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.
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.
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.
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.
Did You Know?
Petroglyphs are sometimes calendars, marking events like the summer solstice with interactions between the glyph, the sun, and natural landscape features.