Late Triassic Chinle Formation Research Articles

A new aetosaur (Archosauria: Pseudosuchia) from the upper Blue Mesa Member (Adamanian: Early–Mid Norian) of the Late Triassic Chinle Formation, northern Arizona, USA, and a review of the paratypothoracin <i>Tecovasuchus</i> across the southwestern USA

A new aetosaur (Archosauria: Pseudosuchia) from the upper Blue Mesa Member (Adamanian: Early–Mid Norian) of the Late Triassic Chinle Formation, northern Arizona, USA, and a review of the paratypothoracin <i>Tecovasuchus</i> across the southwestern USA

BITE MARKS ON AN AETOSAUR (ARCHOSAURIA, SUCHIA) OSTEODERM: ASSESSING LATE TRIASSIC PREDATOR-PREY ECOLOGY THROUGH ICHNOLOGY AND TOOTH MORPHOLOGY

ABSTRACTTrace fossils such as bite marks provide rare, direct evidence of animal behavior, including predator-prey interactions. We present an osteoderm of the aetosaur Typothorax coccinarum from the Late Triassic Chinle Formation of Arizona with several punctures and scores, interpreted here as bite marks, preserved as evidence of predation/scavenging by a large carnivore. The marks include a single bite producing four subparallel fusiform pits on the ventral surface and several additional marks, including striated scores, on the dorsal surface. These traces are described and compared with known contemporaneous carnivorous taxa to determine the source of the bite marks. Some Triassic carnivores, including theropod dinosaurs can be ruled out because of tooth shape and serration densities. Phytosaurs and large paracrocodylomorphs remain as likely candidates based on tooth morphology. Although some phytosaur teeth are too rounded to produce the marks seen in this specimen, we demonstrate that the more lingually flattened teeth typically found in the posterior section of the snout are sufficiently mediolaterally compressed to produce a fusiform pit. A protective function for aetosaur osteoderms cannot be confirmed presently, but the extensive carapace these bones formed would have been a major barrier to both scavengers and active predators and may preserve more feeding/predation traces than previously thought. The bite marks described herein support the hypothesis that aetosaurs were prey items of large archosauromorphs, expanding our understanding of the complex, and seemingly carnivore dominated Late Triassic terrestrial ecosystems of North America.

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.

Magnetochronology of the Entire Chinle Formation (Norian Age) in a Scientific Drill Core From Petrified Forest National Park (Arizona, USA) and Implications for Regional and Global Correlations in the Late Triassic

AbstractBuilding 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 National Park (Arizona, USA). The 335‐m‐thick Chinle section is imprinted with paleomagnetic polarity zones PF1r to PF10n, which we correlate to chrons E17r to E9n (~209 to 224 Ma) of the Newark‐Hartford astrochronostratigraphic polarity time scale. A sediment accumulation rate of ~34 m/Myr can be extended down to ~270 m, close to the base of the Sonsela Member and the base of magnetozone PF5n, which we correlate to chron E14n that onsets at 216.16 Ma. Magnetozones PF5r to PF10n in the underlying 65‐m‐thick section of the mudstone‐dominated Blue Mesa and Mesa Redondo members plausibly correlate to chrons E13r to E9n, indicating a sediment accumulation rate of only ~10 m/Myr. Published high‐precision U‐Pb detrital zircon dates from the lower Chinle tend to be several million years older than the magnetochronological age model. The source of this discrepancy is unclear but may be due to sporadic introduction of juvenile zircons that get recycled. The new magnetochronological constraint on the base of the Sonsela Member brings the apparent timing of the included Adamanian‐Revueltian land vertebrate faunal zone boundary and the Zone II to Zone III palynofloral transition closer to the temporal range of the ~215 Ma Manicouagan impact structure in Canada.

