Crosbysaurus: Another Occurrence of an Engimatic Norian Triassic Archosaur

The first occurrence of the enigmatic archosaur Crosbysaurus (Heckert 2004) from the Chinle Formation of Southern Utah

Authors:

Gay et al

Abstract:

Originally identified as an ornithisichian dinosaur, Crosbysaurus has been found in New Mexico, Arizona, and the type locality in Texas, the genus has been reassessed by other workers in light of revelations about the postcrania of another putative Triassic ornithischian, Revueltosaurus. The understanding of Triassic dental faunas has become more complicated by the extreme convergence between pseudosuchian archosaurus and ornithichian dinosaur dental morphologies. This new specimen does not help resolve the affinities of Crosbysaurus but does extend the range of this taxon into southern Utah. This specimen may also represent the youngest-known member of this genus

An Apex Predator Eat Apex Predator World in the Norian Triassic Chinle Formation

Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America

Authors:

Drumheller et al

Abstract:

Hypotheses of feeding behaviors and community structure are testable with rare direct evidence of trophic interactions in the fossil record (e.g., bite marks). We present evidence of four predation, scavenging, and/or interspecific fighting events involving two large paracrocodylomorphs (=‘rauisuchians’) from the Upper Triassic Chinle Formation (∼220–210 Ma). The larger femur preserves a rare history of interactions with multiple actors prior to and after death of this ∼8–9-m individual. A large embedded tooth crown and punctures, all of which display reaction tissue formed through healing, record evidence of a failed attack on this individual. The second paracrocodylomorph femur exhibits four unhealed bite marks, indicating the animal either did not survive the attack or was scavenged soon after death. The combination of character states observed (e.g., morphology of the embedded tooth, ‘D’-shaped punctures, evidence of bicarination of the marking teeth, spacing of potentially serial marks) indicates that large phytosaurs were actors in both cases. Our analysis of these specimens demonstrates phytosaurs targeted large paracrocodylomorphs in these Late Triassic ecosystems. Previous distinctions between ‘aquatic’ and ‘terrestrial’ Late Triassic trophic structures were overly simplistic and built upon mistaken paleoecological assumptions; we show they were intimately connected at the highest trophic levels. Our data also support that size cannot be the sole factor in determining trophic status. Furthermore, these marks provide an opportunity to start exploring the seemingly unbalanced terrestrial ecosystems from the Late Triassic of North America, in which large carnivores far outnumber herbivores in terms of both abundance and diversity.

Revised Chronostratigraphy of Chinle Formation has Implications for Late Triassic Dinosaur Evolution

Revised chronostratigraphy of the Lower Chinle Formation strata in Arizona and New Mexico (USA): High-precision U-Pb geochronological constraints on the Late Triassic evolution of dinosaurs

Authors:

Ramezani et al

Abstract:

The early history of dinosaurs in North America is obscured by an incomplete fossil record, taxonomic uncertainties and speculative correlations of tetrapod-bearing rocks, as well as poor calibration of the Late Triassic time scale. High-precision U-Pb geochronology provides a reliable means of correlating terrestrial rock formations independent of equivocal lithostratigraphy or vertebrate biostratigraphy, and hence the possibility of properly evaluating models for the early radiation and diversification of Dinosauria. Here we present new, high-precision, U-Pb ID-TIMS zircon geochronology from the presumed lowermost strata of the Upper Triassic Chinle Formation of the Colorado Plateau in Southwest United States, including a mean 206Pb/238U date of 219.39 ± 0.16 Ma from the renowned Placerias Quarry Bone Bed in eastern Arizona. The new results prompt revisions to the chronostratigraphy of the lower Chinle and provide a new temporal context for its rich tetrapod fauna.

The oldest documented dinosaurs of North America coexisted with their non-dinosaurian near-relatives for a minimum of 12 m.y., from ca. 223 Ma to ca. 211 Ma, in the Norian. This early dinosauromorph record follows a ca. 6 m.y. period from which no tetrapod fossils have been documented and which was itself preceded by a ca. 10 m.y. depositional hiatus spanning nearly the entire Ladinian and Carnian stages of the terrestrial North America. The supposed late appearance of dinosauromorphs in North America compared to those in South America thus appears to be an artifact of incomplete preservation, as well as unsubstantiated age interpretations. This, together with the conspicuous biogeographic distinctions among the Triassic dinosauromorph assemblages, invalidates a simple diachronous model for the transcontinental radiation of early dinosaurs.

Fire Scars Found on Petrified Wood From Late Triassic Chinle Formation

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

Authors:

Byers et al

Abstract:

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 (~ 200–225 Ma). 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.

