Persiatherium sp.

Antoine, Pierre-Olivier & Sen, Sevket, 2016, Rhinocerotidae and Chalicotheriidae (Perissodactyla, Tapiromorpha), Geodiversitas 38 (2), pp. 245-259 : 253-256

Persiatherium sp.

( Fig. 3 )

Aceratherium sp. [partim] – Malik & Nafiz 1933: 44.

Aceratherium sp. – Sayar 1953: 9, fig. 2.

Aceratherium cf. kowaleskii [partim] – Nicolas 1978: 456.

MATERIAL EXAMINED. — KÇ300, right P2; KÇ318, left P2-M1 series; MNHN.F.TRQ340, left M1; TRQ342, left M1; TRQ347, right i2; KÇ296, left p2 (germ); KÇ301, right p4;TRQ356, left m1; KÇ360, partial left hemimandible with m2-m3; KÇ311, right d4; TRQ350, right dentary fragment with d4;TRQ365, left pyramidal; TRQ328, right Mc3, proximal fragment.

DESCRIPTION

Upper dentition

The presence of I1 is inferred by the existence of a large and flat wear facet on i2 (MNHN.F.TRQ347). There is no secondary enamel folding on P2-M1, but pinched lingual cusps in occlusal view. Patches of cement are preserved on the ectoloph ( Fig. 3A ). Crowns are worn and enamel is finely wrinkled. Morphology of roots is unknown. The lingual rim of the upper row KÇ318 is straight ( Fig. 3A ). The labial cingulum is low and reduced, restricted to the distalmost part of all teeth (P2-M1). The lingual cingulum is thick and continuous on P2-M1, with salient tubercles closing the median valley. Premolars from the P2-M1 series KÇ318 are large with respect to M1, highly molarized, and wider than long in occlusal view ( Table 1). The prefossette is shallow on P2. A simple crochet is present on P2 (low on KÇ300; Fig. 3B ) and P4 (KÇ318). It has disappeared with wear on P3 and M1 (KÇ318) but also on the M1s TRQ340 and TRQ342. The postfossette is deep and narrow, elongate mesio-distally on P2-M1 ( Fig. 3A ). There is no antecrochet on P2, but a rounded one is discernable on P3-P4, and M1 has a far more marked antecrochet.A mesial wear-facet testifies to the presence of a P 1 in front of P2s. P3 has a pentagonal occlusal outline (KÇ300, KÇ318), due to its convex lingual border. P2 has a protocone unconstricted mesially, while a shallow and smooth constriction is observed on P3-M1. There is a low and thin lingual bridge on P2, with equally developed hypocone and protocone ( Fig. 3A, B ). The metastyle is particularly elongate sagittally on P2-M1. The protoloph is complete on P2, but its labial connection to the ectoloph was low, as testified by the enamel pad preserved on KÇ300 ( Fig. 3B ). On P2, the protoloph is oblique (protocone located behind the paracone) whereas the metaloph is more transversely oriented, at least at early stages of wear (KÇ300). The protoloph is straight on P2 and curved disto-lingually on P3-M1. The protoloph is complete on P2-4. The metaloph is sigmoid, but unconstricted on P2-M1 (no mesiolabial constriction at the base of the hypocone). The postfossette is triangular on fresh teeth (P2 KÇ300) and getting narrower with wear (lingual side oblique: P2-M1 KÇ318). The labial cingulum is restricted to oblique ridges in the anterior and posterior quarters of the ectoloph. The median valley is extremely narrow, with parallel borders, on P2-M1. No medifossette is preserved on P2-M1, at least at advanced stages of wear. Nevertheless, the presence of joined crista and crochet (thus forming a medifossette at early wear stages) can be hypothesized on P3. There is no pseudometaloph on P3. The parastyle is sagittally oriented and the paracone fold weak (P4-M1, P2 KÇ300) or absent (worn P2-3). There is neither mesostyle nor metacone fold on P2-M1. In occlusal view, the ectoloph is thick, forming a labial wall, convex on P2 and straight or concave posteriorly on P3-M1. The metaloph is very short with respect to the protoloph on P4, whereas they have similar lengths on P3 and M1. There is no cristella on M1. The distal cingulum is continuous on P2-M1. The antecrochet and the hypocone are close to each other but not in contact or connected on M1, even at late wear stages. There is no lingual groove on the protocone of P2-M1.

Mandible and lower dentition

The mandible with m2-3 (KÇ360) is only partly preserved ( Fig. 3C, D ). The ramus was low, with a straight lower margin and a height increasing regularly backward (H = 81 under m2; H = 88 under m3; Fig.3C ). There is a long spatium retromolare, equal to the length of m3. The juvenile mandible fragment with d4 (MNHN.F.TRQ350) is much lower (H = 58 below the d4-m1 transition). There is a shallow sulcus mylohyoideus restricted to the posterior part of the preserved area. Other mandibular features are not observable.

