Siwalik Formations are more important as regard to its mammalian fauna. The most distinct and unique feature of the Siwalik rocks are the abundance of vertebrate fossils pertaining to almost all the major eutherian groups. Due to its palaeontological and geological importance, it has attracted a number of paleontologists, geologists and even zoologists from abroad (Lydekker, 1876, 1878; Colbert, 1935; Pilbeam et al., 1977; Barry et al., 2002, 2005; Bibi, 2007). Ruminant fossils in the American Museum of Natural History have been systematically studied by Pilgrim (1937 and 1939). He named several new genera and species of the Siwalik bovids; the genus Selenoportax is one of them. The genus Selenoportax is based upon two species i.e., Selenoportax vexillarius and Selenoportax lydekkeri. The genus Selenoportax is unknown from outside the Siwaliks. Selenoportax vexillarius is known by a partial skull and mandibular fragments and also isolated upper and lower teeth. The present collection consists of upper and lower molars of the species. The specimens are collected from village Dhok Pathan which is the type locality of the Middle Siwaliks (Dhok Pathan Formation). The Dhok Pathan village is situated in Chakwal district at 27 km from Talagang to Rawalpindi road. The village is highly fossiliferous and is known for the presence of tertiary fauna since the 19th century.
MATERIALS AND METHODS
A number of field trips carried out to various localities of village Dhok Pathan.
During field work by the author most of the specimens were found partly exposed
and were excavated, while a few more were found lying completely exposed on
the surface. The embedded material was carefully excavated with the help of
chisels, geological hammers, fine needles, pen knifes, hand lances and brushes.
In the laboratory, the material was carefully washed, cleaned, prepared and
broken parts were assembled by using various types of gums (resins) such as
Elfy, Elite and Fixin. The specimens catalogued number consists of series i.e.,
yearly catalogued number and serial catalogued number, so figures on the specimen
represents the collection year and serial number of that year. For example,
86/211, numerator denotes the collection year and denominator the serial number
of the respective year. Various measurements of the specimens in millimeters
were taken with the help of metric vernier. Tooth length and breadth were measured
at occlusal level. Heights were measured on the metastylid/metastyle of the
lower molar/upper molar. Tooth cusp nomenclature in this study follows that
of Gentry (1994).
||Bovidae Gray, 1821
||Bovinae Gill, 1872
||Boselaphini Simpson, 1945
||Selenoportax Pilgrim, 1937
Type species: Selenoportax vexillarius Pilgrim, 1937.
Included species: Selenoportax vexillarius Pilgrim, 1937; Selenoportax lydekkeri Pilgrim, 1937; Selenoportax tatrotensis Akhtar, 1992; Selenoportax dhokpathanensis Akhtar, 1992.
Selenoportax vexillarius Pilgrim, 1937:
Type specimen: A skull lacking maxilla and dentition and most of the basicranium (AMNH 19748).
Referred specimens: Left M1 (PUPC 86/211; PUPC 02/132), left M2 (PUPC 98/69), left M3 (PUPC 86/213).
Locality: Dhok Pathan, Chakwal district, the Punjab province, Pakistan.
Stratigraphic range: Middle Siwaliks.
Diagnosis: Cheek teeth large and strongly hypsodont, enamel very rugose. Upper molars quadrate with strong and divergent styles near the neck of crown, ribs quite large, entostyle/ectostylid strongly developed. Fossettes without indentations and simple in outline, transverse anterior goat folds poorly developed at front of lower molars.
Distribution: Middle to Upper Siwaliks.
PUPC 86/211 (Fig. 1A) and PUPC 02/132 (Fig.
1B and C) include first molars of left maxilla. The molars
are excellently preserved and shows fully developed major cusps. These are early
stage of wear. The molars are extremely hypsodont, narrow crowned and the enamel
is very thick and rugose. The rugosity is more prominent and well evident on
the buccal side than on the lingual side due to weathering effect. The median
basal pillars are situated at the transverse valley between the protocone and
hypocone. The principal cusps are well developed. The protocone is somewhat
pointed in the later stage of wear. It is narrow transversely than the hypocone.
The paracone is well developed and pointed in the middle with two running ridges.
The metacone is also pointed in the middle with two running ridges anteroposteriorly.
The hypocone is crescentic in shape. The styles are well developed. The parastyles
and mesostyles are very strong and prominent. The anterior median ribs are more
prominent than the posterior ribs. The central cavities are very narrow due
to early stage of wear.
