Although the genus was first named in 1940, material from one species, E. yakovlevi, was originally tentatively referred to Trematosuchus in 1926.[9] Russian paleontologist Ivan Yefremov [Efremov] named it Thoosuchus "active crocodile" (from Ancient Greek θοός (thoos) "nimble, active" and σοῦχος (soukhos) "crocodile") in 1940, "in view of its obviously more active mode of life in water than the mode of life of Benthosuchus" (page 13).[1]
Description
Thoosuchus jakovlevi skull
For its family, Thoosuchus was fairly small, reaching a little over 60 cm with a 15 cm skull.[10]
Thoosuchus superficially resembles the more derived trematosaurids, but can be distinguished from them on the basis of a deep, narrowing otic notch.[11][12] It had widely spaced orbits and a moderately elongated skull roof that was well ornamented with ridges and grooves, especially on the parietals.[13] This ornamentation is also a characteristic of trematosaurids and has been described as representing a "zone of intensive growth".[14][15] The well developed lateral line system of Thoosuchus is indicative of its presumed aquatic lifestyle.
Phylogeny
Thoosuchus in a cladogram after Novikov (2018) with only Early Triassic Eastern Europe taxa included:[16]
^ ab
Efremov, I. A. (1940). Preliminary description of the new Permian and Triassic Tetrapoda from U.S.S.R. Trudy Paleontologicheskogo Instituta10:1–140.
^Getmanov, S.N. (1982). A labyrinthodont from the Lower Triassic of the Obshchiy Syrt Region. Paleontological Journal1982:102-106.
^Damiani, R. J. and Yates, A. M. (2003). The Triassic Amphibian Thoosuchus yakovlevi and the Relationships of the Trematosauroidea (Temnospondyli: Stereospondyli). Records of the Australian Museum55:331–342.
^Hartmann-Weinberg, A. and Kuzmin, F. M. (1936). Untertriadische Stegocephalen der UdSSR Lyrocephalus acutirostris nov. sp. Problems of Paleontology1:63–84.
^Shishkin, M. A. (1964). Stereospondyli. In: Orlpv, I. A., ed. Fundamentals of Palaeontology: amphibians, reptiles and birds Moscow: Nauka. pp. 83–122.
^Shishkin, M. A. (1980). The Luzocephalidae, a new Triassic labyrinthodont family. Paleontological Journal1980:88–101.
^Getmanov, S. N. (1989). Triassic amphibians of the East European platform (family Benthosuchidae Efremov). Trudy Paleontologicheskogo Instituta236:1–102.
^Shishkin, M. A. and Welman, J. (1994). A new find of Trematosuchus (Amphibia, Temnospondyli) from the Cynognathus Zone of South Africa. Palaeontologia africana31:39–49.
^Riabinin, A. N. (1926). Trematosuchus (?) yakovlevi nov. sp. from the Lower Triassic deposits in the surroundings of Rybinsk. Izvestiya Geologicheskago Komiteta45:519–527.
^Yates, A. M. and Warren, A. A. (2000). The phylogeny of the 'higher' temnospondyls (Vertebrata: Choanata) and its implications for the monophyly and origins of the Stereospondyli. Zoological Journal of the Linnean Society128:77-121.
^Damiani, RJ (2001). A systematic revision and phylogenetic analysis of Triassic mastodonsauroids (Temnospondyli: Stereospondyli). Zoological Journal of the Linnean Society133:379-482.
^Shishkin, M. A., Novikov, I. V. and Gubin, Y. M. (2000). Permian and Triassic temnospondyls from Russia. In: Benton, M. J., Shishkin, M. A., Unwin, D. M. and Kurochkin, E. N. (eds.), The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, pp. 35-59.
^Säve-Söderbergh, G. (1937). On the dermal skulls of Lyrocephalus,
Aphaneramma, and Benthosaurus, labyrinthodonts from the
Triassic of Spitsbergen and N. Russia. Bulletin of the Geological
Institution of the University of Uppsala27:189–208.
^Bystrow, A. P. (1935). Morphologische Untersuchungen der
Deckknochen des Schädels der Wirbeltiere. Acta Zoologica16:65–141.
