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Gastornis bone calcium isotopes indicate plant diet



From: Ben Creisler
bcreisler@gmail.com


A news release about the diet of Gastornis diet based on its bone
chemistry, with the original abstract for the Goldschmidt Conference
in Florence, Italy:


http://phys.org/news/2013-08-terror-bird-beak-worse.html

Here is the original abstract. Sorry about the problem with delta
signs and subscripts and superscripts. [It would be interesting to see
how alvarezsaurids and troodontids come out. The diet of placodonts
(controversially suggested as plants) might also be interesting to
check.]


Tütken, T., Held, P. & Galer, S.J.G. (2013)
Isotopes in vertebrate bioapatite: proxies for climate, pCO2 and diet
Mineralogical Magazine 77(5)(abstracts) 2368
http://minmag.geoscienceworld.org/content/77/5/2297.full.pdf+html




Vertebrates integrate bioavailable elements in their skeletal tissues
taken up from the environment via air, water and food. Bones and teeth
archive isotope signatures of these elements over the timespan of
tissue formation and/or remodelling. This enables the reconstruction
of diet (delta13C, delta44/42Ca), climate (delta18O), body temperature
(delta47), atmospheric pCO2 (delta17O) and habitat (delta18O,
87Sr/86Sr) from vertebrate fossils. Bioapatite of fossil hard tissues,
especially enamel, can preserve original isotope compositions over
geological time scales. The isotopes of the two major elements (Ca,
O(PO4)) in bioapatite are least biased by diagenetic alteration.


delta18OPO4 of terrestrial and aquatic vertebrates is a proxy for
meteoric and ambient water delta 18O values, respectively. Enamel
delta 18OPO4 values of fossil large mammals were used to infer the
terrestrial palaeoclimate during the last 35 million years for Central
Europe. Reconstructed air temperatures agree well with other climate
proxy data. The 17O-anomaly (delta17O) of air oxygen is a proxy for
atmospheric pCO2. This anomalous delta17Oair is partially recorded in
bioapatite delta17OPO4 of small mammals (<1kg) with a high metabolic
rate and thus O2consumption. It is preserved in fossil teeth and
delta17OPO4 can be used as a new proxy for palaeo-pCO2 reconstructions
and to monitor diagenetic alteration of bioapatite delta 18OPO4
values.


Calcium isotopes (delta44/42Ca) are a very promising deep time diet
proxy for fossil vertebrates with a high preservation potential, even
in fossil bones. delta44/42Ca values enable us to determine the
consumption of plant versus animal tissues and decrease systematically
with each trophic level along the foodchain. We found a trophic level
effect of ~0.4‰ between bones of extant African mammalian herbivores
(-0.46±0.14‰) and carnivores (-0.89±0.14‰). Ant/termite-feeding
mammals (0.04±0.16‰) have higher delta 44/42Ca values than both
herbivores and carnivores. Whether Ca isotopes are indeed a new
geochemical proxy for insectivory is currently being investigated.
Using Ca isotopes past diets of extinct vertebrates and fossil food
webs can be reconstructed to identify apex predators. T-Rex and
sympatric herbivorous dinosaurs display a similar trophic level effect
as extant mammals. Preliminary delta44/42Ca data for the Eocene terror
bird (Gastornis) are more in accordance with a herbivorous diet.