Article by Adam Marsh, Paleontologist, Petrified Forest National Park
for Park Paleontology Newsletter, Fall 2017
The Antiquities Act of 1906 has given rise to national parks, monuments, and other public lands set aside for specific resources for public enjoyment, scientific knowledge, and ecological conservation. Whether they are redwood forests, Joshua trees, grand canyons, or glaciers, people across the world are attracted to American national parks because they often protect resources that are not found anywhere else in the world. A handful of NPS units are known for their fossil resources like John Day Fossil Beds National Monument, Dinosaur National Monument, Florissant Fossil Beds National Monument, and Badlands National Park. However, the first American national park that was set aside specifically for fossil resources is Petrified Forest National Park (PEFO) in northeastern Arizona. Since 1906, PEFO has encouraged visitors to experience a landscape they have never before seen to learn about our shared evolutionary history of life on Earth. PEFO’s recent expansion offers a rich deposit of plant and animal fossils that continue to teach us about what North America may have looked, smelled, and even sounded like over 200 million years ago.
President Theodore Roosevelt established Petrified Forest as a national monument in 1906 in one of the earliest uses of the Antiquities Act. Federal protection was supported by local residents of Holbrook and surrounding towns like Adamana who made a living from tourism as a result of the fossil forests nearby and noticed that much of the wood was being removed from the area. According to the enabling legislation, PEFO was set aside to “promote the public good” through “the greatest scientific interest and value” of “the mineralized remains of Mesozoic forests” in a specific part of northern Arizona already known as the Petrified Forest. This designation preceded the statehood of Arizona by six years and the National Park Services itself by ten years! Dwight Eisenhower authorized PEFO’s park status in 1958, a designation that went into effect in 1962, and shortly afterwards Lyndon B. Johnson signed the Wilderness Act; PEFO was one of the first parks with designated wilderness areas by 1970.
The most visible portion of Roosevelt’s “Mesozoic forests” is of course the enormous trees that have been silicified by quartz-rich groundwater, deep burial, and subsequent erosion. The areas known as First, Second, and Third forests to John Muir, who lived near PEFO in 1906, were subsequently named Crystal Forest, Jasper Forest, and Rainbow Forest, respectively, and along with the Black Forest in the Painted Desert are some of the best places in the world to see fossilized logjams naturally eroding out of the sedimentary badlands that have entombed them for more than 200 million years.
However, a forest does not just comprise the trees, but rather is an ecosystem that contains all of the flora and fauna living within it. Thus, PEFO does not only protect the fossil logs for which it is so well known, but all of the Triassic fossils that have come to rest within its boundaries. These fossils include a diverse array of gymnosperm trees, cycads, and ferns, freshwater mussels and snails, and a myriad of reptile groups. Two of these groups were particularly diverse during the Triassic, the archosauromorphs and lepidosauromorphs, and are the groups to which modern lizards, snakes, turtles, crocodilians, and birds belong. All of the fossils found at PEFO are from the Chinle Formation, which is a stack of almost 4,000 feet of sedimentary rocks that were formed in an old geographic basin by meandering rivers, stagnant lakes and swamps, and lowland levees and soils.
The most recent boundary expansion to PEFO was authorized by Congress in 2004; the new lands added to the east and west of the existing park were set aside specifically for the paleontological and archeological resources contained therein, however, not much is known specifically about the fossils found inside the new boundary. Paleontologists at PEFO were awarded funding for a three-year project to inventory the new expansion lands, which began in the summer of 2016. The first two summers’ worth of prospecting has resulted in close to 300 new fossil localities, mostly in the former ranch to the east that is checkerboarded with NPS and state of Arizona square-mile sections. One locality called the “pond” represents a Triassic pond bottom complete with large amphibians and crocodile-like phytosaurs but also a diverse microfauna. Screening the sediment from that rock layer has resulted in the first Late Triassic occurrence of the bony-finned fish Saurichthys in North America as well as bones from what might be the earliest lizard in the fossil record.
Nearby lies another site that contains semi-articulated skulls and skeletons of large metoposaurid amphibians, the first such locality in Arizona. Another first of its kind is a shuvosaurid bonebed currently being excavated by research partners from the Burke Museum in Seattle; shuvosaurids are extinct, bipedal dinosaur-like animals that are actually more closely related to crocodilians than they are to dinosaurs. The new boundary expansion project has the potential to find more real dinosaurs, as well. Dinosaurs are actually rare at PEFO; most of the large reptiles from the Chinle Formation are not dinosaurs at all. However, this project has located a site on the new lands that is full of dinosaur limb bones and park paleontologists hope it turns out to be a dinosaur bonebed. The armored aetosaur Typothorax has been found throughout the expansion lands, but this summer the field crew uncovered the pelvis of what might be the largest Typothorax ever found as well as the skeleton of a juvenile Typothorax (from different sites).
Currently, park scientists and collaborating researchers are preparing these new fossils from the expansion lands in order to better study and exhibit them for public education and enjoyment. Scientific papers that are published on fossils from PEFO are available online and more information is available upon request. Without the boundary expansion and project to inventory the new lands at PEFO, these important fossils would remain undiscovered or worse, be lost to erosion forever. A lot has changed since 1906, but Petrified Forest National Park continues to endeavor to protect the “Mesozoic forests” and learn more about their rich fossil history.