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Proamphibos kashmiricus (Bovini: Bovidae: Mammalia) Lower Case From the Pinjor Formation of Pakistan.

Byline: Muhammad Akbar Khan and Muhammad Akhtar

Abstract

Newly discovered fossil material of Proamphibos kashmiricus from the Plio-Pleistocene of the Pinjor Formation (2.6 - 0.6 Ma) in the Upper Siwaliks (Pakistan) is reported and described here. The new specimen is one opisthocranium of a hornless skull attributed to a female individual of P. kashmiricus coming from the Plio-Pleistocene deposits of Rohtas (2.2 Ma) in the Jhelum district, northern Pakistan. The opisthocranium is the largest female individual described so far for this species and the morphology of the present specimen allow examining some skull anatomical features of P. kashmiricus. The validity of the genus Bucapra is also discussed and the synonymy with Proamphibos is proposed.

Keywords: Proamphibos, Pinjor Formation, Upper Siwaliks, Plio-Pleistocene, Bovine.

INTRODUCTION

The late Pliocene and early Pleistocene deposits of the Upper Siwaliks have produced several fossil bovine taxa including Bison, Bubalus, Proamphibos, Leptobos, Bos, Hemibos and Bucapra. This is a time of important radiation in Bovini (Nanda, 1997, 2002; Masini 1989; Corvinus and Rimal, 2001; Opdyke et al., 1979; Hussain et al., 1992; Pilgrim, 1937, 1939; Colbert, 1935) and also it is thought that there was a high rate of origination for mammal species (Gingerich, 1984).

The Upper Siwaliks (Plio-Pleistocene) of northern Pakistan is divided in three units, the Tatrot, the Pinjor and the Boulder Conglomerate Formations (Pilgrim, 1913; Nanda, 2002; Barry et al., 2002). Of these, the Pinjor Formation, which spans 2.58-0.6 Ma (Dennell et al., 2008), is the longest and most fossiliferous including larger taxa such as Elephas hysudricus, Stegodon insignis, Rhinoceros, Sivatherium, Equus sivalensis, Sus spp., Hemibos spp., Bos acutifrons and Cervus palaeindicus (Nanda, 2002, 2008). Several types of bovids are known from the Pinjor Formation, of which the commonest are the medium-sized reduncines and the larger ones belonging to Hemibos, Bison, Bubalus, and Proamphibos (Rutimeyer, 1878; Pilgrim, 1937, 1939; Hooijer, 1958; Nanda, 2008).

The unique characteristic of the Pinjor fauna, is its similarity to the living faunas as it is the youngest fauna of the Siwaliks and largely consistent with an open grassland environment. Regarding the bovid composition of the fauna, the forerunners of Boselaphus tragocamelus, Bubalus arnae, Bison bison, Bos taurus, Bibos banteng and Antilope cervicapra are present in the youngest sediments of the Siwaliks.

LOCALITY AND MATERIAL

The material presented in this paper had been unearthed from sediments of the Pinjor Formation near the village Rohtas (32deg59 N, 73deg38 E) in Jhelum district, northern Pakistan (Fig. 1). The main access to the site is by the Grand Trunk Road (GT Road), the road that connects the cities of Lahore (provincial capital) and Islamabad (country capital). The Rohtas site belongs to the Upper Siwalik subgroup and comprises fluvial deposits of fine-grained sands, silts and clays representing floodplains, gullies and abandoned channels. The type area of the Pinjor Formation is situated in India near Chandigarh, where the Pinjor type locality is located whereas the other type localities of the Siwaliks are located in Pakistan. The Pinjor Formation is mainly characterized by Pleistocene sands and variegated clays (Dennell, 2008).

Magnetostratigraphically and biochronologically, the upper part of the Pinjor Formation is dated 0.6 Ma while the lower boundary of the Formation is considered to be dated at 2.58 Ma (Ranga Rao et al., 1988, 1995; Cande and Kent, 1995; Hussein et al., 1992; Nanda, 2008).

The material was discovered in 1971 and since then it was stored unpublished in the Palaeontology Laboratory of the Punjab University, Lahore, Pakistan. It consists partial skull and a more specifically the opisthocranium of a large female bovid. This specimen is compared with the most common Siwalik genera Hemibos, Bison, Bubalus and a rare specimen of Bucapra as they represent the larger known Plio-Pleistocene genera of the tribe Bovini. The subject of this paper is the description of the newly recorded opisthocranium of the female P. kashmiricus.

