Tag Archives: mosasaur

Fossil tells a new tail

Mosasaurs lived in the world’s oceans during the Late Cretaceous, the last Period from the Age of Dinosaurs (see the geologic time scale). They are close relatives of modern snakes and lizards, and during the Cretaceous they become fully aquatic sea monsters, growing to tremendous sizes, and were the top predators of their environments.

Their fossil remains occur in great numbers in the marine chalk deposits of the Central Plains, and numerous specimens have been preserved in museums all over the world (see posts on the chalk formation and on rock formations in general). Yet despite the great numbers of specimens collected, we still have much to learn about these great beasts.

For example, examination of their bones shows that they are elongate animals, with enlarged tails for propelling their bodies through the water. Their limbs are modified into flippers, useful in controlling the direction and orientation of their bodies in the fluid medium. So, it is clear that they are primarily tail-swimmers.

Early restorations based upon this evidence imagined a tail sort of like a modern crocodile, a thick tail that was slightly compressed laterally, making it taller than thick, but remaining relatively snake-like. Early restorations of the skeleton articulated the tail as a long chain of vertebrate, continuous from base to tip without any remarkable difference along the way.

Here is an illustration of the skeleton of the mosasaur Platecarpus from a classic work on mosasaurs (Williston 1898). Note the rod-like straightness of the back.

Mosasaur Platecarpus from Williston

Mosasaur Platecarpus from Williston

And here is an artist’s illustration of Tylosaurus, the largest of the mosasaurs, from Mike Everhart’s Book, Oceans of Kansas, showing the tail with a slight thickening near the end, but mostly being straight (Everhart 2005, recommended in the Boneblogger store).

Mosasaur Tylosaurus

Mosasaur Tylosaurus from Oceans in Kansas by Mike Everhart

However, frequently the skeletons of mosasaurs were found preserved in the rock with the last third of the tail bent downward, away from the main axis of the base of the tail. And this was not just found in a few skeletons, but it was found frequently enough that scientists speculated, at least in conversations with each other, that perhaps the down turned tip was not an artifact of preservation, but maybe meant something.

Well, a newly described mosasaurs fossil, which has exceptional preservation, provides the answer. This specimen collected in Kansas and now at the L.A. County Museum, preserves not only the bones, but also impressions of skin, impressions of internal organs, and even some of the body outline. The bones of the tail are clearly down-turned, giving the authors of this new study enough confidence to state what has been quietly talked about before—mosasaurs had a bi-lobed tail fluke (Lindgren et al. 2010).

Mosasaur Platecarpus

Mosasaur Platecarpus showing revised body outline

It only takes a single fossil to help overturn past notions about prehistoric life. The next big discoveries are out there, in the rocks and sitting in the museum drawers, waiting to be examined in detail. What will we find next?

Everhart, M. J. 2005. Oceans of Kansas: A Natural History of the Western Interior Sea. Indiana University Press, Bloomington.

Lindgren, J., M. W. Caldwell, T. Konishi, and L. M. Chiappe. 2010. Convergent evolution in aquatic tetrapods: insights from an exceptional fossil mosasaur. PLoS ONE 5(8):e11998.

Williston, S. W. 1898. Mosasaurs. University of Kansas Geological Survey 4(1):81-347.

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What is paleontology

What questions fall within the purview of “Paleontology”?

Quite a wide variety, it turns out, because paleontology is the study of prehistoric life – the exploration of the entire history of life. Since 99.9% of all species that existed are now extinct, that is a lot of biodiversity. The science is multifaceted and diverse because the topic is equally diverse.

Because of the connections with geologic time and rock formations as the context of fossils, most paleontology classes are offered through geology programs at universities. I LIKE teaching introductory courses in geology because I find that people frequently end up taking geology in college as a last resort. Students generally are required to take a science class with a laboratory and they too frequently review their options without much enthusiasm. They took biology in high school and did not like it then, so want to stay away from that now. Chemistry and physics sound like a lot of math, so that leaves geology, they reason.

Fossil collecting in western Kansas. A partial mosasaur skeleton is visable in the middle foreground.

Fossil collecting in western Kansas. A partial mosasaur skeleton is visible in the middle foreground.

On the first day of geology class I like to point out that the study of the Earth and its history involves biology, chemistry, and physics, so we will cover them all. There is usually a little moan from the class at this, and I enjoy my moment of sadism. Paleontology in particular incorporates biology and geology to a very high degree, because to study fossils you have to fully understand the animals as well as the history that you can read from the rock record.

So could we come up with a classification, not of fossils, but of paleontologists?

Since the topic is so multifaceted the science falls naturally into several key areas. For example, individual paleontologists tend to be more oriented toward either geology or biology. The first group might be more interested in the animals themselves: how did they live; how did they move and capture prey; how did they relate to other organisms in their environment.

The second group might be more interested in what the animals can tell them about the Earth’s history: what do the fossils tell us about the movement of plates over the Earth’s surface through time; when did different animals live in geologic time so we can estimate the age of rocks; that sort of thing.

Of course, this is an over simplification.

Paleontologists can also be classified by which group of organisms they work with. Is it plants (maybe fossil forests made of ferns), or invertebrates animals — marine or terrestrial – ranging from the largest squid ever known to fossil spiders, or maybe vertebrate animals.

A lot of the people I know are paleontologists, and they tend to be people with diverse interests, often ending up doing a bit of all of it. For example, many years ago I worked on a fossil locality in southwestern Kansas that included plant, invertebrate, and vertebrate fossils. Having all the groups of organisms was critical to interpreting a much fuller picture of the ancient environment there than any one of the groups alone could have provided.

As a paleontologists I must be a “jack of all trades,” and that is one of the things I love most about it.

Other interesting facts can be found here at Boneblogger. Enjoy.

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