| Placodus | |
|---|---|
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| Placodus gigas | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Placodontia |
| Family: | †Placodontidae Cope, 1871 |
| Genus: | †Placodus Agassiz, 1833 |
| Species | |
Placodus (fromGreek:plax, plakos, "a plate" andGreek:odous, "tooth")[1] is an extinct genus ofmarine reptiles belonging to the orderPlacodontia, which swam in the shallow seas of the middleTriassic period (c. 240 million years ago). Fossils ofPlacodus have been found inCentral Europe (Germany,France,Poland) andChina.
Placodus had a stocky body with a long tail, and reached a total length of 2.5–3 m (8.2–9.8 ft).[2] It had a short neck, and a heavy skull. They were specialized for adurophagous diet of shellfish, such asbivalves.Chisel-likeincisors protruded from theanterior margin of the snout, and were probably used to pluck hard-shelledbenthic prey from the substrate. The back teeth were broad and flattened, and would have helped to crush the prey.[3] Before the animals' anatomy was known, they were regarded as fishes' teeth. Similar smaller teeth were present on thepalatine bones.
Placodus and its relatives were not as well-adapted toaquatic life as some later reptile groups, like the closely relatedplesiosaurs. Their flattened tails and short legs, which probably ended in webbed feet, would have been their main means of propulsion in the water.[3]
Theparietal eye on top of the head assisted the animal with orientation, rather than its vision, and its presence is regarded as a primitive characteristic.[citation needed]
Thevertebral processes ofPlacodus dove-tailed into each other and were firmly connected, so that the trunk was rigid. The abdomen was covered with a special armor formed of the bent, right-angled abdominalribs. Equipped with dense bones, heavybelly ribs, and a row of bony knobs above the backbone,Placodus was a heavily built and negatively buoyant creature that would have had no trouble staying on the seafloor to feed.
This body armour would have offered protection from predators as well, but would have also hampered mobility on land, makingPlacodus slow and clumsy out of water. It was therefore most likely a terrestrial animal that ventured into the sea in search of food.Molluscs,brachiopods,crustaceans, and other inhabitants of the seabed would have formed its staple diet.
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