Mycterosaurus is a relatively small carnivore, estimated to be around 60 cm (23 inches) long with synonyms of Eumatthevia bolli, and possibly Basicranodon fortsillensis.

[2] Restored, Mycterosaurus appears spindly and grotesque in contrast to the majority of "pelycosaurs" in its proportions and especially unlike edaphosaurids, which are commonly stocky in build.

[10] This morphology indicates a highly mobile mesotarsal joint in both Varanops and Mycterosaurus, contrasting earlier beliefs that little movement was present in early synapsids.

The holotype (FMNH-UC 692) was discovered by Mr. Herman Douthitt in 1915 at a deposit of the[3] Lower Permian (Leonardian) Clyde Formation of north-central Texas.

[11] Samuel Wendell Williston analyzed the holotype, describing the skull and other fragmented portions of the skeleton in his publication A New Genus and Species of American Theromorpha.

[3] In 1930, R Broom identified an unstudied fossil collected by Jacob Boll at the American Museum that he believed had been wrongly labeled by collectors as a small labyrinthodont.

[5] The authors note both specimens were affected by different types of crushing, making it difficult to accurately assess the true nature of the skull.

[5] However, Romer and Price estimate the true proportions were likely an intermediate between the narrow shape Williston observed[3] and the broad low type restored by Broom.

[5] Additionally, the authors believe defining features of height, pineal size, and teeth differentiated "Eumatthevia" and "Mycterosaurus" were inaccurate.

[6] In 1953, a new fossil (MCZ 2985), was discovered in Colorado and in 1964 named by Lewis and Vaughn as a new species that they called Mycterosaurus smithae, after Mrs Stockton Smith.

[6] However, a reexamination conducted by Brocklehurst et al (2016) using synchrotron radiation micro-computed tomography revealed observations that prompted the authors to reclassify Mycterosaurus smithae into genus Vaughnictis.

[5] Romer and Price, via their observations of Eumatthevia Bolli and the holotype, concluded that Mycterosaurus longiceps belonged as a primitive form of edaphosaurs.

[11] Berman and Reisz believed the most important edaphosaur features cited by Romer and Price were mistakenly recorded from an isolated specimen piece that had been confused and misidentified.

[11] As a result, Berman and Reisz re-examined all known M. longiceps specimens which led them to the conclusion that Mycterosaurus is best interpreted as a member of the family Varanopidae.

[4][12] Below is a cladogram modified from the analysis of Benson (in press), after the exclusion of Basicranodon:[13] Tseajaia campi Limnoscelis paludis Captorhinus spp.

Protorothyris archeri Caseasauria Ianthodon schultzei Edaphosauridae Sphenacodontia Archaeothyris florensis Varanosaurus acutirostris Ophiacodon spp.

Stereophallodon ciscoensis Archaeovenator hamiltonensis Pyozia mesenensis Mycterosaurus longiceps ?Elliotsmithia longiceps (BP/1/5678) Heleosaurus scholtzi Mesenosaurus romeri Varanops brevirostris Watongia meieri Varanodon agilis Ruthiromia elcobriensis Aerosaurus wellesi Aerosaurus greenleorum Very little has been postulated or hypothesized about the paleobiology of Mycterosaurus due to the small amounts of poorly preserved and incomplete fossil evidence.

[3][11] The Clyde formation belongs to the Wichita group that is almost entirely alternating gray limestone and shale with minuscule amounts of sandstone and siltstone.