It's taken 64 years to for scientists to be sure, but they have finally determined that bones found on the North Slope of Alaska's Brooks Range are those of an ichthyosaur, a giant marine reptile from the time of the dinosaurs.
In a paper published Nov. 25 in the Journal of Vertebrate Paleontology, researchers offer positive identification of the fossil. They further note that fragments found in the vicinity of the animal's stomach provide important information about its diet.
Similar in form to a modern dolphin, the ichthyosaur swam in seas north of the Arctic Circle during the late Triassic Period, about 210 million years ago, said Patrick Druckenmiller, the University of Alaska Museum of the North curator of earth sciences and lead author of the paper.
The skeleton was found in 1950 by a team of U.S. Geological Survey geologists east of Cutaway Creek in Howard's Pass, 170 miles south of Barrow in what is now the National Petroleum Reserve-Alaska.
The discoverers had a pretty good idea of what they were looking at, said Druckenmiller. "They said to themselves: 'Big bones in the Triassic Period. Only one group of animals lived in the ocean at that time.' But that was based on context, not on an analysis of the bones."
There were other possibilities, he said, like a different group of marine reptiles or a dinosaur carcass that washed into the ocean.
A brief note about the fossil was published in the 1970s, but the inability of paleontologists to closely inspect it in a laboratory meant its identity remained uncertain.
In 2002 Roland Gangloff, the museum's earth sciences curator at the time, arranged for the U.S. Army to fly a Chinook helicopter to the site as part of a training mission. Members of B Company, 4th Battalion, 123rd Aviation Regiment at Fort Wainwright, popularly known as the "Sugar Bears" moved the bones in a 12-foot-long slab of rock, encased in protective plaster, to Fairbanks.
"It wasn't until it was actually collected and brought back here that I was able to look at the anatomy," Druckenmiller said.
Cleaning started in 2007. The skull and flippers were missing, but the torso was sufficiently intact to allow identification. Druckenmiller called it the largest and most complete of the three ichthyosaur skeletons found so far in Alaska and definitely the farthest north.
"It would have been a neat find just being a big ichthyosaur from the Brooks Range," he said. "But what makes it significant in terms of global paleontology is that it had gut contents. We could see what it had for its last meals."
Druckenmiller's coauthors included Neil Kelley, an expert on Triassic ichthyosaurs and their prey from the University of California, now at the Smithsonian Institute. Joseph Carter, with the University of North Carolina, a specialist in shell microstructure, confirmed that shell particles found with fish bone fragments were from extinct nautilus-like invertebrates known as ammonites. Michael Whalen of UAF's Department of Geosciences and Christopher McRoberts of the State University of New York analyzed the rock layers in which the fossil was found.
The fragments of bone and shell were in the location of the digestive tract. None were found outside the ichthyosaur. Their identification, in particular, may stir up fresh thinking. "There's a rare example of one from China where they found gut contents that suggested it ate invertebrates off the sea floor," Druckenmiller said. "What we found was that these animals were feeding in the open ocean on free-swimming ammonites and fish."
Based on their shell identification, the paper's authors say, "a re-examination of the mollusk fragments associated with (the Chinese ichthyosaur) is warranted."
In later generations ichthyosaurs became more specialized, Druckenmiller said. They were "teuthophagous," that is, subsisting on soft-bodied squid-like creatures. Many appear to have been toothless. Without the skull, it's impossible to know what kind of teeth, if any, the Alaska animal had.
Nor can it be determined whether the sea-going reptile lived year-round in the Arctic or migrated south during the winter like bowhead whales do. But large modern whales provide a good analogue to the ancient marine vertebrates. Ichthyosaurs, like whales, needed air to breath. Some are known to have given live birth. There is speculation that they may have had warm blood. With a sharp nose and dorsal fin, it strongly resembled a porpoise.
Some reached 50-60 feet or longer. "It was a big animal," Druckenmiller said. "Like modern whales, they probably had to cover a lot of (territory) to gather enough food."
The newly identified fossil will be featured in the museum's new "Expedition Alaska: Dinosaurs" exhibit scheduled to open next year.
"Technically, an ichthyosaur is not a dinosaur," Druckenmiller said. "But they were contemporaries and we want to show people what was up here during the age of dinosaurs."