Plesiohipparion Qiu, Huang & Guo, 1987

Bernor, Raymond L. & Sen, Sevket, 2017, The Early Pliocene Plesiohipparion and Proboscidipparion (Equidae, Hipparionini) from Çalta, Turkey (Ruscinian Age, c. 4.0 Ma), Geodiversitas 39 (2), pp. 285-314 : 305-306

Genus Plesiohipparion Qiu, Huang & Guo, 1987

TYPE SPECIES. — Plesiohipparion houfenense Teilhard de Chardin & Young, 1931 .

Plesiohipparion cf. longipes ( Gromova, 1952) ( Figs 4; 5; 16 ; 17 )

DESCRIPTION

Eisenmann & Sondaar (1998) attributed a complete MTIII (MNHN.F.ACA214; Fig. 16A, B ), a proximal fragment of MCIII (ACA56), one complete (ACA77) and one fragmentary (ACA124) 1PHIII, one complete 2PHIII (ACA82; Fig. 17 ), one complete 3PHIII (ACA87), one complete 3PHIII (ACA112) and three astragali (ACA250, ACA63 and ACA92) ( Eisenmann & Sondaar 1998: figs 1-3, 15A,

B, 16A, tables 1-3; Table 1) from Çalta. The phalanges were all believed to be from the posterior limb, but this is not certain. We further recognize 2 fragmentary MTIII (ACA209 and ACA55) and a single 1PHIII (ACA82; Fig. 17 ). The complete Çalta Plesiohipparion cf. longipes hypodigm, as we recognize it is listed in Table 1.

REMARKS

Gromova (1952) initially described “ Hipparion ” longipes from Pavlodar, Kazakhstan, which she believed was either Late Miocene or Pliocene (MN13 or 14). Gromova (1952) noted the exceptionally elongate metapodials as sufficient to recognize a valid taxon of hipparion. Vangenheim et al. (1993) characterized Pavlodar habitats as being dry. The most characteristic feature of the Çalta Plesiohipparion cf. longipes is the extremely elongate and slender morphology of MTIII ( Figs 5; 16 ) and 1PHIII ( Figs 6; 17 ) well above the Höwenegg ellipse and rivaling Chinese Plesiohipparion ( Figs 6; 8 ; 9 ; 10 ). In fact, Plesiohipparion longipes and Plesiohipparion houfenense have MCIII and MTIII length and width morphology greater than all Siwalik, Pikermi, and Sinap Late Miocene, and eastern African Pliocene hipparions in our sample; it is only paralleled by African Pliocene Eurygnathohippus hasumense Eisenmann, 1976 ( Figs 8C ; 9C ). We believe that this extreme lengthening supports identity with Chinese Plesiohipparion taxa rather than Hipparion s.s., Cremohipparion , Sivalhippus . Eurygnathohippus afarense which clearly have different MCIII and MTIII proportions than our Chinese and Turkish Plesiohipparion sample ( Figs 8C ; 9C ); the latter represents a separate lineage than Eurygnathohippus because of the persistence of large ectostylids on the permanent cheek teeth found particularly in Plio-Pleistocene members of the clade (such as Eu. hasumense ; Bernor et al. 1996, 2015b; Bernor & Sun 2015).

Koufos & Vlachou (2005) referred extensive skeletal material from the MN12 locality of Akkașdağı, Turkey (7.1 Ma; Karadenizli et al. 2005) to Plesiohipparion cf. longipes . The maxillary cheek teeth compare well with Chinese Plesiohipparion houfenense , particularly with regards to length of tooth row (P2-M3 = 162.5-169.0), the elongated P2 anterostyle bent lingually (not common, but does occur in Plesiohipparion ), rich enamel plications, double pli caballins and the elliptical, lingually flattened protocones (Bernor & Sun 2015; Bernor et al. 2015b; Figs 6, 7, 8 ). Akkașdağı MCIIIs ( Figs 4; 8C ) and MTIIIs ( Figs 5; 9C ) are elongate; MCIII ranging in maximum length from 246.4 to 254.0 mm (n = 11; mean = 249.7) and MTIII ranging in maximum length from 276.0 to 302.0 mm (n = 15; mean = 284.7) ( Koufos & Vlachou 2005). TheÇalta Plesiohipparion cf. longipes maximum length (= 319.5 mm) is greater than any Akkașdağı specimen of this taxon, which is an advanced character for this clade. The Çalta MPIII lengthening rivals penecontemporaneous Chinese Plesiohipparion houfenense .

Scott & Maga (2005) undertook an ecomorphological approach on the Akkașdağı hipparionine metapodials to investigate their likely habitat preferences. This study followed those of Bernor et al. (1997, 2003), Bernor & Scott (2003) and Scott et al. (2003) that hipparion metapodial morphology could predict habitat preferences. For both MCIII and MTIII, Scott & Maga (2005; Figs 4, 5) determined that Akkașdağı Plesiohipparion cf. longipes was the most open country adapted of all four Akkașdağı hipparions: Hippotherium brachypus (heavy-light cover), Cremohipparion moldavicum (heavy-light cover), Hipparion dietrichi (light cover-plains, but less open country than Pl. cf. longipes ). Clearly, the very elongate metapodials in Plesiohipparion cf. longipes were the most adapted to open country cursoriality. The Çalta Pleisohipparion cf. longipes is advanced in having more elongate MPIIIs than the Akkașdağı Plesiohipparion aff. longipes as well as other Akkașdağı hipparion lineages.

Sen et al. (1978) used the keel development of hipparionine metapodials, including the robust hipparion from Çalta, as a biostratigraphic index. Eisenmann & Sondaar (1998) estimated that Çalta Plesiohipparion cf. longipes weighed 250-260 kg and that Plesiohipparion longipes from Pavlodar (type locality) weighed between 158-221 kg based on the metapodial proportions.

Figures

FIG. 16. — MNHN.F.ACA214A, Plesiohipparion cf. longipes (Gromova, 1952), MTIII: A, cranial view; B, caudal view. Scale bar: 5 cm.

FIG. 17. — MNHN.F.ACA82, Plesiohipparion cf. longipes (Gromova, 1952), 1PHIII: A, cranial view; B, caudal view. Scale bar: 5 cm.

FIG. 8. — Log10 ratio diagram of MCIII: A, primitive Old World Hipparion; B, robust limbed Old World Hipparion and Çalta Proboscidipparion heintzi (Eisenmann & Sondaar, 1998); C, slender limbed Old World Hipparion and Çalta Plesiohipparion cf. longipes (Gromova, 1952).

FIG. 9. — Log10 ratio diagram of MTIII: A, slender limbed Hipparions; B, robust limbed Hipparions; C, Plesiohipparion spp. compared to Eurygnathohippus afarense Eisenmann, 1976.

FIG. 10. — Log10 ratio diagram of 1PHIII:A, slender limbed Cremohipparion Qiu, Huang & Guo, 1987 and Hipparion campbelli Bernor,1985, 1PHIII Log10 Ratios, Ho Std; B, slender limbed Eurygnathohippus 1PHIII; C, robust limbed Hipparions.