SYSTEMATIC PALAEONTOLOGY

Bovidae Gray, 1821

Bovinae Gray, 1821

BUBALINA Pilgrim, 1939

Proamphibos Pilgrim, 1939

Proamphibos kashmiricus Pilgrim, 1939

Bucapra daviesii Rutimeyer, 1878 (Fig. 2, Table I)

Original diagnosis

A more advanced species of Proamphibos than P. lachrymans; skull lower in every part than that of P. lachrymans; frontal bone more arched, with an incipient transverse ridge; lachrymal fossa slight; horn-cores somewhat more slender and divergent, with sharper postero-internal keel, more extended inward than in P. lachrymans, so that the distance between it and the outer face equals or exceeds that between the primary keels; female hornless; weak temporal crests in female; parietal more reduced; brain case shorter; occipital concave in the vertical plane; condyles larger and projecting more to the rear; basioccipital shallower, with gently rounded surface, more triangular on account of the greater expansion of the posterior tuberosities (Pilgrim, 1939).

Emended diagnosis

Auditory bullae variable; large basisphenoid; mastoid larger than Hemibos. The temporal crests in female are reduced and run almost parallel.

Referred material

PUPC 71/57, opisthocranium (PUPC-institutional abbreviation; Punjab University Palaeontological Collection).

Age

Late Pliocene to Early Pleistocene, ca 2.6-0.6 Ma (Dennell et al., 2006).

Description

PUPC 71/57 is part of the original skull, basically the opisthocranium, which makes it an incomplete specimen retaining only the following: occipital region, occipital condyles, paraoccipital process, part of the parietals, the auditory bullae and the basisphenoid (Fig. 2). The opisthocranium is not compressed dorso-ventrally but the facial part and the dentition are missing. The sutures separating the various bones are almost invisible. Obliterating of suture lines in adults is a characteristic of Bubalina. However, the suture line between the parietal and the supraoccipital is visible. The brain case cast is exposed due to the breakage of the parietal bones and the coronal suture line is visible on the brain case cast as well. The temporal crests are weak. The length of the interparietal suture line is 32.2 mm and judging from the opisthocranium it should correspond to a large and massive skull (Table I).

Table I.-Comparison of the cranial measurements (mm) of Proamphthos, Bucapra and Hemibos.

###Description###P. kashmiricus###P. kashmiricus female Bucapra daviesii###H. triquetricorn

###female###(GSI B817) Pilgrim, (BMNH 36677,###(BMNH 39565

###(PUPC 71/57)###1939###Rutimcyer, 1878)###holotype)

###this paper###Pilgrim, 1939###Pilgrim, 1939

Breadth of skull at mastoid###200###?164###160###189

Height of occipital from bottom

of occipital condyles to summit

of occipital crest###107###?105###-###106

Distance between outer edges of

occipital condyles###105###-###92###102

Width of the braincase###114###112###105###118

Width of posterior tuberosities on

basi-occipital###73.0###-###-###82

Width of anterior tuberosities on

basi-occipital###30###-###-###-

Distance between fronto-parietal

suture to summit of occipital crest###90###-###-###-

Distance between Bregma and lambda###72###-###-###-

Length of interparietal suture###32.2###-###-###-

Length of temporal fossa###114###110###109###120

Length of basi-occipital between

anterior and posterior

tuberosities###44.5###-###-###-

Depth: occipital crest to

top of foramen magnum###66.5###-###-###-

Depth: occipital crest to lower

border of foramen magnum###109###-###-###-

Width of foramen magnum###39###-###-###-

Height of foramen magnum###42.2###-###-###-

Length of auditory bulla###67.6###-###-###-

Width of auditory bulla###45.0###-###-###-

Approximated length of parietal###70.0###-###-###-

The occipital crest is very prominent and thick. It forms a low and wide arch with a short flattened portion at its summit. Below the occipital crest there is a prominent occipital tuberosity and an external occipital crest continues downwards till the upper border of the foramen magnum. The basioccipital is triangular. The paroccipital processes are large and stout. The occipital condyles are well preserved and projected in lateral view. A deep notch separates them from the paroccipital processes. The end of the paroccipital process is broken. The foramen magnum is large and subcircular in shape. The temporal crests are reduced and run almost parallel.

The occipital surface is slightly concave in vertical plane, broad and has an ovoid shape, bordered dorsally and dorsolaterally by a very well marked nuchal ridge. The basioccipital has a prominent median ridge and the posterior tuberosities are large and much expanded laterally. The anterior tuberosities are small but prominent. They lie behind the anterior ends of the auditory bullae. The basisphenoid is attached to the basioccipital with a weak angle. The auditory bullae are well preserved, large and well inflated (Table I).

The temporal fossa is short and high with a length of 114 mm from occipital crest to the anterior border of the temporal fossa. It opens widely above on to the parietal and the supraoccipital. The supraoccipital extends antero-posteriorly on the upper surface of the brain case. Laterally, the supraoccipital lies on the same plane as the hinder surface of the parietal and it is inclined at somewhat more than a right angle to the occipital plane.

