Description of Gazella sp . from the Middle Miocene Siwaliks of Punjab , Pakistan

| The fossil material of Gazella sp. from the Chinji Formation, Chakwal District, Pakistan, is described and discussed in this paper. The dental remains comprise isolated upper and lower molars. The antilopine genus Gazella has great diversity from Middle Miocene to Pliocene from Africa to Eurasia. The morphological characteristics indicate this genus as a conservative bovid with simple morphology. Article History Received: March 01, 2018 Revised: July 27, 2018 Accepted: August 04, 2018 Published: November 13, 2018 Authors’ Contributions AR discovered, identified and processed the samples. RMA improved the manuscript. AI did systematic paleontology and identification of samples. AMK supervised the research and wrote the manuscript.


Introduction
A ntilopinae is an extint subfamily which is divided into tribe Neotargini and Antilopini.According to Gentry (1992), Neotargini is a small group that diverged from African antelopes, among which Antilopini developed.Antilopines are a major group of diversified Siwalik ungulates and are richly represented by the genus Gazella.The earliest record of Gazella sp. is from the Algerian Middle Miocene (Arambourg, 1959;Gentry, 1970Gentry, , 2010)).The great diversity of this genus is recorded from the Middle Miocene to early Pliocene, and from a wide variety of localities in China, Spain and South Africa (Pilgrim, 1937(Pilgrim, , 1939;;Moya-Sola, 1983;Thomas, 1984;Chen, 1997;Bibi et al., 2009;Khan, 2008;Khan et al., 2012).The temporal range of Gazella sp. in the Siwaliks Middle Miocene

Materials and Methods
The studied specimens have been collected from Middle Miocene locality; Dhok Bun Ameer Khatoon.The collected sample were carefully transferred to the Paleontology Laboratory and cleaned well by washing the samples and removing sediments from them.The catalogue numbers are assigned to these fossils starting with abbreviation PUPC (Punjab University Paleontological Collection).The denominator consists of yearly catalogue number (year in which collection was made) and numerator donates the serial catalogue number (serial number of the specimen in that year).The specimens have been housed in the Paleontology Laboratory of Department of Zoology, University of the Punjab, Lahore.The samples were identified on the basis of their morphometric analysis and comparison with the available literature.The measurements were made in mm using Vernier callipers.

Description
The second upper molar (PUPC 13/83) has a quadrate outline with shiny and prominent cusps that indicate its good preservation.The crown is wider in outline from the base and gradually narrows towards the top.The top of the buccal side is slightly bent towards the lingual side perhaps due to early wear and its position in the maxilla.The protocone is more crescentic in outline than hypocone; which is U shaped in outline.The parastyle and ectostyle ribs are strong and prominent.The entostyle is weakly developed.Preprotocrista is at lower level than posthypocrista, indicating slightly inclined position of tooth.The parastyle and metastyle are stronger like ribs (Figure 1).

Results
PUPC 13/116 is a broken anterior conid most probably of right lower molar with high crown, protoconid and metaconid.The metastylid seems to be less prominent and the metaconid rib protrudes slightly (Figure 1).The M2 (PUPC 13/149) and M3 (13/82) are subhypsodont with normal crescent shaped fossettes.Short ectostylid is present in M2 while no ectostylid indicated in M3.The preprotocristid and post protocristids are roughly equal in length in both molars.The posteriorly inclined upward, but not so prominent cingulid is present in M2.The metastylid is less protruding in M2.Hypoconulid of M3 has slight folds towards buccal and lingual side (Figure 1).

Discussion
The genus Gazella is the most species rich and widespread genus of the Siwaliks.It is so diverse that according to Bibi and Guleç (2008), many new species and synonyms are recognized on the basis of slight morphological variations.Some features such as strong ribs and stylids and absence of median basal pillar include this species in the genus Gazella.However, the comparison in the present studies with the other described specimens of the Siwalik Gazella sp.indicates that the M2 in present specimens has the typical Gazella sp.morphology, i.e. absent/rudimentary entostyle, sizes of fossettes, prominent anterior and posterior ribs and overall tooth size similarities with already described Gazella sp.specimens.However, the M2 described in this study is slightly wider than the other studied Si-walik specimens.According to Khan et al. (2016), the antero-posterior diameter of the upper molars of Gazella is greater than transverse diameter.The same is evident in the present specimen of M2.The comparative measurements of the Gazella sp.dentition is given in Table I.According to Khan (2007Khan ( , 2008) ) and Akhtar (1992), Gazella is recorded from Lower and Middle Siwaliks.As per Pilgrim (1937Pilgrim ( , 1939) ) and Khan (2008), the two major species are known from Siwaliks; Gazella sp. from Lower Siwaliks (Middle Miocene) and Gazella lydekkri from Middle Siwaliks (Upper Miocene).Both species can be distinguished based on; (1) tooth size, which is larger in width in Gazella lyddekri and larger in length in Gazella sp., (2) tubercle-like entostyles which are rudimentary in Gazella sp. and slightly larger in Gazella lyddekri and (3) median ribs; prominent in Gazella sp. but paraconus rib stronger than metaconus in Gazella lyddekri.Overall, small sized molars and fine rugose pattern on enamel indicate this as a species of Gazella of medium size (Pilgrim, 1939;Khan et al., 2009).
This species was well adapted to the warm conditions of Middle Miocene.According to Bibi and Güleç (2008) and Kostopoulos (2005), this gazelle community was well adapted for open or bushy lands which were at no great distance.They used to live in herds probably as their defence strategy against their predators (Brashares et al., 2000).
The stratigraphic distribution of Gazella sp.indicates that early migrations and spread of the genus Gazella, according to Agusti and Anton (2002) took place in Middle Miocene from Africa to Eurasia.Thomas (1984) reported that the origin of the genus Gazella in the beds of Chinji Zone was likely during Early Miocene from the region of Majiwa, Kenya.This evidence has made it clear that the origin of Gazella and phylogenetically related antilopines began in Africa, followed by dispersal throughout Eurasia, given favourable environmental conditions (Agusti  , 2002).This view is further confirmed by Made (1999), giving the evidence of migrations of Rodentia and large mammals from Africa to Eurasia during Early Miocene due to exposed land bridges during low ecstatic levels.Discovery of this new material of Gazella sp. from the Middle Miocene deposits of the Siwalik region strengthens the already proposed idea for existence of this migratory route.

Conclusion
On the basis of their comparative morphometric analysis, the studied specimen has represented the presence of Gazella sp. in the middle Miocene Siwaliks of Pakistan.The studies indicate this species as an immigrant from Africa to Eurasia in the Early Miocene.This genus is indicative of vast open and bushy habitat and included in family Bovidae, other ungulate families present during the Middle Miocene period in the Siwaliks of Pakistan are Tragulidae, Suidae, Giraffidae, Anthracotheriidae and Rhinocerotidae.