Petrified Forest National Park Research Articles

Leveraging historical hospitality in the national parks: Fred Harvey, Mary Colter, and the heritage of the American Southwest

ABSTRACT This conceptual paper examines the Fred Harvey Company, a key entity that helped develop tourism at Southwestern national parks, in particular Grand Canyon National Park and Petrified Forest National Park. The article describes some of the influences of this organization on the image of tourism in the Southwest, from the thematic design of spaces to the commercializing of Native American cultural heritage. After examining these impacts, the contemporary state of interpretation in these national parks is highlighted. Drawing on not only the natural and cultural resources of the region, organizations such as the National Park Service or Xanterra Travel Collection employ the historical hospitality foundations of the sites to create a multi-layered image of the national park as well as connect to tourist identities.

THE GEOARCHAEOLOGICAL LANDSCAPE OF WALLACE TANK PUEBLO (AZ Q:1:199 (ASM)), PETRIFIED FOREST NATIONAL PARK, ARIZONA: REHABILITATING THE DAMAGED CULTURAL LANDSCAPE OF A PUEBLO IV VILLAGE

Petrified Forest National Park (PEFO) is a unique landscape of physical beauty and paleontological treasures. Known for its ancient fossils, petrified wood, and awe-inspiring vistas, it is also well-known in the archaeological community as having some of the earliest villages on the southern Colorado Plateau. Additionally, it is home to a few large late precontact pueblos (Pueblo IV period: ~1275-1400 CE) that were once part of an extensive regional network of communities where people and goods moved across the landscape. Wallace Tank Pueblo is the largest Pueblo IV period village within the Park. This once thriving 600-room pueblo was home to the ancestors of the Zuni, Hopi, and other descendant communities. Over time the physical features of the village were damaged by historic ranching activities and natural erosion. It is now a scoured and degraded landscape where the once sustaining natural spring is not even identifiable. Because of the uniqueness of this village within the Petrified Forest environment consultations between the Park and descendant communities should consider management plans that will re-establish a spring-fed wetlands. Such a plan would not only focus on preservation of the cultural features, but also on the health of the environment and that of the descendants who maintain an emotional and spiritual connection to this ancestral village.

THE ALLOKOTOSAUR (REPTILIA: ARCHOSAUROMORPHA) ASSEMBLAGE FROM A MULTITAXIC BONEBED IN THE SONSELA MEMBER (JIM CAMP WASH BEDS, CHINLE FORMATION) AT PETRIFIED FOREST NATIONAL PARK, U.S.A.

Allokotosaurian archosauromorphs (i.e., trilophosaurids and azendohsaurids) are known from Middle Triassic to Upper Triassic terrestrial deposits in Madagascar, Morocco, India, the United Kingdom, southeastern Canada, and the southwestern United States. In western Texas, trilophosaurids and malerisaurine azendohsaurids co-occur in Otischalkian sites, but numerous sites in the Chinle Formation-Dockum Group depobasin of Texas, New Mexico, and Arizona preserve either trilophosaurids or malerisaurines, blurring our understanding of the evolution of these groups and their potential biostratigraphic utility. Here we report an allokotosaurian assemblage from PFV 410 (the Kaye Quarry), a lowermost Revueltian locality in the upper Sonsela Member of the Chinle Formation at Petrified Forest National Park that preserves both trilophosaurid and malerisaurine azendohsaurid taxa, which indicates that these lineages may have co-occurred in the southwestern United States for ~10 million years during the Carnian to Norian. This locality is important because it pre-serves teeth of Trilophosaurus phasmalophos in a maxilla that may help resolve taxonomic uncertainty in that genus, and it shows that malerisaurines persisted at least for some time after the hypothesized Adamanian-Revueltian biotic turnover.