Redescription of the holotype specimen of Chindesaurus bryansmalli Long and Murry, 1995 (Dinosauria, Theropoda), from Petrified Forest National Park, Arizona

ABSTRACTChindesaurus 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 non-eusaurischian saurischian, a herrerasaurid, and/or a non-neotheropod member of Theropoda. Chindesaurus bryansmalli is usually scored for about 25% of the characters in a given phylogenetic analysis, and many characters have been scored secondhand from misidentified elements. Here, we provide a redescription of the holotype specimen of C. bryansmalli, correct misidentifications, introduce previously unknown elements, and discuss novel morphological character observations. Chindesaurus bryansmalli is supported as the sister taxon to the non-neotheropod theropod Tawa hallae from the Chinle Formation at Ghost Ranch, New Mexico. The same two most parsimonious trees, with increasing node support, result from iteratively removing the three most incomplete taxa in the employed data set, suggesting that the relationships of stem-averostran theropods are not highly affected by the inclusion of fragmentary specimens. The Chindesaurus + Tawa clade recovered here may represent a potentially diverse group of early theropods prior to the end-Triassic mass extinction.

First records of diapsid Palacrodon from the Norian, Late Triassic Chinle Formation of Arizona, and their biogeographic implications

First records of diapsid Palacrodon from the Norian, Late Triassic Chinle Formation of Arizona, and their biogeographic implications

First known fire scar on a fossil tree trunk provides evidence of Late Triassic wildfire

Fire scars are well known to fire ecologists and dendrochronologists worldwide, and are used in dating fires and reconstructing the fire histories of modern forests. Evidence of fires in ancient forests, such as fossil charcoal (fusain), is well known to paleontologists and has been reported in geologic formations dating back to the Late Devonian. We describe what we conclude is a fire scar on a fossil tree trunk from the Late Triassic Chinle Formation of southeastern Utah (~200–225Ma). The external features of the prehistoric scar match those of modern fire scars better than those of scars created by other kinds of wounding events. The fossil specimen also exhibits a number of changes in wood anatomy similar to those reported in modern fire-scarred trees, including a band of very small tracheids that indicate growth suppression immediately associated with the scarring event; an area with a tangential row of probable traumatic resin ducts; and a significant increase in tracheid size following the scarring event that indicates a growth release. No fire scar resembling those in modern trees has previously been described in petrified wood as far as we can determine. The presence of a fire scar not only provides further evidence of ancient fires, but also shows that at least some individual trees survived them, indicating that fire could have been an ecological and evolutionary force in forests at least as early as the Late Triassic.

The Earliest Evidence of Holometabolan Insect Pupation in Conifer Wood

BackgroundThe pre-Jurassic record of terrestrial wood borings is poorly resolved, despite body fossil evidence of insect diversification among xylophilic clades starting in the late Paleozoic. Detailed analysis of borings in petrified wood provides direct evidence of wood utilization by invertebrate animals, which typically comprises feeding behaviors.Methodology/Principal FindingsWe describe a U-shaped boring in petrified wood from the Late Triassic Chinle Formation of southern Utah that demonstrates a strong linkage between insect ontogeny and conifer wood resources. Xylokrypta durossi new ichnogenus and ichnospecies is a large excavation in wood that is backfilled with partially digested xylem, creating a secluded chamber. The tracemaker exited the chamber by way of a small vertical shaft. This sequence of behaviors is most consistent with the entrance of a larva followed by pupal quiescence and adult emergence — hallmarks of holometabolous insect ontogeny. Among the known body fossil record of Triassic insects, cupedid beetles (Coleoptera: Archostemata) are deemed the most plausible tracemakers of Xylokrypta, based on their body size and modern xylobiotic lifestyle.Conclusions/SignificanceThis oldest record of pupation in fossil wood provides an alternative interpretation to borings once regarded as evidence for Triassic bees. Instead Xylokrypta suggests that early archostematan beetles were leaders in exploiting wood substrates well before modern clades of xylophages arose in the late Mesozoic.

