''Thalattoarchon'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

ichthyosaur Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

of the western United States. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Thalattoarchon saurophagis'' (meaning "lizard-eating sovereign of the sea" in

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

) was discovered in

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

, USA, in 2010 and formally described in 2013. It is known from a single skeleton,

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

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

orca The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...

s. ''Thalattoarchon'' lived four million years after the first appearance of ichthyosaurs in the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

and is therefore the oldest known

marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. The earliest marine reptile mesosaurus (not to be confused with mosasaurus), arose in the Permian period during the ...

to have been an

apex predator An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...

. 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, measuring at least long and weighing . 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 Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

. ''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 crown In dentistry, crown refers to the anatomical area of teeth, usually covered by enamel. The crown is usually visible in the mouth after developing below the gingiva The gums or gingiva (plural: ''gingivae'') consist of the mucosal tiss ...

s. Most later ichthyosaurs have much smaller cone-shaped teeth. The Late Triassic ichthyosaur ''

Himalayasaurus tibetensis ''Himalayasaurus'' is an extinct genus of ichthyosaur from the Late Triassic Qulonggongba Formation of Tibet. The type species ''Himalayasaurus tibetensis'' was described in 1972 on the basis of fragmentary remains, including teeth, limb bones, ...

'' 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 ''Cymbospondylus'' (a Greek word meaning "boat vertebrae") was a basal early ichthyosaur that lived between the early and middle Triassic period (249-237 million years ago). Previously, the genus was classified as a shastasaurid, but more rec ...

'', 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 A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

from Fröbisch ''et al.'' (2013): A 2016 cladistic analysis recovers ''Thalattoarchon'' as a cymbospondylid rather than a basal merriamosaur.Jiang, Da-Yong; Motani, Ryosuke; Huang, Jian-Dong; Tintori, Andrea; Hu, Yuan-Chao; Rieppel, Olivier; Fraser, Nicholas C.; Ji, Cheng; Kelley, Neil P.; Fu, Wan-Lu; Zhang, Rong (23 May 2016). "A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction". Scientific Reports 6. 26232.

References

{{Taxonbar, from=Q2756895 Middle Triassic ichthyosaurs Middle Triassic reptiles of North America Triassic United States Extinct reptiles Ichthyosauromorph genera

Description

Classification

See also

References