# Placodus

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***Placodus*** (from Greek: *plax, plakos*, "a plate" and Greek: *odous*, "tooth")[1] is an extinct genus of [marine reptiles](/source/Marine_reptile) belonging to the order [Placodontia](/source/Placodont), which swam in the shallow seas of the middle [Triassic](/source/Triassic) period (c. 240 million years ago). Fossils of *Placodus* have been found in [Central Europe](/source/Central_Europe) ([Germany](/source/Germany), [France](/source/France), [Poland](/source/Poland)) and [China](/source/China).

## Palaeobiology

*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 a [durophagous](/source/Durophagy) diet of shellfish, such as [bivalves](/source/Bivalve). [Chisel](/source/Chisel)-like [incisors](/source/Incisors) protruded from the [anterior](/source/Anterior) margin of the snout, and were probably used to pluck hard-shelled [benthic](/source/Benthic) 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 the [palatine bones](/source/Palatine_bone).

*Placodus* and its relatives were not as well-adapted to [aquatic life](/source/Aquatic_ecosystem) as some later reptile groups, like the closely related [plesiosaurs](/source/Plesiosaur). Their flattened tails and short legs, which probably ended in webbed feet, would have been their main means of propulsion in the water.[3]

The [parietal eye](/source/Parietal_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]

The [vertebral](/source/Vertebra) processes of *Placodus* 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 abdominal [ribs](/source/Rib). Equipped with dense bones, heavy [belly ribs](/source/Gastralia), 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, making *Placodus* slow and clumsy out of water. It was therefore most likely a terrestrial animal that ventured into the sea in search of food. [Molluscs](/source/Mollusc), [brachiopods](/source/Brachiopod), [crustaceans](/source/Crustacean), and other inhabitants of the seabed would have formed its staple diet.

## References

1. Colbert, Edwin H. (Edwin Harris) & Knight, Charles Robert (1951). [*The dinosaur book: the ruling reptiles and their relatives*](https://archive.org/details/bookruli00colb/page/152/mode/2up). New York: McGraw-Hill. p. 153.

1. Diedrich, C.G. (2010). ["Palaeoecology of *Placodus gigas* (Reptilia) and other placodontids — Middle Triassic macroalgae feeders in the Germanic Basin of central Europe — and evidence for convergent evolution with Sirenia"](https://www.sciencedirect.com/science/article/pii/S0031018209005161). *Palaeogeography, Palaeoclimatology, Palaeoecology*. **285** (3–4): 287–306. [Bibcode:2010PPP...285..287D](https://ui.adsabs.harvard.edu/abs/2010PPP...285..287D). [doi:10.1016/j.palaeo.2009.11.021](https://doi.org/10.1016/j.palaeo.2009.11.021)

1. Palmer, D. (ed.) (1999). *The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals*. London: Marshall Editions. p. 70. ISBN 1-84028-152-9.

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Adapted from the Wikipedia article [Placodus](https://en.wikipedia.org/wiki/Placodus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Placodus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.