What is Placodont?
{{Automatic taxobox | image = Placodus gigas 2.JPG | image_caption ='''''Placodus''''', [[type genus]] | fossil_range = [[Middle Triassic|Middle]] to [[Upper Triassic]] 235 to 201 mya | taxon = Placodontia | authority = [[Edward Drinker Cope|Cope]], 1871}} [[File:Placodonts.jpg|thumb|right|220px|Three different [[genera]] of placodonts. They had front teeth which grabbed shellfish, and flat back teeth which crushed the shells.]] [[File:Macroplacus raeticus.JPG|thumb|right|230px|''Macroplacus'' skull: note flat teeth ]] [[File:Cyamodus 1.JPG|thumb|right|230px|Fossil of ''Cyamodus'' shows the overall shape of the animal]] '''Placodonts''' were a group of [[Triassic]] [[Ocean|marine]] [[reptiles]] which had heavy flat teeth. These teeth were used for crushing [[shellfish]].<ref name=reign>Benton M.J. 1990. ''The reign of the reptiles''. Crescent, New York. 118&ndash;122</ref> Placodonts are in the [[Order (biology)|Order]] [[Sauropterygia]], the group that includes [[Plesiosaur]]s. Placodonts were mostly between {{convert|1|to|2|m|ft|0}} in length, up to a maximum {{convert|3|m|ft|0}} long. They are found in marine [[sediment]]s of the [[Middle Triassic|Middle]] and [[Upper Triassic]], 235&ndash;250 million years ago.<ref name=reign/><ref>Benton M.J. 2015. ''Vertebrate palaeontology'', 4th ed p150, 152/3.</ref> The first specimen was discovered in 1830, and the group was very widely distributed. Shellfish were common throughout the [[Mesozoic]] period, but this group of shellfish-eaters went extinct at the end of the Triassic. They were clearly a victim of some event which disturbed their lifestyle. The end-Triassic had several [[extinction event]]s which are not well understood. ==Palaeobiology== The earliest forms like '''''Placodus''''', in the early to middle [[Triassic]], looked rather barrel-shaped. Later placodonts had bony plates on their backs which protected their bodies while they were feeding. By the [[Upper Triassic]], these plates had grown so that some placodonts of the time looked like the [[sea