Museum of the North Reports Thalattosaur Fossil Find

. July 30, 2011 . 0 Comments

The Museum of the North at the University of Alaska reports a member of a geological team working in Southeast Alaska chanced upon a find during an extremely low tide.

Something caught team member Eugene Primaky’s eye. “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 fossil of a prehistoric marine reptile called a thalattosaur. It may be the most complete fossil of its kind found in North America.


Photo by Patrick Druckenmiller. An extreme low tide near Kake in Southeast Alaska in May revealed the tail of a thalattosaur fossil.

Tongass National Forest geologist Jim Baichtal immediately sent photos to University of Alaska Museum of the North earth sciences curator Patrick Druckenmiller.

“Then we went through the process of eliminating what it could be,” Druckenmiller said. “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 at the end of 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.
“This is the best preserved and the most articulated specimen of Triassic reptile I have been involved with,” Baichtal said. “Out of this experience, we have developed a relationship with the museum and will be looking for both research and education opportunities throughout the Tongass National Forest.”

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, Druckenmiller said 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 complete 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.

www.uaf.edu/museum

Category: Natural History

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