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Marmarth, ND, United States

Joyce W.G.,University of Tubingen | Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation
Palaeontology | Year: 2010

Abstract: The fossil record of the two primary subclades of softshell turtles (Trionychidae) is exceedingly asymmetric, as a result of a ghost range of total clade Cyclanorbinae that is estimated at 80 Ma. Herein, we present the first phylogenetic analysis of Trionychidae that includes a representative of the poorly studied taxon Plastomenidae, which is known from the Campanian to Eocene of North America. The analysis reveals that plastomenids are stem cyclanorbines, thus significantly reducing the apparent ghost range of total group Cyclanorbinae to approximately 30 Ma. Plastomenids are either an early branching clade of stem Cyclanorbinae, or they represent a paraphyletic grade that gave rise to modern cyclanorbines. Although abundant, the fossil record is still too poorly understood to distinguish between these two primary hypotheses. The previously persistent extremely long ghost range of total clade Cyclanorbinae appears to have been the result of a research bias. © The Palaeontological Association. Source

Joyceab W.G.,University of Tubingen | Lysoncd T.R.,Yale University | Lysoncd T.R.,Marmarth Research Foundation
Journal of Systematic Palaeontology | Year: 2010

We describe a new species of fossil testudinoid from the Indian subcontinent, Pangshura tatrotia sp. nov., and suggest a new clade name, Palatochelydia, for the monophyletic assemblage of South Asian turtles to which it belongs. A combined analysis using recent molecular data and an updated morphological dataset confidently places P. tatrotia as sister to the extant turtle P. tecta. The holotype specimen is unique relative to most previously described palatochelydian material in that it is associated with good quality locality information. We therefore can conclude that this specimen comes from the Pliocene Tatrot Formation of north-eastern Pakistan, which corresponds to an interval of 2.59 to 3.59 Ma. This can now serve as a minimum divergence date for the P. tecta clade. However, given that no other palatochelydian fossils are associated with good quality locality information, this date must also serve as the minimum for all other, more inclusive palatochelydian clades. © 2010 The Natural History Museum. Source

Bates K.T.,University of Liverpool | Schachner E.R.,University of Utah | Schachner E.R.,Marmarth Research Foundation
Journal of the Royal Society Interface | Year: 2012

This study aims to investigate functional disparity in the locomotor apparatus of bipedal archosaurs.We use reconstructions of hindlimbmyology of extant and extinct archosaurs to generate musculoskeletal biomechanical models to test hypothesized convergence between bipedal crocodile-line archosaurs and dinosaurs. Quantitative comparison of muscle leverage supports the inference that bipedal crocodile-line archosaurs and non-avian theropods had highly convergent hindlimb myology, suggesting similar muscular mechanics and neuromuscular control of locomotion. While these groups independently evolved similar musculoskeletal solutions to the challenges of parasagittally erect bipedalism, differences also clearly exist, particularly the distinct hip and crurotarsal ankle morphology characteristic of many pseudosuchian archosaurs. Furthermore, comparative analyses of muscle design in extant archosaurs reveal that muscular parameters such as size and architecture are more highly adapted or optimized for habitual locomotion than moment arms. The importance of these aspects of muscle design, which are not directly retrievable from fossils, warns against over-extrapolating the functional significance of anatomical convergences. Nevertheless, links identified between posture, muscle moments and neural control in archosaur locomotion suggest that functional interpretations of osteological changes in limb anatomy traditionally linked to postural evolution in Late Triassic archosaurs could be constrained through musculoskeletal modelling. © 2011 The Royal Society. Source

Joyce W.G.,University of Tubingen | Parham J.F.,California State University, Fullerton | Lyson T.R.,Yale Peabody Museum of Natural History | Lyson T.R.,Smithsonian Institution | And 4 more authors.
Journal of Paleontology | Year: 2013

Turtles have served as a model system for molecular divergence dating studies using fossil calibrations. However, because some parts of the fossil record of turtles are very well known, divergence age estimates from molecular phylogenies often do not differ greatly from those observed directly from the fossil record alone. Also, the phylogenetic position and age of turtle fossil calibrations used in previous studies have not been adequately justified. We provide the first explicitly justified minimum and soft maximum age constraints on 22 clades of turtles following best practice protocols. Using these data we undertook a Bayesian relaxed molecular clock analysis establishing a timescale for the evolution of crown Testudines that we exploit in attempting to address evolutionary questions that cannot be resolved with fossils alone. Some of these questions, such as whether the turtle crown originated in the Triassic or Jurassic, cannot be resolved by our analysis. However, our results generate novel age-of-origination estimates for clades within crown Testudines. Finally, we compare our fossil calibrations and posterior age estimates to those from other studies, revealing substantial differences in results and interpretation.Copyright © 2013, The Paleontological Society. Source

Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation | Bercovici A.,Wuhan University | Chester S.G.B.,Yale University | And 4 more authors.
Biology Letters | Year: 2011

Modern debate regarding the extinction of nonavian dinosaurs was ignited by the publication of the Cretaceous-Tertiary (K-T) asteroid impact theory and has seen 30 years of dispute over the position of the stratigraphically youngest in situ dinosaur. A zone devoid of dinosaur fossils reported from the last 3 m of the Upper Cretaceous, coined the '3 m gap', has helped drive controversy. Here, we report the discovery of the stratigraphically youngest in situ dinosaur specimen: a ceratopsian brow horn found in a poorly rooted, silty, mudstone floodplain deposit located no more than 13 cm below the palynologically defined boundary. The K-T boundary is identified using three criteria: (i) decrease in Cretaceous palynomorphs without subsequent recovery, (ii) the existence of a 'fern spike', and (iii) correlation to a nearby stratigraphic section where primary extraterrestrial impact markers are present (e.g. iridium anomaly, spherules, shocked quartz). The in situ specimen demonstrates that a gap devoid of non-avian dinosaur fossils does not exist and is inconsistent with the hypothesis that non-avian dinosaurs were extinct prior to the K-T boundary impact event. © 2011 The Royal Society. Source

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