Story last updated at 7/13/2011 - 2:38 pm
A significant fossil discovery in the Alexander Archipelago of Southeast Alaska should help scientists better understand events that took shape early in the time of dinosaurs.
The entombed bones and vertebra are almost certainly part of a Thalattosaur, an enigmatic marine reptile that swam in the tropical waters surrounding the supercontinent Pangea during the late Triassic period of the Mesozoic era, 200 to 230 million years ago. According to Jim Baichtal, geologist for the Tongass National Forest, although a few fossil fragments of Thalattosaurs have been found in the same area previously, this marks the first articulated fossil of its species found in Alaska.
Researchers at the site were impressed that the fossilized skeleton survived intact, given the unfavorable environment for fossils of the volcanic atoll where the marine reptiles had lived long ago in equatorial waters. After the Thalattosaurs died off, intense continental and oceanic tectonic plate activity took place, which eventually converged to slam the fossil laden landmass into North American. Thus the islands where the new discovery lies were born.
Baichtal - along with Sue Karl, geologist for the U.S. Geological Survey in Anchorage, and Jane Smith, Gene Primaky and Linda Slaght with the Forest Service Heritage Program in Petersburg - had been working and camping around the area near Keku Islets. In mid-May they took advantage of the minus tides to monitor a site which had previously yielded fossil vertebrates. Suddenly, in an understated comment, Gene Primaky called out, "Jim, is this anything?"
Upon inspection, Baichtal was more than pleased to see that the object in question was indeed something, and the small cadre of scientists hurried over to inspect the auspicious find. It was obviously a choice specimen, and the odds of finding a complete intact section on an exposed layer of rock in a place where the tide only occasionally leaves it uncovered was amazing. How many more fossils might lie inside the sedimentary layers?
"I just was thrilled!" Sue Karl said later, as we admired the excavated fossil in Baichtal's garage.
Thalattosaurs were similar to iguanas but more streamlined, with a more pointed head. They were thought to average around six feet in length or less. Teeth indicate a probable diet of fish, ammonites, squid, hard-shelled animals and other marine reptiles. Fossils of Thalattosaurs have been discovered at sites around the world, including in Nevada, California, Oregon, British Columbia, Austria, Italy and Switzerland. In China several complete skeletons have been located in the last decade.
Dr. Pat Druckenmiller, Earth Science Curator at the University of Alaska Museum in Fairbanks, was contacted regarding the excavation of the notable fossil and agreed it should be recovered soon. In mid-June Dr. Druckenmiller and Kevin May, paleontologist and operations manager for the museum, arrived on the scene and, assisted by Baichtal and others, prepared for the exciting, yet somewhat tedious, removal process.
Because there was a very good chance that more of the skeleton was still intact inside the dark gray calcareous shale and limestone adjacent to the tail section, a large portion of rock was targeted for removal. The first step was to pop the top off the overhanging ledge and lift it off. To cut the layers of rock free, the team used STIHL Cutquik Professional Cut-Off Machines with 14-inch diamond saw blades. Since the guard on the saw restricted placement, workers had to start cutting top slab layers way back and above the fossil, removing each slab section as they worked their way down in steps. Dust filled the air until the incoming tide poured in and effectively impeded further progress. A slab containing the original discovery was recovered after five hours of excavation. Bones were visible in the adjacent slab and plans were made for a second day of excavation.
The next day the researchers did not stop sawing for another five hours, but it finally paid off. The second fossil-bearing slab came free just as the tide again covered the site. The chilly, misty Southeast Alaska weather couldn't dampen the crew's spirits. With the fossils successfully removed and secured for transportation, the exhausted crew felt gratified. Along with the Thalattosaur fossil, numerous impressions of the bivalves Halobia sp. were present. These mollusks dated the fossils to the middle Norian age in the late Triassic period.
Significant fossil remains of the marine reptile Ichthyosaur (literally, "fish lizard"), dating from the Triassic, Jurassic and Cretaceous periods of the Mesozoic era, have been successfully excavated in two locations of Southeast Alaska in recent years. These reptiles swam the oceans as dinosaurs walked on land, actually appearing slightly earlier than most dinosaurs, and looked somewhat like dolphins.
What will become of the Thalattosaur fossil now? It has been shipped to the University of Alaska Museum in Fairbanks where Dr. Druckenmiller and staff will process the slabs with x-rays, hydrofluoric acid and micro-sandblasters. It is hoped more significant fossil remains can be isolated from inside the slabs with the remaining part of the skeleton. Eventually, images and casts of the fossil will be shared with the public.
It's difficult to think in terms of hundreds of millions of years, but the evolution of life can be learned from evidence contained in something as basic as a rock. Given the amazing, diverse life forms that have existed on planet Earth, adaptation to environmental changes has shaped the characteristics of the survivors. We have only to be able to read and interpret the fossil message.
Carla Petersen writes from Prince of Wales. She may be reached at firstname.lastname@example.org.