Some New Remains of Gazella ( Bovidae ) Discovered from the Dhok Pathan Formation of the Siwaliks , Northern Pakistan

| Newly discovered dental remains of a medium sized gazelle from the Dhok Pathan Formation in northern Pakistan, are described in this paper. The specimens comprise mandibular fragment and isolated teeth. The specimens are on the basis of rigorous comparison ascribed to Gazella lydekkeri, a late Miocene antelope. The Dhok Pathan Formation is late Miocene to early Pliocene in age. Article History Received: March 01, 2018 Revised: June 13, 2018 Accepted: June 20, 2018 Published: August 31, 2018 Authors’ Contributions ZS processed the samples. AMK supervised the research and drafted the manuscript. AI contributed in discussion and helped in identification of samples. MA collected the samples.


Introduction
G azella is a genus in Subfamily Antilopini and Fam- ily Bovidae.Today it is represented by the species distributed in Asia and Africa (Gentry, 1964).There are nineteen living species of genus Gazella according to Integrated Taxonomic Information System (ITIS).These animals has a body weight of 12-75 Kg.The largest gazelle named as Dama gazelle has a height of 137-168 cm.Living gazelle has 30-40 meters per hour speed during its running.These animals also show stotting behavior.They are herbivores and typically leaves, grasses and shoots of the plants are the part of their diet.Pilgrim (1937) described the dental remains of Gazella lydekkeri from late Miocene deposits of the Siwaliks of India and Pakistan.The studied species shows similarities to the living *Corresponding author: Abdul Majid Khan majid.zool@pu.edu.pkgazelles for their small and slender skull.Gazella lydekkeri is basically a primitive species but shows a degree of hypsodonty, a more derived dental feature.In the fossil record, the genus Gazella is known from Eurasia and Africa and in the Siwaliks from the Middle Miocene to Early Pliocene deposits (Pilgrim, 1937;Chen, 1997;Bibi et al., 2009;Khan et al., 2013).Gazelles were rarely found in the early Pliocene in Europe for unfavorable cooler climate but they are well represented in the Middle East and Africa.The primitive member of the group found from Turkey is G. ancyrensis that can be distinguished from other member of genus Gazella by their small size and spiky horns (Kostopoulos, 2009).The primitive members of genus Gazella have low crowned teeth with long row of premolars and molars with lack of posterior lobe (Gentry, 1990).

Geological context
The village Dhok Pathan (Lat.33° 07' N: Long.72° 14' E) is located in the Chakwal district, northern Pakistan (Figure 1).The type area for the Dhok Pathan Formation is located at the Soan River about 75 km from Rawalpindi at Rawalpindi-Sargodha road and consists of substantial Neogene freshwater sedimentary rocks.It is situated in proximity to the Dhok Pathan Rest House close to the Soan River at an altitude of 1073 feet and the thickness of the sequence around this area is about 500 m (Barry et al., 2002).The Dhok Pathan Formation consists of siltstone and sandstone, with some clays and lenses of conglomerate in the upper part.Near the village Dhok Pathan the sandstone is light gray in color and consists of fine to medium grained, medium bedded and cross bedded particles.To the northeast, buff sandstones are more common, the clay stone is primarily dark brown and orange red in color ( Johnson et al., 1985).The lower part of the Dhok Pathan Formation is dated to about 10.1-9.0Ma and the upper part extends into the early Pliocene (Barry et al., 2002).Pickford (1988) made an initial biochronological assessment of the formation.Paleomagnetic correlations provide a precise geochronology of the Mio-Pliocene Dhok Pathan Formation (Figure 1) (Barry et al., 2002).
Here we describe the newly recovered dental remains of gazelle from near the Dhok Pathan Rest House.According to Khan et al. (2013), only a small number of fossils of gazelle have been described from the late Miocene Siwaliks since the beginning of the last century and there is no extensive and new gazelle data for this fossiliferous area.The only available records are those published by Pilgrim (1937), Khan (2007) and Khan et al. (2013).

