Thalattoarchon

Thalattoarchon is an extinct genus of ichthyosaur from the Middle Triassic of the western United States. The type species Thalattoarchon saurophagis (meaning "lizard-eating sovereign of the sea" in Greek) was discovered in Nevada, USA, in 2010 and formally described in 2013. It is known from a single skeleton, holotype FMNH PR 3032, consisting of a partial skull, vertebral column, hip bones, and parts of the hind fins. The total length of "Thalattoarchon" is estimated to have been at least . "Thalattoarchon" is thought to have been one of the first marine macropredators capable of eating prey that was similar in size to itself, an ecological role that can be compared to that of modern orcas. "Thalattoarchon" lived four million years after the first appearance of ichthyosaurs in the Early Triassic and is therefore the oldest known marine reptile to have been an apex predator. It lived eight million years after the Permian-Triassic extinction event, indicating a fast recovery of marine ecosystems after the mass extinction.
Description.
"Thalattoarchon" is a large-bodied ichthyosaur that is estimated to have grown at least in length. The only known skeleton of "Thalattoarchon" is incomplete, but it can be inferred on the basis of other early ichthyosaurs to have had an elongated body and a weakly developed caudal fin. "Thalattoarchon" is diagnosed by a single distinguishing feature that is unique among ichthyosaurs: large, thin teeth that bear two cutting edges and that have smooth tooth crowns. Most later ichthyosaurs have much smaller cone-shaped teeth. The Late Triassic ichthyosaur "Himalayasaurus tibetensis" also has large teeth with cutting edges, but can be distinguished from "Thalattoarchon saurophagis" by the presence of grooves across the surfaces of its tooth crowns. "Thalattoarchon" is very similar in appearance to "Cymbospondylus", another large-bodied Middle Triassic ichthyosaur, but differs in having a head that is about twice as large as that of "Cymbospondylus" relative to its body.
Classification.
Below is a cladogram from Fröbisch "et al." (2013):
A 2016 cladistic analysis recovers "Thalattoarchon" as a cymbospondylid rather than a basal merriamosaur.