The i2MNHN.F.TRQ347 is cylindrical and slightly curved. The crown is short and tear-shaped in cross section. The root is circular in cross section. The wear facet is wide and flat, unambiguously corresponding to occlusion with an I1.

Enamel is thinly wrinkled on lower teeth, sometimes showing superimposed horizontal increments (p2 KÇ296; “squared enamel” sensu Antoine et al. 2010: 152; Fig. 3F ) and patches of cement in inner valleys (e.g., p4 MNHN.F.TRQ353; Fig. 3G, H ). The left p2 is totally unworn (germ), with an angular trigonid and a rounded talonid ( Fig. 3E ). The paralophid is straight and oblique (neither sagittal nor transverse), with no constriction. The paraconid is strongly developed. There is no vertical external rugosity. The external groove is developed, sharp, and reaching the neck. The lingual cingulum is low and reduced, restricted to the anterior tip of the tooth and to oblique ridges at the lingual side of the metaconid and the entoconid. These cusps are not constricted, but a small ridge is visible at the top of the entoconid (corresponding to a “pre-entocristid”). The anterior valley is shallow, with a subvertical bottom. The posterior valley is deep and narrow, with a V-shaped bottom in lingual view. There is no labial cingulid. The right p4 KÇ301 has a simple pattern, with a deep and V-shaped ectolophid groove ( Fig. 3G ). Enamel is thick. There is neither lingual nor labial cingulid. Lingual cusps are not constricted. The trigonid is smooth and rightangled. Lophids are oriented transversely. Lingual valleys have a V-shaped bottom, widely open lingually ( Fig. 3H ).

The m1 MNHN.F.TRQ356 is small and brachydont, with a bulbous aspect ( Fig. 3I ; Table 1). In occlusal view, the trigonid forms a closed angle, with a sharp ridge. The talonid is smooth and open-angled (hypolophid oblique). There is neither constriction on the metaconid nor on the entoconid. The labial cingulum is low but complete, parallel to the neck. The ectolophid groove is shallow, V-shaped, pointing up- and frontward, and partly covered by patches of cement. Both lingual valleys have smoothed V-shaped bottoms. The lingual border of the lingual cusps is not flattened. There is no lingual cingulum. The posterior cingulum is low and smooth.

On the fragmentary mandible KÇ360, roots are exposed, especially on the labial side molar. Therefore molar necks are located c. 10 mm above the mandibular margin.The ectolophid groove is moderately deep on m2-m3, pointing up- and front - ward in labial view, and it reaches the neck. The trigonid is rounded and it forms an open angle. The lingual cusps are not constricted. The anterior valley (U-shaped bottom) is really shallow with respect to the talonid valley (V-shaped bottom). There is no labial cingulid, but a reduced lingual cingulid, closing the entrance of both valleys in m2-3. The hypolophid of m2-3 is moderately oblique in occlusal view. There is no lingual groove on the entoconid.

The d4s KÇ311 (moderately worn; Fig. 3J ) and MNHN.F.TRQ350 (germ) are highly similar in terms of size and morphology. They are brachydont, with a simple pattern. The trigonid and the hypolophid form a rounded U (paralophid long and transverse) and an open angle (hypolophid oblique) in occlusal view, respectively. The protoconid is the higher cusp. It lacks a fold. The metaconid is constricted, contrary to the entoconid ( Fig. 3J ). The latter has a flat and vertical lingual side, without any groove. The lingual valleys have a rounded V-shaped bottom in lingual view. There is neither lingual nor labial cingulum. The ectolophid groove is shallow and not reaching the neck.

Postcranial skeleton

The left pyramidal MNHN.F.TRQ365 is almost isometric (H = 49; TD = 37.5; APD = 47). In proximal view, it has a quarter-circle outline, with a semi-circular ulna-facet. The pisiform-facet is tear-shaped in proximal view. There is no strong tubercle on the lateral side (contrary to what occurs in Ceratotherium neumayri ). The medial facets for the semilunate are low and remote ( Fig. 3K ). The proximal one forms a low sagittally elongated strip. The distal one is crescent-like, slightly higher posteriorly. In distal view, the unciform-facet has a circular outline. It is flat transversally and concave sagittally. MNHN.F.TRQ328 is a proximal fragment of a right Mc3 ( Fig. 3L, M ). In proximal view, it is wider (TD = 44) than deep (APD = 37). The scaphoid-facet is small and oblique ( Fig. 3M ). The semilunate-facet is pear-shaped, concave transversely, but elongate and convex sagittally. The unciform-facet is flat transversely and separate from the former by a sharp ridge (c. 90°). A strong tubercle for the insertion of the m. extensor carpalis runs along the proximal border or the anterior side. In anterior view, the magnum-facet is visible ( Fig. 3L ). There is only one Mc2-facet, restricted to a low tear-shaped strip, located anteriorly. The Mc4-facets are remote, with similar heights. The anterior one is high, narrow, and tear-shaped. The posterior one is oval, higher than wide. The diaphysis was wide and flattened sagittally. This bone is globally similar to TRQ330 (referred to Chilotherium schlosseri ), but it differs from it in several features (angle between proximal facets in anterior view; shape of unciform-facet; proportions of proximal outline). It also resembles the specimen AS.91.229 from the late Miocene of Sinap area (locality 26, c. 8 My-old), tentatively referred to as Acerorhinus sp. by Fortelius et al. (2003).

