Taphonomy In Blue Paleosols and Its Implications for the Biostratigraphy of Vertebrate Taxa In the Petrified Forest National Park, Arizona, USA

The biostratigraphy of the Late Triassic nonmarine record is based on the abundant remains of phytosaurs, aetosaurs, and metoposaurs. These groups represent the majority of fossils found in the Chinle Formation of the Petrified Forest National Park in Arizona, USA. Other Late Triassic pseudosuchians as well as dinosaurs are also known from the Park, though their numbers do not approach those of these Chinle index fossils.

Preliminary assessment of the taphonomy of these assemblages reveals a pattern in their preservation: dinosaurs and non-phytosaurian and aetosaurian pseudosuchians are common in blue floodplain paleosols, whereas phytosaurs, aetosaurs, and metoposaurs occur in most facies and are common in red- and grey-hued floodplain deposits. The restriction of dinosaurs to particular facies may be a major factor influencing our understanding of dinosaur diversification relative to that of other vertebrate faunas in the Late Triassic. The differing faunal assemblages and their association with particular facies suggest that preservation, along with evolution, likely influenced the biostratigraphic distribution of Chinle vertebrates.