A LATERAL OSTEODERM FROM KRYPHIOPARMA CAERULA (PSEUDOSUCHIA: AETOSAURIA) FROM THE UPPER TRIASSIC (NORIAN) CHINLE FORMATION OF ARIZONA

Recent collecting of fossil vertebrates in the Chinle Formation at Petrified Forest National Park (PEFO) and reinvestigation of historic collections resulted in the recognition of a new aetosaurian taxon, Kryphioparma caerula. Although distinctive, K. caerula was initially described from several fragmentary paramedian osteoderms from PEFO and the nearby Placerias Quarry, however the anatomy of the lateral osteoderms remained unknown. Here, we refer an isolated lateral osteoderm from the Placerias Quarry to K. caerula based on an ornamentation composed of large elliptical-to-rounded pits on the dorsal surface that are randomly arranged, a prominent anterior bar, a strongly obtuse angle between two partially preserved flanges, an elongate lateral eminence (spine) with a strongly embayed posterior margin, and sharp anterior ridge. This combination of anatomical features of the isolated lateral osteoderm is clearly aetosaurian and differs in significant ways from the other known aetosaurian taxa from the site. A parsimony analysis recovers K. caerula nested within the inclusive clade Typothoracinae. This lateral osteoderm demonstrates that K. caerula was a spinose aetosaur, a bauplan observed in both typothoracine and desmatosuchin aetosaurians. Thus, further highlighting observed convergence between these groups and indicating a need for a reevaluation of lateral osteoderm characters used for phylogenetic analyses.

New perspectives on NPS paleontological resource stewardship: Scientific, curatorial, and educational outcomes at Petrified Forest National Park

New perspectives on NPS paleontological resource stewardship: Scientific, curatorial, and educational outcomes at Petrified Forest National Park

RESILIENCE OF THE GLADIATOR MILKVETCH (ASTRAGALUS XIPHOIDES), A RARE, ENDEMIC PLANT OF PETRIFIED FOREST NATIONAL PARK, OVER A CENTURY AND THROUGH PROLONGED DROUGHT

Hiding among eroding badlands, hoodoos, and ephemeral washes of Petrified Forest National Park is a rare, narrow endemic with a peculiar name, the Gladiator milkvetch (Astragalus xiphoides). First discovered in the park in 1940, its scarcity and range were largely unknown until the 1980s when the species was designated as a candidate for listing under the Endangered Species Act. Focused surveys for the species were conducted in Petrified Forest National Park in 1989, identifying 16 distinct populations. Beginning in 1995, the park experienced a 27-year period of prolonged drought ending in 2022. This article summarizes the recent efforts by the National Park Service to locate these 16 populations in order to assess the plants resilience through prolonged drought. Eight of the populations surveyed in 1989 persist today, with some populations declining in density by 80–90 percent and others remaining stable with modest increases in density.

JAVELINA (DICOTTYLES TAJACU) RANGE EXTENSION INDICATED BY NEW SIGHTINGS IN PETRIFIED FOREST NATIONAL PARK

Javelina sightings in Petrified Forest National Park (PEFO) are increasing after the first recorded observation in 2018. The current seven recorded sightings detailed in this report are just the latest observations in an apparent northward expansion of this species. While not surprising due to unrecorded sightings from Arizona Game and Fish Department (AZGFD) and increased surveillance, javelina have not been officially documented in this region before. Habitat change due to overgrazing and drought as well as warmer temperatures may play a factor in this expansion.

Incongruent ontogenetic maturity indicators in a Late Triassic archosaur (Aetosauria: Typothorax coccinarum).

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., Coahomasuchus kahleorum) and 5 m (e.g., Desmatosuchus spurensis). A new, very large specimen of the aetosaurian Typothorax coccinarum from Petrified Forest National Park in northeastern Arizona is nearly twice the size of all other known specimens of Typothorax and is the largest aetosaur specimen currently known worldwide. The specimen lacks co-ossified neurocentral sutures in the trunk vertebrae which may suggest that the individual had not yet reached skeletal maturity, yet smaller specimens of T. coccinarum exhibit partially or fully co-ossified neurocentral sutures in the same region. If body size correlates with skeletal maturity in aetosaurs, this discrepancy warns that timing of neurocentral suture co-ossification in aetosaurs may not be a reliable indicator of ontogenetic stage. Osteohistological observations of a trunk rib demonstrate that although PEFO 42506 showsa large body size, the specimen did not deposit an external fundamental system despite depositing as many as 19 growth lines, further indicating that it had not yet reached skeletal maturity. Thus, at least within Aetosauria, neurocentral suture co-ossification and skeletal maturity may correlate, whereas body size can be incongruent in comparison. Furthermore, this specimen indicates that non-desmatosuchin aetosaurs could exhibit large body sizes and suggests that some aetosaurs may have experienced indeterminate growth.

