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

A press release and news stories about the eggshell study:




On Tue, Oct 13, 2015 at 8:43 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
> 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
> http://www.nature.com/ncomms/2015/151013/ncomms9296/full/ncomms9296.html
> 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
> https://peerj.com/articles/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
> problematic.