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Benthosuchus; Temporal range: Early Triassic, 251–247 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Skull of Benthosuchus sushkini
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Temnospondyli
Suborder:	†Stereospondyli
Family:	†Benthosuchidae; Efremov, 1940
Genus:	†Benthosuchus; Efremov, 1937
Species
	†B. sushkini (Efremov, 1929 [originally Benthosaurus sushkini]) (type); †B. korobkovi Ivachnenko, 1972; †B. bashkiricus Otschev, 1972; †B. gusevae Novikov, 2012; †B. lukyanovi Morkovin, 2020;

Life restoration of *Benthosuchus sushkini*

Benthosuchus (meaning "deep water crocodile") is an extinct genus of temnospondyl amphibian from the Early Triassic of Russia. It was primarily aquatic, living in rivers and lakes. Multiple species are known, with the largest reaching about 2.5 meters in length.

Russian paleontologist Ivan Yefremov [Efremov] called the genus Benthosaurus "deep water lizard" (from Ancient Greek βένθος (benthos) "depth, deep water") in his original 1929 description, "in view of its clearly indicated adaptation to life in deep water" shown by "the position of the orbits and the flatness of the skull." The type species B. sushkini honored his late teacher Petr Sushkin. The generic name was preoccupied by Benthosaurus Goode & Bean, 1886, a fish, and he renamed the genus Benthosuchus ("deep water crocodile") in 1937.^[2]^[3]

Benthosuchus has traditionally been considered a member of the temnospondyl superfamily Trematosauroidea, and the family Benthosuchidae was established in 1940 to include Benthosuchus and the related trematosauroid Thoosuchus. Some recent phylogenetic studies have removed Benthosuchus from Trematosauroidea entirely, placing it as a closer relative of Mastodonsauroidea, another group of Triassic temnospondyls. Other studies retain Benthosuchus within Trematosauroidea, but since Benthosuchus and Thoosuchus have successively basal positions on these trees they form a paraphyletic grouping, not a valid clade.^[4] Benthosuchidae was widely considered to be a monotypic family containing only Benthosuchus, until the discovery of the related Kwatisuchus in 2024.^[5]

Description

Benthosuchus skull is about 0.75 m long (it is comparatively short in young individuals but lengthens with age), and the overall body length is about 2.5 m. It existed in widely overflowing rivers of the East Russian Depression.^[6]

Phylogeny

Benthosuchus is traditionally considered a close relative of a group of temnospondyls called capitosaurids. In particular, it bears a close resemblance to the capitosaurid Wetlugasaurus. Many of the early large-scale phylogenetic analyses of temnospondyls place Benthosuchus within a clade called Capitosauria. However, more recent analyses such as that of Fortuny et al. (2011) recover Benthosuchus within another clade called Trematosauria. Occasionally it is grouped near the trematosaurid family Trematosauridae as a basal member of the group Trematosauroidea.^[7] Fortuny et al. found that Benthosuchus positioned outside Trematosauroidea as a more basal trematosaurian. Below is a cladogram from Fortuny et al. (2011) showing the phylogenetic placement of Benthosuchus:^[8]

Stereospondyli

Lydekkerina huxleyi

Rhinesuchidae

	Rhineceps nyasaensis

	Uranocentrodon senekalensis

Capitosauria

Wetlugasaurus angustifrons

	Odenwaldia heidelbergensis

	Vladlenosaurus alexeyevi

	Edingerella madagascariensis

	Watsonisuchus spp.

Xenotosuchus africanus

Cherninia denwai

Paracyclotosaurus crookshanki

	Stanocephalosaurus pronus

	Stanocephalosaurus birdi

Procyclotosaurus stantonensis

	Eocyclotosaurus spp.

	Quasicyclotosaurus campi

Parotosuchus orenburgensis

Calmasuchus acri

	Cyclotosaurus robustus

	Tatrasuchus wildi

	Eryosuchus garjainovi

	Mastodonsaurus giganteus

Trematosauria

Benthosuchus sushkini

Trematosauroidea

Thoosuchus yakovlevi

	Angusaurus spp.

	Trematosaurus brauni

Cladogram after Novikov (2018) with only Early Triassic Eastern Europe taxa included:^[9]

	Poryolosuchus

	Parotosuchus

Selenocara

	Wetlugasaurus

	Vladlenosaurus

Qantas

	Inflectosaurus

	Trematosaurus

Syrtosuchus

Benthosuchus

Yarengiidae

	Vyborosaurus

	Yarengia

Benthosuchidae

Qantasidae

Lydekkerinidae

References

^ Igor Novikov (July 2012). "New data on trematosauroid labyrinthodonts of Eastern Europe: 4. Genus Benthosuchus Efremov, 1937". Paleontological Journal. 46 (4). doi:10.1134/S0031030112040089.
^ Efremov, I. A. (1929). Benthosaurus sushkini, ein neuer Labyrinthodont der permotriassischen Ablagerungen der Sharschenga Flusses. Bulletin of the Academy of Sciences of the USSR 8:747-770. [English translation: https://paleoglot.org/files/Efremov%201929b.pdf]
^ Efremov, I.A. (1937). On the Stratification of Continental Permian and Triassic the Soviet Union Based on the Terrestrial Vertebrate Fauna. Doklady Akademii Nauk SSSR. Nov. Ser. 16(2): 125–132.
^ Damiani, R.J.; Yates, A.M. (2003). "The Triassic amphibian Thoosuchus yakovlevi and the relationships of the Trematosauroidea (Temnospondyli: Stereospondyli)" (PDF). Records of the Australian Museum. 55 (3): 331–342. doi:10.3853/j.0067-1975.55.2003.1388.
^ Pinheiro, Felipe L.; Eltink, Estevan; Paes‐Neto, Voltaire D.; Machado, Arielli F.; Simões, Tiago R.; Pierce, Stephanie E. (2024-01-19). "Interrelationships among Early Triassic faunas of Western Gondwana and Laurasia as illuminated by a new South American benthosuchid temnospondyl". The Anatomical Record. doi:10.1002/ar.25384. ISSN 1932-8486.
^ "Benthosuchus". Retrieved Oct 16, 2020 – via The Free Dictionary.
^ Shishkin, M.A.; Sulej, T. (2009). "Early Triassic temnospondyls of the Czatkowice 1 tetrapod assemblage" (PDF). Palaeontologica Polonica. 65: 31–77. Archived from the original (PDF) on 2012-03-01. Retrieved 2012-08-02.
^ Fortuny, J.; Galobart, À.; Santisteban, C. D. (2011). "A New Capitosaur from the Middle Triassic of Spain and the Relationships within the Capitosauria". Acta Palaeontologica Polonica. 56 (3): 553. doi:10.4202/app.2010.0025.
^ Novikov A.V. (2018). Early Triassic amphibians of Eastern Europe: evolution of dominant groups and peculiarities of changing communities (PDF) (in Russian). Moscow: RAS. p. 138. ISBN 978-5-906906-71-7. "Archive copy" (PDF). December 8, 2023.