Kansas Submerged! Western Interior Sea Transgression as Polar Ice Melted, Elevating Sea Levels Worldwide

In his zealously-written and deeply-researched book titled “Oceans of Kansas”, Michael J. Everhart jolts sensibilities with the astonishing reality that Kansas and most of the Midwest was once submerged by a vast warm inland seaway as large as the Mediterranean Sea is today. (1) This relatively shallow saltwater sea—variously termed the Western Interior Sea, Cretaceous Seaway, North American Inland Sea, and the Inland Sea—developed during the Cretaceous period (144-66 million years ago) when polar ice caps completely melted, resulting in markedly elevated sea levels worldwide.

In spite of a sometimes confusing writing style that copy-editing could improve, Everhart demonstrates an unfailing commitment to educating the world about Kansas’ remarkable and vastly underappreciated geology and paleontology through publication of “Oceans of Kansas” in 2005 AND through his educational website at: http://www.oceansofkansas.com/index.html (accessed August 11, 2006). Everhart is not an academic; rather he is adjunct curator of vertebrate paleontology at a most unusual marine museum located in the heart of bone-dry Kansas: the Sternberg Museum of Natural History, Fort Hays State University, Hays, Kansas (along Interstate 70).

Development of the Western Interior Sea

The Western Interior Sea developed slowly in two main phases and with many intermittent regressions and transgressions relative to the surrounding landscape. The first phase began during the mid-Cretaceous when the Arctic Ocean (to the north) spread southward over western North America. Later, in the late Cretaceous, the Gulf of Mexico, which was an extension of the Tethys Sea, moved northward to complete the seaway. From the growing Rocky Mountains to the west and the Appalachians to the east, geologists estimate that the seaway was about 600 miles wide at its greatest extent. It was perhaps 600 feet deep on average and 2000-3000 feet deep in some areas, which is shallow for seaways (consider that the Mediterranean Sea is on average about 4,500 feet deep and 20,000 deep in the Calypso Deep of the Ionian Sea). At its greatest extent, the Western Interior Sea covered most of what we today know as Texas, New Mexico, Oklahoma, Colorado, Kansas, Nebraska, South Dakota, North Dakota, Wyoming and Montana, parts of Missouri, Iowa, and Minnesota, as well as central Canada.

The rising Rockies on the western shore of the seaway sent vast amounts of soil, sand, and gravel along the western borders of the seaway. These deposits formed intermixed layers of sedimentary rock including sandstones, shales, and mudstones, which are clearly visible today, particularly since the plateau uplifted to place Kansas at some 2,000 feet above sea level in the middle of the state today. In the clear waters of the middle of the great seaway during the Cretaceous lived billions of microscopic organisms with calcium carbonate shells (calcareous algae) whose delicate carcasses sank to the bottom of the seaway to produce the thick layers of limestone and chalk observed today. Cretaceous means “abounding in chalk”. Thick Cretaceous chalk beds and limestones are distributed throughout the world because of the Cretaceous climate and oceans of the era. Examples include the chalky White Cliffs of Dover, England and the strata beneath and in the environs of Paris, France.

The sea-going animals of the world’s Cretaceous seas—though less well known than the contemporaneous land-based dinosaurs—were abundant, varied, and often huge. They included giant sharks, giant turtles, elasmosaurs, pliosaurs and polycotylids and mosasaurs. Indeed, in terms of the sheer number and ferocity of its marine predators, the Cretaceous oceans rank as the most dangerous seas of all time, according to one source. (2) Not appreciated by many people is the rich Cretaceous fossil record of marine organisms that exists in the Midwest where these creatures once plied the waters.

The Western Interior Sea in Kansas

The Western Interior Sea was so vast that performing the initial descriptive work of its stratigraphy and paleontology, followed by conflating work performed in various states and in Canada, is ongoing. Everhart wisely restricted the scope of “Oceans in Kansas” to the natural history of the Western Interior Sea IN KANSAS. This natural history by itself is quite complex. In fact, Everhart spends most of his book on the natural history of a small piece of Kansas known as the “Smoky Hill Chalk”, which was deposited in the Western Interior Sea during a relatively short (geologically speaking) span of five million years, between 87 and 82 million years ago. The spectacular Smoky Hill Chalk, located in northwest Kansas, is a member of the much larger Niobrara Chalk. The Niobrara Chalk is, in turn, a member of the Niobrara Formation, which covers all or part of six states—North Dakota, South Dakota, Nebraska, Kansas, Wyoming, and Colorado. The vast Smoky Hill Chalk beds have preserved spectacular Cretaceous fossils that have been collected for over 130 years, early on by Charles Steinberg and many others. These Mesozoic Cretaceous marine fossils adorn the museums of the world. (3)

