Ben Creisler
Some recent non-dino papers:
K. C. Sellers, ÂA. B. Schmiegelow Â& C. M. Holliday (2019)
The significance of enamel thickness in the teeth of Alligator mississippiensis and its diversity among crocodyliforms.
Journal of Zoology (advance online publication)
doi:
https://doi.org/10.1111/jzo.12707https://zslpublications.onlinelibrary.wiley.com/doi/10.1111/jzo.12707Enamel is the hardest tissue in the vertebrate body. Although variation in enamel microstructure is often linked with diet, the gross proportions of the tissues that compose vertebrate teeth remain relatively unexplored in reptiles. To investigate the patterns of enamel thickness in crocodyliforms, we used microâcomputed tomography scanning to evaluate enamel thickness in teeth of Alligator mississippiensis from rostral, intermediate and caudal locations in the tooth row from an ontogenetic range of animals. We also evaluated enamel thickness in the derived teeth of several extinct crocodyliforms with disparate craniodental morphologies. Our data show that enamel thickness scales isometrically with skull length. We also show that enamel is relatively thicker in caudal teeth than teeth in more rostral positions, concordant with the higher bite forces they experience during feeding. We compared our data with existing enamel thickness data reported from dinosaurs and mammalian taxa to find that archosaurs have markedly thinner enamel than most mammals. These findings serve as a basis for future investigations into the diversity and function of the proportions of dental tissues.
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Mathieu G. FaureâBrac, FranÃois Pelissier & Jorge Cubo (2019)
The influence of plane of section on the identification of bone tissue types in amniotes with implications for paleophysiological inferences.
Journal of Morphology (advance online publication)
doi: Â
https://doi.org/10.1002/jmor.21030https://onlinelibrary.wiley.com/doi/10.1002/jmor.21030The proportion of woven bone (WB) to parallelâfibered bone has been extensively used to infer bone growth rates and resting metabolic rates of extinct organisms. The aim of this study is to test in a variety of amniotes how reliably WB content can be measured using transverse sections. For this, we analyzed femoral transverse midâdiaphyseal thin sections of 14 extant and extinct taxa and the corresponding longitudinal sections for comparative purposes. We used the following characters to identify WB in transverse sections because they are known to be distinct from those observed in parallelâfibered bone: an isotropic bone matrix at tissue scale; an anisotropic microlamellar arrangement in former osteoblast secretory territories at cellular scale; no alignment between osteocytes; and canaliculi running radially from large irregular osteocyte lacunae. Our null hypothesis predicts no differences between the amount of WB quantified in the transverse and longitudinal sections of a given long bone. Qualitatively, when a stripe or a patch of WB was identified in a transverse section, the corresponding stripe or patch of WB was always found at the same location in the corresponding longitudinal section. Quantitatively, a Wilcoxon signedârank nonparametric paired test did not detect a significant difference in the WB content of the two section planes. Thus, the null hypothesis is not rejected. Considering that paleohistology is a destructive method, we recommend a workflow to efficiently establishing the proportion of WB: quantifying it in transverse sections; preparing and analyzing longitudinal sections only in cases where an ambiguity remains; reanalyzing the corresponding transverse sections.
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Brian K. McNab (2019)
What determines the basal rate of metabolism?
Journal of Experimental Biology: jeb.205591 (advance online publication)
doi: 10.1242/jeb.205591
https://jeb.biologists.org/content/early/2019/06/29/jeb.205591The basal rate of metabolism (BMR) is the most reported estimate of energy expenditure in endotherms. Its principal determinant is body mass, but it also correlates with a variety of behavioral not determine basal rate, they are byproducts of the mechanisms that are its determinate. In mammals, mass-independent basal rate increases with muscle mass when it is>40% of body mass. Then basal rates in mammals areâ100% of the values expected from mass. Mammals with muscle masses<30% of body mass have lower basal rates, a diminished capacity to regulate body temperature, and often a reduced level of activity. At muscle masses<42% of body mass, birds have body temperatures and basal rates higher than mammals with the same muscle mass. Their high basal rates derive from a high blood flow and mitochondrial density in their pectoral muscles. These factors also occur in the flight muscles of bats. Oxygen transport to the pectoral muscles of birds is facilitated by an increase in heart mass and hematocrit. This arrangement avoids transporting a large muscle mass to fuel flight, thereby reducing the cost of flight. Pectoral muscle masses<9% of body mass correlate with a flightless condition in kiwis, rails, and ducks. Some fruit pigeons have basal rates as low as kiwis, while remaining volant. The mass-independent basal rates of endotherms principally reflect changes of muscle activity and mass. An increase in muscle mass may have contributed to the evolution of endothermy.
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Free pdf:
Maureen A. OâLeary, Mamadou L. BouarÃ, Kerin M. Claeson, Kelly Heilbronn, Robert V. Hill, Jacob McCartney, Jocelyn A. Sessa, Famory Sissoko, Leif Tapanila, Elisabeth Wheeler, and Eric M. Roberts (2019)
Stratigraphy and paleobiology of the Upper Cretaceous-Lower Paleogene sediments from the Trans-Saharan Seaway in Mali.
