On the invalidity of Halitherium schinzii Kaup, 1838 (Mammalia, Sirenia), with comments on systematic consequences

Manja Voss

doi:10.3897/zse.90.7421

Abstract

The holotype of the sirenian species Halitherium schinzii Kaup, 1838 from the Alzey Formation (early Oligocene) of the Mainz Basin, western Germany, is reviewed in detail and revised. It is concluded that the type specimen, an isolated premolar, is non-diagnostic, because it reveals no characters of taxonomic value. Therefore, the taxon name H. schinzii is regarded as a nomen dubium, thus cannot be applied to any currently proposed sirenian species. The name of the genus “Halitherium”, which is based on the type species “H. schinzii”, cannot be applied to other species previously assigned to congeneric taxa. Consequently, taxonomic and systematic re-assessment is required. Due to the fact that “Halitherium” is the taxonomical basis of the Halitheriinae, conclusions are drawn on the inappropriateness of this subfamily.

Highlights

The name of the genus “Halitherium”, which is based on the type species “H. schinzii”, cannot be applied to other species previously assigned to congeneric taxa
The genus Halitherium includes a number of fossil sirenian species, or sea cows, ranging from the late Eocene to early Miocene
A description and figure of another premolar (HLMD-WT Az 48) under the same species name was given by Kaup (1838), who subsequently transferred it to the genus Halitherium, which seemingly is the correct generic name for the species as indicated by later studies (e.g., Kaup 1855; Lepsius 1882; Sickenberg 1934)

Summary

Introduction

The genus Halitherium includes a number of fossil sirenian species, or sea cows, ranging from the late Eocene to early Miocene. As it can be inferred from the description above, the taxonomic value of the holotype of H. schinzii is doubtful and its assignment to a certain species remains ambiguous This is corroborated by comparative morphological investigations with species lumped under the genus Halitherium. While the vertebrae are clearly identified as belonging to a sirenian, there are serious doubts on the taxonomic assignment of the skull fragment, which might be referable to a reptile (Sickenberg 1934: 207) This is supported by personal investigations of the material in question Crassitherium is not considered as a useful or valid replacement name. Beside the juvenile status of this specimen that already tempted Sickenberg (1934) to declare this genus to be invalid, the preserved material is not considered to reveal diagnostic features for a reliable taxonomic assignment on the species level. The present study emphasises that the “Halitheriinae”, comprising amongst others the Eocene dugongids and the genus Metaxytherium, constitute one of the most questionable sirenian groups, which is the focus of the following discussion

Discussion

Conclusions