Multispectral satellite imaging improves detection of large individual fossils

AbstractPalaeontological field surveys in remote regions are a challenge, because of uncertainty in finding new specimens, high transportation costs, risks for the crew and a long time commitment. The effort can be facilitated by using high-resolution satellite imagery. Here we present a new opportunity to investigate remote fossil localities in detail, mapping the optical signature of individual fossils. We explain a practical workflow for detecting fossils using remote-sensing platforms and cluster algorithms. We tested the method within the Petrified Forest National Park, where fossil logs are sparse in a large area with mixed lithologies. We ran both unsupervised and supervised classifications, obtaining the best estimations for the presence of fossil logs using the likelihood and spectral angle mapper algorithms. We recognized general constraints and described logical and physical pros and cons of each estimated map. We also explained how the outcomes should be critically evaluated with consistent accuracy tests. Instead of searching for fossiliferous outcrops, our method targets single fossil specimens (or highly condensed accumulations), obtaining a significant increase in potential efficiency and effectiveness of field surveys. When repeatedly applied to the same region over time, it could also be useful for monitoring palaeontological heritage localities. Most importantly, the method here described is feasible, easily applicable to both fossil logs and bones, and represents a step towards standard best practices for applying remote sensing in the palaeontological field.

Puercosuchus traverorum n. gen. n. sp.: a new malerisaurine azendohsaurid (Archosauromorpha: Allokotosauria) from two monodominant bonebeds in the Chinle Formation (Upper Triassic, Norian) of Arizona

AbstractNon-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 postcranial body plan but evolved disparate cranial features that converge on later dinosaurian anatomy, including sauropodomorph-like marginal dentition and ceratopsian-like postorbital horns. Here we describe a new malerisaurine azendohsaurid from two monodominant bonebeds in the Blue Mesa Member, Chinle Formation (Late Triassic, ca. 218–220 Ma); the first occurs at Petrified Forest National Park and preserves a minimum of eight individuals of varying sizes, and the second occurs near St. Johns, Arizona. Puercosuchus traverorum n. gen. n. sp. is a carnivorous malerisaurine that is closely related to Malerisaurus robinsonae from the Maleri Formation of India and to Malerisaurus langstoni from the Dockum Group of western Texas. Dentigerous elements from Puercosuchus traverorum n. gen. n. sp. confirm that some Late Triassic tooth morphotypes thought to represent early dinosaurs cannot be differentiated from, and likely pertain to, Puercosuchus-like malerisaurine taxa. These bonebeds from northern Arizona support the hypothesis that non-archosauriform archosauromorphs were locally diverse near the middle Norian and experienced an extinction event prior to the end-Triassic mass extinction coincidental with the Adamanian-Revueltian boundary recognized at Petrified Forest National Park. The relatively late age of this early-diverging taxon (Norian) suggests that the diversity of azendohsaurids is underrepresented in Middle and Late Triassic fossil records around the world.UUID: http://zoobank.org/e6eeefd2-a0ae-47fc-8604-9f45af8c1147.

A geochronologically-constrained stable isotope record of the Upper Triassic Sonsela Member (Chinle Formation) at Petrified Forest National Park (Arizona, USA): Testing for paleoenvironmental linkages with biotic change and the Manicouagan impact

The Upper Triassic Chinle Formation, cropping out in and around Petrified Forest National Park (PFNP) in northern Arizona, U.S.A., preserves an important non-marine biotic and sedimentologic record of Late Triassic key Earth-life events. In 2013, the Colorado Plateau Coring Project (CPCP) obtained a 520-m-long core of the Triassic strata at PFNP to study this sedimentary record in unequivocal superposition and, among other goals, to test hypotheses about the paleoenvironmental and biotic changes preserved in the Sonsela Member of the Chinle Formation, and specifically their link to the Manicouagan impact and the Adamanian-Revueltian biotic turnover event (A-R transition). We sampled the Sonsela Member of CPCP core 1A for bulk organic material and for pedogenic carbonates to establish the δ13Corg, δ13Ccarb, and δ18Ocarb records. Throughout much of the Sonsela Member, the stable isotope record is characterized by a relatively narrow range of values (δ13Corg = ~ −25 to −30‰; δ13Ccarb = ~ −7 to −10‰; and δ18Ocarb = ~ −5 to −8‰). Based on these data, we estimate mean annual precipitation and correlate our isotope record to two previously developed, high resolution, multi-proxy age models for the CPCP core. Our new data set supports three main conclusions based on these observations: (1) whereas the A-R transition and the Manicouagan impact event might correlate in time, establishing a causal relationship between those two events remains challenging; (2) the Manicouagan impact as well as the A-R transition are not linked to a clear geochemical perturbation preserved in the CPCP core; and (3) multiple proxies agree the climate became more arid throughout the Sonsela Member, possibly contributing to the Adamanian-Revueltian biotic turnover.