Bulletin of the American Museum of Natural History 436: 1-177
URI:
http://digitallibrary.amnh.org/handle/2246/6950doi:
https://doi.org/10.1206/0003-0090.436.1.2Free pdf:
http://digitallibrary.amnh.org/handle/2246/6950An epicontinental sea bisected West Africa periodically from the Late Cretaceous to the early Eocene, in dramatic contrast to the current Sahara Desert that dominates the same region today. Known as the Trans-Saharan Seaway, this warm and shallow ocean was a manifestation of globally elevated sea level associated with the rapid break-up of the supercontinent Gondwana in the late Mesozoic. Although it varied in size through time, the Trans-Saharan Seaway is estimated to have covered as much as 3000 km2 of the African continent and was approximately 50 m deep. The edges of the sea were defined in part by the high topography of the Precambrian cratons and mobile belts of West Africa. Over its approximately 50 million year episodic existence, through six major periods of transgression and regression, the Trans-Saharan Seaway left behind extensive nearshore marine sedimentary strata with abundant fossils. The waters that yielded these deposits supported and preserved the remains of numerous vertebrate, invertebrate, plant, and microbial species that are now extinct. These species document a regional picture of ancient tropical life that spanned two major Earth events: the Cretaceous-Paleogene (K-Pg) boundary and the Paleocene-Eocene Thermal Maximum (PETM). Whereas extensive epeiric seas flooded the interior portions of most continents during these intervals, the emerging multicontinental narrative has often overlooked the Trans-Saharan Seaway, in part because fundamental research, including the naming of geological formations and the primary description and analysis of fossil species, remained to be done. We provide such synthesis here based on two decades of fieldwork and analyses of sedimentary deposits in the Republic of Mali. Northern parts of the Republic of Mali today include some of the farthest inland reaches of the ancient sea. We bring together and expand on our prior geological and paleontological publications and provide new information on ancient sedimentary rocks and fossils that document paleoequatorial life of the past. Ours is the first formal description of and nomenclature for the Upper Cretaceous and Lower Paleogene geological formations of this region and we tie these names to regional correlations over multiple modern territorial boundaries. The ancient seaway left intriguing and previously unclassified phosphate deposits that, quite possibly, represent the most extensive vertebrate macrofossil bone beds known from anywhere on Earth. These bone beds, and the paper shales and carbonates associated with them, have preserved a diverse assemblage of fossils, including a variety of new species of invertebrates and vertebrates, rare mammals, and trace fossils. The shallow marine waters included a wide range of paleoenvironments from delta systems, to hypersaline embayments, protected lagoons, and carbonate shoals. Our overarching goal has been to collect vertebrate fossils tied to a K-Pg stratigraphic section in Africa. We provide such a section and, consistent with prior ideas, indicate that there is a gap in sedimentation in Malian rocks in the earliest Paleocene, an unconformity also proposed elsewhere in West Africa. Our phylogenetic analyses of several vertebrate clades across the K-Pg boundary have clarified clade-by-clade species-level survivorship and range extensions for multiple taxa. Few macrofossil species from the Trans-Saharan Seaway show conspicuous change at either the K-Pg boundary or the PETM based on current evidence, although results are very preliminary. Building on our earlier report of the first record of rock-boring bivalves from the Paleocene of West Africa, we further describe here a Cretaceous and Paleogene mollusk fauna dominated by taxa characteristic of the modern tropics. Among the newly discovered fossil osteichthyans, large body size characterizes both the pycnodonts and a new freshwater Eocene catfish species, one of the largest fossil catfishes found in Africa. Our new paleoecological and faunal reconstructions show an evergreen, broadleaf forest that included some of the oldest mangroves known. The ancient Malian ecosystem had numerous apex predators including Crocodyliformes, Serpentes, and Amiidae, some of which were among the largest species in their clades. The Trans-Saharan Seaway exhibited intermittent isolation from major seas. This environmental variable may have created aquatic centers of endemism, stimulating selection for gigantism as previously observed for species on terrestrial islands.
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Kilian Eichenseer, Uwe Balthasar, Christopher W. Smart, Julian Stander, Kristian A. Haaga & Wolfgang Kiessling (2019)
Jurassic shift from abiotic to biotic control on marine ecological success.
Nature Geoscience (advance online publication)
DOI:
https://doi.org/10.1038/s41561-019-0392-9https://www.nature.com/articles/s41561-019-0392-9Environmental change and biotic interactions both govern the evolution of the biosphere, but the relative importance of these drivers over geological time remains largely unknown. Previous work suggests that, unlike environmental parameters, diversity dynamics differ profoundly between the Palaeozoic and post-Palaeozoic eras. Here we use the fossil record to test the hypothesis that the influence of ocean chemistry and climate on the ecological success of marine calcifiers decreased throughout the Phanerozoic eon. Marine calcifiers build skeletons of calcite or aragonite, and the precipitation of these calcium carbonate polymorphs is governed by the magnesium-to-calcium ratio and temperature in abiotic systems. We developed an environmental forcing model based on secular changes of ocean chemistry and temperature and assessed how well the model predicts the proliferation of skeletal taxa with respect to calcium carbonate polymorphs. Abiotic forcing governs the ecological success of aragonitic calcifiers from the Ordovician to the Middle Jurassic, but not thereafter. This regime shift coincides with the proliferation of calcareous plankton in the mid-Mesozoic. The deposition of biomineralizing plankton on the ocean floor buffers CO2 excursions and stabilizes Earthâs biochemical cycle, and thus mitigates the evolutionary impact of environmental change on the marine biota.
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