Marmarth Research Foundation

Marmarth, ND, United States

Marmarth Research Foundation

Marmarth, ND, United States
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Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation | Joyce W.G.,University of Tbingen | Joyce W.G.,Yale University
Journal of Vertebrate Paleontology | Year: 2010

A fragmentary skull from the Hell Creek Formation (Maastrichtian) of southwestern North Dakota represents a new taxon of baenid turtle named herein Gamerabaena sonsalla. The length of the frontals, jugal contribution to the labial ridge, and convex contact between the vomer and the pterygoids indicate its affinities with the clade Palatobaena, but the new taxon clearly lacks the great posterior expansion of the triturating surface, complete absence of a lingual ridge, subrectangular skull, and wide angle between the maxillae that diagnose Palatobaena spp. A maximum parsimony analysis provides strong support for G. sonsalla as sister taxon to Palatobaena spp. Gamerabaena sonsalla has several morphological features that are intermediate between Plesiobaena antiqua and the morphologically disparate Palatobaena spp., including orbits that are oriented slightly dorsally and moderately expanded posterior triturating surfaces. Our phylogenetic analysis, combined with stratigraphic arguments, indicates that our skull-based taxon G. sonsalla could belong to the shell-based taxon "Baena" hayi. Similarly, the skull taxa Hayemys latifrons and Eubaena cephalica may be synonymous with the shell taxa Thescelus insiliens and "Baena" hatcheri, respectively. © 2010 by the Society of Vertebrate Paleontology.

Joyce W.G.,University of Tübingen | 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.

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.

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.

Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation | Joyce W.G.,University of Tübingen | Knauss G.E.,SWCA Environmental Consultants Inc. | Pearson D.A.,Pioneer Trails Regional Museum
Journal of Vertebrate Paleontology | Year: 2011

For over a century, the baenid turtle Boremys has been recognized as being restricted to the Campanian of North America. Herein we describe new material of Boremys sp. from the Hell Creek Formation (Maastrichtian) and Fort Union Formation (Puercan) of southwestern North Dakota and eastern Montana, increasing the stratigraphic range of this taxon by 11 million years. The material was recovered from the base of the Hell Creek Formation to 14 m above the pollen-calibrated K/T boundary in the basal Fort Union Formation. Most of the specimens consist of isolated shell elements, which are easily misidentified as belonging to a kinosternid or chelydrid turtle, but complete shells are present as well. The presence of Boremys sp. in the Hell Creek formation increases the baenid taxonomic diversity of this particular rock unit to nine and the overall turtle diversity to 20 taxa, and the presence of Boremys sp. in the Fort Union Formation increases the number of baenid lineages that survive the K/T extinction event to eight. © 2011 by the Society of Vertebrate Paleontology.

Joyce W.G.,University of Tübingen | 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.

Joyceab W.G.,University of Tübingen | 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.

Joyce W.G.,University of Tübingen | Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation
Journal of Paleontology | Year: 2011

Plastomenidae is a poorly diagnosed clade of extinct soft-shelled turtles (Trionychidae) known from the Campanian to Eocene of North America. Five skulls, a mandible, two carapaces, and numerous plastral remains from the Hell Creek Formation (Late Cretaceous, Maastrichtian) of North Dakota and Montana are referable to Gilmoremys lancensis nov. comb., a taxon previously known from a carapace and xiphiplastron only. Gilmoremys lancensis is diagnosed by a carapace that is covered by elongate sinusoidal grooves, distally expanded second costals, hyoplastral shoulders, an extensive secondary palate with accessory ridges, an extremely elongate mandible, a contribution of the parietal to the wall of the orbit, and a posterior ossified narial canal. A phylogenetic analysis of all well-known plastomenid turtles establishes Gilmoremys lancensis as the most basal known plastomenid and reveals that cranial characters are more reliable in diagnosing plastomenid turtles, in particular the contribution of the parietal to the orbit wall and the extensive secondary palate. All plastomenid turtles with a locked entoplastron are placed in Hutchemys. Assuming that all taxa are monophyletic, the phylogenetic analysis implies that the G. lancensis lineage is the only one to go extinct at the K/T boundary, whereas the four remaining plastomenid lineages survive. Extensive ghost ranges are nevertheless apparent. Taphonomic considerations indicate that G. lancensis was a riverine turtle, whereas more derived plastomenids preferred swampy habitats. © 2011 The Paleontological Society.

Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation | Joyce W.G.,University of Tübingen
Journal of Paleontology | Year: 2011

The skull of the enigmatic turtle Compsemys victa Leidy, 1856 is described. A number of unique characteristics are apparent, including the extremely thick nature of all cranial bones, the presence of rod-like epipterygoids, placement of the foramen posterius canalis carotici interni halfway along the contact between the pterygoid and basisphenoid, lack of cheek emarginations, and the reduction of the size of the cavum tympani relative to the orbit. Two differing global turtle analyses and one paracryptodiran analysis were performed to determine the phylogenetic placement of C. victa. Both global analyses converged by placing C. victa within Paracryptodira, herein defined as the most inclusive clade that includes Pleurosternon bullockii and Baena arenosa, but no species of living turtle, whereas the paracryptodiran analysis places C. victa outside of Baenoidea, herein defined as the least inclusive clade that contains P. bullockii and B. arenosa. Although a number of similarities are apparent between C. victa and the uncommon, extant testudinoid Platysternon megacephalum, the available data indicate that these similarities are convergent, likely due to their carnivorous diet. Taphonomic evidence reveals that basal paracryptodires, including C. victa, preferred slow moving or ponded water environments. The riverine habitat preference of baenodds must therefore be derived. © 2011 The Paleontological Society.

Lyson T.R.,Yale University | Lyson T.R.,Marmarth Research Foundation | Longrich N.R.,Yale University
Proceedings of the Royal Society B: Biological Sciences | Year: 2011

We examine patterns of occurrence of associated dinosaur specimens (n = 343) from the North American Upper Cretaceous Hell Creek Formation and equivalent beds, by comparing their relative abundance in sandstone and mudstone. Ceratopsians preferentially occur in mudstone, whereas hadrosaurs and the small ornithopod Thescelosaurus show a strong association with sandstone. By contrast, the giant carnivore Tyrannosaurus rex shows no preferred association with either lithology. These lithologies are used as an indicator of environment of deposition, with sandstone generally representing river environments, and finer grained sediments typically representing floodplain environments. Given these patterns of occurrence, we argue that spatial niche partitioning helped reduce competition for resources between the herbivorous dinosaurs. Within coastal lowlands ceratopsians preferred habitats farther away from rivers, whereas hadrosaurs and Thescelosaurus preferred habitats in close proximity to rivers, and T. rex, the ecosystem's sole large carnivore, inhabited both palaeoenvironments. Spatial partitioning of the environment helps explain how several species of large herbivorous dinosaurs coexisted. This study emphasizes that different lithologies can preserve dramatically dissimilar vertebrate assemblages, even when deposited in close proximity and within a narrow window of time. The lithology in which fossils are preserved should be recorded as these data can provide unique insights into the palaeoecology of the animals they preserve. © 2010 The Royal Society.

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