mesozoic, 252-66 million years ago, the seas were ruled by a variety of marine reptiles. One of the earliest groups were the nothosaurs, voracious semi-aquatic hunters with elongate bodies and paddle-like limbs. They were the top predators of the Triassic coasts, some 245 million years ago.
Their mode of swimming has long been debated: did they row themselves along with a back-and-forth motion of their limbs, or did they 'fly' underwater, sweeping their forepaddles in a figure-eight motion like a modern penguin?
Scientists from the University of Bristol and colleagues in China studied trackways formed on an ancient seabed which were recently discovered in Yunnan, southwest China. The tracks consist of slots in the mud arranged in pairs, and in long series of ten to fifty that follow straight lines and sweeping curves.
The size and spacing of the paired markings indicate that they were created by the forelimbs of nothosaurs, representing animals ranging in size from over 3 metres to less than a metre in length.
They demonstrate that that these reptiles moved over the seafloor by rowing their forelimbs in unison, the first direct evidence of how these creatures propelled themselves in the water.
Two types of nothosaurs, the large Nothosaurus and the diminutive Lariosaurus, known from complete fossil skeletons from the Triassic of southern China, are the likely trackmakers.
Professor Qiyue Zhang from Chengdu Center of China Geological Survey, leader of the research, said: "We interpret the tracks as foraging trails. The nothosaur was a predator, and this was a smart way to feed. As its paddles
|Contact: Hannah Johnson|
University of Bristol