Charles Steinberg: Early Kansas Fossil Hunter

A famous early fossil hunter in Kansas was Charles Sternberg, who was born in rural upstate New York in 1850. His brother George, a medical officer with the Union Army (and later known for his work in bacteriology and as Surgeon General of the Army during the Spanish-American War), was posted at Fort Harker near the town of Ellsworth, Kansas, in the center of Kansas. Kansas then was a “hard frontier country where Indians bitterly resisted the intrusion of the railroad into their hunting grounds and buffalo chips were still used as fuel to boil coffee.” (4). The upstate New York Steinberg family, including eight of their children, moved to the Kansas prairie to be with George in 1867. At age 17 years, Charles became enrapt with the beautifully preserved plant fossils he found in the Late Cretaceous Dakota Sandstone in north central Kansas. In the Niobrara chalk he writes that he “found the remains of great Cretaceous marine reptiles, long-necked plesiosaurs with short bodies and great oar-like paddles, streamlined mososaurs with powerful jaws armed with formidable teeth, and twelve-foot sea turtles.” (4)

Sternberg proudly distributed his specimens to all the major museums of the world, including the American Museum of Natural History, the British Museum, the Museum of Natural History in Paris, the Senckenberg Museum in Frankfurt-am-Main, and the Smithsonian. Charles Steinberg’s three sons—George, Charles, and Levi--accompanied him on his fossil-hunting trips and became curators and fossil authorities in their own rights.

Three Famous Denizens of the Western Interior Seaway at Smoky Hill Chalk    

1. Mosasaurs of Kansas

Mosasaurs—serpentine carnivorous marine reptiles--were the dominant predator in the oceans of the late Cretaceous and were the marine equivalent of Tyrannosaurus rex living in North America. (5) The first mosasaur ever found was in the Netherlands along the Meuse River (Latin Mose means “Meuse River) in an underground mine near Maastricht in about 1780, an event that predated discovery of dinosaurs by about half a century. The Dutch mosasaur was one of the largest known mosasaur specimens ever recovered.

Mosasaurs are somewhat ignored in the paleontology literature in favor of the more popular ichthyosaurs and plesiosaurs. Everhart reasons that their superficial resemblance to alligators and crocodiles and snakes makes them too familiar, and their abundance (thousands of specimens from more than 20 known species) in the fossil record on every continent, including Antarctica, make them too common. Interestingly, most mosasaurs have been collected from Kansas and South Dakota. One observer noted: “Kansas, par excellence, has been the great collecting ground of the world for these reptiles.” (6). Probably the first mosasaur discovered in the Western Interior Sea was by the Lewis and Clark Expedition of 1804-1806, which recorded a “petrified skeleton of a very large fish, seen in Sioux country, on the Big Bend of the Missouri River…forty-five feet long, and lay on the top of a high cliff.” (7)

Mosasaurs breathed air and gave birth to about 4-5 live young at a time (one specimen discovered in South Dakota has the remains of several unborn young preserved inside what was the mama mosasaur’s abdomen). (8) Their closest modern relatives are probably monitor lizards like the Komodo dragon. The mosasaur’s ancestors were shore-dwellers that well into the Cretaceous period seemed to adapt to life in the sea. “Mosasaurs are not the first terrestrial reptiles to return to the sea, but they were probably the most successful in terms of their diversity and eventual dominance,” observes Everhart. (9)

The mosasaurs appeared suddenly in the fossil record of the Western Interior Sea beginning even before the Smoky Hill Chalk was being laid down. Tylosaurus proriger was the largest of the mosasaurs in the Western Interior Sea during the deposition of the Smoky Hill Chalk, reaching 30 or more feet in length and weighing up to 20 tons. Tylosaurus fed on fish, plesiosaurs (more on these reptiles below), birds and smaller mosasaurs. They were excellent swimmers in the open seaway because their remains are abundant in the Smoky Hill Chalk of western Kansas, which was in the center of the Western Interior Sea far from shore. Their long tails, which account for more than half of their bodies, were flattened from side to side and propelled them through the water by undulating back and forth, like a snake. “While swimming at cruising speeds, the head and body of a mosasaur would have been held fairly stiff, with the paddles probably folded against the body, while the tail undulated from side to side. In most cases the paddles were probably used only for steering.” (10)

They became extinct after about 25 million years of dominance along with the land-based dinosaurs at the end of the Cretaceous at the infamous K-T (Cretaceous-Tertiary) border. For more information on the mosasaurs, see #11 below.

