Placodont

Taxobox
name = Placodonts

---

image_caption = "Paraplacodus"
fossil_range = Triassic
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Sauropterygia
ordo = Placodontia
ordo_authority = Cope, 1871
subdivision_ranks = Families
subdivision =
Paraplacodontidae
Placodontidae
Henodontidae
Cyamodontidae
Placochelyidae

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 one to two metres in length, with some of the largest measuring three metres long.

In appearance, many resembled stout- or barrel-bodied newts, or lizard, while others looked more turtle-like due to large bony plates on their backs. They had short limbs and were highly robust.

Because of their dense bone and heavy armour plating, these creatures would have been too heavy to float in the ocean and would have used a lot of energy to reach the water surface. For this reason and because of the type of sediment found accompanying fossils it is suggested they lived in shallow waters and not in deep oceans.

Their diet consisted of marine bivalves, brachiopods, and other invertebrates. They were notable for their large, flat, often protruding teeth which they used to crush molluscs and brachiopods, which they hunted on the sea bed (another way in which they were similar to walruses). The palate teeth were adapted for durophagy, being extremely thick and large enough to crush thick shell. The first specimen was discovered in 1830, and they have since been discovered throughout Europe and the Middle East.

Classification

* Class Sauropsida
** Superorder Sauropterygia
*** ORDER PLACODONTIA
**** Genus "Saurosphargis"
**** Family Paraplacodontidae
***** Genus "Paraplacodus"
**** Family Placodontidae
***** Genus "Placodus"
**** Superfamily Cyamodontoidea
***** Family Henodontidae
****** Genus "Henodus"
***** Family Cyamodontidae
****** Genus "Cyamodus"
****** Genus "Protenodontosaurus"
***** Family Placochelyidae
****** Genus "Placochelys"
****** Genus "Psephoderma"

External links

*http://www.oceansofkansas.com/placodnt.html
*http://users.unimi.it/vertpal/galleriafossili/best-retilli/PSEPHODERMAMORFFUNZ.html
*http://rainbow.ldgo.columbia.edu/courses/v1001/9.html
*http://palaeos.com/Vertebrates/Units/220Lepidosauromorpha/220.100.html#Placodontia
* [http://www.oceansofkansas.com/placodnt.html Oceans of Kansas Palaeontology] Mike Everhart