21 JUNE 2007
You glide across the ice and wrench your back, and you might wind up in a CT scanner.
You glide through the air above a lake, miscalculate the distance to the tree where you intend to perch, and drop into the water and drown. If you are an ancient, four-legged, two-winged reptile, and have the patience to wait, say, 220 million years, you might also wind up in a CT scanner -- assuming your health insurance is paid up.
Courtesy Tim Ryan, Center for Quantitative Imaging, Penn State University.
This month, the Journal of Vertebrate Paleontology carries a report of a new species of four-legged reptile that apparently ate insects living on trees, glided between trees, and sported an unusually long neck. Two specimens, recovered from a quarry on the Virginia-North Carolina border, have been saddled with the moniker Mecistotrachelos apeoros. In Greek, that means something like "gliding, long-necked reptile," but we can't pronounce the name any better than you, so with apologies to Linnaeus, we'll call this long, lizard-like creature "Long Liz."
Even stranger than Long Liz's gawky neck and clunky name, however, is the technique used to get a peek at her: X-rays in a CT scanner. Her fine bones were crushed flat and trapped in a thin layer of rock in a quarry, says Nick Fraser of the Virginia Museum of Natural History, and the standard techniques for extracting fossils from rock either failed or damaged the fossils.
Courtesy Karen Carr.
Long Liz almost never made it into the CT scanner, however, as she was a fairly unflashy fossil. While Fraser was collecting with Paul Olsen of Lamont Doherty Earth Observatory in 1994, he noticed a subtle fossil, but even though Fraser thought he saw part of a leg, the pair figured the fossil was probably a common, ancient fish called the coelacanth (this antique oddity survives in the oceans, and is often considered the most ancient living animal).
In 2003, at the same quarry, Fraser noticed a flat rock that was about one-quarter inch thick. "I was prepared to toss it over my shoulder when the sun caught it with a raking light, I could see these ridges, and I thought it was a coelacanth, so I kept it," he says. "At the end of the day, I looked again, and thought, 'This tail's got a neck and a skull. This is not a fish. This is a gliding reptile!'"
Why gliding? Because Long Liz had an array of long, arched bones that were obviously part of wings, he says. Why gliding? Because there was no attachment point for the strong muscles that flapping wings require.
Before Long Liz could get a proper scientific name, however, she had to be described, and the fossils refused to be removed from the rocky matrix. "Something peculiar was going on in the depositional environment that probably has been the factor that allows this fantastic preservation," Fraser says, "but at the same time, it makes it very difficult to prepare these fossils, because you can't get the sediment off the surface of the bone. If we couldn't get them out, what would we ever be able to do with them?"
Enter Penn State's industrial-strength CT scanner, which has been used to view the detailed structure of batteries, rocks and fossils. While the instrument functions much like a doctor's CT scanner, Penn State research associate Tim Ryan says it can see much finer detail. In anthropology, Ryan's specialty, the scanner has been used to look at primate fossils and at an arrow wound in a human knee.
Courtesy Tim Ryan
The scans revealed plenty of detail on the crushed and flattened fossil (luckily for science, the corpse was not disturbed by scavengers while protective sediments gathered around it). The CT scans revealed "a beautiful hind foot," says Fraser. While a typical reptile-like animal from this time [220 million years ago] has long toes and large back limbs, "These had fairly short back feet, preserved in a hooked posture, which you never see in reptiles." The hook suggests a purpose: grasping and climbing trees.
The new article, describing research funded by the National Science Foundation and the National Geographic Society, introduces Long Liz as a new genus and species. The glider is apparently a protorosaur, which Fraser describes as "a bizarre group of animals, mostly from the Triassic, that lasted about 50 million years." Long Liz's closest known relative is Tanystropheus, whose fossils, found in Switzerland and Northern Italy, show a 12-foot-long animal with a 6-foot neck. "This is a bizarre, drain-cleaning animal with the long neck that is fairly characteristic of the protorosaurs," says Fraser.
Only one genus of four-legged, winged reptile is known to survive: the Draco, which lives in the rainforests of Malaysia and Thailand.
Eventually, Long Liz could play a role in sorting out the lineage of the dinosaurs and the pterosaurs -- the flying reptiles that ruled the skies while the dinosaurs clambered about at ground level. The exact lineage of the dinos and pteros is "a can of worms," Fraser says. "Conventional wisdom says pterosaurs and dinosaurs share a common ancestor, but we don't know what it was. There is a possibility that protorosaurs are related to pterosaurs, in which case, the pterosaurs and dinosaurs are more distantly related than conventional wisdom says. That would be a major change in our understanding, but we are a long way from that point." Maybe after a few more CT scans, we'll know the relationship between the dinos, the pteros, and the drain-cleaning reptiles. Long Liz: hold on to your health insurance card!
-- David Tenenbaum
• A New Gliding Tetrapod (Diapsida: ?Archosauromorpha) from the Upper Triassic (Carnian) of Virginia, N. C. Fraser et al, Journal of Vertebrate Paleontology, 27(2):261-265, June 2007.