Petrified Forest National Park: A Project to Improve Weather Data Collection Helps Preserve Ancient Ruins

The Badlands in Petrified Forest National Park.Petrified Forest National Park (or PEFO as the rangers and scientists call it), which resides along the famous Route 66 highway (now Interstate 40), i...

Osteology and relationships of Revueltosaurus callenderi (Archosauria: Suchia) from the Upper Triassic (Norian) Chinle Formation of Petrified Forest National Park, Arizona, United States.

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 combination of plesiomorphic and derived character states that help clarify ingroup relationships within Pseudosuchia. A phylogenetic analysis recovers R. callenderi in a clade with Aetosauria and Acaenasuchus geoffreyi that is named Aetosauriformes. Key autapomorphies of R. callenderi include a skull that is longer than the femur, a complete carapace of dermal armor including paramedian and lateral rows, as well as ventral osteoderms, and a tail end sheathed in bone. Histology of the femur and associated osteoderms demonstrate that R. callenderi was slow growing and that the individuals from the bonebed were not young juveniles but had not ceased growing. A review of other material assigned to Revueltosaurus concludes that the genus cannot be adequately diagnosed based on the type materials of the three assigned species and that only R. callenderi can be confidently referred to Revueltosaurus.

Magnetostratigraphy of the Triassic Moenkopi Formation From the Continuous Cores Recovered in Colorado Plateau Coring Project Phase 1 (CPCP‐1), Petrified Forest National Park, Arizona, USA: Correlation of the Early to Middle Triassic Strata and Biota in Colorado Plateau and Its Environs

AbstractThe 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 cores to construct a high‐resolution magnetostratigraphy of MF strata, and progressive demagnetization data yield well‐defined, interpretable paleomagnetic results. Each lithostratigraphic member of the MF (Wupatki, Moqui, and Holbrook members) contains authigenic and detrital hematite as the dominant magnetic carrier with distinguishing rock magnetic characteristics. Magnetostratigraphy of MF strata in both CPCP‐1 cores consists of six normal and six reverse polarity magnetozones, from the youngest to the oldest, MF1n to MF6r. Recent single‐crystal chemical abrasion–thermal ionization mass spectrometry (CA‐TIMS) U‐Pb data from a sample in magnetozone MF1n yield a latest Anisian/earliest Ladinian (241.38 ± 0.43 Ma) age. Correlation of the CA‐TIMS‐calibrated magnetostratigraphy with the astronomically tuned polarity timescale for the Middle Triassic deep‐marine Guandao (GD) section of South China ties the magnetozone MF1n with GD8 and MF6r with GD2r, and implies that the MF spans, at most, the earliest Anisian (Aegean) to latest Anisian (Illyrian)/earliest Ladinian stages (ca. 246.8 to 241.5 Ma). This age estimate for the MF suggests that the timespan of the regional, pre‐Norian disconformity is about 17 Ma, which demonstrates that MF vertebrate fossil assemblages in east‐central Arizona are millions of years (minimally 3–4 Ma) younger than previously suggested and are all Anisian in age, with no indications of substantial hiatuses in the MF section.

