Oceans of Kansas, Second Edition: A Natural History of the Western Interior Sea
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ISBN-13: 9780253026323
Media Type: Hardcover(Second Edition)
Publisher: Indiana University Press
Publication Date: 09-11-2017
Pages: 460
Product Dimensions: 6.90(w) x 10.10(h) x 1.50(d)
Age Range: 18 Years
Series: Life of the Past
Michael J. Everhart, Adjunct Curator of Paleontology at the Sternberg Museum of Natural History in Hays, Kansas, is an expert on the Late Cretaceous of western Kansas. He is the creator of the award-winning "Oceans of Kansas" paleontology website at www.oceansofkansas.com. He lives in Derby, Kansas.
Introduction An Ocean in Kansas? The bright midday sun glinted off the calm waters of the Inland Sea and silhouetted the long, sinuous form of a huge mosasaur lying motionless amid the floating tangle of yellow-green seaweed. At 20 years old, more than 30 feet in length, and weighing over a ton, the adult mosasaur was almost full grown and was much larger than any of the fishes or sharks that lived in the shallow seaway. A swift and powerful swimmer over short distances, the mosasaur used surprise and the thrust of his muscular tail to overtake his prey with a short burst of speed. His jaws were more than four feet long and were lined with sharp, conical teeth that he used to seize and kill his prey. Several unusual adaptations in his lower jaws allowed them to flex in the middle and enabled him to easily swallow the large fish and other animals he caught. This adaptation to life in the ocean was essential to the mosasaur because he had to hold on to his prey with his teeth or risk losing it. If he let go of his prey in the middle of the ocean, there was a good chance a hungry shark would grab it or it would sink to the bottom and be lost. The mosasaur was floating at the surface with his eyes and nostrils just above the water. His dark upper body absorbed the hot rays of the Late Cretaceous sun as dozens of tiny fishes emerged from hiding in the seaweed and darted cautiously around his submerged bulk. They were feeding on parasites and other small invertebrates that had attached themselves to his scaly hide. He breathed slowly and quietly through his nostrils as his ears and other senses remained on the alert for the telltale sounds made by approaching prey. A patient hunter, he preferred to let his victims come to him instead of wasting energy swimming around the vast seaway in search of food. Overhead, winged reptiles of various sizes floated lazily through the cloudless sky, riding the thermals above the warm water while looking for schools of small fishes feeding near the surface. Occasionally, one would skim the surface of the water and grab an unwary fish with its narrow beak. The mosasaur had recently tried to eat the floating carcass of a dead pteranodon, but found the thin wings difficult to get into his mouth. After tearing off the small body, he had let the rest of the flyer sink to the bottom. The living ones overhead could see him clearly from above and avoided feeding near him. Amid an ever-changing mixture of background noises made by a variety of creatures in the ocean, he noticed a faint buzz of clicking sounds that was getting louder, alerting him to a group of hard-shelled ammonites feeding nearby. Though not his favorite prey, they were all that had approached him since he had taken a large, solitary fish early in the morning. Even with that recent meal, his appetite was still unsatisfied, and hunger was beginning to gnaw at him. The adaptations that made it possible for mosasaurs to return to the sea included an increased rate of metabolism; this kept him warm, but required large amounts of food to support a more active lifestyle. Exhaling most of the air from his lungs, he slowly submerged his head, leaving behind only the faintest of ripples. His large eyes immediately located the brightly colored coiled shells of the ammonites as they approached, bobbing and darting below him. Propelled by water forced through their internal siphons, they moved generally backward through the water with their short tentacles trailing behind them. Instinctively, he knew that their large shells would hide him from their view until they had moved well past him. He would make his attack from above, long before they had a chance to sense the danger. Using his four large paddles, the mosasaur carefully maneuvered his snakelike form into an attack position, watching intently for any indication that the ammonites had detected the danger from above. Singling out a slightly larger ammonite at the edge of the group, he dived downward with a powerful slash of his