Saturday, February 6, 2010

Spinosaurs show semi-aquatic oxygen isotopes

Both of these are posts to the Dinosaur Mailing List:

From: Ben Creisler

In case this ref has not been mentioned yet:

Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods.

Romain Amiot, Eric Buffetaut, Christophe Lécuyer, Xu Wang, Larbi Boudad, Zhongli Ding, François Fourel, Steven Hutt, François Martineau, Manuel Alfredo Medeiros, Jinyou Mo, Laurent Simon, Varavudh Suteethorn, Steven Sweetman, Haiyan Tong, Fusong Zhang, and Zhonghe Zhou

Geology 38: 139-142 (February 2010)

Abstract:
Spinosaurs were large theropod dinosaurs showing peculiar specializations, including somewhat crocodile-like elongate jaws and conical teeth. Their biology has been much discussed, and a piscivorous diet has been suggested on the basis of jaw as well as tooth morphology and stomach contents. Although fish eating has been considered plausible, an aquatic or semiaquatic lifestyle has seldom been suggested because of the apparent lack of corresponding adaptations in the postcranial skeleton of spinosaurs, which on the whole is reminiscent of that of other large terrestrial theropods. On the basis of the oxygen isotopic composition of their phosphatic remains compared with those of coexisting terrestrial theropod dinosaurs and semiaquatic crocodilians and turtles, we conclude that spinosaurs had semiaquatic lifestyles, i.e., they spent a large part of their daily time in water, like extant crocodilians or hippopotamuses. This result sheds light on niche partitioning between large predatory dinosaurs, since spinosaurs coexisted with other large theropods such as carcharodontosaurids or tyrannosaurids. The likely ichthyophagy and aquatic habits of spinosaurids may have allowed them to coexist with other large theropods by reducing competition for food and territory.

And:

Hi everyone,

Here is an recent press release by the French CNRS, regarding an incoming paper on the oxygen isotopic ratios in spinosaurids:

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:

[Same authors and reference as above.]

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

Posted via email from Garth's posterous

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