Thalattoarchon is an extinct genus of large predatory ichthyosaurs that lived during the Anisian stage of the Middle Triassic in what is now North America. The only known species is T. saurophagis, described in 2013 from a single specimen discovered in the Favret Formation, Nevada (United States). 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, its size being estimated at around 8.6 meters (28 ft) long, although the authors are uncertain about the exact measurements. 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 12 centimeters (0.39 ft), which would have been well suited for attacking large prey. Although the fossils are incomplete, it is estimated that 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. Thalattoarchon would have been an apex predator, its sharp and cutting teeth suggesting that it would have mainly preyed on contemporary marine reptiles. Its position as a apex predator is generally comparable to that of orcas, which have a similar lifestyle.
The only known specimen of Thalattoarchon was discovered in 1997 by the paleontologist Jim Holstein during a field expedition in the Augusta Mountains, located in Nevada, United States.[1] It was with the support and a grant from the National Geographic Society that the fossils were completely exhumed in 2008,[1][3][a] after a period of work of three weeks. The recovered material where transported by an helicopter and a truck out of the field.[4] The fossils were excavated in the Taylori Zone of the Fossil Hill Member in the Favret Formation, dating to approximately 244.6 million years ago, from the beginning of the late Anisian of the Middle Triassic. The specimen, cataloged as FMNH PR 3032, consists of a major part of the skull and the axial skeleton, including parts of the pelvic girdle and rear swimming paddles.[1]
It was in 2013 that this specimen was designated as the holotype of a new genus and species of ichthyosaurs by Nadia B. Fröbisch and colleagues, under the name of Thalattoarchon saurophagis in the scientific journal Proceedings of the National Academy of Sciences. The genus name comes from Ancient Greek θάλασσα (thálassa, "sea"), and ἄρχον árchon, "ruler"),[1] directly referencing the animal's imposing size and position as an apex predator of the Triassic seas.[4] The species name also comes from Ancient Greek and is derived from the words σαῦρος (saûros, "lizard") and φᾰγεῖν (phageîn, "to eat"), in reference to its carnivorous diet.[1][5]