long, broad tail. The ammonites reacted quickly and instinctively to the disturbance, scattering in all directions below him, but not before his heavy jaws closed across the soft forebody of his victim. His sharp teeth shattered the front edge of the ammonite's shell, destroying its buoyancy and rendering the ammonite helpless. Without his captive pocket of air, the ammonite would sink swiftly to the bottom of the seaway. With practiced ease, the mosasaur flexed his body upward and brought the ammonite toward the surface. Then he released it and grabbed the tentacles of the immobilized creature with his teeth as it began to sink. Far too late, the ammonite released a cloud of jet-black ink into the water. The mosasaur ignored the bitter taste of the ammonite's last defense as he gave a quick jerk of his head to pull the ammonite's soft body from its shell. The heavy shell and several fragments slipped sideways through the water and quickly disappeared into the murky depths. Opening and closing his jaws rapidly, the mosasaur swallowed the fleshy morsel in a single gulp. Looking around for more prey, he saw another ammonite swimming in confused circles nearby. A swift lunge, and his sharp teeth crunched through the ammonite's hard shell. Moments later, the soft body of the second ammonite followed the first into the mosasaur's stomach. The rest of the ammonites had jetted away as fast as they could and were no longer in view. His hunger briefly satisfied, the mosasaur rose slowly to the surface to breathe and resume his ambush position rather than chase after the fleeing cephalopods. He had hardly settled into waiting when he sensed noises made by the approach of another mosasaur. Female mosasaurs tended to band together in pods for the protection of their young, while males were solitary and territorial. The approaching mosasaur was probably a young male searching for his own place in the expanse of the Inland Sea. With one swift, fluid motion, the older mosasaur turned and began to swim toward the sounds made by the approaching intruder. With flippers held tightly against his body, he moved quickly through the water just beneath the surface. His tail broke through the water's surface repeatedly as he intentionally made as much noise as possible, wanting to sound threatening to the other mosasaur. Although he was prepared to fight for his territory, he would first try to frighten off this other male with his size and ferocity. Long-healed scars on his body showed that even the winners in such fights could be badly hurt. He had been lucky several times earlier in his life and had survived injuries that easily could have been fatal. As he had gotten older, he had learned to avoid such battles whenever he could. The older mosasaur's course intercepted the other broadside in a patch of open water. Turning quickly to face the threat, the smaller animal displayed a mouth filled with sharp teeth. Despite being nearly 10 feet shorter and much less massive, the invader refused to turn and flee. The big mosasaur circled warily around his now stationary foe, watching intently as the other animal almost doubled back upon itself as it continued to show its open jaws. Trying to appear as threatening as possible, the younger animal still refused to turn and run. The larger mosasaur was in no mood for such tactics. Making a large splash with his tail to distract the intruder, he surged forward and seized the smaller animal across the throat and back of the head. For a moment, the smaller mosasaur struggled helplessly as the powerful grip of the larger animal threatened to crush his skull. Then the larger mosasaur moved his head quickly, snapping the other mosasaur's neck. The smaller mosasaur gave a brief shudder, then went limp. Angrily, the big mosasaur shook the slender body again, making certain that his foe was no longer a threat. Realizing that his victim was too large for him to swallow, the mosasaur released his grip and moved away. The body of the dead mosasaur rose slowly toward the surface and floated there until most of the remaining air had escaped from its lungs. Then it began to sink headfirst toward the bottom. Still enraged by the invasion of his territory, the big mosasaur searched about for any other interlopers as he swam in a large circle back to his ambush site. The commotion caused by the brief battle had frightened any prey away and would certainly draw sharks to the area to feed on the remains of the dead mosasaur. Sharks also seemed to be attracted to the undulating movement of a mosasaur's tail. Although he was too large for them to be much of a threat to him, any shark bite could cause a wound that could