Marine Reptile Fossil Exposed at Low Tide
It is an apt location to find the fossilised remains of a 220-million-year-old marine reptile, in the inter-tidal zone of a rock strewn beach After all, marine reptiles were very much at home in the sea, although many types did return to the land to lay eggs, to bask in the sun and so forth. However, for one team of dedicated researchers having to extract what could be the best preserved fossil of a thalattosaur ever found in North America meant a tricky job with time and tides against them.
Thalattosaurs were a group of diapsid, marine reptiles known from Middle and Upper Triassic aged strata. These animals superficially resembled monitor lizards, but they were not closely related to modern lizards (Order Squamata). Their fossilised remains have been found all over the world – North America, Europe and China, a number of families have been identified although their taxonomic relationship to other marine reptiles such as the ichthyosaurs remains uncertain. Some of thalattosaurs (the name means “ocean lizards”) grew to lengths in excess of 4 metres. Finding an almost complete fossil skeleton of such a creature is an extremely rare event.
Scientists believe that the thalattosaurs evolved from terrestrial reptiles, but adapted to an aquatic life style. Gradually the skulls become longer and the chests deeper as these creatures evolved.
Working in very difficult conditions, Ken Olson (Museum of the Rockies) realised that he and his colleagues would need some more expert help if fossils of rare marine reptiles were to be recovered from the intertidal zone. He turned to Patrick Druckenmiller, (Earth Sciences Curator at the University of Alaska Museum of the North), who had recently been involved in a project to excavate plesiosaur fossils in Norway. In May of this year, an intriguing vertebrate fossil had been noticed partly exposed out of rock, but to excavate this specimen would be difficult due to the fact that for most of the time the fossil was covered in sea water, the site only being exposed at very low tides.
Tongass National Forest geologist Jim Baichtal immediately sent photographs to University of Alaska Museum of the North Earth Sciences Curator Patrick, 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.
Druckenmiller and his museum colleague, Kevin May, travelled to the site in mid-June to collect the specimen from the semi-exposed outcrop near the small Alaskan town of Kake. The location lies in the intertidal zone, the tide problem 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, (Spring tide) to retrieve the fossil. If they missed their chance, the outcrop wouldn’t be exposed again until October (the next period of extremely low tides at which the fossil would be exposed again).
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, 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 slabs of rock, weighing over 200 kilogrammes between them were transported by boat to Thorne Bay, from there, they went onto to the fossil preparation laboratory at the museum. It will take many months to reveal the rest of the skeleton but the researchers are optimistic that they have recovered an large portion of the fossil, including skull material.
Patrick went on to state:
“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.”
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.
After the specimen has been prepared and formally studied and the results published, the fossil will be available for display at the museum.