100 million-year-old crabs found in a 97-year-old shell

A microscopic crab preserved in amber dating back 100 million years has been found more than 1,000 miles south of the Arctic Circle and only a hundred miles from the caldera of ancient Mount…

100 million-year-old crabs found in a 97-year-old shell

A microscopic crab preserved in amber dating back 100 million years has been found more than 1,000 miles south of the Arctic Circle and only a hundred miles from the caldera of ancient Mount St. Helens.

The discovery was made on that fossilized shell in February, at a site known as the St. Helen Site. It comes from the class of protozoan described as the paleontology equivalent of the da Vinci butterfly.

The little crustacean was about the size of a human thumb and weighed about a pea, said Dana J. Geopelis, curator of invertebrate paleontology at the Smithsonian’s National Museum of Natural History and lead author of a paper describing the fossil just published in the journal Plos One. It lived about 70 million years before the dinosaurs disappeared and grew about 7 inches in length.

The creature was spotted about four years ago by a scientist studying the large marine shells collected by amateur paleontologists from beaches in Oregon and Washington state. But it took time to identify it as a new species, and to figure out where it lived — a spot close to where hundreds of millions of years ago the confluence of two tectonic plates gave birth to the Great Basin.

Among other things, scientists think the tiny crab — known formally as “Holmino aerie –a, albeit little — lived in an ecosystem that included some fairly odd creatures such as the “flemish groove,” a carbon-rich soup of insects, crustaceans and other critters formed by crustaceans rubbing the remains of their mollusks against one another.

All of that marine life living 100 million years ago was buried by volcanic eruptions in the Cretaceous period, about 65 million years before the mass extinction event that rendered the dinosaurs extinct.

But don’t expect to see any giant scorpions or mosquito-eating wasps in the amber photos. The size of the creature was unusual for protozoa of this class, and the evidence so far is that the crab was deceased at the time the tissue was collected, Geopelis said.

“If you move through that cyst, that tissue is well preserved,” Geopelis said. “That means you’re not going to see microscopic pustules that were alive when the egg sac was fully formed.”

But even if the species is gone, its remains are certain to make a splash in the world of palaeontology. Its fossils are “an interesting new thing to look at” and “should attract a lot of attention,” said David Hisey, a curator at the New Mexico Museum of Natural History and Science who is not involved in the study.

The ancient crab found in Oregon and Washington was close enough to be a living, breathing creature, a very strange thing for an invertebrate to be. Geopelis suspects the little guy made it into the amber before it died, but probably died in a much more organic state.

That’s a massive contrast to the comical protozoa pictured in the textbooks and found today in single-celled life forms in nutrient-rich lakes. And while scientists have found most of them in caves, they’ve yet to find anything like this one, which is a good thing, says Geopelis.

“When we look at fossil crayfish of this period, we find in every location crayfish that are solid,” Geopelis said. “These critters are burrowing down into soft shells. But the little crab, it’s totally preserved alive.”

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