William G Parker

National Park Service | NPS · Division of Resource Management

Fossils of embryonic and hatchling individuals can provide invaluable insight into the evolution of prenatal morphologies, heterochronies, and allometric trajectories within Archosauria but are exceptionally rare in the Triassic fossil record, obscuring a critical aspect of archosaurian biology during their evolutionary origins. Microvertebrate sam...

A newly referred specimen of Coahomasuchus kahleorum (TMM 31100‐437) from the lower part of the Upper Triassic Dockum Group of Texas preserves much of the skeleton including the majority of the skull. Introduced in the literature in the 1980s as the “carnivorous aetosaur”, TMM 31100‐437 bears recurved teeth that previously were considered unique am...

Reptile feeding strategies encompass a wide variety of diets and accompanying diversity in methods for subduing prey. One such strategy, the use of venom for prey capture, is found in living reptile clades like helodermatid (beaded) lizards and some groups of snakes, and venom secreting glands are also present in some monitor lizards and iguanians....

Maximum individual body size in pseudosuchian archosaurs is not well constrained in the fossil record, but it may be influenced by a variety of factors including basal metabolic rate, evolutionary relationships, and environmental conditions. Body size varies among the Aetosauria in which estimated total length ranges between 1 m (e.g., Coahomasuchu...

he Late Triassic Chinle Formation in northern Arizona and Dockum Group in northwestern Texas preserve a high aetosaur biodiversity within the Adamanian teilzone, including Desmatosuchus spurensis, Desmatosu- chus smalli, Calyptosuchus wellesi, Adamanasuchus eisenhardtae, Typothorax coccinarum, Paratypothorax sp., Tecovasuchus chatterjeei, and Sierr...

Living amphibians (Lissamphibia) include frogs and salamanders (Batrachia) and the limbless worm-like caecilians (Gymnophiona). The estimated Palaeozoic era gymnophionan–batrachian molecular divergence¹ suggests a major gap in the record of crown lissamphibians prior to their earliest fossil occurrences in the Triassic period2–6. Recent studies fin...

Non-archosaur archosauromorphs are a paraphyletic group of diapsid reptiles that were important members of global Middle and Late Triassic continental ecosystems. Included in this group are the azendohsaurids, a clade of allokotosaurians (kuehneosaurids and Azendohsauridae + Trilophosauridae) that retain the plesiomorphic archosauromorph postcrania...

Archosauromorph reptiles underwent rapid lineage diversification, increases in morphological and body size disparity, and expansion into new adaptive landscapes. Several of the primary early archosauromorph clades (e.g. rhynchosaurs) are easy to differentiate from others because of their characteristic body types, whereas the more lizard‐like and c...

Doswellia kaltenbachi is a long-snouted non-archosaur archosauriform known from the Late Triassic of the United States (Virginia and Texas). New material from the Chinle Formation of Arizona represents the first occurrence of D. cf. D. kaltenbachi from that formation and state. This occurrence is from the type section for the Adamanian estimated ho...

Once known solely from dental material and thought to represent an early ornithischian dinosaur, the early‐diverging pseudosuchian Revueltosaurus callenderi is described from a minimum of 12 skeletons from a monodominant bonebed in the upper part of the Chinle Formation of Arizona. This material includes nearly the entire skeleton and possesses a c...

The Colorado Plateau Coring Project Phase 1 (CPCP‐1) acquired three continuous drill cores from Petrified Forest National Park (PFNP), Arizona, U.S.A., two of which (CPCP‐PFNP13‐1A and CPCP‐PFNP13‐2B) intersected the Upper Triassic Chinle Formation, Lower(?)‐Middle Triassic Moenkopi Formation (MF) and Permian Coconino Sandstone. We examined both co...

The only exposure of Mesozoic rocks at Grand Canyon National Park is found at Cedar Mountain near Desert View and is limited to the Triassic Moenkopi Formation and Shinarump Member of the Chinle Formation. Prior to this inventory, the only detailed geological study of Cedar Mountain occurred in 1922 (three years after the park was established), and...

Our understanding of Typothorax coccinarum is primarily based on postcranial material, along with a few isolated cranial elements. Here we describe the first complete articulated skull of Typothorax coccinarum from the Owl Rock Member of the Late Triassic Chinle Formation in Petrified Forest National Park. We assessed the relationships and defining...

Dinosauromorph specimens from Petrified Forest National Park have been recovered from four major collecting efforts since 1982, including the most recent paleontological inventory of new park lands acquired in 2011. Additionally, an emphasis on understanding the stepwise acquisition of character traits along the dinosaurian lineage has helped ident...

Acaenasuchus geoffreyi is a diminutive armored archosaur from the Upper Triassic Chinle Formation of northern Arizona, U.S.A., with uncertain evolutionary relationships and skeletal maturity. Known only from osteoderms, the taxon has been considered a valid taxon of aetosaur, juvenile specimens synonymous with the aetosaur Desmatosuchus spurensis,...

