PALAEOSYOPINAE

Mader, Bryn J., 2010, A species-level revision of the North American brontotheres Eotitanops and Palaeosyops (Mammalia, Perissodactyla), Zootaxa 2339, pp. 1-43 : 15-16

Subfamily PALAEOSYOPINAE Steinmann and Döderlein 1890

Included genera: Palaeosyops (= Limnohyus , Limnohyops, Eometarhinus ).

Diagnosis: Same as for member genus, Palaeosyops (see below). Sister taxon to all brontothere subfamilies except for the Eotitanopinae (see cladogram in Mader 1998, Fig. 36.5)

Discussion: Palaeosyops is the sole member of the Palaeosyopinae (Steinmann & D derlein 1890). Because the subfamily Palaeosyopinae consist of only a single genus, the diagnosis of the subfamily does not differ from that of its member genus.

Although Palaeosyopinae is recognized here as the valid name for this subfamily, it should be noted that the invalid name Limnohyinae predates it by fifteen years. Marsh (1875) compared Diplacodon to the "Limnohyidae," a previously unpublished family-group name. Marsh did not specify which taxa were to be included under this name, although it is obvious that it must include Lymnohyus (a junior synonym of Palaeosyops ). According to the Principle of Coordination (Article 36, International Code of Zoological Nomenclature, Ride et al. 1999) this simultaneously established the subfamily name Limnohyinae with Marsh (1875) as the author. If the names Limnohyidae and Limnohyinae were to be valid, therefore, the subfamily name Limnohyinae would be a senior synonym of Palaeosyopinae .

Although Marsh did not explicitly specify a type genus for the Limnohyinae, the subfamily name cannot be invalidated on this basis since the type genus ( Limnohyus ) can be clearly inferred from the construction of the name (Article 11.7.1.1 International Code of Zoological Nomenclature). Furthermore, even though the genus Limnohyus is now recognized as a junior synonym of Palaeosyops , the family-group name Limnohyinae cannot be invalidated on this ground (Article 40.1).

However, according to Article 11.7.1.2, in order for a family group name to be valid, it must be clearly used by the original author to "denote a suprageneric taxon and not merely as a plural noun or adjective referring to the members of a genus...". The name Limnohyinae is invalid, therefore, because it is not clear from the context of Marsh's paper whether the term Limnohyidae was intended to apply to Limnohyus and some of the other brontothere genera then recognized (such as Palaeosyops and Telmatherium ), or merely to the three species of Limnohyus described by Marsh and Cope up to that time.