Semi-aquatic habits of spinosaurids

[Jocelyn Falconnet <j.falconnet@gmail.com>]

Hi everyone,

Here is an recent press release by the French CNRS, regarding an in
coming paper on the oxygen isotopic ratios in spinosaurids:
http://www2.cnrs.fr/presse/communique/1778.htm

For non-French speakers (or
non-Google-tried-unsuccessfully-to-Translate users), it says that
French, English, Moroccan, Brazilian, Chinese, and Thai
paleontologists analyzed and compared the oxygen isotopic ratios of
dinosaurs - including spinosaurids - and amphibious crocodiles, and
turtles. And the ratios obtained for spinosaurids were close to those
of crocodiles and turtles, but significantly different from those of
other dinosaurs... No more details for the moment, but the team
analyzed at least *Siamosaurus*, and most likely also Moroccan,
English, Chinese, and Brazilian spinosaurids (ok, it's not surprising,
but that would mean they have a pretty large taxonomic sampling given
the number of spinosaurids now known). Be patient until the release of
the February issue of Geology ! Here are the references given in the
press release:

Amiot R., Buffetaut E., Lécuyer C., Wang X., Boudad L., Ding Z.,
Fourel F., Hutt S., Martineau F., Medeiros A., Mo J., Simon L.,
Suteethorn V., Sweetman S., Tong H., Zhang F. & Zhou Z., (2010).
Oxygen isotope evidence for semi-aquatic habits among spinosaurid
theropods. Geology, 38, 139-142.

See also a previous isotopic analyze of Thai vertebrate faunas
including *Siamosaurus* which suggested the same semi-aquatic habits
for this taxon:

Amiot R., Buffetaut E., Lécuyer C., Fernandez V., Fourel F., Martineau
F. & Suteethorn V. 2009. Oxygen isotope composition of continental
vertebrate apatites from Mesozoic formations of Thailand;
environmental and ecological significance. In: Buffetaut E., Cuny G.,
Le Loeuff J. & Suteethorn V. (eds.), Late Palaeozoic and Mesozoic
Ecosystems in SE Asia. Geological Society, London, Special
Publications 315: 271-283. doi: 10.1144/SP315.19

Phosphatic remains (tooth enamel, turtle shell fragments and fish
scales) of continental vertebrates (freshwater fish, crocodilians,
turtles, and theropod and sauropod dinosaurs) recovered from eight
localities of NE Thailand ranging in age from the Late Jurassic to the
late Early Cretaceous have been analysed for their oxygen isotopic
compositions ({delta}18Op). From these preliminary data, local
meteoric water {delta}18Ow values estimated using {delta}18Op values
of crocodilians and turtles range from –4.1±2{per thousand} at the end
of the Jurassic to –8.3±2{per thousand} during the Early Cretaceous,
suggesting a transition from dry to wetter climates with increasing
amount of seasonal precipitation from several hundred millimetres per
year to several thousand millimetres. Measurable offsets in
{delta}18Op values observed between dinosaur taxa (the spinosaurid
theropod Siamosaurus, other theropods and nemegtosaurid sauropods) are
interpreted in terms of differences in water strategies, and suggest
that Siamosaurus had habits similar to those of semi-aquatic
vertebrates such as crocodilians or freshwater turtles.

All this reminds me of a recent paper in which Billon-Bruyat et al.
(2004) found typical frankly marine oxygen isotopic ratios in the
cryptodiran turtle *Talassemys*, while it shows no morphological
adaptation for an aquatic lifestyle !

-- 
Jocelyn Falconnet