Low tide reveals rare marine reptile fossil find
JULY 2011 - When Ken Olson of The Museum of the Rockies was planning a trip to salvage a plesiosaur fossil from the Charles M. Russell National Wildlife Refuge in Montana -- an experience that would include a mile-and-a-half trek each way through knee deep mud, deerfly swarms and a field of chest-high sweet clover -- he wanted to include one of the world's marine reptile experts.
"I know just the person to lead the expedition to excavate this creature," he said.
He meant Patrick Druckenmiller, the earth sciences curator at the University of Alaska Museum of the North, who is also part of a team excavating plesiosaurs from an island in Norway and who recently helped remove a complete thalattosaur from a rocky underwater outcrop in Southeast Alaska. In May a member of a geological team noticed something on that beach during an extremely low tide.
"It caught my eye," Eugene Primaky said. “I instantly thought ‘fish’ and brushed it with my boot to make sure it wasn’t a branch.” The "fish" turned out to be a prehistoric marine reptile called a thalattosaur. It may be the most complete fossil of
Tongass National Forest geologist Jim Baichtal immediately sent photos to University of Alaska Museum of the North earth sciences curator Patrick Druckenmiller, who went through the process of eliminating what it could be “We know the rocks are about 220 million years old. Based on the age of the rocks and what I could see in the picture, I was 99 percent sure that’s what it was.”
Thalattosaurs are rare, prehistoric marine reptiles. They range in length from between three and ten feet and have long, flattened tails and paddle-like limbs. Some have downturned snouts, like modern lizards. They evolved from land-dwellers and became extinct after the Triassic Period.
Druckenmiller and his museum colleague, Kevin May, traveled to the site in mid-June to collect the specimen from an outcrop near Kake. The location lies in the intertidal zone, so the fossil would only be exposed during extreme low tides. That meant they needed to excavate during a two-day window and would only have four hours each day, when the tide was at its lowest, to retrieve the fossil. If they missed their chance, the outcrop wouldn’t be exposed again until October.
The team used rock saws to hack a series of steps down to the layer of rock surrounding the fossil. On the first day, they were able to complete the excavation just five minutes before the site was submerged. Druckenmiller spotted more bone penetrating the rock, so the team removed an even larger section on the second day, hoping it would contain the rest of the skeleton. “We couldn’t see anything that day,” Druckenmiller said. “We thought, ‘it’s probably here and the animal is probably this long, so we’ll take out a slab about that big.’”
The two rock slabs containing the specimen were placed on a boat and taken back to Thorne Bay, where they were shipped north to Fairbanks. The fossil is embedded in approximately 500 pounds of rock. In early July, the specimen was shipped to the fossil preparation lab at the museum, where the earth sciences team will slowly chip away at the rock until the fossil is exposed, a process that will take many months to complete. Because the tail and hind bones are well-preserved, Druckenmiller hopes to uncover the rest of the skeleton, including the skull.
“It’s reasonably complete and once we reveal more of the skeleton, we will be able to compare it to other thalattosaurs to see if it is a new species,” said Druckenmiller. But even if it is a known species, it will be one of the best specimens ever found in North America and possibly anywhere else in the world. The thalattosaur is currently one of Alaska’s most compete fossil vertebrates.
The animal died in the ocean and then settled into mud at the bottom of the sea floor. The mud eventually turned to rock, entombing the skeleton for nearly 220 million years. Because this preservation of a complete fossil is a rare event, the specimen is a major find. After it is studied and the results are published, the fossil will be available for display at the museum.