Uranium–lead (U–Pb) geochronology was conducted by laser ablation – inductively coupled plasma mass spectrometry (LA-ICPMS) on 7175 detrital zircon grains from 29 samples from the Coconino Sandstone, Moenkopi Formation, and Chinle Formation. These samples were recovered from ∼ 520 m of drill core that was acquired during the Colorado Plateau Coring...

The Upper Triassic Chinle Formation is a critical non-marine archive of low-paleolatitude biotic and environmental change in southwestern North America. The well-studied and highly fossiliferous Chinle strata at Petrified Forest National Park (PFNP), Arizona, preserve a biotic turnover event recorded by vertebrate and palynomorph fossils, which has...

Allokotosauria, including Trilophosauridae and Azendohsauridae, is an extinct archosauromorph group that reached a near-Pangean distribution in the Middle Triassic to Late Triassic and evolved a broad range of cranial and dental morphologies. Within the Chinle Formation of western North America, allokotosaurs span the Norian-aged Blue Mesa Member (...

The coincidence of a diverse vertebrate assemblage with a high-precision geochronology and lithostratigraphy in Petrified Forest National Park (Arizona, USA) allows Bayesian quantification of the dynamics of a Late Triassic vertebrate extinction and replacement, the Adamanian/Revueltian (A/R) faunal turnover. This approach uniquely identifies proba...

Building on an earlier study that confirmed the stability of the 405‐kyr eccentricity climate cycle and the timing of the Newark‐Hartford astrochronostratigraphic polarity time scale back to 215 Ma, we extend the magnetochronology of the Late Triassic Chinle Formation to its basal unconformity in scientific drill core PFNP‐1A from Petrified Forest...

We present two remote sensing methods used to enhance the probability of fossil discovery in the field. The two methodologies depend on either the use of high-resolution satellite images or standard camera photos; the former procedure allows researchers to work from the office and is applicable to large tetrapods, while the latter is important duri...

U-Pb geochronology was conducted by Laser Ablation-Inductively Couple Plasma Mass Spectrometry (LA-ICPMS) on detrital zircon grains from twenty-nine samples from the Coconino Sandstone, Moenkopi Formation, and Chinle Formation. These samples were recovered from ∼520 m of drill core that was acquired during the Colorado Plateau Coring Project (CPCP)...

Chindesaurus bryansmalli is an early dinosaur of uncertain affinities from the Late Triassic Chinle Formation at Petrified Forest National Park, Arizona. Since its first description in 1995, the taxon has been considered a plateosaurid, a noneusaurischian saurischian, a herrerasaurid, and/or a non-neotheropod member of Theropoda. Chindesaurus bryan...

This volume, prepared as part of the Geological Society of America Annual Meeting in Phoenix, includes field guides covering aspects of the spectacular geology of southwestern North America. Field guides tackle the geology of the southern Colorado Plateau, from paleoenvironments of Petrified Forest National Park, to Jurassic sand dunes of southern...

Metoposaurids are non-marine temnospondyls that are among the most common constituents of Late Triassic deposits, but despite their abundance, the evolutionary relationships of the group are poorly resolved and have not been fully addressed with modern phylogenetic methods. The genus Anaschisma is one of a number of poorly resolved metoposaurid tax...

The Sonsela Sandstone bed was first named as an informal unit in the lower part of the Chinle Formation in northern Arizona, USA, and it was later assigned a type section near the Sonsela Buttes, where it is composed of two prominent sandstone units separated by a predominately siltstone unit. The Sonsela Sandstone bed has been correlated to a numb...

Crown-group frogs (Anura) originated over 200 Ma according to molecular phylogenetic analyses, though only a few fossils from high latitudes chronicle the first approximately 60 Myr of frog evolution and distribution. We report fossils that represent both the first Late Triassic and the earliest equatorial record of Salientia, the group that includ...

Phase 1 of the Colorado Plateau Coring Project (CPCP-I) recovered a total of over 850 m of stratigraphically overlapping core from three coreholes at two sites in the Early to Middle and Late Triassic age largely fluvial Moenkopi and Chinle formations in Petrified Forest National Park (PFNP), northeastern Arizona, USA. Coring took place during Nove...

Stagonolepis robertsoni , from the Late Triassic of Scotland, was the first named aetosaurian. Known mostly from a series of natural molds from two localities, the osteology of this taxon has been difficult to interpret. Detailed work on this material in the late 1950s resulted in a monograph that set the standard for the understanding of aetosauri...

Metoposaurids are Late Triassic temnospondyls that are abundant components of freshwater depositional settings. Although metoposaurids are represented by hundreds of specimens in collections around the world, the vast majority pertain to large-bodied, relatively mature individuals, and as a result, the early stages of ontogeny are still poorly char...

Subsurface fluid systems are important for chemical weathering, ore formation and thermal evolution of the crust. Changes in the dynamics and distribution of subsurface fluid flow systems are controlled by changes in global and regional terrestrial climate, tectonics, and elevation. This paper concerns the dating of changes in ancient subsurface hy...

