NH Notes: Discovery of a Marine Reptile Fossil Trackway

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.

Excavation site of Nothosaur fossil tracks in China.   Image from Center of China Geological Survey

Excavation site of Nothosaur fossil tracks in China.  Notice the forest in the upper portion that is at much lower elevation.  Image from Center of China Geological Survey

Close-up of a few of the Nothosaur prints in a newly pried open slab of rock.  Image: PR from Bristol University and China Geological Survey

Close-up of a few of the Nothosaur prints in a newly pried open slab of rock. Image: PR from Bristol University and China Geological Survey

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.

Nothosaur - a marine reptile with webbed feet, elongated jaw and long tail.

Nothosaur – a marine reptile with webbed feet, elongated jaw and long tail.  The one that made the prints found in China was probably a lariosaur which had much more flipper-like legs.

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.

An artistic rendering of the "Sea-rex" Nothosaur. Image from screenshot from the IMAX film "Sea Rex 3D: Journey to a Prehistoric World"

An artistic rendering of the “Sea-rex” Nothosaur. Image from screenshot from the IMAX film “Sea Rex 3D: Journey to a Prehistoric World”

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.

A small nothosaur fossil displayed at the Fryx Museum in ??? Indiana.

A small Nothosaur fossil displayed at the Fryxell Museum in Rock Island, IL.

Journal Reference:
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

Comments

  1. On (mostly) some marine fossils, I see that YECs are claiming Bill Nye got something wrong at the Ham debate:
    http://www.piltdownsuperman.com/2014/06/fossils-in-wrong-place-thwart-evolution.html
    http://www.icr.org/article/8167/
    (they appear to be saying that ‘living fossils’ manage to ‘thwart’ evolution and evolutionary timescales – and simply point to a catastrophic recent flood ha ha)

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  2. Thanks for writing on this interesting discovery! I did have a question, though, about this passage:

    “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.”

    I am definitely a layperson when it comes to any field of science, but I’m wondering if this statement is a correct inference. Is it not simply possible that the fraction of the fossil record we have explored has just happened to have come upon marine reptiles and we may have discovered most of them already? I ask this not as a challenge but rather to try to better understand. Must it follow that we will find more if we found a bunch already?

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    • It is possible that that we have found many of them already but very unlikely. Several things suggest that there are many more species of marine reptiles than we know about. First, most new fossils found are recognized as new species or even new genera. There are hundreds of genera recognized but most of those genera only are represented by a single species and most of those by a single specimen. if you look around today at living animals you would very hard-pressed to find many genera of animals for which there is only a single living species (humans are one as the only “Homo”). This suggests that many other species existed. Second, since most new finds are recognized as new genera we should expect that more will be found. Imagine a box with 10,000 marbles in it consisting of 1000 different colors and 10 of each color. If you randomly draw out 10 marbles all 10 will probably be a different color. As you continue to randomly draw colors the chance of getting a new color will go down over time. The chances of drawing a new color can be predicted with statistics and so you can ask on the 1000th draw what is my chance of getting a new color. Now we don’t know how many total marine mammals there were but we can use stats to look at the current pace of new finds and how many represent new taxa and predict into the future how many are yet to be found.
      But, there is a problem, we may predict that there will be 10,000 species found but if there were a time in the past when the conditions were very unfavorable for preservation (say an ice age and the oceans were lowered below the continental shelves so that marine reptiles would have much less opportunity to be preserved where they would be found in the future) then we may not find as many as we predict. Of course that works both ways, if there were a 70 million year gap where few fossils were formed then we also wouldn’t be seeing in during that time at all and so they are already missing from out estimate and thus we will be underestimating the total species that lived. Third, the rare nature of fossilization to begin with means that to find individuals of as many species as we have already means that billions of individuals in thousands of species must have existed just to allow to find what we have. Now the YEC has a different expectation, in flood geology essentially every individual alive at the onset of the flood is likely preserved in the record. They dont’ expect gaps in discovery since the whole record is there. Old earth expects there to be massive gaps in the fossil record since many time periods were not conducive to making fossils. I think the pattern of the fossil record is very much as we would expect if there Earth had experienced changing geological conditions over time.

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