Materials and Methods
The studied material was recovered from the late Miocene sediments at Dhok Pathan type locality, Punjab, Pakistan (Figure 1).The sample comprises a right mandibular fragment, isolated lower second molar, an isolated right upper first molar, an isolated right upper third molar, an isolated right upper second molar, right upper third and fourth premolars, and an isolated right lower fourth premolar.
The studied material is present in the palaeontological collections of the Zoology Department of Punjab University, Lahore.While cataloguing the specimen; a yearly index number as numerator and a serial list number as denominator are used in combination with the institutional abbreviation PUPC, which stands for Punjab University Palaeontological Collection (PUPC 13/60).Upper dentition is expressed by the capital letter (e.g.P, upper premolar; M, upper molar) and Lower dentition is denoted by small letters (e.g.p-lower premolar; m-lower molar).

Stratigraphic range
The Middle Siwaliks.

Description
Upper dentition: The upper dentition is represented by premolars and molars (PUPC 13/57, PUPC 09/111, PUPC 13/58 and PUPC 13/59).The premolars are hypsodont with high crowned cusps.The paracone is slightly higher than the protocone and the parastyle is sharp and visible.The third premolar is asymmetric and semi-triangular.The third molar can be easily distinguished as the median rib is more prominent.The enamel extension connects the protocone to the hypocone.The median rib in the P3 is present in the middle unlike in the P4, and it is crescent shaped.The lingual cingulum is observed in the upper 2 nd and 3 rd premolar of the studied samples and in both the teeth it is moderately strong.
The molars are quadrate shaped and the cones are pointed and visible.The protocone is projected outwards which makes it appear V shaped and the hypocone is crescentic.The paraconus and metaconus ribs are visible.All of the styles can be seen and the transverse valley is present on the lingual side.The anterior and posterior interdental wear facet depressions distinguish the 2 nd Molar from other molars.
Lower dentition: The lower dentition (PUPC 13/61, PUPC 13/60, and PUPC 09/105) is represented by premolars and molars.The teeth are rectangular in shape and have narrow crowns.The fourth premolar is pentaconid and the parastylid connected with the paraconid to form the anterior valley.The large protoconid and metaconid are connected with each other and the space between these two conids constitutes the median valley.The entoconid is connected to the protoconid labially and forms a posterior valley.The entostyle is present posterolingually.
The fossettes of the molars are relatively narrow and shallow.The molars have hypoconids that protrude bucally, which is characteristic of these teeth.The metaconid and entoconid are present on the lingual side, while protoconid and hypoconid are labial.An ectostylid is present in the transverse valley on the labial side.The studied specimen PUPC 09/105 is a part of right mandible, and a prominent hypoconulid is present at the posterior extent of the last tooth, which is a feature of the lower third molar.A well-developed goat folds is also present in the lower molars.

