Pterosphenus Lucas, 1899

Rage, Jean-Claude, Bajpai, Sunil, Thewissen, Johannes G. M. & Tiwari, Brahma N., 2003, Early Eocene snakes from Kutch, Western India, with a review of the Palaeophiidae, Geodiversitas 25 (4), pp. 695-716 : 700-701

Genus Pterosphenus Lucas, 1899

Pterosphenus Lucas, 1899: 637 , 638, pls 45, 46.

Moeriophis Andrews, 1901: 438-440 , fig. 2.

TYPE SPECIES. — Pterosphenus schucherti Lucas, 1899 , by monotypy.

The inclusion of one of the species from Kutch in Pterosphenus leads to a slightly altered diagnosis of the genus proposed by Rage (1984) (see also Rage 1983a; Holman 2000).

EMENDED DIAGNOSIS. — Vertebrae strongly compressed laterally; pterapophyses high; prezygapophyses markedly reduced; paradiapophyses situated low; zygosphene convex dorsally; anterior border of the neural spine close to the anterior border of the zygosphene or originating from the top of the latter border.

THE SPECIES OF PTEROSPHENUS

Four species were referred to Pterosphenus : Pt. schucherti , the type species of the genus, is known from the Priabonian (late Eocene) and the late Lutetian or early Bartonian (middle Eocene) of

the USA. Parmley & Case (1988) reported Pt. schucherti from the Yazoo Clay (Louisiana) and they stated that this Formation is early Eocene in age. This is likely a lapsus; the Yazoo Clay is Jacksonian, i.e. Priabonian (late Eocene).

Pt. schweinfurthi ( Andrews, 1901) has been found in the Priabonian of Egypt and Libya. Rage (1984) erroneously indicated that the Birket Qarun Formation ( Egypt), that produced this species, is late Lutetian (= Biarritzian) in age. Gingerich (1992) has shown that the age of this Formation is Priabonian. The vertebral morphology of Pt. schweinfurthi is similar to that of Pt. schucherti . According to Rage (1984), Pt. schweinfurthi differs from Pt. schucherti in having a thicker roof of the zygantrum and shorter pterapophyses. But, in specimens belonging to Pt. schucherti , described by Westgate & Ward (1981) and Westgate (1989), the zygantral roof is as thick as that of Pt. schweinfurthi . The height of the pterapophyses remains the only feature that distinguishes the two species, but it might represent only intracolumnar variation. Pt. schweinfurthi might be a junior synonym of Pt. schucherti , but this cannot be demonstrated on the basis of the available material.

Pt. sheppardi Hoffstetter, 1958 comes from the late Eocene (Jacksonian, i.e. Priabonian) of Ecuador. It is represented by a single specimen, i.e. some articulated vertebrae exposed in lateral view; therefore, thorough comparison with other species is not possible. It is distinguished from the above two species by its shorter pterapophyses. This may result from intracolumnar variation and this casts doubts on the validity of the species.

Pterosphenus muruntau Averianov, 1997 , from the Bartonian of Uzbekistan, is represented by only two poorly preserved vertebrae. Apart from one feature (“pterapophyses incipient” according to Averianov), the characters cited in the diagnosis of this species are either characters diagnosing the genus Pterosphenus or characters connected to ontogeny (neural canal small, external walls of vertebrae relatively thick) or taxonomically nonsignificant (lateral and pterapophyseal marrow cavities present). The small size of the pterapophyses would be a feature of interest because in other species they are high. But they are broken away in the two known specimens and their remaining bases do not permit inference that they were small or incipient. In summary, these two specimens are too poorly preserved, and this species should be considered a nomen dubium.