Ichthyosauria

Ichthyosauria is an extinct clade of marine reptiles that lived during the Mesozoic Era. Its members evolved streamlined bodies and other adaptations for swimming in the sea.

Amniota: Amniota is the vertebrate clade whose embryos develop within protective membranes, including reptiles, birds, and mammals. Ichthyosaurs belong to this broader group of land-vertebrate descendants.
Ichthyosaur locomotion: Ichthyosaur locomotion is the swimming movement produced chiefly by lateral strokes of the tail. A crescent-shaped tail fin supplied propulsion in many later ichthyosaurs.
Early Triassic: The Early Triassic is the first epoch of the Triassic Period, spanning about 251.9 to 247.2 million years ago. The oldest known ichthyosaur fossils appear soon after the end-Permian mass extinction.
Stenopterygius: Stenopterygius is a Jurassic ichthyosaur genus represented by exceptionally preserved fossils from Germany. Fossils preserve body outlines, skin impressions, and embryos in this genus.
Mesozoic marine revolution: The Mesozoic marine revolution was a long-term escalation of predation and defensive adaptations in marine ecosystems. Ichthyosaurs were major marine predators within these changing Mesozoic food webs.
Diapsid: Diapsids are amniotes characterized ancestrally by two openings behind each eye socket in the skull. Ichthyosaurs are placed among diapsid reptiles in current evolutionary classifications.
Caudal fin: A caudal fin is a tail fin that helps an aquatic animal generate thrust and steer. The lower lobe was supported by the downward-bent end of the vertebral column.
Utatsusaurus: Utatsusaurus is an Early Triassic ichthyosauriform from Japan and Canada, retaining relatively primitive features. Its anatomy illuminates early stages in the evolution of aquatic ichthyosaur relatives.
Temnodontosaurus: Temnodontosaurus is a large Early Jurassic ichthyosaur genus with several recognized species. Its large skull and varied species illustrate early ichthyosaur diversity.
Marine reptile: A marine reptile is a reptile adapted to live in the sea, whether continuously or for part of its life. Ichthyosauria is one of the most specialized extinct marine-reptile lineages.

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