Western Interior Seaway facts for kids
The Western Interior Seaway was a huge inland sea that once covered the middle part of North America. It split the continent into two halves for a long time during the mid- and late-Cretaceous Period. This ancient sea was incredibly big: it could be up to 760 meters (2,500 feet) deep, 965 kilometers (600 miles) wide, and over 3,200 kilometers (2,000 miles) long!
How the Seaway Formed
During the Cretaceous Period, sea levels around the world were much higher than they are today. At the same time, the central part of North America slowly sank down. This happened because a large tectonic plate was sliding underneath the continent, pulling the land down with it.
As the land sank, the ocean waters flowed in from both the north and the south, creating this vast inland sea. The seaway came and went a few times during the Cretaceous Period. Scientists believe the water was warm and tropical. This warm water allowed many tiny sea creatures to thrive, leaving behind chalky deposits that give the Cretaceous Period its name. When the seaway became smaller, it was sometimes called the Pierre Seaway.
Amazing Animals of the Seaway
The Western Interior Seaway was a busy place, full of incredible marine life. It was home to giant reptiles that hunted in the water. These included plesiosaurs and mosasaurs, which could grow up to 18 meters (60 feet) long!
Other creatures living in the seaway included:
- Large sharks like Squalicorax.
- The huge shellfish-eating shark Ptychodus mortoni, thought to be 10 meters (33 feet) long.
- Advanced bony fish such as the massive Xiphactinus, which was 5 meters (16 feet) long. This fish was bigger than any modern bony fish!
The seaway also teemed with smaller invertebrates. These included molluscs, ammonites (which looked like coiled snails), and squid-like belemnites. Tiny plankton also floated in the water, including coccolithophores, foraminiferans, and radiolarians.
Even early birds lived around the Western Interior Seaway. One was the flightless Hesperornis, which had strong legs for swimming. Another was the tern-like Ichthyornis, an early bird with a beak full of teeth! These birds shared the sky with large pterosaurs like Nyctosaurus and Pteranodon. Pteranodon fossils are very common, showing they were a big part of the ecosystem, especially in the southern parts of the seaway.
On the seafloor, giant clams called Inoceramus left many fossils. These clams had very thick shells. Scientists think their huge size helped them live in murky waters where there wasn't much oxygen. A large gill area would have allowed them to breathe better.
Related pages
- Sundance Sea (from the Jurassic period)
Images for kids
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Elasmosaurus platyurus in the Rocky Mountain Dinosaur Resource Center
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A broken concretion with fossils inside; late Cretaceous Pierre Shale near Ekalaka, Montana.
See also
In Spanish: Mar interior occidental para niños