DISCUSSION

The concerned remains can be referred to as documenting an aceratheriine rhinocerotid, thanks to the presence of wrinkled enamel on cheek teeth, of equally developed protocone and hypocone on P2, of a continuous protoloph (connected to the ectoloph) on P2, of a weak protocone fold on M1-2, to the usual absence of a labial cingulid on lower molars, and of a protoconid fold on d4. It is further recognizable as a “chilothere” sensu lato, in sharing a constricted protocone on P3-4, a crista on P3, an antecrochet on upper molars, an ectolophid groove reaching the neck, a U-shaped occlusal outline of the trigonid on lower cheekteeth, and a curved paralophid on p2, but also in having no labial cingulum on upper molars or on lower premolars, and no crista on upper molars. This early diverging chilothere is differentiated from representatives of Shansirhinus , Acerorhinus , and Chilotherium (including the other chilothere recognized at Küçükçekmece, Chilotherium schlosseri ) in retaining I1s, in having a continuous lingual cingulum on upper premolars but neither labial cingulum nor lingually expanded antecrochet on upper molars, in bearing a weaker protocone constriction on M1-2 and a constricted metaconid on lower milk teeth. It further differs from Aceratherium incisivum Kaup, 1832 in bearing higher crowned teeth and laterally expanded lingual cusps on upper cheek teeth but no medifossette on upper molars. Among aceratheriine chilotheres, this middle-sized taxon is closer to Aceratherium depereti Borissiak, 1927 from the early Vallesian of Sevastopol, Ukraine, Persiatherium rodleri Pandolfi, 2016 from the late Vallesian of Kopran (Maragheh, Iran), and to Persiatherium huadeensis ( Qiu, 1979) from the late Miocene of Inner Mongolia ( Qiu 1979; Pandolfi 2016), than to any other known species. These three species notably share with the chilothere from Küçükçekmece the presence of a lower cheek tooth row oblique with respect to the long axis of the corpus, the absence of a labial cingulum on upper premolars and of a constricted hypocone on M1, the usual presence of a lingual cingulid on lower cheek teeth, and the presence of a labial cingulid on lower molars. It can be differentiated from A. depereti in having lingually expanded lingual cusps and a lingual cingulum with V-shaped median incision on upper cheek teeth, and a developed ectolophid groove on lower cheek teeth, but no metaloph constriction on P2-P4, likewise P. rodleri and P. huadeensis ( Borissiak 1927; Lu 2013; Pandolfi 2016).

However, it is distinct from P. rodleri in showing a straight lingual rim on the upper cheek tooth row, an antecrochet on upper molars, and a narrow postfossette but no labial cingulum on upper premolars, and from P. huadeensis in having a lingual cingulum and an antecrochet on upper premolars, but no pseudometaloph ( Lu 2013; Pandolfi 2016). It can be further differentiated from both P. rodleri and P. huadeensis thanks to the presence of lower crowns, of a lingual bridge (appearing with wear) on P2, of a constricted protocone on P3-4, of a long metaloph on M1, and of a straight ectoloph on M1-2.

To sum up, morphological comparison allows for referring unambiguously this taxon to Persiatherium Pandolfi, 2016 , so far documented in the Vallesian of Iran and Inner Mongolia ( Pandolfi 2016), but it seems to have no closer affinities to P. rodleri than to P. huadeensis . Therefore, pending a revision of Eastern Mediterranean Vallesian aceratheriines, we choose to refer to it as Persiatherium sp.

Suborder ANCYLOPODA Cope, 1889 Superfamily CHALICOTHERIOIDEA Gill, 1872 Family CHALICOTHERIIDAE Gill, 1872 Subfamily CHALICOTHERIINAE Gill, 1872

Figures

FIG. 3. — Tapiromorph perissodactyls from the upper Miocene locality of Küçükçekmece, Thrace, Turkey,Persiatherium sp.: A, KÇ318, left P2-M1 series in occlusal view; B, KÇ300, right P2 in occlusal view; C, D, KÇ360, left dentary with m2-m3 in labial (C) and occlusal views (D); E, F, KÇ296, left p2 (germ) in occlusal (E) and lingual views (F); G, H, KÇ301, right p4 in occlusal (G) and lingual views (H); I, MNHN.F.TRQ356, left m1 in occlusal view; J, KÇ311, right d4 in occlusal view; K, TRQ365, left pyramidal in medial view;L, M, TRQ328, right Mc3 (proximal fragment) in anterior (L) and proximal views (M). Scale bar:A,B, 20 mm;C, K-M,30 mm.