Postcranial anatomy of Angistorhinus, a Late Triassic phytosaur from West Texas

We describe here an incomplete postcranial skeleton associated with a complete skull and jaws of the phytosaur Angistorhinus grandis Mehl from the Otischalkian (late Carnian) Colorado City Formation of the Chinle Group in Howard County, Texas. The skeleton consists of two cervical vertebrae and parts of others, complete sacrum and pelvis, 12 ribs, 30 gastralia, an incomplete fibula, fragments of other long bones, and 32 scutes. Particularly interesting features include: (1) the thin neural spines of the sacral vertebrae; (2) the ilia of Angistorhinus do not appear to differ significantly from that of Rutiodon (= "Machaeroprosopusfl), casting doubt on the taxonomic use of differences in phytosaur ilia; and (3) Angistorhinus apparently possesses dermal armor that is unique among phytosaurs in having few pits, most of them small, on the dorsal surface of the primary scutes

Diminutive metoposaurid skulls from the Upper Triassic Blue Hills (Adamanian:latest Carnian) of Arizona

We describe two tiny metoposaurid specimens from the lower part of the Chinle Group in the Blue Hills of east-central Arizona. The more complete of these specimens is an incomplete skull anterior to the orbits (45 mm preorbitallength) and numerous skull roof and palate fragments. The less complete specimen is a 25-mm-long skull roof fragment surrounding the left orbit. Based on the sutural relationships of the skull bones anterior to the orbit, we identify the more complete specimen as a juvenile of Buettneria perfecta Case, 1922 and tentatively identify the less complete specimen as Apachesaurus gregorii Hunt, 1993. These fossils are particularly important because they indicate that cranial sutures do not change significantly during metoposaurid ontogeny

Oldest records of the Late Triassic theropod dinosaur Coelophysis bauri

Coelophysis bauri is a well-known theropod dinosaur from the Upper Triassic of the southwestern United States. Prior to this study, it was only known from extensive remains from the Whitaker quarry, in the Rock Point Formation, of north-central New Mexico. Here, we document fossils of C. bauri from the Upper Triassic Snyder quarry, north-central New Mexico and from the Petrified Forest National Park. Both of these new records are from the Painted Desert Member of the Petrified Forest Formation, stratigraphically below the Rock Point Formation. This extends the biostratigraphic range of C. bauri to the early Revueltian (early-middle Norian) through the Apachean (late Norian-?Rhaetian). Thus, C. bauri is no longer an index taxon of the Apachean landvertebrate faunachron

A Late Cretaceous Mosasaur from North-Central New Mexico

We describe a partial vertebral column of a mosasaur identified as cf. Tylosaurus sp. from the lower Niobrara interval of the Mancos Shale south of Galisteo in Santa Fe County, New Mexico. Invertebrate fossils collected from the same horizon include the inoceramids cf. Inoceramus (Cremnoceramus) deformis and cf. Inoceramus (Platyceramus ) platinus and dense growths of the oyster Pseudoperna congesta. They suggest a Coniacian age. This is the oldest documented mosasaur from New Mexico

Body mass estimates of phytosaurs (Archosauria: Parasuchidae) from the Petrified Forest Formation (Chinle Group: Revueltian) based on skull and limb bone measurements.

Phytosaurs were the largest and most common semi-aquatic predators of the Late Triassic. Although their skulls are relatively common in the fossil record, articulated, or even associated skeletons are extremely rare, so it has always been difficult to gauge just how large (mass or length) an individual phytosaur may have been. Body mass in particular is an important physiological variable, often used for the scaling of organs, biomass determination, biomechanics, and locomotion. We take advantage of phytosaurs’ general similarity to extant crocodilians to attempt to reconstruct body mass and length based on measurements of the skulls and limbs of phytosaurs from the Upper Triassic Snyder and Canjilon quarries in north-central New Mexico. These quarries, in the Painted Desert Member of the Petrified Forest Formation (Revueltian: early-mid Norian) preserve catastrophic death assemblages that appear to well-represent discrete populations of phytosaurs. We also utilize a snout-vent measurement based on an articulated skeleton from the Canjilon quarry to compare the accuracy of different equations based on discrete limb elements. Body mass estimates for Snyder quarry phytosaurs range between 25 and 500 kg, with most specimens yielding estimates of approximately 200-350 kg. The Canjilon quarry sample encompasses fewer juveniles and more robust adults, including one individual that may have weighed as much as 535 kg. From equations based on nine extant crocodilian genera, these Revueltian phytosaurs appear to have approached 4.5 m total body length for a ~ 400 kg phytosaur. The prevalence of subadult to adult phytosaurs in both quarries based on body mass estimates corroborates qualitative estimates of the population structure based on skull sizes alone, thereby reinforcing the hypothesis that both quarries are catastrophic assemblages

The oldest North American prosauropod, from the Upper Triassic Tecovas Formation of the Chinle Group (Adamanian: latest Carnian), West Texas.