THE BARK OF THE LATE TRIASSIC ARAUCARIOXYLON ARIZONICUM TREE FROM PETRIFIED FOREST NATIONAL PARK, ARIZONA

This paper contains a description of the only known non-banded bark in the geologic record. The bark is attached to a branch of the Araucarioxylon arizonicum tree that was found recently in the Late Triassic Chinle Formation (~ 220 Mya) in Arizona. In the fossil the vascular cylinder is almost totally enclosed in rough bark 2–11 mm in thickness. The inner bark is less than 1 mm thick and comprises a very narrow zone of presumed phloem containing infrequent fibers. The outer bark varies in thickness up to 10 mm, and consists of curving lenses of sequent periderm free of both dilation tissue and resin canals but is quite unlike the banded bark of Araucaria heterophylla. Wide zones of very thin-walled rectangular parenchyma cells arranged in radial files and groups of thin-walled spongy parenchyma, and small clusters as well as solitary sclerenchyma occur in the rhytidome. The vascular cambium contains 1–4 fusiform cells per radial file. Uniseriate rays are common in the secondary xylem and extend to the cambial zone. Small (1 mm in diameter), simple tunnels in the bark and wood indicate that the branch was attacked by phytophagous insects. A possible petrified beetle larva similar in form and size to Anobium is associated with these tunnels.

A Late Triassic Invertebrate Ichnofauna from Ghost Ranch, New Mexico

Invertebrate trace fossils are reported from the Late Triassic Chinle Formation at Ghost Ranch, New Mexico, for the first time. They occur in beds higher in the section than the Coelophysis Quarry. Six ichnotaxa are recognized: Steinichnus milfordensis, Planolites montanus, Palaeophycus tubularis, Taenidium serpentium, ?Arenicolites sp. and Skolithos sp. This ichnofauna is consistent with the Scoyenia ichnofacies, considered typical of lake margins in semiarid to arid regions.

Late Triassic charcoal from Petrified Forest National Park, Arizona, USA

Fossil charcoal has been found in the Late Triassic Chinle Formation in Petrified Forest National Park, a location that is world famous for its silicified tree trunks. The material consists of charcoalified secondary wood, and has sufficiently well preserved plant anatomy to show it may be described as ‘araucarian type’, although it does display some minor differences from the anatomies described for the silicified gymnosperm trunks in the park. The presence of the charcoal proves that on occasion natural wildfires, most probably ignited by lightning, must have occurred in the Chinle Triassic palaeoenvironments, with resulting impacts on the biota of those times. It is currently impossible to estimate how often these fires occurred, as the incidence of charcoal here and in the whole fossil record apart from the frequency of ancient fires also reflects the preservation and burial conditions of the material. There is scant mention of Triassic charcoal in the literature, a notable absence given the abundance of charcoal that has been recorded in the Carboniferous, Jurassic, and Cretaceous periods. This lack of charcoal may support the theory that atmospheric oxygen levels were lower during the Triassic than in the Carboniferous.

The oldest evidence of a sauropod dinosaur in the western united states and other important vertebrate trackways from grand staircase‐escalante national monument, Utah

Recent discoveries of abundant fossil footprints from the new Grand Staircase‐Escalante National Monument of southern Utah, have important implications for the spatial and temporal distribution of Mesozoic vertebrates in Triassic and Jurassic time. Since the monument's creation in 1996, fossil footprints have been reported from at least seven formations in the Mesozoic (Triassic‐Cretaceous) within the monument. By far the most significant of these discoveries are sauropod and theropod tracks from the upper part of the Middle Jurassic Entrada Sandstone and a large Apatopus trackway from the Late Triassic Chinle Formation. Tracks in the Entrada Sandstone are found at the same stratigraphic level as those in the Moab megatracksite, and so considerably extend this large ichnological complex. A wide‐gauge sauropod trackway (cf. Brontopodus) from this unit represents the first reported from the Entrada Sandstone, and so is the oldest known from the western United States. This trackway also reveals a tail trace, which is the first reliable record of a sauropod tail trace.

