Ben Creisler
Some recent non-dino papers:
Stefan Reiss, Udo Scheer, Sven Sachs & Benjamin P. Kear (2018)
Filling the biostratigraphical gap: first choristoderan from the Lowerâmid-Cretaceous interval of Europe.
Cretaceous Research (advance online publication)
Choristodera is a clade of extinct aquatic reptiles whose fossils have been found in freshwater and marginal marine deposits from Europe, Asia and North America. The European record is the most extensive, spanning at least the Middle Jurassic to early Miocene, and incorporates the stratigraphically oldest and youngest members of the group. Despite this, there is an unexplained ~70 Ma gap in European choristoderan fossil occurrences. Here we fill this hiatus with the discovery of an isolated choristoderan dorsal vertebra from the lower Cenomanian 'Rotkalk' red limestone facies of the Essen Greensand Formation in MÃlheim an der Ruhr, North Rhine-Westphalia, western Germany. This specimen represents the first identifiable European choristoderan from the KimmeridgianâCampanian interval, and displays a diagnostic state combination including an amphiplatyan centrum with synapophyses on the transverse processes that are level with the neurocentral suture. The palaeobiogeographical distribution of choristoderans thus likely transected the entire Laurasian landmass throughout the Cretaceous, with perceived stratigraphical interstices being a result of incomplete sampling.
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F. Clarac & A. Quilhacc (2018)
The crocodylian skull and osteoderms: A functional exaptation to ectothermy?
Zoology (advance online publication)
Highlights
The crocodylian skull and osteoderms are involved in the heat transfers with the environment when basking.
The heat transfers in both the skull and the osteoderms rely on the set-up of a flow-controlled vascular network.
The temperature of the crocodylian braincase is regulated depending on the environmental temperature variations.
Abstract
The crocodylians are ectothermic semi-aquatic vertebrates which are assessed to have evolved from endothermic terrestrial forms during the Mesozoic. Such a physiological transition should have involved modifications in their cardio-vascular system allowing to increase the heat transfers with the surrounding environment by growing a peripheral vascularization which would be mainly located in the dermal skeleton: the dermatocranium and the osteoderms. In order to assess the implication of these anatomical regions in thermal exchanges, we have recorded the temperature above a set of representative skin areas in order to draw comparisions between the skull, the osteoderms, and the rest of the body parts which present either none or residual dermal ossification. We computed the data after the specimens were successively laid in different stereotyped environmental conditions which involved significant variations in the environmental temperature. Our results show that the osteoderms collect the external heat during the basking periods as they become significantly warmer than the surrounding skin; they further release the heat into the core of the organism as they turn out to be colder than the surrounding skin after a significant cooling period. In disregard of the environmental temperature variations, the skull table (which encloses the braincase) remains warmer than the rest of the cranial regions and shows less temperature variations than the osteoderms; a result which has lead us to think that the braincase temperature is monitored and controlled by a thermoregulatory system. Therefore, as hypothesized by previous others regarding the skull of the crocodylians and of other ectothermic vertebrates such as the squamates, we assume that the crocodylian skull possesses shunting blood pathways which tend to maintain both the braincase and the main sensory organs at the nearest to the optimal physiological temperature depending on the external temperature variations. Concerning the skin vascularization, the study of an albino Alligator mississippiensis specimen permitted to observe the repartition of the superficial blood vessels by transparency through the skin. We thus testify that the skin which covers either the skull or the osteoderms is more vascularized than the skin which does not present any subjacent dermal ossification. We consequenly deduce that the significant contrast in the thermal behavior between the dermal skeleton and the rest of the body is indeed correlated with a difference in the relative degree of skin vascularization. This last assessment confirms that the development of the dermal skeleton should have played a functional role in the crocodylian transition from endothermy to ectothermy through the set-up of a peripheral vessel network.
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Free pdf:
Walter G. Joyce, Virginie S. Volpato, and Yann Rollot (2018)
The skull of the carettochelyid turtle Anosteira pulchra from the Eocene (Uintan) of Wyoming and the carotid canal system of carettochelyid turtles.