become seriously infected. He already had several healed scars from past shark bites on his tail and flippers. Later in the afternoon, he sensed the noisy approach of a group of swimming birds. Large and wingless, these birds migrated through the seaway every year during their journeys to and from their nesting grounds to the north. They were fast swimmers and fed on the abundance of small fishes and squid that lived in the sea, catching them in their toothy beaks. He submerged quietly until he was well below the surface, then swam slowly toward the birds. From the sounds he heard, he could tell they were feeding. In the past, he had been able to ambush careless stragglers from below as they rested between dives for food. Nearing the flock, he could see the darker bodies of the birds silhouetted against the sunlit surface as they dived and fed on a school of small silvery fishes they had trapped. Slashing his powerful tail from side to side, he surged upward toward the body of the nearest bird. His mouth opened just before he reached the surface and quickly closed on the bird as his momentum carried his upper body several feet out of the water. Crushed by his powerful jaws, the bird struggled briefly and died. When he was certain his prey would not escape, he moved the limp body around in his mouth until it was pointed headfirst into his throat. Then he lifted his head out of the water and allowed gravity to help him swallow the bird. The noise made by the rest of the retreating flock was already fading in the distance. The hours passed by and the dark clouds of an approaching storm covered the sun as it sank toward the horizon. Driven by the changing weather, the waves became larger and larger. It became difficult for the mosasaur to maintain his stationary position and nearly impossible for him to sense the approach of possible prey against the increasing background noise caused by the wind and rain. Instinctively, he knew it was time to move to open water. Moving forward with rhythmic undulations of his tail, he headed toward the edge of the seaweed mat. An Ocean in Kansas Imagine, if you will, the middle of North America covered by a vast inland sea. Most of Texas, New Mexico, Oklahoma, Colorado, Kansas, Nebraska, South Dakota, North Dakota, Wyoming, and Montana; parts of Missouri, Iowa, and Minnesota; and the central regions of Canada were underneath a shallow ocean. Not just any ocean, but one that stretched for hundreds of miles from Utah to Minnesota, and from the Gulf of Mexico past the Arctic Circle (Fig. 1.1). At times, this ancient ocean was as large, though not as deep, as the present-day Mediterranean Sea and was the home of many kinds of strange creatures that have been extinct for more than 65 million years. This shallow, saltwater sea covered Kansas and the rest of the Midwest during most of the last 40 million years of the Age of Dinosaurs, and almost until the very end of the Cretaceous period, which lasted from about 144 Ma (million years ago) until 65 Ma. Drainage from the older North American continent to the east and the mountains rising from the new land to the west carried vast amounts of soil, sand, and gravel into this seaway, creating intermixed layers of sandstone, shale, and mudstones along the shorelines. In the clear waters at the center of the seaway, the calcium carbonate shells of billions and billions of microscopic, single-cell algae produced thick layers of chalk. In Kansas, the geological record of the Cretaceous begins with marine and nearshore deposits of the Cheyenne Sandstone and Kiowa Shale formations that lie on top of the Wellington Formation (Permian) in the central part of the state. The last Cretaceous rocks are the Sharon Springs, Weskan, and Lake Creek members of the Pierre Shale Formation, in the northwest corner of Kansas. Almost 30 million years of geologic history is preserved in between. One of the deposits near the top layer of the Cretaceous rocks in Kansas is referred to as the Niobrara Formation. It contains a unique upper member called the Smoky Hill Chalk. This chalk is composed mostly of calcium carbonate, very similar to the white cliffs near Dover, England. The Smoky Hill Chalk was deposited in Kansas during a 5- million-year time span, roughly between 87 and 82 Ma. During that time, the Western Interior Sea was gradually retreating from its greatest expansion. The deposition of these chalky marine sediments occurred during the last half of the Cretaceous period, and ended about 17 million years before the end of the Age of Dinosaurs. In Kansas, the Smoky Hill Chalk is about 600 feet thick and lies above the Fort Hays Limestone and below the Pierre