2. Plesiosaurs of Kansas

Mary Anning (1799-1847) in 1821 discovered the first Cretaceous plesiosaur (meaning “near-reptile) in a cliff in Lyme Regis in Dorset in the south of England, not too far from Dover, England. (12) Dr. Theophilus Turner (1841-1869) discovered the first nearly complete plesiosaur specimen in North America near Fort Wallace in western Kansas in 1867. Turner was an US Army surgeon who, according to his letters, found “the remains of the huge animal while exploring exposures of the Pierre Shale along the right-of-way of the approaching Union Pacific railroad near McAllaster Butte in present-day Logan County, Kansas.” (13) The skeleton, which was packed up and sent to Philadelphia for description and study. It was named “Elasmosaurus” and was the first of many very long-necked, small-headed plesiosaurs (elasmosaurs) discovered from the late Cretaceous deposits in the Midwest. Like the mosasaurs, elasmosaurs would be found in Cretaceous marine deposits on almost every continent, including Antarctica. In North America they are most prevalent in the Cretaceous beds of western Canada, and are extremely rare in the Gulf states.

The carnivorous plesiosaurs fascinate Everhart, “both for what we know and don’t know about them.” (14) They come in two types—the long necked, small-headed elasmosaurs and the short-necked, large-headed polycotylids. The plesiosaurs reached lengths of 45 feet and weighed many tons, but not as many as the modern whales.

The elasmosaurs are the basis of Nessie, the Loch Ness monster; Champ, the Lake Champlain monster; and other sea and lake “serpents” spotted around the world.

Elasmosaurs are sometimes found with gastroliths—rounded and usually polished stones—where their stomachs would have been in the skeletal remains. Researchers argue about what these stones were used for: as an aid to digestion, buoyancy control, or adjusting attitude/longitudinal balance. The egg-sized quartz or other igneous gastroliths were not found in the limey mud of the Cretaceous sea bottoms in Kansas. Thus, the plesiosaurs probably traveled long distances to locate these stones in places like granite exposures in southeastern South Dakota or the Quachita Mountains in western Arkansas.

Plesiosaurs’ greatest diversity and numbers was probably during the Jurassic or Early Cretaceous. They may have been driven to extinction by the explosion of the mosasaurs in the Late Cretaceous, who ate them or ate their food. The greatest number of Cretaceous plesiosaur fossils in Kansas are found at the same time as mosasaurs first make their appearance in the Western Interior Sea.   

3. Sharks of Kansas

Kansas is a long way from the Pacific Ocean, the Atlantic Ocean, the Arctic Ocean, and the Gulf of Mexico, yet sharks’ teeth abound in the Cretaceous shales and chalks. Charles Steinberg discovered the remains of a very large ancient shark in the lower chalk of the Smoky Hill Chalk, and sent it to the Ludwig-Maximilian University of Munich (the specimen was destroyed during World War II), where it was examined by an American student studying in Germany named Charles R. Eastman. The shark’s vertebral column, though of cartilaginous material, was almost complete, and 250 teeth were in position. Recall that sharks’ cartilaginous skeletons do not fossilize well. Only their teeth are bony, and they have many teeth and are constantly shedding them, which explains why shark teeth are the most abundant vertebrate fossils in Cretaceous Kansas rock.

Summary

For non-Kansasians, the richness of geologic and paleontologic history that exists in the  treeless flatlands of central and western Kansas may come as a surprise. Kansas was the bottom of an epicontinental ocean teeming with reptilian marine life for some 80 million years during the Cretaceous period when polar ice caps melted and the sea level rose.

Sources:

1. Michael J. Everhart: “Oceans of Kansas: A Natural History of the Western Interior Sea.” Indiana University Press, July 2005.

2. “The Seven Deadliest Seas of All Time” available at:  http://www.bbc.co.uk/sn/prehistoric_life/tv_radio/wwseamonsters/deadliest_seas1.shtml; accessed August 11, 2006.

3. See: Charles H. Steinberg: “The Life of a Fossil Hunter.” Indiana University Press, 1990. Originally published 1909 by Henry Holt and Company.

4. Ibid, p. xvi.

5. See “Mosasaurs: Last of the Great Marine Reptiles” by Michael Everhart at: http://www.oceansofkansas.com/Greatrep.html; accessed August 11, 2006.

6. Everhart, p. 174.

7. Ibid, p. 172.

8. Ibid, p. 180.

9. Ibid, p. 161.

10. Ibid, p. 177.

11. For more on mosasaurs, see: http://www.oceansofkansas.com/mus-tylo.html; http://www.oceansofkansas.com/page10.html;

http://www.oceansofkansas.com/SDSMT.html; http://www.oceansofkansas.com/nz-aus.html; accessed August 11, 2006.

12. See: “Mary Anning” at: http://www.ucmp.berkeley.edu/history/anning.html; accessed August 11, 2006.

13.  Everhart, p. 128.

14. Everhart, p. 129.