Significance Rhythmic climate cycles of various assumed frequencies recorded in sedimentary archives are increasingly used to construct a continuous geologic timescale. However, the age range of valid theoretical orbital solutions is limited to only the past 50 million years. New U–Pb zircon dates from the Chinle Formation tied using magnetostratig...

The evolution of the braincase and brain of early pseudosuchians through to the earliest crocodylomorphs is poorly understood given the paucity of specimens, lack of well-preserved material, and lack of consensus on the phylogenetic relationships of the major clades of Pseudosuchia. Here, we describe three differently sized braincases diagnosable a...

Vertebrates from the Triassic Period have broadly disparate tooth shapes and dentition patterns, the result of intense morphospace experimentation following the Permo-Triassic extinction. Here, we describe fragmentary tooth-bearing jaw elements of the rare Gondwanan Middle Triassic taxon Palacrodon that represent first occurrences from the Upper Tr...

Calyptosuchus wellesi is a medium-sized desmatosuchian aetosaur common in Adamanian (early to middle Norian) age rocks from the Chinle Formation and Dockum Group of the Western United States. Known chiefly from osteoderms, this taxon has never been fully described and non-osteoderm material assigned toCalyptosuchushas been done so based on question...

List of aetosaurian elements from the Placerias Quarry. List of all identified aetosaurian elements from the Placerias Quarry at the UCMP listed with the field number assigned during the 1930s excavations.

Metoposaurids are typically large-bodied freshwater temnospondyls that are among the most commonly recovered vertebrate fossils in Late Triassic nonmarine deposits. Traditional interpretations of metoposaurid evolution have argued in favor of a size turnover in the southwest of North America from the large-bodied Koskinonodon in the early Norian to...

The scientific rigor of paleontologic and biostratigraphic studies is reliant on thorough documentation of data and methodology, as well as publication with an emphasis on repeatability. Taxonomic identifications require the use of apomorphy-based methods and the use of voucher specimens for documentation. Lithostratigraphic studies require the use...

Recently developed rigorous and testable stratigraphic models, improved vertebrate systematics, and radioisotopic calibration allow the Late Triassic land vertebrate “faunachrons” of western North America to be extensively revised and codified. Recognizing that reliable biochronology depends on well-documented and testable biostratigraphic models,...

Magnetic polarity stratigraphy is a method that can be invaluable for correlation of terrestrial strata when combined with other stratigraphic and/or geochronologic data sets. Recent revisions to the lithostratigraphy of the Chinle Formation within Petrified Forest National Park (PEFO), northern Arizona, have demonstrated that a stratigraphic gap c...

Fossil plant assemblages including spores and pollen grains provide useful information on past ecosystems and the response of terrestrial biotas to various environmental perturbations. New quantitative palynological data from the Chinle Formation of the American Southwest suggest that a floral turnover occurred in the middle Norian (between 217 and...

Citation for this article: Kligman, B. T., W. G. Parker, and A. D. Marsh. 2017. First record of Saurichthys (Actinopterygii) from the Upper Triassic (Chinle Formation, Norian) of western North America. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1367304.

The Chinle Formation and the lower part of the overlying Wingate Sandstone and Moenave Formation were deposited in fluvial, lacustrine, paludal, and eolian environments during the Norian and Rhaetian stages of the Late Triassic (~230 to 201.3 Ma), during which time the climate shifted from subtropical to increasingly arid. In southern Utah, the Shi...

The sacrum – consisting of those vertebrae that articulate with the ilia – is the exclusive skeletal connection between the hindlimbs and axial skeleton in tetrapods. Therefore, the morphology of this portion of the vertebral column plays a major role in the evolution of terrestrial locomotion. Whereas most extant reptiles only possess the two ples...

Terrestrial Depositional Systems: Deciphering Complexities through Multiple Stratigraphic Methods is the first collection of contributed articles that not only introduces young geoscientists to biostratigraphy, chemostratigraphy, magnetostratigraphy, and lithostratigraphy, but also provides seasoned practitioners with a standard reference that show...

Metoposaurids are temnospondyl amphibians that are well known from Upper Triassic deposits in North America, Europe, India, and Africa. Two species of metoposaurids, Koskinonodon perfectus and Apachesaurus gregorii, are among the most common fossils found in the Petrified Forest National Park (PEFO) of the southwestern United States. The two are di...

Phyllosilicate and sulfate deposits are widely observed on Noachian and Early Hesperian terrains on Mars, and the association of similar ancient terrestrial deposits with high concentrations of organics makes these martian deposits viable and attractive targets in the search for organics. Here, we examine sediments from a Mars-analog material, the...

The Chinle Formation and the lower part of the overlying Wingate Sandstone and Moenave Formation were deposited in fluvial, lacustrine, paludal, and eolian environments during the Norian and Rhaetian stages of the Late Triassic (~230 to 201.3 Ma), during which time the climate shifted from subtropical to increasingly arid. In southern Utah, the Shi...