Cremohipparion nikosi, Bernor & Tobien, 1989

Bernor, R. L., & Tobien, H., 1989, Two small species of Cremohipparion (Equidae, Mammalia) from Samos, Greece, Bayerische Staatssammlung für Paläontologie und historische Geologie 29, pp. 206-226 : 215-219

Cremohipparion nikosi n. sp.

Fig-2

Hipparion matthewi, T obien, 1938 Hipparion matthewi, G romova, 1952 , in part

Holotype: Male skull fragment, BSP 1899 VII 31 b. Type Locality: Island of Samos ( Greece, without locality). Etymology: Named in honor of Dr. Nikos Solounias as a tribute to his long and exhaustive work on the stratigraphy and paleontology of Samos. Age: Turolian, ca. 8.5—5.7 Ma. Geographic Distribution: Greece .

Diagnosis: As for Cremohipparion matthewi except that the nasals are strongly retracted to the mesostyle of P4. Lower jaws are not known for this species.

Description: The type specimen of Cremohipparion nikosi n. sp. ( Fig. 2 ) is an old adult male individual including the snout, nasals, maxilla and anteroventral aspect of the orbits, both canines and left P2—M3.

As with the holotype of C. matthewi , this is a small species. The specimen preserves an approximately subtriangular, anteroventrally oriented POF with a large anteroventrally placed infraorbital foramen. The POF is less than 10 mm deep medially, has no posterior pocketing, preorbital bar is quite short (19.2 mm) and while not clear, the lacrimal most probably invaded the posterior aspect of the POF because of the POB’s very short length. As with C. matthewi , there is no visible caninus fossa. The nasal notch is clearly very strongly retracted to mesostyle of P4. The dorsal premaxillary tubercles are far less developed in this specimen than in C. matthewi . The canines are large and quite robust, and suggest, that it was a male individual. The cheek teeth are in an advanced stage-of-wear, suggesting that this was an old individual. P2 anterostyle is shortened. Protocones are rounded on all cheek teeth; P2’s protocone is connected with the protoloph due to its late wear-stage. When preserved, pli caballins are short, but either single or double. The pre- and postfossettes are heavily worn, but reveal that the individual had shallow amplitude, moderately complex plications of the cheek teeth. However, wear is too advanced to reliably account for how many plications the younger middle stage-of-wear adults had. The hypoglyphs are essentially obliterated on P2 3, shallow on P4—M2, and deep on M3.

Remarks: The only previous citations of the type specimen, BSP 1899 VII 31b, were Tobien (1938: Taf. 1) and G romova ( 1952), both of whom referred it to Hipparion matthewi , based on its size.

This species is remarkably similar to C. matthewi in its size and morphology, except for the strong retraction of the nasal bones. This single contrast is significant, in that the ratio of measurement 30 versus 31 (length of the naso-incisival notch from prosthion to the back of the narial opening versus the length of the narial opening to the anteriormost limit of the orbit; re: Eisenmann et al., 1988: Fig. 3a ) is 136.0/74.9 (= 181.6) in Cremohipparion nikosi versus 99.1/ 110.6 (= 89.7) in Cremohipparion matthewi . Moreover, we know of no case where a single species of hipparion exhibits a variability in nasal retraction ranging from anterior limit of P2 to mesostyle of P4.

