Thalattoarchon

Thalattoarchon is a genus of large, Middle Triassic predatory ichthyosaur from North America, containing the single species T. saurophagis. The taxon was described in 2013 from a single partial skeleton discovered in Nevada. The generic name, meaning "ruler of the seas", refers to its status as an apex predator, while the specific epithet, meaning "lizard eater", alludes to its carnivorous diet. As an ichthyosaur, Thalattoarchon had flippers for limbs and a fin on the tail. It is a large ichthyosaur, with an estimated length between . The animal has a long, slender body but with a proportionally large head and a straight, elongated tail. The jaws of Thalattoarchon feature large teeth with two cutting edges of up to . Although the fossils are incomplete, the animal would have had a skeleton comprising at least 60 presacral vertebrae.

The classification of this genus within the ichthyosaurs is much debated, being either classified within the clade Merriamosauria or in the more basal family Cymbospondylidae. As its scientific name indicates, its sharp, cutting teeth suggest that it could easily have preyed upon other marine reptiles of its time, indicating that it most likely occupied the highest position in the food chain. Its behavior as an apex predator is sometimes compared to that of orcas, which have a similar lifestyle. Thalattoarchon is known from the Favret Formation, which during the Anisian represented a coastal oceanic region inhabited by a wide variety of aquatic life, including numerous other ichthyosaurs. The different ichthyosaurs in this area likely adopted distinct feeding strategies to avoid competition.