Warm-blooded beasts

My fish guys will be talking out thermal relationships tomorrow, and we'll discuss the way in which certain fish like tuna are able to maintain body temperatures considerably higher than ambient.  This gives them a significant advantage in hunting down the other fish on which they feed.  Which makes this new Science paper particularly interesting.  Seems that some of the marine reptiles that were so dominant in Mesozoic seas may have used the same strategy.  The French researchers who led the work employed stable isotopes of oxygen in the phosphates of tooth enamel from fossil ichthyosaurs, plesiosaurs, and mosasaurs.  They compared the ratios to those of fish fossils from the same time period.  Isotope ratios in the poikilothermic fish can be used as a gauge to water temperatures - 18O/16O ratios increase with decreasing water temperature.  The results demonstrated that the body temperature of the aquatic reptiles remained relatively constant, even in changing water temperatures.  The reptiles maintained body temperatures in the neighborhood of 35-39 degrees Celsius, while water temperatures ranged as low as 12 degrees.