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US Department of the Interior

2014 Mesozoic Partner Highlight

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Fossil plants such as this grape family member ("Vitis" stantoni) and scraps of dawn redwood (Metasequoia, lower right) are important evidence of the Hell Creek ecosystem. The specimen here shows two types of insect damage. The larger holes show places where an insect chewed through the leaf and consumed the tissue. The smaller dark bumps are signs of an insect that pierced the leaf to suck juices from within. Photograph courtesy Nan Arens. UCMP specimen 153644.

Bureau of Land Management (Montana and Dakotas)

Hell Creek—Not just tyrannosaurs

Article by Greg Liggett (Paleontologist), Bureau of Land Management, Montana/Dakotas.

The dinosaurs and their relatives were the dominant life form on Earth for an amazing 186 million years. Then, at the end of the Cretaceous, about 65 million years ago, the world changed forever. Many organisms went extinct, including the "terrible lizards," leaving the world to be inherited by their avian descendants and the furry mammals. One of the best places on Earth to study this transition is the exposures of Hell Creek rocks in Montana and North and South Dakota.

The Hell Creek beds were first explored for fossils in about 1902, and among the earliest finds was the type specimen of Tyrannosaurus rex, the "tyrant lizard king." The rocks are also rich in other large dinosaurs, such as Triceratops, the three-horned dinosaur closely associated with T. rex, and hadrosaurs like Brachylophosaurus and Edmontosaurus.

Every year, researchers from around the country who are interested in the dinosaurs' last days on Earth come to central Montana and the western Dakotas, and many of them—for example, the University of California Museum of Paleontology work on public lands managed by the Bureau of Land Management. Here they are uncovering a picture of the rich environment of the Hell Creek. They are uncovering what happened immediately before and following the death of the last dinosaurs.

The Hell Creek rocks are rich in a variety of fossils, preserving a large collection of plants as well as smaller animals. The plants show a landscape dominated by large-leafed angiosperms (flowering plants) adapted to a warm and wet climate. Many of the plant fossils also show indirect evidence of insects in the Hell Creek ecosystem, displaying feeding damage and other insect activity.

This reconstruction of a Hell Creek ecosystem shows the diversity of dinosaur, other reptiles, and plants represented by fossils from the formation. Note the bolide streaking across the sky! Artwork by Carl Buell.

Animals much smaller than Tyrannosaurus are found in abundance too. Many freshwater sharks and rays and bony fish like gar, as well as turtles swam in the coastal waterways that bordered the retreating Cretaceous Interior Sea. Crocodiles, and crocodile-like champsosaurs, also plied the waters, feeding on fish and any other animals that got too close. Amphibians were present, as well as smaller species of dinosaurs such as dromaeosaurs.

The end of the Cretaceous also hosted a variety of mammals on land, fur-balls scampering among the foliage at the feet of the dominating dinosaurs. None were larger than today's raccoon, and most were much smaller. Fossil teeth are the main evidence of their presence. These mammals would be among the animals to make it past the end-Cretaceous event, and would be on hand to take advantage of the ecological niches made available by the vanishing of the giant dinosaurs.

Perhaps more than any other extinction event, the disappearance of the dinosaurs from the Earth has fascinated people. What could have brought down those diverse and successful animals that dominated the landscape for so long? One event that is now known to have occurred at the end of the Mesozoic, and which contributed to this dramatic tale, was the impact of a large asteroid in what today is the Gulf of Mexico. Large amounts of dust and debris, much of it enriched in a rare element called iridium, were ejected from the impact and sent around the world, forming a geologically-instant marker bed that has been traced to many parts of the world. That marker unit is clearly seen in the Hell Creek of Montana and the Dakotas.

Intense research into the last two million years of the Cretaceous and into the first few million years of the Paleocene is slowly revealing the circumstances that witnessed the last of the dinosaurs. The emerging picture is more complex than previously thought. However, it is this complexity that continues to bring scientists to the Hell Creek beds, where they are discovering far more than just the amazing tyrannosaurs.

Learn more about BLM paleontology, as well as Hell Creek research and fossils...

bulletBureau of Land Management (BLM) Fossils in Montana and theDakotas

bulletBLM Paleontology

bulletMontana Dinosaur Trail

bulletHow the type specimen of Tyrannosaurus made it to the Carnegie Museum of Natural History in Pittsburgh

2014 Mesozoic Monthly feature articles:

| January: Fossils of the 2014 National Fossil Day Artwork | February: Petrified Forest National Park | March: Garden Park Paleontology Society | April: Big Bend National Park | May: Fossil Cycad National Monument | June: Alaskan National Parks | July: Dinosaur State Park | August: Bureau of Land Management, Hell Creek fossils | September: Ruth Hall Museum of Paleontology at Ghost Ranch | October: Mesozoic Mammals | November: Egg Mountain | December: Mesozoic Rift Basins

Last updated: July 31, 2014