A field crew studying fossil tracks near Lake Powell recently discovered an "extremely rare" set of prehistoric fossils along a stretch of the reservoir in Utah, officials announced on Friday. The crew of paleontologists was documenting tracksites last spring when they came upon the unusual find: a tritylodontid bonebed in the Navajo Sandstone in Utah. 

It was the first tritylodontid bonebed discovered there, the National Park Service said in a news release. The park service called the find "one of the more important fossil vertebrate discoveries in the United States this year." The bonebed included "body fossils," like bones and teeth, which are rarely seen in the Navajo Sandstone, a geologic formation in the Glen Canyon area that are typically seen in southern Utah.

"This new discovery will shed light on the fossil history exposed on the changing shorelines of Lake Powell," the park service said. Lake Powell is a major artificial reservoir along the Colorado River that runs across southern Utah and into Arizona.

Paleontologists discovered the bonebed in March of this year. While documenting tracksites along Lake Powell, the crew found a rare group of fossils with impressions of bones, and actual bone fragments, of tritylodontid mammaliaforms. The creatures were early mammal relatives and herbivores most commonly associated with the Early Jurassic period, which dates back to approximately 180 million years ago. Scientists have estimated that mammals first appeared on Earth between 170 million and 225 million years ago, so the tritylondontid creatures would have been some of the earliest kind.

Field crews were able to recover the rare fossils during a short 120-day window during which they could access the location in the Navajo Sandstone, the park service said, noting that the site "had been submerged by Lake Powell's fluctuating water levels and was only found because the paleontologists were in the right place at the right time before annual snowmelt filled the lake." Another rare bonebed was found nearby in the Kayenta Formation, which is slightly older than the sandstone where the tritylondontid discovery was made, according to the park service.

"The crew collected several hundred pounds of rocks encasing the fossil bones and skeletons at the site," the agency said. Those rocks will be scanned using X-ray and computerized tomography at the University of Utah South Jordan Health Center before being studied further at the St. George Dinosaur Discovery Site at Johnson Farm by laboratory and collections crew volunteers. The Petrified Forest National Park and the Smithsonian Institution will support the project as the fossils become part of the Glen Canyon National Recreation Area museum collections.

"Studying these fossils will help paleontologists learn more about how early mammal relatives survived the mass extinction at the end of the Triassic Period and diversified through the Jurassic Period," the National Park Service said.

In:
• National Park Service
• Utah
• Fossil