the dominant phytoplankton in the oceans. In the Triassic, secondary endosymbiotic algae became the most important plankton. Fauna Marine invertebrates In marine environments, new modern types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of Devonian or modern times. Serpulids appeared in the Middle Triassic. Microconchids were abundant. The shelled cephalopods called ammonites recovered, diversifying from a single line that survived the Permian extinction. Fish The fish fauna was remarkably uniform, with many families and genera exhibiting a global distribution in the wake of the Permian-Triassic mass extinction event. Ray-finned fishes (actinopterygians) went through a remarkable diversification during the Triassic, leading to peak diversity during the Middle Triassic; however, the pattern of this diversification is still not well understood due to a taphonomic megabias. Large predatory actinopterygians such as saurichthyids and birgeriids appeared in the Early Triassic and became widespread and successful during the period as a whole. Lakes and rivers were populated by lungfish (Dipnoi), such as Ceratodus, which are mainly known from the dental plates, abundant in the fossils record. Hybodonts, a group of shark-like cartilaginous fish, were dominant in both freshwater and marine environments throughout the Triassic. Amphibians Temnospondyl amphibians were among those groups that survived the Permian–Triassic extinction. Once abundant in both terrestrial and aquatic environments, the terrestrial species had mostly died out during the extinction event. The Triassic survivors were aquatic or semi-aquatic, and were represented by Tupilakosaurus, Thabanchuia, Branchiosauridae and Micropholis, all of which died out in Early Triassic, and the successful Stereospondyli, with survivors into the Cretaceous Period. The largest Triassic stereospondyls, such as Mastodonsaurus, were up to in length. Some lineages (e.g. trematosaurs) flourished briefly in the Early Triassic, while others (e.g. capitosaurs) remained successful throughout the whole period, or only came to prominence in the Late Triassic (e.g. Plagiosaurus, metoposaurs). The first Lissamphibians (modern amphibians) appear in the Triassic, with the progenitors of the first frogs already present by the Early Triassic. However, the group as a whole did not become common until the Jurassic, when the temnospondyls had become very rare. Most of the Reptiliomorpha, stem-amniotes that gave rise to the amniotes, disappeared in the Triassic, but two water-dwelling groups survived: Embolomeri that only survived into the early part of the period, and the Chroniosuchia, which survived until the end of the Triassic. Reptiles Archosauromorphs The Permian–Triassic