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Dinosaur body temperatures from eggshell istopes + Ostrich cranium finite element model

Ben Creisler

New papers:

Robert A. Eagle, Marcus Enriquez, Gerald Grellet-Tinner, Alberto
Pérez-Huerta, David Hu, Thomas Tütken, Shaena Montanari, Sean J. Loyd,
Pedro Ramirez, Aradhna K. Tripati, Matthew J. Kohn, Thure E. Cerling,
Luis M. Chiappe & John M. Eiler (2015)
Isotopic ordering in eggshells reflects body temperatures and suggests
differing thermophysiology in two Cretaceous dinosaurs.
Nature Communications 6, Article number: 8296
doi: 10.1038/ncomms9296

Our understanding of the evolutionary transitions leading to the
modern endothermic state of birds and mammals is incomplete, partly
because tools available to study the thermophysiology of extinct
vertebrates are limited. Here we show that clumped isotope analysis of
eggshells can be used to determine body temperatures of females during
periods of ovulation. Late Cretaceous titanosaurid eggshells yield
temperatures similar to large modern endotherms. In contrast,
oviraptorid eggshells yield temperatures lower than most modern
endotherms but ~6 °C higher than co-occurring abiogenic carbonates,
implying that this taxon did not have thermoregulation comparable to
modern birds, but was able to elevate its body temperature above
environmental temperatures. Therefore, we observe no strong evidence
for end-member ectothermy or endothermy in the species examined. Body
temperatures for these two species indicate that variable
thermoregulation likely existed among the non-avian dinosaurs and that
not all dinosaurs had body temperatures in the range of that seen in
modern birds.


Andrew R. Cuff, Jen A. Bright & Emily J. Rayfield (2015)
Validation experiments on finite element models of an ostrich
(Struthio camelus) cranium.
PeerJ 3:e1294
doi: https://dx.doi.org/10.7717/peerj.1294

The first finite element (FE) validation of a complete avian cranium
was performed on an extant palaeognath, the ostrich (Struthio
camelus). Ex-vivo strains were collected from the cranial bone and
rhamphotheca. These experimental strains were then compared to
convergence tested, specimen-specific finite element (FE) models. The
FE models contained segmented cortical and trabecular bone, sutures
and the keratinous rhamphotheca as identified from micro-CT scan data.
Each of these individual materials was assigned isotropic material
properties either from the literature or from nanoindentation, and the
FE models compared to the ex-vivo results. The FE models generally
replicate the location of peak strains and reflect the correct mode of
deformation in the rostral region. The models are too stiff in regions
of experimentally recorded high strain and too elastic in regions of
low experimentally recorded low strain. The mode of deformation in the
low strain neurocranial region is not replicated by the FE models, and
although the models replicate strain orientations to within 10° in
some regions, in most regions the correlation is not strong. Cranial
sutures, as has previously been found in other taxa, are important for
modifying both strain magnitude and strain patterns across the entire
skull, but especially between opposing the sutural junctions.
Experimentally, we find that the strains on the surface of the
rhamphotheca are much lower than those found on nearby bone. The FE
models produce much higher principal strains despite similar strain
ratios across the entirety of the rhamphotheca. This study emphasises
the importance of attempting to validate FE models, modelling sutures
and rhamphothecae in birds, and shows that whilst location of peak
strain and patterns of deformation can be modelled, replicating
experimental data in digital models of avian crania remains