Ben Creisler
Recent non-dino papers:
Stephanie M. Smith, Courtney J. Sprain, William A. Clemens, Donald L. Lofgren, Paul R. Renne Â& Gregory P. Wilson (2018)
Early mammalian recovery after the end-Cretaceous mass extinction: A high-resolution view from McGuire Creek area, Montana, USAÂ
Geological Society Association Bulletin (advance online publication)
Changes in mammalian faunal composition and structure following the CretaceousâPaleogene mass extinction are central to understanding not only how terrestrial communities recovered from this ecological perturbation but also the evolution of archaic groups leading to extant mammalian clades. Here, we analyzed changes in mammalian local faunas during the earliest Paleogene biotic recovery on a small spatiotemporal scale. We compiled samples of mammals from four localities in the Hell Creek Formation and Tullock Member of the Fort Union Formation, in the McGuire Creek area, McCone County, Montana, USA, and placed these localities into a high-precision chronostratigraphic framework using 40Ar/39Ar tephra ages and magnetostratigraphy. Within this framework, we quantitatively compared faunal composition, heterogeneity, and richness among McGuire Creek local faunas and made broader comparisons to other earliest Paleogene faunas from throughout the Western Interior of North America. In the first ~320 k.y. of the recovery, mammalian local faunas at McGuire Creek, all of which can be placed in the Puercan 1 North American Land Mammal Age (NALMA) interval zone, underwent modest increases in taxonomic richness and heterogeneity, indicating the beginning of biotic recovery; however, no McGuire Creek fauna reached fully recovered levels of taxonomic richness. Further, appearance of immigrant taxa such as Purgatorius in younger McGuire Creek faunas demonstrates important compositional changes within the Pu1 of McGuire Creek. These results highlight the difficulties with describing the nuanced mammalian recovery process using the NALMA system and emphasize the increasing importance of high-precision dating, especially when comparing faunas across large geographic distances.
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Bryan M. Gee & William G. Parker (2018)
Morphological and histological description of small metoposaurids from Petrified Forest National Park, AZ, USA and the taxonomy of Apachesaurus.
Historical Biology (advance online publication)
Metoposaurids are Late Triassic temnospondyls that are abundant components of freshwater depositional settings. Although metoposaurids are represented by hundreds of specimens in collections around the world, the vast majority pertain to large-bodied, relatively mature individuals, and as a result, the early stages of ontogeny are still poorly characterised. Small-bodied metoposaurids from North America have traditionally been assigned to Apachesaurus gregorii, interpreted as a diminutive taxon, but this interpretation has not been rigorously tested. Here we provide a morphological description of two new small-bodied metoposaurid specimens from Petrified Forest National Park, AZ, USA. Both provide various anatomical details that improve our understanding of small-bodied metoposaurids and their taxonomic placement within Metoposauridae. Furthermore, we perform a histological analysis on associated intercentra of these specimens, which indicates that these are relatively immature individuals. These findings support the growing consensus that Apachesaurus is a juvenile metoposaurid, thereby providing additional data regarding the early stages of metoposaurid ontogeny and evidence of the persistence of large-bodied forms into the late Norian. Accordingly, these findings merit a reevaluation of the taxonomic validity and diagnosis of the taxon and of the previous interpretations of its paleobiology.
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free pdf:
Kevin Jagnandan & Timothy E Higham (2018)
How rapid changes in body mass affect the locomotion of terrestrial vertebrates: ecology, evolution and biomechanics of a natural perturbationÂ
Biological Journal of the Linnean Society, bly056 (advance online publication)
Animals rarely move through their natural habitat without experiencing an environmental perturbation, such as an obstacle or drop in height. However, rapid perturbations due to mass changes are little studied, and these can have significant impacts on the ecology and evolution of animal locomotion due to associated changes in relative muscle mass, altered body shape, shifts in the position of the centre of mass and changes in the overall load on the animal. These ecologically important situations arise during gravidity, parturition/oviposition, feeding, load bearing and autotomy. How these ubiquitous changes shape the function of animals in their natural habitat will have profound impacts on survival, and are thus crucial for understanding the functional ecology of locomotion. We first discuss locomotor perturbations, with an emphasis on the duration associated with them. We then address how commonly studied modes of rapid mass changes (e.g. parturition, autotomy, feeding) perturb locomotion by examining the effects of natural and artificial changes in mass on locomotor performance, kinematics, kinetics and muscle function in terrestrial animals, with an emphasis on non-human vertebrates. After a detailed discussion of the functional ecology of rapid mass changes, we generate a framework for future studies, including predictions for why some animals are more robust to changes in mass.
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