Life in Water - and changes in their diets as new prey...

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Life in Water The bivalves recovered from the Jurassic extinctions and again became major reef- formers in the numerous shallow marginal seas that encroached onto the continents during the Cretaceous. Ammonites continued their dominance, as did their relatives the straight-shelled belemnites. Modern teleost fish appeared during the Cretaceous and may have competed for the same prey as the ammonites. The teleost fish were apparently stronger and swifter swimmers than the fish of the Jurassic. Some paleontologists speculate that the extinction of ichthyosaurs during the Cretaceous may have been hastened by the rise of these new faster fish that would have been difficult for the ichthyosaurs to catch and eat.
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The plesiosaurs from the Jurassic continued their diversification. Ichthyosaurs, however, declined during the early Cretaceous before becoming extinct well before the end-of-the-Cretaceous extinction. Both the long-necked plesiosaurs, and the short- necked pliosaurs were present during the Cretaceous. Despite inevitable competition
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Unformatted text preview: and changes in their diets as new prey evolved, plesiosaurs were doing well up until the extinction at the close of the Cretaceous. To the list of swimming reptiles we add the mosasaurs, essentially swimming "lizards". These ferocious predators reached lengths to 30 feet (9 meters). Mosasaurs are usually considered relatives of the monitor lizards, although some recent analyses suggest a closer link to snakes is a distinct possibility. Mosasaurs were predators of the Cretaceous seas. Many ammonite fossils have been found that have tooth marks suggesting mosasaurs actively sought and ate ammonites. Some paleontologoists believe that mosasaurs became so successful because they were able to utilize the role in the marine environment that was opened once the ichthyosaurs went extinct. Mosasaurs apparently gave birth to live young and perhaps had some level of parental care for their young....
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Life in Water - and changes in their diets as new prey...

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