Australia: The Land Where Time Began

A biography of the Australian continent 

Placodonts - "Table Teeth"

A group of marine reptiles from the Triassic that had gone extinct by the end of the Period. They were about 1-2 m (3.3-6.6 ft) long, the largest known being 3 m (9.8 ft) long

The earliest forms such as Placodus from the Early to Middle Triassic looked somewhat similar to modern marine iguanas. Unlike the iguanas, they appear to have eaten molluscs because they had flat, tough teeth that were often protruding, suited to crushing hard objects such as mollusc shells. Later forms of Placodonts had developed bony plates on their backs, probably to protect them from other marine reptiles that had evolved such as ichthyosaurs and nothosaurs. Still later forms had even more bony plates on their backs, probably reflecting the increasing threat for the marine reptiles. By the Late Triassic, the bony plates had become so large that they resembled sea turtles, in genera such as Henodus and Placocheyls. Some, such as Psephoderma had articulated plates that more resembled those or horseshoe crabs and trilobites.

They would have needed to expend a large amount of energy to rise to the surface to breath because of the weight of their armour as they would not have been able to float. This, and the type of sediment they were fossilised in, suggest they lived in shallow water.

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                                                                                           Author: M.H.Monroe  Email:     Sources & Further reading