PUPC 98/69 (Fig. 1D and E) is the second
molar of left mandibular ramus. It is well preserved except hypocone which is
missing. It is in the middle early stage of wear and extremely hypsodont. The
enamel is moderately thick and rugose. The median basal pillar is small and
not well developed. It is practically unworn. It is narrow at the apex and broad
at the base. It is situated in the transverse valley between the protoconid
and the hypoconid. The principal conids are well developed and crescentic in
their general appearance. The anterior ridge of protoconid is narrower than
||Selenoportax vexillarius; A: Lingual view of the first
upper molar (PUPC 86/211); B: Occlusal view of the first upper molar (PUPC
02/132); C: Buccal view of the first upper molar (PUPC 02/132); D: Buccal
view of the second lower molar (PUPC 98/69); E: Lingual view of the second
lower molar (PUPC 98/69); F: Occlusal view of the broken third lower molar
(PUPC 86/213); G: Buccal view of the broken third lower molar (PUPC 86/213)
||Comparative measurements of the cheek teeth of Selenoportax
|* The studied specimens; M1: First upper molars;
M2: Second lower molars; M3: Third lower molars
The metaconid is pointed in the middle with the running ridges anteroposteriorly.
The metaconid is somewhat higher vertically than entoconid. The entoconid is
also pointed in the middle, but less than metaconid. The stylids are moderately
developed. The anterior and posterior central cavities are narrow and filled
with sandstone. PUPC 86/213 (Fig. 1F and G)
is well preserved except the metaconid and protoconid which are damaged. Talonid
is well preserved and look like a pillar. The comparative measurements of all
the specimens are provided in Table 1.
Four isolated teeth are described and discussed in this study, which are collected from the Dhok Pathan Formation of the Middle Siwaliks, Pakistan. The collected molars have crescentic cusps and conids. Proboscideans show lophs and plates in their crown pattern where as Perissodactyls are characterized by lophs in their molars but Artiodactyls have crescentic cusps and conids. The collected molars exhibit selenodonty (crescentic pattern) which confirm their inclusion to Artiodactyls. The specimens have complete crescentic pattern of cones which is present in ruminants, the Artiodactyl sub order. The sub order Ruminantia has four extinct families found from the Siwaliks: Tragulidae, Cervidae, Giraffidae and Bovidae. The tragulids and cervids are small but giraffids and bovids are large in size. The studied molars are large enough to exclude them from tragulids and cervids but not enough to include those giraffids. So the collected specimens on the basis of size, styles/stylids, median basal pillars and enamel rugosity are included to family Bovidae. In bovids the genera Selenoportax and Pachyportax are larger than the other genera but the Pachyportax is characterized by quadrate and heavy styles/stylids molars comparatively than Selenoportax. The specimens are narrow and have less bulky styles/stylids so they belong to genus Selenoportax.
The described specimens show all typical morphological features of the species Selenoportax vexillarius as stated by Pilgrim (1937) such as quadrate with strong and divergent styles near the neck of crown, ribs quite large, median basal pillar strongly developed. All the specimens resemble in anteroposterior length but slightly differ in transverse crown width (Table 1). The first molars compare metrically and morphologically with the GSI (Geological Survey of India) B569 type specimen and found close resemblance with the type specimen. The described second lower molars PUPC (Punjab University Palacontological Collection, housed in the Department of Zoology, Punjab University, Lahore, Pakistan) 98/69, PUPC 86/213 are extremely hypsodont and narrow crowned. The lower second molar and third molar compare with the AMNH (American Museum of Natural History, New York) 19844, AMNH 19514, AMNH 29917 and AMNH 19514 and found close similarities with the referred specimens (Table 1). The enamel is wrinkled externally as well as internally. However the wrinkles are more prominent on the protoconid and hypoconid than on the inner side. The median basal pillars are present in both lower molars and very prominent. All these morphological features exhibited by the studied specimens are the characteristics of the species Selenoportax vexillarius. So, the specimens belong to the species Selenoportax vexillarius and the presence of the species in the village Dhok Pathan is confirmed. Janis (1982) noted that Siwalik bovids show increases in size, hypsodonty and molarization, suggesting a move towards more fibrous diets and more open habitats. The evolution of large body size and robust dento-gnathic morphology in the panbovine clade was a consequence of climatic changes, namely the intensification of the dry season in southern Asia during the late Miocene. More arid conditions, even if present only seasonally, would have increased inter-specific competitive pressures among herbivores and driven the evolution of morphologies allowing for greater niche differentiation within the large herbivore guild (Bibi, 2007).