Shale (Fig. 1.2). For the most part, the chalk is composed of compacted shells (coccoliths) of microscopic, golden-brown algae (Chrysophyceae) that lived and died by the untold billions in the warm, shallow sea. Besides making up the chalk, these microscopic plants were the basis for a complex food web that supported vast numbers of small fishes and many large predators, including sharks, larger fishes, plesiosaurs, mosasaurs, pteranodons, and birds. The Western Interior Sea, sometimes just called the Inland Sea, was formed by the flooding of low-lying areas of the North American continent during a period of the earth's history when there were no polar ice caps and sea levels were at their highest. Near the center of the sea, the water was probably less than 600 feet deep (Hattin, 1982) and the limey mud bottom was relatively flat and featureless. In the area where Kansas is now located, the sediments were deposited at a rate that would ultimately produce about an inch of solid chalk for every 700 years of time (ibid.). The chalk also contains more than 200 thin layers of bentonite clay, most of which are rusty red in color, that are the residuals of volcanic ash deposited from periodic major eruptions in what is now Nevada, Utah, Idaho, and Montana. These ash deposits (Fig. 1.3) can be traced for miles across the chalk beds and are currently used as chronological markers when describing the stratigraphy of the formation. In addition, several species of vertebrate and invertebrate marine life that lived in the Western Interior Sea at different times during the deposition of the chalk are useful in determining the age and biostratigraphy of widely separated exposures (Chapter 13). This shallow ocean was home to a variety of marine animals that are now extinct. These included giant clams, rudists, crinoids, squid, baculites, belemnites, ammonites, numerous sharks and bony fishes, turtles, plesiosaurs, mosasaurs, pteranodons, and even several species of primitive marine birds with teeth. Although it seems unlikely that you would find dinosaur fossils in the middle of the Western Interior Sea, the partial remains of several of them (two hadrosaurs and a dozen or more nodosaurs) have been collected from the Smoky Hill Chalk since 1871. Relatively few in number, these specimens have been well documented (Marsh, 1872; Wieland, 1909; Eaton, 1960; Carpenter et al., 1995; Everhart, 2004; Everhart and Hamm, 2005; Liggett, 2005; Everhart and Ewell, 2006; Carpenter and Everhart, 2007). In order to get to where they have been discovered, the bodies of these dinosaurs must have somehow floated hundreds of miles out to sea before sinking to the bottom (Fig. 1.4). It is possible that they died during catastrophic floods and were carried out to sea in large, tangled mats of trees and other vegetation. However they arrived, there is no doubt that there are dinosaurs buried among the marine reptiles and fishes in the Smoky Hill Chalk. Over a period of about 5 million years, the remains of many of these animals were preserved as fossils in the soft, chalky mud of the sea bottom. When this mud was compressed under the weight of hundreds of feet of overlying shale, it became a deposit of chalk that is about 600 feet thick in western Kansas. Much of the massive chalk formation that once covered Kansas has been eroded away over the last 65 million years, however, and is now exposed only in relatively small areas along the rivers in the northwest quarter of the state. The eastern edge of this part of Kansas is also known as the Smoky Hills, which provided the name for the Smoky Hill River that flows through it and, ultimately, for the geological formation known as the Smoky Hill Chalk. Read an Excerpt
Oceans of Kansas
A Natural History of the Western Interior Sea
By Michael J. Everhart Indiana University Press
Copyright © 2017 Michael J. Everhart
All rights reserved.
ISBN: 978-0-253-02715-3
CHAPTER 1
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Excerpted from Oceans of Kansas by Michael J. Everhart. Copyright © 2017 Michael J. Everhart. Excerpted by permission of Indiana University Press.
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Table of Contents
Preface
Acknowledgments
Abbreviations
1. Introduction: An Ocean in Kansas?
2. Our Discovery of the Western Interior Sea
3. Invertebrates, Plants, and Trace Fossils
4. Sharks: Sharp Teeth and Shell Crushers
5. Fishes, Large and Small
6. Turtles: Leatherback Giants
7. Where the Elasmosaurs Roamed
8. Pliosaurs and Polycotylids
9. Enter the Mosasaurs
10. Pteranodons: Rulers of the Air
11. Feathers and Teeth
12. Dinosaurs?
13. The Big Picture
Epilogue: Where Did It Go?
References
Index