K oufos and M elentis ( 1984) described an important and previously poorly known collection of Samos hipparions from the PMMS, Samos, Greece. This collection originates from the Stefanidis or Andrianos Ravine, and is believed by the authors to be identical to Quarry 1 of the AMNH collection (B rown, 1927). K oufos and M elentis ( 1984) describe a smaller horse in this which they referred to Hipparion sp. II; the most complete specimen being a skull, PMMS 9 (Plate II, pg. 69; Plate III, pg. 70). They characterize this taxon as being (K oufos and M elentis, 1984: 66): “ size middle; moderate developed preorbital fossa, situated near the orbit; long muzzle; short tooth series, closed (= close to) H. matthewi ; simple enamel plication; protocone connected to the protoloph; moderate protostylid”. The cheek tooth characters are most probably not diagnostic because of their later wear-stage. Length of the cheek tooth series is somewhat greater (P2—M3 length = 122.1 mm), than the type C. matthewi (= 111.8 mm) and C. nikosi (= 105.5 mm). Preorbital bar length for PMMS 9 (= 29 mm; Table 1: 54) falls within the uppermost portion of the range of length for Cremohipparion species (B ernor, 1985: 264, Tab. 14; C. aff. moldavicum from Middle Maragheh has one of the highest ranges for this lineage, = 23.6—29.8 mm). Also, reference to Table 1 here reveals that the values for measurements 30 (= 142 mm) and 31 (= 135 mm) are greater overall than C. matthewi and C. nikosi , while its ratio of these measurements (= 105.2) is somewhat different than C. matthewi (= 89.6 mm), and much different than C. nikosi (= 181.6 mm). This feature of Hipparion sp. II suggests a relatively intermediate snout length/nasal retraction.

It is presently difficult to determine what the evolutionary relationships of " Hipparion ” sp. II are. The length of preorbital bar is within the range of variation for Cremohipparion aff. moldavicum from Maragheh, as is the length of the maxillary cheek tooth row (= 120.0—141.3 for C. aff. moldavicum ; B ernor, 1985: 264, Tab. 14) especially given the fact that PMMS 9 is an old individual. However, PMMS’s POF would not appear to be as strongly developed in its medial depth and peripheral rim as Cremohipparion moldavicum . Therefore, there is no apparent basis to refer PMMS 9 to either C. matthewi nor C. nikosi , and it may or may not prove to be a member of the Cremohipparion lineage. However, further details on POF, lacrimal and caninus fossa morphology are particularly needed to determine its phylogenetic affinities.

The AMNH houses some small horse postcranials from Samos. Measurements for metapodials ( Table 5), humerus ( Table 6) radius ( Table 7), ulna ( Table 8) and astragalus ( Table 9) are given here. Figure 3 compares the proportions of metacarpal III and metatarsal III maximum length (var. 1) versus distal articular width (= DAW; var. 11) in comparison with 95% and 99 % confidence ellipses for the Howenegg hipparions (Bernor et al., in press). This figure illustrates that there were a number of different species, belonging to distinctly different later Miocene equid lineages that decreased size. The two species of Cremohipparion reported here are amongst the more elongate and slender species, and contrast most sharply with “Sivalhippus” platyodus from China ( Qiu et al., 1987: 94—95; Tab. 10), which had relatively short and broad proportions (and indeed was not a true dwarf form as is seen from its skull dimensions). These observations reinforce our assertions that size cannot be used alone in defining a hipparion species, nor can it alone support assertions of phylogenetic relationship and time correlation.

Figures

Figure 2: Cremohipparion nikosin. sp., BSP 1899 VII31 b. A. Skull fragment, left lateral view; B. Left maxillary cheek tooth series.

Figure 3: Comparison of Samos “Cremohipparion matthewi” species with selected later Miocene Holarctic and Ethiopian smaller horses. A. MC III maximum length (ML) versus distal articular width (DAW). B. MT III ML versus DAW. 1 = “Cremohipparion matthewi” (Samos; AMNH: 23054b—e, 22933,23054, Q5 no numbers, 22893; Bernor, personal observation); 2 = “Hipparion macedonicum” (Ravin de Pluie, Greece; RPL 38; Koufos, Table 9 — insert); 3 = sitifense (Sahabi, Libya; 27P25B, MC III; 1P25B, MT III; Bernor et al., 1987); 4 = gromovae (La Fontana, Spain; Tobien, personal observation); 5 = “S*. platyodus (China; Qiu et al., 1987:95);6 = Calippus (XMAS Quarry, Nebraska AMNH 98 (Bernor, personal observation); 7 = Pseudhipparion sp., XMAS Quarry AMNH 202 (Bernor, personal observation).