The Western Interior Sea and Kansas Sea

¶ … Western Interior Sea is the name given to the seaway that split the North American continent in the cretaceous period near the end of the age of dinosaurs. Estimated to exist between 65 and 100 million years ago the seaway was relatively wide stretching as far west as Utah and as far east as the western Appalachians, south to the Gulf of Mexico and North into the northern most reaches of Canada. The Seaway serves as one of the most direct examples of the evolution of the earth's geology, as the majority of the region is now relatively arid and yet, the region was underwater for more than all of recorded history. (Everhart 2010) the Western Interior Seaway goes by several names, the Cretaceous Sea and the Kansas Seaway being the most common but all the names are referring to the large, shallow inland sea shown in the graphic below. The seaway is most known in the modern era for the rich fossil examples that are found throughout the region and represent a time shift when the last of the prehistoric dinosaurs existed and the first amphibians and birds began to appear. The rich Paleolithic history of the Western Interior Seaway, also known again as the Kansas Sea and the Cretaceous Sea, leaves a multitude of fantastic examples for modern science to better understand the development of life in the era. (Everhart 96)

The Western Interior Seaway was formed by both high sea levels and platonic movement that forced the central aspect of the continent up, a movement which created the Rocky Mountains. The seaway developed inland and was affected by storm rather than tide movement and was home to thousands of what seem today to be unearthly animal species, specially adapted to deal with the unique environment of the seaway with its limited oxygen supply, shallow levels and heavy silt coated bottom. (Baldridge 190-197) "The Late Cretaceous Western Interior Seaway of North America has an abundant and well-studied record of fossil marine reptiles." (Nicholls & Meckert 1591) Nicholls and Meckert go on to say that the fossil record is so rich in the region that is thought to be the geological home of the seaway that fossil records elsewhere pale in comparison, with a single or just a few recorded finds of certain animal groups, as compared to the thousands recorded in the Western Interior Seaway region. (1591-1592)

It was a shallow sea with diverse marine life including predatory marine reptiles, such as mosasaurs growing up to 18 meters long, ichthyosaurs, and plesiosaurs. There were abundant sharks, such as Squalicorax, and advanced bony fish including Pachyrhizodus, Enchodus, and the huge 18-foot long Xiphactinus, a fish larger than any extant bony fish, and another monster, Ichthyodectes. Other sea life included invertebrates such as mollusks, ammonites, squid-like belemnites, and plankton including coccolithophores that secreted the chalky platelets that give the Cretaceous its name, foraminiferans and radiolarians. The sea was probably less than 600 feet deep in most areas, and had a relatively flat and soft, oxygen-depleted mud bottom fostering fossilzation. One of the more famous fossil sites is the so-called Kansas Chalk (Niobrara chalk formation). Near the middle of the sea in what is now Kansas sediments were deposited at a fast rate creating about an inch of compacted chalk each 700 years. Some of the worlds finest fossils have been discovered here. The crinoid Uintacrinus and fish Ichthyodectes are two examples. (Fossilmuseum.net NP)

When other regions have such finds they are news, while the shelf and chalk deposit areas of the Western Interior Seaway boast finds nearly every digging season, by both hobbyists and professional scholars. While other scholars are quick to point out that marine fossils are abundant the vertebrate fossil record is relatively barren, this is likely due to the significantly fossil bearing conditions of the silt sea bottom and its storm driven record keeping system, where large silt deposits moved rapidly over large areas in short periods of time and created a relative recording of the living and dead creatures in its wake. (Baldridge 58)

The demise of the Western Interior Sea was again a result of regional shifts and changes that resulted in seaway becoming increasingly shallow, losing its connection to the oceans in both the northern and southern aspects of the region, due in part to land shifting as well as ocean recession. When this occurred fresh water lakes, rivers, swamps and streams filled the crevasses and valleys left by the seaway and massive formations of vegetation and other matter collected to create the coal deposits that we mine today and that serve as the majority of energy for nearly the whole of the Midwest and east coast of the U.S. (Brigham 400)