Surveying New Land at Petrified Forest National Park for Triassic Fossils

A phytosaur skull collected from the top of a tall butte (image from NPS’s page).

Park paleontologists found close to 300 new fossil localities in the first two summers of a survey of Petrified Forest National Park’s newest lands, including an ancient pond bottom, a possible earliest lizard and the first locality of its kind in Arizona. The account is by Adam Marsh, the park’s paleontologist, in the Park Paleontology News newsletter.

A park made for fossils

President Theodore Roosevelt made Petrified Forest a national monument in 1906, one of the earliest uses of the Antiquities Act. Residents of Holbrook and nearby towns such as Adamana, who earned a living from fossil-forest tourism, supported protection after noticing that much of the wood was being carted away. The enabling law set the area aside to “promote the public good” because of “the greatest scientific interest and value” of “the mineralized remains of Mesozoic forests.” Dwight Eisenhower authorized park status in 1958, effective in 1962, and by 1970 it was one of the first parks with designated wilderness. Marsh describes it as the first national park set aside specifically for fossil resources.

The best-known remains are the enormous silicified trees, turned to quartz by mineral-rich groundwater, deep burial and later erosion. The areas John Muir knew as the First, Second and Third Forests became the Crystal, Jasper and Rainbow Forests, and with the Black Forest in the Painted Desert they are among the world’s best places to see fossil logjams eroding out of the badlands that have buried them for more than 200 million years.

A forest is an ecosystem, though, and the park protects everything from the Triassic: gymnosperm trees, cycads and ferns, freshwater mussels and snails, and many groups of reptiles, among them the archosauromorphs and lepidosauromorphs, the groups to which modern lizards, snakes, turtles, crocodilians and birds belong. All come from the Chinle Formation, almost 4,000 feet of rock laid down by meandering rivers, stagnant lakes and swamps, and lowland levees and soils.

The expansion lands

Congress authorized the latest boundary expansion in 2004, adding land east and west of the park for its paleontological and archeological resources, but little was known about the fossils inside. A three-year inventory began in the summer of 2016. Two summers of prospecting produced close to 300 new localities, mostly in a former ranch to the east, checkerboarded with square-mile sections of NPS and State of Arizona land.

A survey point marks the corner of four square-mile sections in the new lands (image from NPS’s page).

Highlights so far:

• The “pond.” A Triassic pond bottom with large amphibians and crocodile-like phytosaurs and a diverse small fauna. Screening its sediment produced the first Late Triassic occurrence of the bony-finned fish Saurichthys in North America and bones from what might be the earliest lizard in the fossil record.
• Metoposaurids. A site with semi-articulated skulls and skeletons of large amphibians, the first such locality in Arizona.
• A shuvosaurid bonebed. Being excavated with partners from the Burke Museum in Seattle. Shuvosaurids are extinct, bipedal, dinosaur-like animals more closely related to crocodilians than to dinosaurs.
• Dinosaurs. True dinosaurs are rare at the park, since most large reptiles of the Chinle are not dinosaurs, but one new site is full of dinosaur limb bones, and the team hopes it is a bonebed.
• Typothorax. The armored aetosaur turns up across the lands, and the crew uncovered the pelvis of what might be the largest one ever found, and the skeleton of a juvenile, at different sites.

A paleontologist’s perch can be precarious, as at this new locality in the expansion lands (image from NPS’s page).

Park scientists and collaborators are now preparing the fossils to study and exhibit them. Marsh says that without the expansion and the inventory these fossils would remain undiscovered or be lost to erosion for good.

Sources

• Adam Marsh, Paleontologist, Petrified Forest National Park, “Survey of New Park Lands at Petrified Forest National Park,” Park Paleontology News, Fall 2017 (https://www.nps.gov/articles/park-paleo-fall-2017-marsh-pefo.htm); rewritten in hubnx's own words. Photographs of people are left out.