Research Activities

fossil excavation

Stagonolepis Dig: Dr. David Gillette excavating aetosaur skeleton.

Since the summer of 2001 Petrified Forest National Park has seen significant strides made in paleontological research, particularly with the fossil vertebrates. Funded mainly by the Recreation Fee Demonstration Program the park initiated an exhaustive paleontological inventory to assess resources in the park, including relocating and documenting all known paleontological sites. At the time of project initiation, over 200 fossil plant, invertebrate and invertebrate sites have been documented over the last 80 years. By 2004 more than half of these sites were relocated and documented. In addition, over 50 new sites were discovered.

In 2001 the partial skeleton of the aetosaur Calyptosuchus wellesi was discovered. C. wellesi was previously only known from two other partial skeletons, one from Texas and a second from Arizona. The new Petrified Forest skeleton is the most complete of these, providing much needed information about this animal and its relationships with other aetosaurs.

excavation area

Gobstopper Hill: Trent Hall (left) and Bill Parker (right) excavating phytosaur skeleton. May 2002

NPS Photo

A phytosaur skeleton was discovered on the first day of the 2002 field season. Although the skull was missing, enough of the skeleton was present to make this a substantial find. Crew member Randall Irmis, a graduate student from Northern Arizona University, featured this specimen in a research project. He found that phytosaurs showed changes in the skeleton as a result of physical maturation very similar to those of crocodiles. Thus crocodylian maturation rates can be used for extinct animals as well. Other substantial finds from the 2002 field season included armor plates from a new species of aetosaur, the skull roof of a new species of phytosaur, and a partial skeleton of the crocodylomorph Parrishia.

fossil skull bones protected inside a plaster jacket

Saurian Valley Phytosaur. Partially prepared skull. 2003

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The 2003 field season featured the successful excavation of a complete phytosaur skull from the Saurian Valley area of the Devils Playground. This is the first complete skull collected from the park in 17 years and probably belongs to the species Leptosuchus crosbiensis. Other significant finds from the 2003 field season included plates from an aetosaur, Heliocanthus chamaensis, previously known only from New Mexico, the first recorded jaw material of Trilophosaurus ever found in the park, a partial skeleton of the rare enigmatic reptile Vancleavea, and several important fossil plant discoveries by Dr. Sidney Ash and Dr. Rodney Savidge. Dr. Ash also published reconstructions of the Triassic trees Woodworthia and Schilderia in the journal Palaeontology.
Ranger Ted Bolich uses hammer and chisel to carefully remove rock from around the fossil bones.

Rainbow Forest Phytosaur: Ranger Ted Bolich chiseling trench around phytosaur skull. 2003

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Another phytosaur skull was found during the 2003 field season embedded in a hard sandstone block. It was removed with the skill and hard work of Interpretation Ranger Ted Bolich and the Petrified Forest Maintenance Division. This skull was the feature of a 2002 scientific paper by Dr. Adrian Hunt from the New Mexico Museum of Natural History in Albuquerque.
excavation in progress

Revueltosaurus Quarry. May 2004

NPS Photo

As good as these past few seasons were, the 2004 field season provided the best new fossil material to date. Two new sites in the Painted Desert area of the park, the Revueltosaurus Quarry and The Giving Site, have provided a wealth of important new material. At least a dozen skeletons of the pseudosuchian archosaur Revueltosaurus callenderi were excavated from the Revueltosaurus Quarry in the summer of 2004. This is an important find as Revueltosaurus was previously only known from the teeth and was believed to represent an early Ornithischian dinosaur. The fact that this animal is more closely related to crocodiles instead has important implications for the global fossil record of early dinosaurs. A paper on these findings was published in the Proceedings of the Royal Society Series B in May of 2005.

excavation site

Giving Site: Lori Browne (left) and Jeff Martz (right) prospecting at the Giving Site. May 2004.

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The Giving Site has proven to be one of the most productive sites in the park, and possibly for any other site representing the Late Triassic within the American Southwest. To date the site has provided remains of rauisuchians, aetosaurs, phytosaurs, lungfish, and dinosaurs. Dinosaur finds are extremely rare in the Triassic and the Giving Site has provided a plethora of material. Also in the 2004 field season, what appears to be another new species of aetosaur was excavated from a new site called the “Milkshake Quarry.”
digging for fossils

Devils Playground: Crew members Dylan Rust (left) and Michelle Stocker (right) excavating a phytosaur skull. 2005

NPS Photo

The 2005 field season saw the collection of another well-preserved phytosaur skull from the Devils’ Playground area and an excellent skeleton of Revueltosaurus from the Revueltosaurus Quarry. In addition, more material from metoposaurs, aetosaurs, and phytosaurs was collected from various sites throughout the park.

In 2006 the Revueltosaurus Quarry was reopened and an even more exquisite skeleton of Revueltosaurus was collected. This specimen is nearly complete and enhances our knowledge of this animal. Other significant finds from 2006 included more theropod, rauisuchian, and crocodylomorph material from the Giving Site.


2006 also was the centennial year for Petrified Forest National Park and in conjunction the park hosted a scientific symposium centering mainly on Late Triassic paleontology. This symposium was accompanied by the publication of a research volume (Museum of Northern Arizona Bulletin 62) on Late Triassic geology and paleontology. Papers in this volume describe four new fossil trees, several fossil plants, and two new fossil animals from the park including the new phytosaur collected in 2002 (Pseudopalatus jablonskiae) and the new trilophosaurid collected in 2003 (Trilophosaurus dornorum).

2007 saw some of the first forays into newly acquired expansion lands, areas that had not been prospected since the 1980s or earlier. Our first field day was extremely successful when we uncovered a phytosaur skull within stones throw of the old boundary fence. Also notable in 2007 was the publication by Rod Savidge (University of New Brunswick) describing several new taxa of wood from the park as well as reevaluation the status of the name Araucarioxylon arizonicum.

As inventory work and exploration continues over the next few years, new discoveries will shed even more light on the unique period of time in the earth’s history known as the Late Triassic.

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