Placodonts - Placodont, Placodus, Henodus, Cyamodus, Paraplacodus, Psephoderma, Placochelys (Paperback)

Chapters: Placodont, Placodus, Henodus, Cyamodus, Paraplacodus, Psephoderma, Placochelys. Source: Wikipedia. Pages: 24. Not illustrated. Free updates online. Purchase includes a free trial membership in the publisher's book club where you can select from more than a million books without charge. Excerpt: CyamodontidaeHenodontidaeParaplacodontidaePlacochelyidaePlacodontidae Placodonts ("Tablet teeth") were a group of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. It is believed that they were related to the Sauropterygia, the group that includes Plesiosaurs. Placodonts were generally between 1 to 2 metres (3 to 7 ft) in length, with some of the largest measuring 3 metres (10 ft) long. The first specimen was discovered in 1830, and they have since been discovered throughout Europe, North Africa, and the Middle East. Macroplacus raeticusThe earliest forms like Placodus, which lived in the early to middle Triassic, resembled barrel-bodied lizards somewhat similar to the marine iguana of today, but larger. But unlike the marine iguana, which feeds on algae, the placodonts ate molluscs and so their teeth were flat and tough to crush their shells. In the earliest periods their size was probably enough to take away the top sea predators of the time: the sharks. However, as time passed other kinds of carnivore reptiles began to colonize the seas, such as ichthyosaurs and nothosaurs, and later placodonts developed bony plates on their backs to protect their bodies while feeding. By the Late Triassic, these plates had grown so much that placodonts of the time such as Henodus and Placochelys resembled the sea turtles of modern day more than their ancestors without bony plates. Other placodonts like Psephoderma developed plates as well, but in a different articulated manner that resembled the shells of horseshoe crabs and trilobites more than those of sea turtles. All these adaptations ...More: http: //booksllc.net/?id=288993