Prosantorhinus, Heissig, 2017

Heissig, Kurt, 2017, Revision Of The European Species Of Prosantorhinus Heissig, 1974 (Mammalia, Perissodactyla, Rhinocerotidae), Fossil Imprint 73 (3 - 4), pp. 236-274 : 242

? Prosantorhinus tagicus ( ROMAN et TORRES, 1907)

N o t e. All the small rhinocerotids cited with this species name, except the type specimen, turned out to be Protaceratherium minutum ( CUVIER, 1822). These specimens are omitted here from the synonymy list which concerns only the different citations of the holotype .

1907 v Rhinoceros ( Ceratorhinus ?) tagicus nov. sp. – Roman and Torres, p. 42, pl. 3, fig. 1.

1960 Ceratorhinus tagicus – Antunes, p. 258.

1972a Brachypodella tagica (Roman 1907) – Heissig, p. 70.

1979 Prosantorhinus tagicus (Roman) – Ginsburg and Antunes, p. 493.

1983 Protaceratherium tagicum (Roman 1907) – Antunes and Ginsburg, p. 22, pl. 1, fig. 1.

1989 Protaceratherium minutum ( Cuvier 1822) – Cerdeño, p. 60.

1996 Protaceratherium minutum – Cerdeño, p. 112.

H o l o t y p e. Upper cheek tooth rows, right P2 – M3 and left P3 – M2, partially fragmentary.

T y p e l o c a l i t y. Lisbon ( Horta das Tripas ).

S t r a t u m t y p i c u m. Early Miocene (MN 3a).

O t h e r o c c u r r e n c e s. Unknown.

D i a g n o s i s. Smallest species of the genus Prosantorhinus with prominent but not fused crista and crochet in premolars, small crista in molars. Premolars semimolariform with lingual bridge lower than transverse lophs. All teeth except P2 with antecrochet. Posterior protocone furrow in all teeth, anterior one in P4 and the molars. Anterior hypocone furrow only in M1 and M2, in both separated from the medisinus base line by a cingulum cone. A trace of a posterior hypocone fold only in M2. Labial side of P3 with two broad, slightly converging ribs, no mesostyle. Metacone rib also present in M1 and M2, but only in M2 separated from the mesostyle swelling by a small furrow. M3 triangular with short but well developed distal cingulum and a somewhat lingually shifted crochet.

D e s c r i p t i o n. See diagnosis.

R e m a r k s. The smallest and probably earliest species of Prosantorhinus may be P. tagicus ( ROMAN et TORRES, 1907). This species name, originally attached to “ Ceratorhinus ”, was later applied to many small rhinoceroses, which turned out to be Protaceratherium minutum ( CUVIER, 1822), a species of Aceratheriini , of nearly the same size as P. tagicus. The type and only specimen from the type locality Horta das Tripas (Lisbon) (MN 3a), however, has nothing in common with all these specimens except for its small size. The upper cheek teeth show several characters which exclude this specimen from Protaceratherium minutum and even from the tribe Aceratheriini . The most important is a posterior hypocone furrow on the second molar, which is typical for many Teleoceratini and excludes the species from the Aceratheriini . This character is also absent in all Early Miocene Elasmotheriini . A strong metacone fold on the ectoloph of the upper premolars, less accentuated but also present in the molars, is similar to that of the small sized Prosantorhinus germanicus , but absent in Aceratheriini . In most early Rhinocerotinae it is even more pronounced than in Prosantorhinus tagicus, which leads to its superficial similarity to early Elasmotheriini . The lingual side of the upper premolars, however, is fundamentally different from any elasmothere. The bridge connecting the main lingual cusps remains in a lingual position in elasmotheres ( Heissig 1972b: pl. 6, fig. 4), whereas it is more labially positioned in Prosantorhinus tagicus, leaving a considerable space between the bridge and the horizontal cingulum. This incomplete cingulum crosses the medisinus entrance, where it is more pronounced than at the bases of the lingual cusps. In elasmotheres it is more or less reduced to steep ledges which do not meet below the medisinus. The forked or multiple crochet of the premolars, and the clearly triangular outline of the last upper molar with a very short distal cingulum on the distolingual corner of the tooth, are more widespread features among rhinoceroses.

In particular Protaceratherium minutum shows no similarities with Prosantorhinus tagicus. In Protaceratherium there is only a faint trace of a metacone rib on the premolars and no trace of it in the molars ( Roman 1924: pl. 3, fig. 1, pl. 5, fig. 1, 1a). The lingual cingulum of the premolars is generally complete, at least in some of the premolars. There is no trace of a posterior hypocone furrow in either the molars or milk molars in any Aceratheriini . The last molar is trapezoidal in Protaceratherium with a rather long distal cingulum, a character generally present in all Early and Middle Miocene age Aceratheriini . It is triangular with a short distal cingulum in most Prosantorhinus species. So the identification by Antunes and Ginsburg (1983: 22) and Cerdeño (1989: 60) of the holotype from Horta das Tripas as a member of Protaceratherium is by far less probable than its inclusion in Prosantorhinus . The presence of a crista in the premolars, which is used by Antunes and Ginsburg (1983: 22) as an important common character of Prosantorhinus tagicus and Protaceratherium minutum is a variable character which also occurs in 11% of the P4 and 4% of the P3 of P. germanicus from Sandelzhausen ( Peter 2002: 35) and in a lot of other rhinoceroses in different tribes.

Unfortunately most isolated specimens of MN 3 a age in Western Europe cannot be determined at species level. Therefore we can assign to this species only the holotype with a rather limited set of characters. The lack of information regarding skull and postcranial characters makes the separation from other small species doubtful. Some characters, e.g. the strong cristae, characterise it as an independent species .