New Gymnosperms From Triassic Chinle Formation

Contributions to the Upper Triassic Chinle flora in the American southwest

Authors:

Ash

Abstract:

This article summarises an investigation of three selected species of fossil gymnosperms collected from the Upper Triassic Chinle Formation of the American southwest. Included here is an emended diagnosis of Lindleycladus arizonicus (Daugherty) comb. nov., a description of Elatocladus puercoensis sp. nov., and a redescription, based on new material, of the contentious plant fossil Dechellyia gormanii Ash. Also, the evidence (excisions and galls) of insect predation found on some of the leaves of the new specimens of D. gormanii is described and compared with that reported earlier on other fossil leaves in the Chinle Formation.

Floodplain Paleobotany in the Upper Triassic of the Sonsela Member of the Chinle Formation

DETERMINING FLOODPLAIN PLANT DISTRIBUTIONS AND POPULATIONS USING PALEOPEDOLOGY AND FOSSIL ROOT TRACES: UPPER TRIASSIC SONSELA MEMBER OF THE CHINLE FORMATION AT PETRIFIED FOREST NATIONAL PARK, ARIZONA

Authors:

1. AISLYN M. TRENDELL (a,c)
2. LEE C. NORDT (a)
3. STACY C. ATCHLEY 9a)
4. STEPHANIE L. LEBLANC (a,b)
5. STEPHEN I. DWORKIN (a)

Affiliations:

a.  Baylor University, Department of Geology, One Bear Place #97354, Waco, Texas 76798-7354, USA

b. Oklahoma State University, Boone Pickens School of Geology, Stillwater, Oklahoma 74078, USA, sleblan@ostatemail.okstate.edu

c. Listed in authors, but not in text

Abstract:

The Upper Triassic Sonsela Member of the Chinle Formation is an alluvial succession containing interbedded sandstone and pedogenically modified mudstone. Despite preservation of silicified logs within channel sandstone beds, the Sonsela plant ecosystem is less understood than other intervals due to decreased preservation of nonconifer plant taxa. Sonsela paleosols and rhizoliths are evaluated using macromorphology, micromorphology, and geochemistry to determine the spatial distribution of paleosol characteristics and plant sizes and densities across the study area. Three pedotypes identified within the Sonsela are classified as Inceptisols and Vertisols that exhibit fining of matrix textures (from clayey siltstone to claystone) and reduced drainage with distance from the paleochannel. Overall, Sonsela paleosols are immature, suggesting that the Sonsela fluvial system experienced high rates of lateral migration and cannibalization of overbank sediments in a low-subsidence regime. Rhizohalos within the Sonsela Member are likely diagenetic and commonly include silicified roots (silica root petrifactions). Silicified roots provide information on root size and density that is not commonly afforded by other rhizolith types. Diagenetic rhizohalo diameters may be controlled by paleosol matrix textures within the Sonsela Member. Rhizolith characteristics suggest that channel-proximal paleosols contained only small-stature plants while distal floodplain paleosols may have hosted both small-stature and arborescent plants. Paleosols within the Sonsela Member do not contain rhizoliths whose size or abundance are reflective of a dense coniferous forest. Floodplain plants were commonly small of stature and immature, unable to evolve into more mature communities due to high rates of floodplain cannibalization during fluvial migration.

New Species of Doswellia from the Triassic of New Mexico

A NEW SPECIES OF THE ENIGMATIC ARCHOSAUROMORPH DOSWELLIA FROM THE UPPER TRIASSIC BLUEWATER CREEK FORMATION, NEW MEXICO, USA

Authors:

1. ANDREW B. HECKERT (a,*)
2. SPENCER G. LUCAS (b)
3. JUSTIN A. SPIELMANN (b)

Affiliations:

a. Department of Geology, Appalachian State University, ASU Box 32067, Boone, NC 28608-2067, USA

b. New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104-1375, USA

*. Corresponding author: e-mail: heckertab@appstate.edu

Abstract:

Doswellia sixmilensis is a new species of the doswelliid archosauromorph genus Doswellia named for an incomplete skeleton from the Upper Triassic Bluewater Creek Formation of the Chinle Group in west-central New Mexico, USA. D. sixmilensis differs from D. kaltenbachi Weems, the type and only other known species of Doswellia, in its larger size, higher tooth count and greater heterodonty, possession of keels on the cervical centra and the presence of discrete knobs or spikes on some osteoderms. The holotype of D. sixmilensis is the fourth occurrence of Doswellia and only the second occurrence of a Doswellia skull, which includes the previously unknown premaxilla and maxilla (and therefore the best dentition) and has the best-preserved cervical vertebrae. Although it adds to our knowledge of the anatomy of Doswellia, this new information does not alter previous concepts of the phylogenetic relationships of the doswelliid genera, largely because they are so poorly known anatomically. The genus Doswellia is known from the Newark Supergroup in Virginia, and the Chinle Group in Texas, New Mexico and Utah, in strata of Otischalkian–Adamanian age. The type locality of D. sixmilensis is c. 43 m stratigraphically below a bed from which U-Pb dating of detrital zircons yields a maximum depositional age of c. 220 Ma, so this is a reasonable approximate numerical age for D. sixmilensis.