Field Museum team helps uncover T. rex of the sea

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Research and planning are often key factors scientists cite when they make a great discovery. Only rarely does being out of shape play a role.

But Field Museum scientist Jim Holstein said being dog-tired after a long day of trekking through a Nevada mountain range led to his find of a new type of prehistoric marine reptile that on Monday was laid out, in fossil form, on a table in the Chicago museum.

The 28-foot-long animal is now known as Thalattoarchon saurophagis, "lizard-eating ruler of the seas," a member of the very successful ichthyosaur family that lived, for the most part concurrently with dinosaurs, for 160 million years.

It died roughly 244 million years ago and is the earliest type of ichthyosaur — and only the second on record — to show signs of being a "superpredator" that ate animals of its own size atop the marine food chain in a manner similar to a killer whale, said Nadia Frobisch, lead author of the paper describing the new species that appeared in Monday's electronic issue of the Proceedings of the National Academy of Sciences.

Before getting its new scientific name, it was known simply as "Jim," after Holstein, who credits his discovery to being the most exhausted of the original search party 141/2 years ago.

He was in central Nevada's Augusta Mountains, returning to camp along a high ridge after a day of searching for fossils in an ancient seabed turned mountainside.

His colleagues, Martin Sander and Olivier Rieppel, were seasoned climbers, cheery as they contemplated dinner. Holstein was not, and was especially tired after a long hot day toward the end of an exhausting expedition.

"They both walked over this animal," Holstein said Monday. "My head hung low."

And because of that he saw in the rock, near some juniper bushes along a wild mustang trail, the skull of the ichthyosaur that, upon closer examination, turned out to have a distinctive feature.

Ichthyosaurs — from the Greek for "fish lizard" — were once plentiful in what is now Nevada. The creature, a reptile that evolved from a land to sea animal and resembled a dolphin, is the official state fossil.

But most had more modest teeth, suitable only for dining on smaller marine life. The teeth of the specimen Holstein found were large and had two cutting surfaces, suggesting it might have killed and eaten other large animals.

Finding a big specimen is one thing. Excavating it is quite another.

"It's very, very difficult terrain, very difficult to get these fossils out of these mountains," said Rieppel, the Field's Rowe Family Curator of Evolutionary Biology.

In addition to that, the trio didn't fully understand the potential significance of what they had found, Sander said in an email. So "Jim" was entered into Sander's field notes for the expedition on July 24, 1998 and essentially forgotten for seven years, when it caught the attention of some of Sanders' students at the University of Bonn in Germany.

"Lars (Schmitz) and I stumbled over the notes that Martin had taken on that last field day ... which said 'large ichthyosaur discovered with cutting edges on the teeth,'" Frobisch, then a University of Chicago postdoctoral scholar who now works at a museum in Berlin, recalled via email.

"This immediately gripped our attention, as there is only one very poorly preserved ichthyosaur known from the Himalaya region to have cutting edges on the teeth."

Sander recalled Schmitz, Frobisch and another student "storming into my office one day and demanding to go" and see this animal.

After a 2005 scientific conference in Arizona, Sander, Frobisch and Schmitz returned to the scene and confirmed the finding. "We knew it was quite likely it was a new taxon," or population group, said Schmitz, who now teaches at the Claremont Colleges in California

The National Geographic Society's Committee for Research and Exploration provided a $20,000 grant to excavate the fossil, a spokeswoman said. An almost monthlong trip in 2008 brought the skeleton, encased in an estimated 3,000 pounds of rock, to the Field, where preparators have been working on separating it from earth since.

The Field hopes to eventually put the relatively intact skeleton on display, Rieppel said, but the top priority has been to examine the most significant parts of the fossil in order to identify it definitively as a previously unknown ichthyosaur.

For now, the head and a roughly 3-foot vertebrae section from near the tail are in a third-floor office at the museum. Chunks of rocks containing other bones rest on an adjacent table.

It looks a little rough. Holstein described the head, flattened and condensed by fossilization, as looking "like a killer pancake right now." But it is a killer pancake with scientific significance.

"Our 'Jim' was the first in a long row of 'T. rexes' of the sea," Sander said. "At the level of the ecosystem, the discovery is important because the presence of a top predator indicates that (roughly) 242 million years ago, 8 million years after the catastrophe (when life on earth nearly ended at the end of the Permian period, 250 million years ago), the modern ecosystems had evolved in the sea. Nothing fundamentally happened since then. The food web remained the same, only the players changed.

"To put it in one sentence, the discovery shows two new things: What the first top predator in the sea was like and how quickly it evolved after the catastrophe."

sajohnson@tribune.com

Twitter @StevenKJohnson

Copyright © 2014, Los Angeles Times
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