First occurrence of Doswellia cf. D. kaltenbachi (Archosauriformes) from the Late Triassic (middle Norian) Chinle Formation of Arizona and its implications on proposed biostratigraphic correlations across North America during the Late Triassic

ABSTRACT 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 holochronozone (Late Triassic: middle Norian) in Petrified Forest National Park and firmly establishes the presence of this taxon in the Adamanian. This occurrence adds to the diverse vertebrate assemblage of the upper part of the Blue Mesa Member of the Chinle Formation (Adamanian). More broadly, the new occurrence strengthens biogeographic links to the older (latest Carnian or earliest Norian) Otischalkian from Texas and the possibly older Sanfordian/Conewagian assemblages of Virginia. The spatiotemporal distribution of Doswellia underscores the similarity of North American continental vertebrate assemblages across the Carnian–Norian boundary prior to the Adamanian–Revueltian boundary.

Cranial anatomy and dentition of the aetosaur Typothorax coccinarum (Archosauria: Pseudosuchia) from the Upper Triassic (Revueltian–mid Norian) Chinle Formation of Arizona

ABSTRACT 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 synapomorphies for some of the major clades within Aetosauria by using a combination of morphological characters in the cranium of Typothorax coccinarum. Based on the descriptions of skulls from a variety of aetosaur species including Aetosaurus ferratus, Aetosauroides scagliai, Coahomasuchus chathamensis, Neoaetosauroides engaeus, Paratypothorax andressorum, Stagonolepis olenkae, Stenomyti huangae, Scutarx deltatylus, and now Typothorax coccinarum, it is apparent that the two major aetosaurian clades vary in their overall skull morphologies. The stagonolepidoids share a more robust, elongate skull, with varying degrees in the lateral expansion of the premaxillary tips. On the other hand, aetosaurines share an overall shorter, more gracile skull with tapered premaxillae. These new characters are mapped onto a revised phylogenetic tree for the Aetosauria. Historically, aetosaurs were interpreted as being predominantly herbivorous. In recent years, the discovery of new aetosaur cranial material, like that of Neoaetosauroides engaeus and Aetosauroides scagliai, suggested an omnivorous diet for at least some aetosaur taxa. The dentition of Typothorax coccinarum possesses the most strongly developed heterodonty for an aetosaur, therefore challenging the historical interpretation by expanding the range of dentition types within Aetosauria. This supports the more recent hypothesis that aetosaurs exhibited diverse feeding strategies beyond just herbivory.

Fire-scarred fossil tree from the Late Triassic shows a pre-fire drought signal

Exploring features of wood anatomy associated with fire scars found on fossil tree trunks is likely to increase our knowledge of the environmental and ecological processes that occurred in ancient forests and of the role of fire as an evolutionary force. In Petrified Forest National Park, Arizona, where Late Triassic fossil trees are exposed, we found 13 examples of fossil logs with external features resembling modern fire scars. One specimen with the unambiguous external features of a fire scar was collected for analysis of its fossilized wood. A light-colored band composed of compressed and distorted tracheids was associated with the scarring event. Cell lumen diameter and cell wall thickness in the pre-scarring fossilized wood show a response similar to that described in modern trees experiencing drought conditions. Tracheids in the post-scarring wood are initially smaller, and then become larger than average following a recovery period, as is often observed in modern conifers following fire. The responses in external morphology and wood anatomy to drought and fire were similar to those of some modern trees and support the view that some forests may have experienced conditions favoring the evolution of fire-adapted traits for more than 200 million years.

New dinosauromorph specimens from Petrified Forest National Park and a global biostratigraphic review of Triassic dinosauromorph body fossils

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 identify previously collected specimens in museum collections. Here we briefly describe and use apomorphies to identify 32 additional dinosauromorph specimens found at Petrified Forest National Park, bringing the total number of dinosauromorph specimens presently known from the park to 50, a 600% increase since the year 2000. These specimens are all Norian in age and come from the Blue Mesa Member, Sonsela Member, and Petrified Forest Member of the Chinle Formation. These include the proximal end of a tibia that represents the oldest unambiguous dinosaur specimen from the Chinle Formation. We then contextualize these specimens with the dinosauromorph assemblages from the Norian of Utah, Colorado, New Mexico, and Texas, as well as the Carnian and Norian dinosauromorph assemblages from South America, Africa, and Europe. Despite increased sampling we still find no evidence for sauropodomorph and ornithischian dinosaurs in Western North America. An increase in sampling, combined with the use of apomorphies to identify collected specimens, will continue to improve the global dinosauromorph fossil record that can be used to answer questions on biochronology and the evolutionary history of the avian lineage.

