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Meet the marine life of the Sundance Sea

Mission Jurassic is officially underway, with top paleontologists from around the world working together within the Jurassic Mile in Wyoming to find and excavate fossils and learn more about life in the Jurassic Period. Here’s a closer look at some of the prehistoric animals the Mission Jurassic team hopes to uncover.

Meet the marine life of the Sundance Sea

The Sundance Sea was a large inland sea in North America, which was a new continent at the time. It was in this area where the Western United States and Pacific Northwest are today. It formed around the middle of the Jurassic Period, then periodically advanced and retreated until it receded into the ocean for good in the late Jurassic. The Sundance Formation, where paleontologists have found fossils from the Sundance Sea, is slightly older than the Morrison Formation, where they have found fossils of dinosaurs and other land animals. This means that while the Jurassic Mile team may find fossils of both land animals and sea animals, the two didn’t live during the same time period.

Much like today, there were many different kinds of marine animals in the Jurassic Period. In the Sundance Sea in particular, paleontologists have found evidence of fish, sharks, and ammonites, which were shelled mollusks similar to the modern-day nautilus. Some of the animals that lived in the Sundance Sea are:


Ophthalmosaurus - artist rendering

Ophthalmosaurus (“op-thal-mo-sore-us”) was an aquatic reptile, or ichthyosaur, that looked a little like modern-day dolphins. It could grow to 20 feet long and weigh up to 2 tons. Its name, which means “eye lizard” in Greek, comes from its unusually large eyes –up to 9 inches across! It had bony rings around its eyes to keep them in place under high pressure, which means those gigantic eyes may have helped it catch prey in deep water where there wasn’t much light. This ability to dive into deep water may also have helped it to avoid larger predators.

Unlike some predators that had rows of sharp teeth, Ophthalmosaurus had more rounded, cone-like teeth. Its long jaws helped it catch its prey, made up of mainly fish and squid.

There were lots of different types of ichthyosaurs during the Jurassic, but Ophthalmosaurus is the only one that has been found in the Sundance Sea so far.


Gryphaea fossils - "Devil's toenails"

A fossilized shell named Gryphaea (“gry-fee-ah”) is particularly prominent in the area around the Jurassic Mile. Sometimes called “devil’s toenails,” Gryphaea were a type of oyster that lived in the Jurassic period. They first appeared all the way back in the Triassic Period, around 230 million years ago, and lived until the Paleogene period, about 23 million years ago. However, their population was highest during the Triassic and Jurassic Periods.

As a bivalve, Gryphaea was made up of two halves: the larger gnarly-shaped shell called the “toenail,” which sat in the mud on the sea floor, and a smaller, flattened shell called the “lid.” The soft part of the animal lived between the two shells and fed on tiny food particles in the water. It often fed in large groups in shallow water. Aside from the Sundance Formation in the Western United States, where the Jurassic Mile is located, Gryphaea specimens have also been found in parts of England and Scotland, where they were once believed to cure arthritis!


Pachteuthis - artist rendering

Pachyteuthis (“pack-e-tooth-is”) was a belemnite, or squid-like animal, that lived during the Jurassic Period. It was a fast-moving carnivore, using tiny hooks on its tentacles to ensnare prey like small fish and crustaceans. But it wasn’t the only predator in the Jurassic seas—if it wasn’t careful, a Pachyteuthis could easily become a snack for an ichthyosaur!

Mission Jurassic is a $27.5-million project that will be brought to life through the generosity of donors. Donate now on our website, or for extraordinary naming opportunities check out our Mission Jurassic Field Guide or contact Amy Kwas at 317-334-4608 or AKwas@childrensmuseum.org.