An isolated tooth from the Tecovas Formation of the Chinle Group, Crosby County, West Texas, represents the oldest definitive record of a prosauropod dinosaur from North America. Its age is Adamanian (latest Carnian, approximately 225 Ma) based on vertebrate biostratigraphy, palynostratigraphy and other data. It is clearly distinguished from isolated ornithischian teeth by a combination of prosauropod dental synapomorphies. The addition of this tooth to other recent discoveries of late Carnian prosauropod material from Brazil and Madagascar, as well as the Moroccan Azendohsaurus, indicates a Pangea-wide distribution for prosauropods near their oldest occurrences

The rhynchosaur Hyperodapedon from the Upper Triassic of Wyoming and its global biochronological significance

Fragmentary fossils collected by one of us (NH) from the Upper Triassic Popo Agie Formation represent the first occurrence of the rhynchosaur Hyperodapedon in the Chinle Group. The Wyoming record is of Otischalkian (Late Triassic: late Carnian) age. Globally, Hyperodapedon occurrences define a Hyperodapedon biochron of late to latest Carnian (Otischalkian-Adamanian) age for strata in North America, Scotland, India, Tanzania, Zimbabwe, Madagascar, Argentina, and Brazil. This resolution is coarser than that achieved using other taxa, principally phytosaurs and aetosaurs, but helps to correlate strata in which these taxa are rare or absent

Stratigraphy and Paleontology of the Lower Chinle Group (Adamanian: latest Carnian) in the Vicinity of St. Johns, Arizona

Topographically low exposures of Upper Triassic Chinle Group strata near St. Johns, Arizona, overlie the Middle Triassic Moenkopi Formation and can be assigned to four formation-rank units. These are, in ascending order, the Zuni Mountains (= “mottled strata”), Shinarump, Bluewater Creek (= “Mesa Redondo”), and Petrifi ed Forest formations. Petrifi ed Forest Formation strata in the vicinity of St. Johns pertain to three members, the basal Blue Mesa, medial Sonsela, and upper Painted Desert members. There are two principal unconformities in this section, the Tr-3 unconformity at the base of the Chinle and the Tr-4 unconformity at the top of the Blue Mesa Member. The Sonsela Member of the Petrifi ed Forest Member disconformably overlies the Blue Mesa Member throughout this region. However, although the Sonsela consists of basal extrabasinal conglomerates overlain by coarse-grained sandstones, it does not always form a persistent bench or ledge, and often must be identifi ed by lithology alone, not merely by topographic expression. In the northern and easternmost Blue Hills northeast of St. Johns, the Painted Desert Member of the Petrifi ed Forest Formation crops out as badlands of reddish-brown, bentonitic mudstone

Taxonomic status of Seismosaurus hallorum, a Late Jurassic sauropod dinosaur from New Mexico

The holotype of the Late Jurassic sauropod dinosaur Seismosaurus hallorum consists of part of the thoracic and caudal vertebrae, most of the sacrum and pelvis, some ribs and chevrons and an incomplete femur. Reexamination of the holotype indicates that Seismosaurus hallorum differs little from Diplodocus, and none of the morphological differences are significant enough to justify a separate genus. Particularly important to this conclusion has been careful re-examination and further preparation of the ischium of the S. hallorum holotype, which indicates that the distal, hook-like process originally described was actually the tip of a vertebral neural spine and sandstone matrix adhering to the ischium. We consider Seismosaurus to be a junior subjective synonym of Diplodocus. We suggest that Diplodocus hallorum is also a junior subjective synonym of D. longus, but a careful taxonomic revision of the species of Diplodocus is needed to verify this suggestion

The type locality of Belodon buceros Cope, 1881, a phytosaur (Archosauria: Parasuchidae) from the Upper Triassic of north-central New Mexico

Here we establish the stratigraphic and geographic provenance of the "Belodon" buceros Cope. The holotype, originally collected by David Baldwin in 1881, is an incomplete phytosaur skull discovered near "Huerfano Camp" in north-central New Mexico. This skull is the first phytosaur skull described from the American West, and its precise provenance has never been established. Baldwin's use of the term Huerfano Camp may refer to Orphan Mesa, an isolated butte just south of Arroyo Seco. Fossils collected by Baldwin, and our subsequent collections from Orphan Mesa, are from a fossiliferous interval high in the Petrified Formation of the Chinle Group. These strata yield a tetrapod fauna including the aetosaur Typothorax coccinarum and the phytosaur Pseudopalatus, both index taxa of the Revueltian (early-mid Norian) land-vertebrate faunachron. "Belodon" buceros is correctly referred to Pseudopalatus buceros (Cope) and is an index taxon of the Revueltian land-vertebrate faunachron