Following up on a new Ichythosaur discovery last week (When Marine Reptiles Ruled the Sea) the fossilized footsteps of a Nothosaur have been unveiled. This time we go to China where a geological surveyor stumbled onto a few fossil tracks on a small ledge. Cutting back into the side of the mountain, paleontologists exposed 350 prints as part of at least 15 different trackways.
I said the footprints of a Nothosaur were found but really these prints are something between a footprint and a flipper print. Nothosaurs and their relatives where carnivorous marine reptiles that lived in the Triassic. Unlike the Plesiosaurs and Ichthysaurs I have been written about recently (Mary Anning: Plesiosaurs, Pterosaurs and The Age of Reptiles), Nothosaurs usually had distinct legs with webbed feet rather than fully developed flippers though some species had nearly flipper-like appendages like the one that created these imprints. Nothosaurs likely came onto land to lay eggs much like marine turtles do today. But like seals and sea turtles today, they probably were more at home in the water than on land. They had long necks and tails and very long jaws with hundreds of outwardly pointed teeth and probably fed on fish and crustaceans.
Nothosaurs are members of a large group of marine reptiles called Sauropterygians. By my count (see list HERE) there are over 250 recognized species of Sauropterygians which include the Plesiososaurs but not the Mososaurs and Ichthyosaurs of which there are several hundred species. Given the pace of discovery of new kinds of marine reptiles and the fact we have only observed a tiny fraction of the fossil record there must be thousands of new kinds of marine reptiles yet to be found.
These prints are particularly interesting because they allow inferences about the swimming behavior of these animals. Did they paddle in the water or row through the water with their legs? This chance fossil find of imprints on the sea-bed floor make it clear that at least some of the time they rowed their legs like oars through the water pushing off on the sea bed. These trackways have long sets of pairs of tracks that even loop around as this animal skimmed the sea bed looking for prey.
A Remarkable Discovery
It is difficult enough for footprints of a land-dwelling dinosaur to be preserved in rock much less the trackways of animals underwater. But the right conditions for their preservation did happen even if infrequently and we have been able to forensically piece together what must have happened long ago. These tracks are not like any track that any living animal would leave behind. They were found in rock that has been clearly identified as marine in origin based on the thousands of marine fossils that have been found in them during the past 20 years. The presence of marine reptile fossils in the same region and rocks of China and the fact that only a few genera of Nothosaurs have the size to fit the measurements of these trackways all point to their being the author/cause of these footprints.
Qiyue Zhang, Wen Wen, Shixue Hu, Michael J. Benton, Changyong Zhou, Tao Xie, Tao Lü, Jinyuan Huang, Brian Choo, Zhong-Qiang Chen, Jun Liu, Qican Zhang. Nothosaur foraging tracks from the Middle Triassic of southwestern China. Nature Communications, 2014; 5 DOI: 10.1038/ncomms4973