The Late Triassic Araucarioxylon Arizonicum trees of the Petrified Forest National Park, Arizona, USA

Examination and measurement of many of the trunks attributed to Araucarioxylon arizonicum Knowlton eroded from the Late Triassic Chinle Formation in the Petrified Forest National Park, Arizona demonstrate that the living tree did not closely resemble any of the present‐day Araucaria trees of the southern hemisphere as postulated in past reconstructions. The research indicates that it was a tall monopodial tree with branches occurring in a disordered manner on the trunk from the base to the crown. Calculations using the allometric method of Niklas indicate that the trees were of considerable size. The largest recorded trunk has a basal diameter of nearly 3 m and may represent a tree 59 m high, when living. The root system of the A. arizonicum tree consisted of a ring of four to six steeply inclined lateral roots and a massive, vertically directed tap root. Many of the trunks still have their root systems attached, a circumstance that indicates their felling by the cut‐bank operations of the local river system. The massive roots of these trunks, particularly the large tap root, are consistent with growth in soft, deep, alluvial soil, and the thin scale bark is to be expected in a tropical climate free from frost.

Vertebrate paleoecology of the Chinle formation (Late Triassic) of the Southwestern United States

The Late Triassic Chinle Formation is an extensive series of fluvial and lacustrine sediments exposed mostly in the Colorado Plateau region. Fossil vertebrates occur in local concentrations throughout the vertical and horizontal extent of the formation, although the most diverse accumulations occur within the Petrified Forest Member in Arizona and New Mexico. Successive faunas are known from the Lower and Upper Units of the Petrified Forest Member and can be subdivided into terrestrial and aquatic communities. Faunal turnover occurs among herbivores, phytosaurs, and metoposaurs between the Lower and Upper Units. No major change is observed in fish faunas throughout Chinle deposition. Mass accumulations of vertebrate fossils in the Chinle occurred on floodplains, in bogs and small ponds, and in or near fluvial channels. Paleontological and sedimentological evidence supports the interpretation of Chinle paleoclimates as having significant precipitation but being strongly seasonal. Vertebrate occurrences do not clearly reflect the gradual aridification at the end of Chinle deposition suggested by sedimentological study.

Fertile organs and in situ spores of ferns from the late Triassic Chinle Formation of Arizona and New Mexico, with discussion of the associated dispersed spores

The fertile structures of four late Triassic leptosporangiate fern species are described, as are their isolated spores. The spores are compared both with in situ spores of other known fertile species of the same genera and with the most similar dispersed spores of the Chinle Formation palynoflora. The species included in this study are Todites fragilis Daugherty emend. Ash (family Osmundaceae), Wingatea plumosa (Daugherty) Ash (family Gleicheniaceae?), Phlebopteris smithii (Daugherty) Arnold emend. Ash et al. (family Matoniaceae), and Clathropteris walkeri Daugherty emend. Ash (family Dipteridaceae). The fluvial and lacustrine, calcareous, bentonitic silstones of the Petrified Forest and Monitor Butte Members of the late Triassic Chinle Formation, from which these fern specimens were collected, bear an abundant and diverse dispersed palynoflora containing Brodispora striata, Camerosporites secatus, Enzonalasporites vigens, Granulatisporites infirmus, Ovalipollis pseudoalatus, Patinasporites densus, Pyramidosporites traversei, Pseudoenzonalasporites summus, Vallasporites ignacii, and other species. The presence of these species suggests a mid-to-late Carnian age for these strata, as was previously reported by several authors. It may be possible to place the assemblage more precisely in the late Carnian (Tuvalian substage), based on the presence of Brodispora striata and Pseudoenzonalasporites summus, the absence of Carollina, and the almost complete absence of striate bisaccate forms. In these characteristics this assemblage is similar to that in strata of the Dockum Group of the southwestern United States, parts of the “Newark Supergroup” of the eastern United States, and portions of the late Triassic of Europe.