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Which marine animals first colonized expanding continental shelves during the Triassic?
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Triassic Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the early Triassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
As sea levels rose during the Triassic Period, the expanding continental shelves were colonized for the first time by large marine reptiles and reef-building corals of modern aspect.12
These marine reptiles included:
- Placodonts: Shell-crushing animals that bore a superficial resemblance to turtles.3
- Nothosaurs: Fish-eating members of the sauropterygian order.3
- Ichthyosaurs: Large, streamlined, and efficient hunters that resembled dolphins in profile and were adapted for rapid swimming.3
Additionally, the tropical and subtropical shelf seas supported the development of reefs. While early Triassic corals were absent due to the Permian-Triassic extinction, small reeflike mounds appeared in the Middle Triassic, eventually evolving into more extensive reef complexes dominated by scleractinian (stony) corals and calcareous pharetronid sponges by the Late Triassic.4