Western Interior Seaway – Found World Media

FIELD NOTES
Date: Cretaceous Period
Site: Western Interior Seaway
Subject: Giant Squid
Participants: C. Monroe

Millions of years ago, North America was split in two by a shallow sea known as the Western Interior Seaway. Throughout the Cretaceous Period, this sea was warm, nutrient-rich, and full of life. Sharks, fish, plesiosaurs, and ammonites shared the water with another, more mysterious creature: the giant squid.

Very little is known about the giant squid that lived in the Western Interior Seaway. Unlike fish and ammonites, squid do not have hard bones or shells that easily fossilize. This means that most of a squid’s bulk will rot away before any fossilization can occur. However, two squid body parts are tough enough to enter the fossil record. The first is the squid’s hard, birdlike beak. The second is a spoon-shaped structure known as the gladius, which helps support the mantle, or body, of the squid. Based on these two body parts, scientists have tried to figure out what an ancient squid would have been like.

Because paleontologists have very little evidence to work with, they don’t always agree with each other! Some scientists believe that the ancient squid known as Tusoteuthis might have been up to twenty-five feet long. Others think it was shorter and squatter, perhaps only about eleven feet long. Some paleoartists – artists who draw scenes from the Mesozoic Era – have created pictures that show giant squid fighting with other Cretaceous marine monsters, like mosasaurs. Others point out that there’s no evidence battles like that ever happened!

There is one thing all scientists do agree on: there were squid in the Western Interior Seaway, and they were large. As more fossils are found, who knows what new discoveries they might make?

Marginal comment: The only way to know for sure what the giant squid of the Cretaceous were like would be to go back and take a look at one…

Want to learn more? Check out these sources!
http://www.prehistoric-wildlife.com/species/t/tusoteuthis.html
https://www.wired.com/2012/08/giant-squid-vs-mosasaur/ (content warning: mild language)

FIELD NOTES
Date: Cretaceous Period
Site: North America
Subject: The Western Interior Seaway
Participants: C. Monroe

In the Cretaceous Period, North America looked very different from what we know today. The middle of the continent was covered by a shallow sea that connected the Gulf of Mexico in the south to the Arctic Ocean in the north. This means that states like Colorado, Wyoming, Nebraska, and Kansas used to be entirely underwater! Scientists call this sea the Western Interior Seaway, or the North American Inland Sea.

The sea was formed when the Rocky Mountains began to rise. The motion that caused the mountains to rise also caused land east of the mountains to dip. Because the planet was very warm at the time, there was no ice at the poles and sea levels were much higher. The high water flowed into the dip and split North America in two.

Because the sea was so shallow – only about 2,500 feet deep – it was very warm and full of life. The bottom of the sea contained little oxygen, which means that animals who died there were easily fossilized. Scientists have found fossils of huge marine reptiles like plesiosaurs and mosasaurs, as well as giant bony fish, huge clams, and turtles the size of cars! They have also found evidence of cartilaginous animals, like giant sharks, which are not normally fossilized. Some of the most spectacular fossil finds in the world have been found in the area that was once covered by the Western Interior Seaway.

What happened to the Western Interior Seaway? At the end of the Cretaceous Period, Earth underwent sudden cooling, likely due to the same massive asteroid strike that ended the time of the dinosaurs. As water began to freeze at the poles, sea levels fell. Eventually, the Western Interior Seaway dried completely, leaving the flat, dry land we know today.

Marginal comment: Scientists have also found evidence of giant squid in the Western Interior Seaway.

Want to learn more? Check out these sources!
https://www.realclearscience.com/blog/2019/10/26/what_lived_in_north_americas_ancient_inland_sea.html
https://www.cretaceousatlas.org/geology/