Scientist at Work Blog: Fossils in the First Days

Randall Irmis, curator of paleontology at the Natural History Museum of Utah and an assistant professor at the University of Utah, is investigating the rise of dinosaurs in southeastern Utah.

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Tuesday, Aug. 28

Several days after arrival, our team is now firmly settled among the 220- to 200-million-year-old rocks of the Chinle Formation, south of Moab, Utah. Even in the short amount of time we?ve been here, we?re already beginning to tease fossil discoveries out of the rocks.

One of our first priorities this field season was to further investigate a site that was discovered last year. This fossil locality contains the remains of a phytosaur ? a reptile that looks like modern alligators and crocodiles but is only distantly related.

This similarity is an excellent example of what evolutionary biologists and paleontologists call ?evolutionary convergence,? where two groups of organisms separately evolve a similar appearance (for example, bats and birds).

Phytosaurs dominated freshwater aquatic environments during the Late Triassic era (235 to 201 million years ago) in North America, and are one of the more common vertebrate fossils that we find in the Chinle Formation. This particular site preserves jaws and teeth that need to be extracted for preparation and study.

Because fossils are fragile, we try to leave them encased in rock when we remove them from the field; they can then be carefully exposed and stabilized later in the lab.

We encase this fossil-filled rock with plaster-soaked burlap to make sure that it doesn?t fall apart in transport, with an intervening layer of paper towel or toilet paper to ensure that the plaster doesn?t stick directly to the fossil. In the past two days, we?ve successfully removed many teeth and jaw bones from the site.

Our discoveries aren?t limited to phytosaur bones. Recent fossil finds include fish jaws, footprints of early dinosaurs and other reptiles, and bony armor from aetosaurs.

It?s this last group of animals, the armadillolike reptiles I mentioned in an earlier post, that we think might provide evidence for the climate story we?re hoping to uncover.

As we find more fossils, we?re beginning to see that nearly all of the aetosaur fossils are from the oldest rock layers. Could this indicate that as the climate changed through time, the area became less hospitable for aetosaurs? Or is it simply a preservational artifact, where aetosaur bones are less likely to be preserved in the younger rocks?

To answer this question and others about environment, we?ll be looking closely at the rocks themselves, to see what clues they might provide. We know that these sediments were deposited by streams and rivers. But details visible in the rocks can tell us whether these rivers or streams changed in size through time, and whether they flowed throughout the year or were seasonal like the ephemeral washes in the American Southwest today. These types of data are often just as important as the fossils themselves in understanding ancient ecosystems.

This research is supported by a grant from the National Geographic Society?s Committee for Research and Exploration, and is conducted with research permits from the Bureau of Land Management.

Source: http://scientistatwork.blogs.nytimes.com/2012/08/31/fossils-in-the-first-days/?partner=rss&emc=rss

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