Fossil Record 21: 301-310
Free pdf:
Here we document the morphology of the only known skull of a carettochelyid turtle from North America. The specimen originates from the middle Eocene (early Uintan) Washakie Formation of Sweetwater County, Wyoming, and is referred to Anosteira pulchra based on temporal considerations. The skull of Anosteira pulchra broadly corresponds in its morphology to that of other carettochelyids but exhibits numerous differences that are related to it being more gracile. As a meaningful outgroup is lacking, it is not possible to determine if the gracile morphology seen in this taxon is apomorphic or plesiomorphic for the AnosteiraâAllaeochelys clade. Anosteira pulchra and Carettochelys insculpta lack an ossified palatine canal. We conclude by reference to extant trionychids that the palatine (mandibular) canal is likely present but branches from the cerebral (pseudopalatine) canal following its exit from the sella turcica. As in trionychids, the vidian branch of the facial nerve (VII) of Anosteira pulchra and Carettochelys insculpta mostly traverses the palatine.
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Free pdf:
Ruchira Somaweera, Mathew L. Brien, Steven G. Platt, Charlie Manolis & Bruce L. Webber (2018)
Direct and indirect interactions with vegetation shape crocodylian ecology at multiple scales.
Freshwater Biology (advance online publication)
Free pdf:
As one of the world's largest predators of freshwater environments, crocodylians play an important role in shaping their community. In turn, many aspects of crocodylian life histories are influenced and have been shaped by characteristics of their environment, especially vegetation. However, our understanding of just how vegetation impacts crocodylian life histories remains limited, particularly in regard to indirect interactions. Such interactions can be critical for understanding population dynamics and, therefore, for informing conservation management decisions.Â
We reviewed contemporary understanding of these plantâcrocodylian interactions in peerâreviewed journals and the grey literature, synthesising life historyâshaping dynamics against aspects of their ecology. We then conceptualised how global environmental change, including climate change, species invasions and land use change, may threaten these critical dependencies, and how future conservation plans need to account for these pressures.
We identified five primary aspects of crocodylian ecologyâhabitat selection, nesting ecology, communication, physiology, and feeding ecologyâthat are probably shaped by vegetation interactions at different spatial scales. These interactions include direct and indirect impacts, with both positive and negative outcomes from a crocodylian perspective.
Anthropogenic impacts on environments via global environmental change drivers is causing unprecedented change to vegetation dynamics. What is often overlooked is how these changes impact large aquatic predators such as crocodylians. Our synthesis shows that while many impacts can be identified, their magnitude and mechanism are not well understood, making management driven mitigation challenging. We recommend that future studies prioritise quantifying how vegetation communities shape the suitability of crocodylian nest sites, and how to best detect the fingerprint of impacts caused by invasive alien plants on demographic change in crocodylians over longer durations. An improved understanding of the impact of vegetation impacts on crocodylians is essential for building effective conceptual frameworks and management agendas for the conservation of these iconic reptiles.
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Callum F. Ross, Laura B. Porro, Anthony Herrel, Susan E. Evans & Michael J. Fagan (2018)
Bite force and cranial bone strain in four species of lizards.
Journal of Experimental Biology 221: jeb180240Â
doi: 10.1242/jeb.180240Â
In vivo bone strain data provide direct evidence of strain patterns in the cranium during biting. Compared with those in mammals, in vivo bone strains in lizard skulls are poorly documented. This paper presents strain data from the skulls of Anolis equestris, Gekko gecko, Iguana iguana and Salvator merianae during transducer biting. Analysis of variance was used to investigate effects of bite force, bite point, diet, cranial morphology and cranial kinesis on strain magnitude. Within individuals, the most consistent determinants of variance in bone strain magnitude were gauge location and bite point, with the importance of bite force varying between individuals. Inter-site variance in strain magnitude â strain gradient â was present in all individuals and varied with bite point. Between individuals within species, variance in strain magnitude was driven primarily by variation in bite force, not gauge location or bite point, suggesting that inter-individual variation in patterns of strain magnitude is minimal. Between species, variation in strain magnitude was significantly impacted by bite force and species membership, as well as by interactions between gauge location, species and bite point. Independent of bite force, species differences in cranial strain magnitude may reflect selection for different cranial morphology in relation to feeding function, but what these performance criteria are is not clear. The relatively low strain magnitudes in Iguana and Uromastyx compared with those in other lizards may be related to their herbivorous diet. Cranial kinesis and the presence or absence of postorbital and supratemporal bars are not important determinants of inter-specific variation in strain magnitude.
