Plesiosaurs, mosasaurs, and icthyosaurs were fearsome predators of the deep during the Mesozoic period, flourishing between 251 million to 65 million years ago. In a study published in the June 11, 2010 issue of the journal Science, researchers argue that the success of these three main groups of marine reptiles may have been due to their ability to maintain a constant body temperature as they dove in pursuit of prey.
Ectothermy and Modern Reptiles
Many modern reptiles, including most lizards, crocodiles, alligators, and turtles are ectothermic, or "cold-blooded." This refers not to the temperature of their bodies per se, but to their lack of an internal mechanism to regulate body temperature. Most reptiles must lie in the sun for long periods of time in order to attain a temperature conducive to movement; in cold climates they are sluggish or nearly immobile.
Homeothermy and Ancient Reptiles
In the paper, the researchers describe a study of the three major groups of Mesozoic sea predators, all of which were reptiles. These included the mosasaurs, the icthyosaurs, and the plesiosaurs. The large creatures mainly fed on fish, mollusks, and cephalopods, like modern marine mammals do; also like marine mammals, they seemed able to sustain their body temperature at a relatively warm level, which may have made their muscles work more efficiently and helped them dive deeper than an ectothermic animal could have. There is also speculation that the reptiles might have had some type of specialized circulatory system or perhaps a layer of blubber that kept their temperatures constant.
By studying the ratio of oxygen isotopes in the fossilized teeth and comparing it with that of cold-blooded fish, the researchers were able to determine that the predators were unlike other reptiles or ectothermic animals and more resembled modern dolphins, whales, and tuna in their ability to sustain body heat. Earlier research had already suggested that this might be the case, as plesiosaurs and icthyosaurs were thought to have high metabolic rates in tune with their "cruising" lifestyle that somewhat resembled that of modern sharks.
How Warm Were They?
The Science paper gave a range for the body temperatures the reptiles might have maintained, but specific figures are still elusive. Study researcher Christophe Lecuyer of the University of Lyon in France estimates that the ancient reptiles' temperatures probably fell into the same range as that of modern dolphins and whales: Between 95 and 102 degrees Fahrenheit (35–39 degrees Celsius).
But paleontologist Ryosuke Motani of the University of California, Davis, who published a commentary in the same issue of the journal, thinks the temperatures might be exaggerated due to loss of oxygen-18 in the fossils over time. His estimate was closer to that of modern tuna, around 75 degrees Fahrenheit (24 degrees Celsius), though he agreed that the body temperature of the mosasaurs could have been maintained at around 97 degrees F (36 degrees Celsius).
Sources:
Minkel, JR. "How Ancient Sea Reptiles Became Ferocious Predators". LiveScience. June 10, 2010
Motani, Ryosuke. "Warm-Blooded "Sea Dragons"?". Science. June 10, 2010
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
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