Using Manual Ungual Morphology to Predict Substrate Use in the Drepanosauromorpha and the Description of a New Species

ABSTRACT Fossils of drepanosauromorphs, a clade of non-saurian diapsids, were once considered relatively rare in the Chinle Formation of the southwestern United States as well as in Upper Triassic rocks globally. Recent discoveries have shown that there are at least four drepanosauromorph taxa present in the Chinle Formation including Dolabrosaurus aquatilis, Drepanosaurus sp., Ancistronychus paradoxus, and a new genus and species described here, Skybalonyx skapter. This new taxon is represented by disarticulated manual unguals and is preserved in a microvertebrate bearing bone-bed in the Blue Mesa Member (∼223–220 Ma) of the Chinle Formation at Petrified Forest National Park, which was deposited in a fluvio-lacustrine setting in equatorial Pangaea during the mid-Norian. Different types of substrate use have been hypothesized for the Drepanosauromorpha. By performing discriminant function analyses using the manual unguals of 173 mammal and 13 reptile species with known substrate use, we hope to infer the ecomorphology of drepanosauromorphs. We found that the enlarged second manual unguals of Drepanosaurus sp. are similar to hook-and-pull digging taxa (e.g., Tamandua mexicana and Cyclopes didactylus) although the smaller manual unguals referred to this taxon (likely pertaining to digits other than digit II) are similar to modern arboreal taxa. Our results support the inference of arboreality in some drepanosauromorph species. However, we found that the manual unguals of Ancistronychus paradoxus and Skybalonyx skapter fit within the range of variation of modern fossorial and subterranean taxa, which expands the functional diversity of the Drepanosauromorpha within the Chinle Formation.

LA-ICPMS U–Pb geochronology of detrital zircon grains from the Coconino, Moenkopi, and Chinle formations in the Petrified Forest National Park (Arizona)

Abstract. 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 Project (CPCP), located in Petrified Forest National Park (Arizona). A sample from the lower Permian Coconino Sandstone yields a broad distribution of Proterozoic and Paleozoic ages that are consistent with derivation from the Appalachian and Ouachita orogens, with little input from local basement or Ancestral Rocky Mountain sources. Four samples from the Holbrook Member of the Moenkopi Formation yield a different set of Precambrian and Paleozoic age groups, indicating derivation from the Ouachita orogen, the East Mexico arc, and the Permo-Triassic arc built along the Cordilleran margin. A total of 23 samples from the Chinle Formation contain variable proportions of Proterozoic and Paleozoic zircon grains but are dominated by Late Triassic grains. LA-ICPMS ages of these grains belong to five main groups that correspond to the Mesa Redondo Member, Blue Mesa Member and lower part of the Sonsela Member, upper part of the Sonsela Member, middle part of the Petrified Forest Member, and upper part of the Petrified Forest Member. The ages of pre-Triassic grains also correspond to these chronostratigraphic units and are interpreted to reflect varying contributions from the Appalachian orogen to the east, Ouachita orogen to the southeast, Precambrian basement exposed in the ancestral Mogollon Highlands to the south, East Mexico arc, and Permian–Triassic arc built along the southern Cordilleran margin. Triassic grains in each chronostratigraphic unit also have distinct U and thorium (Th) concentrations, which are interpreted to reflect temporal changes in the chemistry of arc magmatism. Comparison of our LA-ICPMS ages with available chemical abrasion thermal ionization mass spectrometry (CA-TIMS) ages and new magnetostratigraphic data provides new insights into the depositional history of the Chinle Formation, as well as methods utilized to determine depositional ages of fluvial strata. For parts of the Chinle Formation that are dominated by fine-grained clastic strata (e.g., mudstone and siltstone), such as the Blue Mesa Member and Petrified Forest Member, all three chronometers agree (to within ∼ 1 Myr), and robust depositional chronologies have been determined. In contrast, for stratigraphic intervals dominated by coarse-grained clastic strata (e.g., sandstone), such as most of the Sonsela Member, the three chronologic records disagree due to recycling of older zircon grains and variable dilution of syn-depositional-age grains. This results in LA-ICPMS ages that significantly predate deposition and CA-TIMS ages that range between the other two chronometers. These complications challenge attempts to establish a well-defined chronostratigraphic age model for the Chinle Formation.