The Dinosaurs and Prehistoric Animals of Washington

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Which Dinosaurs and Prehistoric Animals Lived in Washington?

columbian mammoth
The Columbian Mammoth,a prehistoric animal of Washington. Wikimedia Commons

For much of its geologic history — stretching all the way back to the Cambrian period, 500 million years ago — the state of Washington was submerged under water, which accounts for its relative lack of dinosaurs or, for that matter, any large terrestrial fossils from the Paleozoic or Mesozoic eras. The good news, though, is that this state sprang to life during the latter part of the Cenozoic Era, when it was traversed by all sorts of megafauna mammals. On the following slides, you'll discover the most notable dinosaurs and prehistoric animals discovered in Washington.

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An Unidentified Theropod

washington dinosaur
The dinosaur bones discovered in Washington. University of Washington

In May of 2015, field workers in Washington state's San Juan Islands discovered the partial remains of an 80-million-year-old theropod, or meat-eating dinosaur — the same family of dinosaurs that includes tyrannosaurs and raptors. It will take a while to conclusively identify this first-ever Washington dinosaur, but the discovery raises the possibility that the northwestern United Sates was teeming with dinosaur life, at least during the later Mesozoic Era.

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The Columbian Mammoth

columbian mammoth
The Columbian Mammoth, a prehistoric animal of Washington. Wikimedia Commons

Everyone talks about the Woolly Mammoth (Mammuthus primigenius), but the Columbian Mammoth (Mammuthus columbi) was even bigger, albeit lacking that long, fashionable, shaggy coat of fur. The official state fossil of Washington, the remains of the Columbian Mammoth have been discovered all over the Pacific northwest, to which it immigrated hundreds of thousands of years ago from Eurasia via the newly opened Siberian land bridge.

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The Giant Ground Sloth

The Giant Ground Sloth, a prehistoric animal of Washington. Wikimedia Commons

The remains of Megalonyx — better known as the Giant Ground Sloth — have been discovered all across the United States. Washington's specimen, dating to the late Pleistocene epoch, was unearthed decades ago during the construction of Sea-Tac Airport, and is now on display at the Burke Museum of Natural History. (By the way, Megalonyx was named in the late 18th century by future president Thomas Jefferson, after a specimen discovered near the East Coast.) 

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Menoceras, a close relative of Diceratherium. Wikimedia Commons

In 1935, a group of hikers in Washington stumbled upon the fossil of a small, rhinoceros-like beast, which became known as the Blue Lake Rhino. No one is quite sure of the identity of this 15-million-year-old creature, but a good candidate is Diceratherium, a double-horned rhinoceros ancestor named by the famous paleontologist Othniel C. Marsh. Unlike modern rhinos, Diceratherium sported only the tiniest hint of double horns, arranged side-by-side on the tip of its snout.

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Aetiocetus, a close relative of Chonecetus. Nobu Tamura

A close relative of Aetiocetus, a fossil whale from neighboring Oregon, Chonecetus was a smallish prehistoric whale that possessed both teeth and primitive baleen plates (meaning it simultaneously ate large fish and filtered plankton from the water, thus making it a true evolutionary "missing link."). Two specimens of Chonecetus have been discovered in North America, one in Vancouver, Canada and one in Washington state.

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Trilobites and Ammonites

A typical ammonite, of the type that have been discovered in Washington State. Wikimedia Commons

An essential part of the marine food chain during the Paleozoic and Mesozoic eras, trilobites and ammonites were small- to medium-sized invertebrates (technically part of the arthropod family, which also includes crabs, lobsters and insects) that have been preserved especially well in ancient geologic sediments. The state of Washington boasts a wide assortment of trilobite and ammonite fossils, which are greatly prized by amateur fossil hunters.  

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Strauss, Bob. "The Dinosaurs and Prehistoric Animals of Washington." ThoughtCo, Aug. 25, 2020, Strauss, Bob. (2020, August 25). The Dinosaurs and Prehistoric Animals of Washington. Retrieved from Strauss, Bob. "The Dinosaurs and Prehistoric Animals of Washington." ThoughtCo. (accessed March 20, 2023).