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Free pdf:
Stilson, Christine E. Wall and Callum F. Ross (2018)
Inter-stride variability triggers gait transitions in mammals and birds.
Proceedings of the Royal Society B 285: 20181766
Free pdf:
Speed-related gait transitions occur in many animals, but it remains unclear what factors trigger gait changes. While the most widely accepted function of gait transitions is that they reduce locomotor costs, there is no obvious metabolic trigger signalling animals when to switch gaits. An alternative approach suggests that gait transitions serve to reduce locomotor instability. While there is evidence supporting this in humans, similar research has not been conducted in other species. This study explores energetics and stride variability during the walkârun transition in mammals and birds. Across nine species, energy savings do not predict the occurrence of a gait transition. Instead, our findings suggest that animals trigger gait transitions to maintain high locomotor rhythmicity and reduce unstable states. Metabolic efficiency is an important benefit of gait transitions, but the reduction in dynamic instability may be the proximate trigger determining when those transitions occur.
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Landon Burgener, Ethan Hyland, Katharine W. Huntington, Julia R. Kelson & Jacob O. Sewall (2018)
Revisiting the equable climate problem during the Late Cretaceous greenhouse using paleosol carbonate clumped isotope temperatures from the Campanian of the Western Interior Basin, USA.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
Highlights
Cretaceous soil carbonate clumped isotopes suggest hot summer temperatures >30âÂC.
Mid-latitude Cretaceous mean annual range in temperature (MART) was 21â29âÂC.
These new estimates are similar to modern and in agreement with model simulations.
Abstract
Greenhouse climates such as the Late Cretaceous period provide important reference frames for understanding modern anthropogenic climate change. Upper Cretaceous terrestrial climate proxies have been interpreted as evidence for âequableâ climates with reduced seasonal variations in temperature. However, climate models have largely failed to reproduce these reconstructions unless parameters such as atmospheric CO2 concentrations are set to unreasonable values. To help resolve such model-proxy disagreements, we reconstruct mean annual range in temperature (MART) for the Campanian (~75âMa) Kaiparowits (south-central Utah) and Two Medicine (northwest Montana) Formations using warmest mean monthly temperature reconstructions from the clumped isotope composition of paleosol carbonate nodules, and reconstructions of local mean annual air temperatures from other methods. An evaluation of the applicability of bulk elemental soil geochemistry temperature proxies in these deposits supports the use of previous leaf physiognomy-based estimates of mean annual temperature for our MART reconstructions. We test the validity of several common assumptions made in reconstructing MART in two novel ways. First, MART is commonly calculated as twice the difference between local mean annual air temperature and warmest mean monthly temperature, and we validate this method by estimating modern MART for a range of environments using climate reanalysis data. Second, we constrain the effect of radiative soil heating on our soil carbonate temperature estimates by showing that for most environments likely to be preserved in the geologic record, summer soil temperatures are <3âÂC higher than air temperatures. Our findings suggest that warmest mean monthly temperatures were 30 to 35âÂâ4âÂC at the two study sites, and that MART was 21 to 29âÂC for the Kaiparowits Formation, and 21 to 27âÂC for the Two Medicine Formation. Mid-latitude Late Cretaceous MARTs were similar to modern ranges in mid-latitude seasonal temperature, and much (>9âÂC) larger than previous proxy reconstructions of Late Cretaceous MART. These results add to a growing body of literature showing that terrestrial MART during ancient greenhouse periods was not significantly different from modern seasonal temperature variations. Finally, the similarity in MART between the Kaiparowits and Two Medicine formations suggests that latitudinal changes in MART did not contribute to the faunal provincialism that has been proposed by some paleontologists.