Comparison and Discussion
There is some morpho-metric variation within the known Gazella species from the Miocene Siwaliks of Pakistan; and various genera and species have been erected.Many of them are considered as probable synonyms of each other (Bibi and Guleç, 2008).The present material shows affinities with Gazella lydekkeri and observed dental characters are similar to the holotype of Gazella lydekkeri (AMNH 19663) described by Pilgrim (1937), from the Middle Siwaliks.After the boselaphines, the antilopine Gazella lydekkeri is the most abundant taxon in the middle Siwaliks stratigraphic sequence (Pilgrim, 1939;Barry et al., 2002).
In our sample the presence of sharp median ribs and sharp styles with lack of median basal pillars in the upper molars and the presence of sharp median ribs and sharp styles with median basal pillars in the lower molars, conforms with the holotype of Gazella lydekkeri (Pilgrim 1937(Pilgrim , 1939;;Akhtar, 1992;Khan, 2008;Khan et al., 2009).
The upper premolars are conical in shape (Figure 1A-C; Table I) with the pointed main cusps at the occlusal outline.The lingual cones are selenodont in shape but the paracone is higher as compared to the protocone.The hypocone and metacone are less prominent in the premolars.In P3, the paraconus rib is more visible and is located towards the parastyle while in P4 the paraconus rib is present in the center of the teeth.P3 has a weak metastyle.In comparison with the dental features to Gazella lydekkeri reported from the Middle Siwaliks by Pilgrim (1937), Akhtar (1992), Khan et al. (2009) and ( 2013), PUPC 13/57 is consistent in having a long P3 relative to P4 and the presence of sharp parastyle and weaker metastyle in P3, with the anterobuccal paraconus rib.I) with the pointed major cusps.The lingual cones are crescent shaped and the posthypoc-rista is longer as compared to the prehypocrista.The fossettes are selenodont, narrow and not very deep.The paraconus rib is sharper than the metaconus rib at their bases.The mesostyle is prominent but the transverse valley is surrounded by a small tubercle at the lingual side.The specimens show resemblance with Gazella lydekkeri in having; presence of well-developed median ribs, the rib of anterior lobe is stronger than that of the posterior lobe, absence of median basal pillar, and presence of narrow styles.
There are two reported species of genus Gazella in the Siwaliks of Pakistan.One is Gazella lydekkeri and other is Gazella sp.The absence of median basal pillar, strong ribs and strong stylids are the dental feature of Gazella lydekkeri that it share with other Siwalik species of genus Gazella but there is also dental morphological differences between the two species, entostyle are rudimentary in Gazella sp. but are slightly larger in Gazella lydekkeri.
Slight metric variation exists among our material in comparison with data provided by Pilgrim (1937).The specimens in the present study are slightly longer and broader but show similar morphology (Table I).The larger size of the studied sample may be due to intraspecific variations.
The isolated 4 th lower premolar, the lower m 2, and the fragment of lower mandible with m 1 -m 3 , have identical morphology to the specimens described by Pilgrim (1937).According to Pilgrim (1937), the goat folds are prominent on the anterior side, and in our material, the goat folds are more prominent at the outer side than the inner side.The most prominent character is the presence of ectostylid which is only present on the lower molars.However according to Chen (1997) the acceptable range of individual interspecific variations among fossil taxa is yet need to be resolved.Merceron et al. (2006) described the microwear of Gazella from Bulgaria.Their analysis indicates that these gazelles were usually browsers or mixed feeders.According to Khan et al. (2013), Gazella lydekkeri is abundantly found, second to the boselaphines, recorded from the Dhok Pathan and Hasnot areas.Remains exist in all the lithological deposits of the Middle Siwaliks (Pilgrim, 1937(Pilgrim, , 1939;;Barry et al., 2002).Gazella lydekkeri spanned the late Miocene and early Pliocene of the Dhok Pathan Formation in a seasonally humid environment (Barry et al., 2002).Gazella lydekkeri may be considered as an important member of the ungulate fauna from the Dhok Pathan Formation including; Family Bovidae (Selenoportax, Tragoportax, Pachyportax and Elachistoceras), Family Tragulidae (Dorcatherium and Dorcabune), Family Anthracotheriidae (Merycopotamus), Family Giraffidae (Giraffa and Bramatherium), Family Elephantidae (Stegolophodon), Family Suidae (Propotamochoerus, Hippohyus and Hip-popotamodon), Family Equidae (Sivalhippus) and Family Rhinocerotidae (Brachypotherium and Alicornops) (Pilgrim, 1937(Pilgrim, , 1939;;Barry et al., 2002;Bhatti et al., 2012).
The faunal deposits of the Dhok Pathan Formation indicate a mixture of vegetation cover and forest condition.The artiodactyls in the late Miocene of the Dhok Pathan Formation suggest a variety of environments ranging from open woodland to riverine and forested settings.The assemblage of such taxa in the sedimentary area suggests an open environment with some grass, and may include a small amount of harsh vegetation ( Janis et al., 2002).

Conclusion
The fossils discussed in this paper have been identified as Gazella lydekkeri, a late Miocene antelope.They augment the currently recognized suite of gazelline fossils and will contribute to future studies of the evolutionary history of Antilopini in Pakistan.

Figure 1 :
Figure 1: Map showing various Siwalik localities in the Potwar Plateau, Pakistan, with the temporal range of the study shaded (Behrensmeyer and Barry, 2005).

Table I : Comparative measurement of the cheek teeth of Gazella lydekkeri (Pilgrim, 1937).
*Studied specimen