Six fossil localities in the Abo Formation in the McLeod Hills of Sierra County, New Mexico, produce tetrapod body fossils (jaw of a sphenacodont pelycosaur), fossil plants (Calamites pith cast, Walchia and seed-fern foliar impressions) and tetrapod footprints of the ichnotaxa Batrachichnus delicatulus (Lull), d. Batrachichnus sp., Gilmoreichnus hermitanus (Gilmore), Dimetropus sp. and indeterminate reptilian ichnotaxa. These ichnotaxa O!;Cur in Abo red beds that lack intertongued marine facies and indicate persistence of the Batrachichnus-Dromopus ichnofacies from marine shorelines to facies well inland.
Here we report a tooth of a large archosauriform from the Upper Triassic of New Mexico, USA that displays developmental anomalies of carina formation. This tooth has two supernumerary carinae, both on the lingual side of the tooth. Previously, carina anomalies of this sort were primarily known from theropod dinosaurs, but always from the labial surface. Integrating this specimen into a reassessment of the published accounts of carina anomalies in other fossil diapsids reveals that supernumerary carinae are more widespread throughout Archosauriformes than previously reported. Our interpretation of this developmental anomaly highlights the present lack of understanding of tooth development in archosaurs, particularly carina formation, and suggests that crown morphology development in archosauriforms may be constrained differently than it is in mammals. This developmental constraint may explain the differences observed between the complexity found in mammal and archosauriform cusp morphology.
The Triassic Period (252–201.5 Ma) records a great expansion of saurian diversity and disparity, particularly in skull morphology. Stem archosaurs exhibit substantial cranial disparity, especially by taxa either shortening or elongating the skull. This disparity is exemplified in the North American Late Triassic proterochampsians by the ‘short-faced’ Vancleavea and the ‘long-faced’ doswelliids. To critically investigate skull elongation and character evolution in these proterochampsians, we evaluate ‘Doswellia’ sixmilensis, known from much of a skull, cervical centra, and osteoderms from the Bluewater Creek Member of the Chinle Formation of New Mexico. We redescribe the holotype based on extensive repreparation of the holotype material, resulting in the identification of the orbit and clarifying the extent of related bones. As such, the diagnosis of the taxon is substantially modified and a new genus, Rugarhynchos, gen. nov., is erected. Rugarhynchos sixmilensis, gen. et comb. nov., exhibits an elongate snout with characteristics known in stem and crown archosaurs, including a downturned premaxilla and fluted teeth. We included R. sixmilensis in a phylogenetic analysis of archosauromorphs consisting of 677 characters and 109 taxa under both parsimony and Bayesian models. We recover R. sixmilensis as a doswelliid, sister to Doswellia kaltenbachi. Our parsimony and Bayesian models differ in the placement of Doswelliidae, either as sister to or within Proterochampsidae, respectively. We use archosauromorph relationships from the Bayesian model to estimate cranial disparity between stem and crown archosaurs and find a narrow breadth of morphological disparity in the stem. Our results suggest that crown archosaurs evolved disparate crania from a low-disparate archosauriform condition.
The Upper Triassic Snyder quarry of north-central New Mexico yields the remains of numerous individuals of the phytosaur Pseudopalatus buceros, as well as other vertebrates. The majority of the phytosaurian skeletal elements in the quarry are associated with skulls, so the phytosaur postcrania are clearly those of P. buceros. We describe the postcranial material of
P. buceros, with accompanying illustrations and metrics. In examining this suite of postcranial
material, it is apparent that sexual dimorphism in P. buceros is restricted solely to the skull, as none of the postcrania differ substantially. There is no obvious quantitative relationship between length of any given appendicular element and its midshaft width, though it appears that
the midshaft width may increase more than the length, leading to a more robust bone in adults.
This thickening of the midshaft could aid in supporting the weight of an adult animal.
Keywords: Parasuchidae, archosaur, postcrania, dimorphism, phytosaur
Tetrapod footprints from a locality near Prewitt, Cibola County, New Mexico, are in the lower part of the Anton Chico Member of the Moenkopi Formation. These Perovkan age (early Anisian) footprints represent three tetrapod ichnotaxa: swimming traces, Chirotherium and Therapsipus. These New Mexican Moenkopi tracks are part of a Euaramerican Chirotherium ichnofauna of Early-Middle Triassic age. They also reaffi rm that the tetrapod ichnofauna of the Moenkopi Formation, which is archosaur and dicynodont dominated, is sampling a different vertebrate fauna than the temnospondyl-dominated body fossil assemblages of the unit.
A long-term goal of vertebrate biostratigraphers is to construct a microvertebrate biostratigraphy for lower Mesozoic rocks that complements and extends the mammal-based biostratigraphy in place for Upper Cretaceous-Recent deposits. Here we report substantial progress toward achieving this goal based on the distribution of microvertebrate fossils in the Upper Triassic Chinle Group of the western USA. This biostratigraphic hypothesis independently corroborates the existing macrovertebrate biostratigraphy, recognizing four temporally successive assemblages—the Otischalkian, Adamanian, Revueltian, and Apachean, with subdivisions of the Adamanian (St. Johnsian and Lamyan) and Revueltian (Barrancan and Lucianoan). Many microvertebrate taxa, unfortunately, have long stratigraphic ranges and thus, while widespread and easily recognized, are not reliable index fossils. These taxa include the chondrichthyans Lissodus and Reticulodus synergus, most lepidosauromorphs(including sphenodontians), and various microvertebrate archosauromorphs. However, other taxa have relatively short stratigraphic ranges and occur in multiple localities and thus have some utility as index taxa. Adamanian index taxa include the procolophonid(?) Colognathus obscurus and the putative ornithischians Tecovasaurus murryi, Crosbysaurus harrisae and Krzyzanowskisaurus hunti. Revueltian index taxa include the chondrichthyan Reticulodus synergus, the crurotarsan Revueltosaurus callenderi and the cynodont Pseudotriconodon chatterjeei. Sphenodontian taxa appear to have relatively little utility as biostratigraphic markers at this time scale, although similar forms cooccur at the Placerias quarry in Arizona and correlative strata in the Tecovas Formation of West Texas. The best candidates for index taxa are those that, like therian mammals, have complex teeth and thus are identifiable to the genus or species level based on isolated teeth or tooth fragments. Many of these taxa are rare in the macrovertebrate record but common in some microvertebrate assemblages.
Based on U-Pb dating of two dinosaur bones from the San Juan Basin of New Mexico (United States), [Fassett et al. (2011)][1] claim to provide the first successful direct dating of fossil bones and to establish the presence of Paleocene dinosaurs. Fassett et al. ignore previously published work that
A representative selection of enigmatic denticulate/dentigerous plates from the Chinle Group previously assigned to Colobodontidae or Perleididae (“Perleidiformes”: Actinopterygii) were reinvestigated and compared to purportedly similar remains of diverse provenance and known identity. The histology of these isolated elements and fragments was also investigated to re-evaluate the former identifications and the tooth-like remains are compared to other Permo-Triassic fish groups. None of the fossils studied can be positively identified as a (crushing) toothplate of a colobodontid or a perleidid. Instead, our preliminary morpho-histologic investigation suggests that the majority of remains do not represent toothplates – despite the denticles’ striking similarity with crushing teeth. Most fragments represent denticulate dermal bone with a unique histology belonging to as-yet unidentified osteichthyans. Most purported “molariform teeth” from the Upper Triassic of the American Southwest are therefore interpreted as multiple series of dermal denticles and there is no evidence in these strata of “colobodontids” or “perleidids,” groups that were widely distributed during the Early-Middle Triassic.
