Ben Creisler
Recent non-dinoÂpapers:
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Gen. et sp. indet.
Nathan D. Smith, Peter J. Makovicky, Christian A. Sidor & William R. Hammer (2020)
A kannemeyeriiform (Synapsida: Dicynodontia) occipital plate from the Middle Triassic upper Fremouw Formation of Antarctica.
Journal of Vertebrate Paleontology Article: e1829634
doi:
https://doi.org/10.1080/02724634.2020.1829634 https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1829634A kannemeyeriiform dicynodont is described on the basis of an occipital plate from the upper Fremouw Formation (Middle Triassic) Gordon Valley locality in the Beardmore Glacier region of Antarctica. The Antarctic specimen is comparable in size to Kannemeyeria simocephalus from the well-known Cynognathus Assemblage Zone of the Beaufort Group of South Africa, and represents the largest therapsid currently known from the upper Fremouw Formation. The presence of an occipital condyle with distinct contributions from the exoccipital and the basioccipital; a wide, tri-radiate occipital condyle; and a well-developed tympanic process of the paroccipital, which is situated below the level of the occipital condyle, represent a combination of character states hitherto unknown among Kannemeyeriiformes. Combined with the possible autapomorphic feature of slender, dorsoventrally elongate basal tubera, this may suggest the Antarctic specimen represents a new kannemeyeriiform taxon. This specimen represents the most complete, and only the fourth definitive, dicynodont specimen known from the upper Fremouw Formation, and the contradictory phylogenetic character data from these specimens adds support for the presence of multiple (at least two) kannemeyeriiform taxa within the upper Fremouw tetrapod assemblage. Taken together, these kannemeyeriiform specimens provide additional support for a correlation with the Cynognathus Assemblage Zone, particularly the Trirachodon-Kannemeyeria or Cricodon-Ufudocyclops subzones (= subzones B or C), as well as an Anisian or younger age for the upper Fremouw tetrapod fauna.
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Krijn B Michel, Tim G West, Monica A Daley, Vivian R Allen & John R Hutchinson (2020)
Appendicular muscle physiology and biomechanics in Crocodylus niloticus.
Integrative Organismal Biology, obaa038 (advance online publication)
doi:
https://doi.org/10.1093/iob/obaa038https://academic.oup.com/iob/advance-article/doi/10.1093/iob/obaa038/5956721Archosaurian reptiles (including living crocodiles and birds) had an explosive diversification of locomotor form and function since the Triassic ~250 million years ago. Their limb muscle physiology and biomechanics are pivotal to our understanding of how their diversity and evolution relate to locomotor function. Muscle contraction velocity, force and power in extinct archosaurs such as early crocodiles, pterosaurs or non-avian dinosaurs is not available from fossil material, but is needed for biomechanical modelling and simulation. However, an approximation or range of potential parameter values can be obtained by studying extant representatives of the archosaur lineage. Here, we study the physiological performance of three appendicular muscles in Nile crocodiles (Crocodylus niloticus). Nile crocodile musculature showed high power and velocity values--the flexor tibialis internus 4 muscle, a small "hamstring" hip extensor and knee flexor actively used for terrestrial locomotion, performed particularly well. Our findings demonstrate some physiological differences between muscles, potentially relating to differences in locomotor function and muscle fibre type composition. By considering these new data from a previously unstudied archosaurian species in light of existing data (e.g., from birds), we can now better bracket estimates of muscle parameters for extinct species and related extant species. Nonetheless, it will be important to consider the potential specialization and physiological variation among muscles, because some archosaurian muscles (such as those with terrestrial locomotor function) may well have close to double the muscle power and contraction velocity capacities of others.
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Ralph L. Albuquerque & Theodore Garland, Jr (2020)
Phylogenetic analysis of maximal oxygen consumption during exercise (VÌO2max) and ecological correlates among lizard species.
Journal of Experimental Biology: jeb.229013 (advance online publication)
doi: 10.1242/jeb.229013
https://jeb.biologists.org/content/early/2020/11/01/jeb.229013
The maximum amount of oxygen consumed during forced exercise (VÌO2max) sets the upper limit to the effort that can be sustained over relatively long periods and can limit activity levels in nature. Among ectotherms, VÌO2max is primarily affected by body size and body temperature, but it should also coadapt with behavior, ecology, and life history aspects. We compiled published data from 11 different families of lizards, including 58 species and 7 populations (total 65 data points) and tested whether VÌO2max was related to diet (herbivore, insectivore, insectivore/carnivore, carnivore, and omnivore), climate (tropical, temperate, and arid), nocturnality, viviparity, or family. We fitted models that included body mass and measurement temperature as covariates, and all possible combinations of other independent variables using ordinary least-squares (OLS) and phylogenetic regressions assuming an Ornstein-Uhlenbeck model of residual trait evolution (RegOU). The sum of Akaike weights for each independent variable revealed viviparity (âwi=0.996) and the combined set of dummy variables coding for helodermatids, varanids, and skinks (âwi=0.996) as the most important predictors. These three families had relatively high VÌO2max. They are composed mainly of active foragers that probably benefit from higher VÌO2max. Viviparity had a negative effect on VÌO2max. Ecological or behavioral factors associated with viviparity (e.g., activity levels), but not included here, may explain this effect. The average allometric slope of VÌO2max from the top eight models (which accounted for 99% of the cumulative evidence) was 0.803, which is similar to that reported previously for lizards and for mammals in general.
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