Comparisons

The opisthocranium is characterized by the slightly concave occipital in vertical plane, an expansion of the posterior tuberosities, the large auditory bulla, the triangular shaped basioccipital and the reduced temporal lines. The occipital condyles are large and clearly projected beyond the summit of the occipital crest. The opisthocranium is narrow in shape with a flattened occipital summit. The triangular basioccipital associates the studied specimen to Bovinae (Pilgrim, 1939). The development of temporal lines is correlated with the presence or absence of horn cores. The studied opisthocranium differs from the respective ones of Bison, Bubalus, Bos, Leptobos and male Proamphibos in the absence of strong temporal lines (Martinez-Navarro et al. 2007).

The weak temporal lines of the opisthocranium are the features found in Bucapra, Hemibos and female Proamphibos. Bucapra is characterized by a narrow and high skull, large occipital condyles that do not project beyond the summit of the occipital crest, small anterior tuberosities and large auditory bullae (Pilgrim, 1939). The occipital condyles are very large and they are projected to the rear of the occiput in the studied opisthocranium, unlike in Bucapra. The backwardly projected occipital condyles are absent in Bucapra but they are present in Hemibos and Proamphibos. The studied specimen is wider than Bucapra and approaches Hemibos and Proamphibos. The large auditory bullae are absent in Hemibos but in some individuals of Proamphibos they are quite large. In the studied specimen the auditory bulla is large, long, stout and reaches far below the level of the basioccipital.

The flattened occipital surface and reduced temporal lines are present in H. triquetricornis and H. acuticornis (Pilgrim, 1939; Martinez-Navarro and Palombo, 2004). But the parietal is very short in Hemibos (Hooijer, 1958). The studied opisthocranium is distinguished from Hemibos being closer to Proamphibos in the widened mastoid (Table I). The temporal fossa opens widely on to the parietal as well as on to the supraoccipital than that of Hemibos. The opisthocranium is narrower than that of the earlier described skull of Hemibos (Pilgrim, 1937; 1939). Furthermore, the small width at the mastoid in the studied skull associates it to Proamphibos in distinction from Hemibos (Pilgrim, 1937). The anatomy of the specimen confirms that it is a member of the genus Proamphibos, a primitive Bubaline.

Proamphibos is represented in the Siwaliks by two species P. lachrymans and P. kashmiricus. P. lachrymans occipital condyles are not projected backward in the high degree as those of P. kashmiricus. Proamphibos kashmiricus and the studied skull have more projected occipital condyles than P. lachrymans (Pilgrim, 1939). The minimum distance apart of the two temporal fossae in the studied skull is 34 mm, same as in the holotype GSI B561 of P. kashmiricus (Pilgrim, 1939). The surface of the opisthocranium is not rugose because the rugosity is normally absent in the female P. kashmiricus. According to its dimensions the studied skull is of similar size with that of a female P. kashmiricus (Table I). In addition, the weak development of the temporal lines indicates that the specimen belongs to a hornless female of P. kashmiricus.

Based on the comparison, the studied opisthocranium shares the morphotypical conditions of Proamphibos and particularly of the species P. kashmiricus. Regarding the width of the skull at the mastoid process, the narrowness of the skull, the height of the occiput, the width of the occipital condyles and the large auditory bulla the specimen PUPC 71/57 fits pretty well with the previously described specimen of P. kashmiricus (Table 1 with comparative measures). The animal is somewhat larger with relatively longer and thicker occipital crest than the hitherto described material of a female P. kashmiricus.

DISCUSSION

Nobody had described a new Proamphibos female skull after Pilgrim (1939). After more than 130 years, a new specimen of P. kashmiricus was recovered. Bucapra is characterized by a narrow and high skull, large occipital condyles do not project beyond the summit of the occipital crest, small anterior tuberosities of the basioccipital and large auditory bulla (Rutimeyer, 1878; Pilgrim, 1939). These features are variables and can be seen on crania of Proamphibos (Pilgrim, 1939). In addition the species Bucapra daviesii is a problematic taxon. Rutimeyer (1878) erected this species based on the holotype (broken skull) which does not bear distinguishing characteristics, and he erroneously attributed it to Caprinae, an act criticized by Pilgrim (1939) and placed the specimen in the primitive Bubaline group. Therefore, the systematic status of Bucapra is not clear and according to Pilgrim (1939), its systematic status is also uncertain.

The main defining features of Bucapra are variables and these are represented in Proamphibos skull from the Tatrot and the Hasnot sediments (Pilgrim, 1939). The exhibited features of the studied skull: the parietal and the adjacent bones, the narrow occipital, the temporal fossae that open partially to the parietal and partially to the supraoccipital, the greater expansion of the posterior tuberosities, the weak temporal crests agree very well with those of the holotype BMNH 36677 of Bucapra and the female Proamphibos skull (Table I). The only difference of the holotype BMNH 36677 Bucapra from the studied skull is the smaller size and the backward projection of the occipital condyles. Rutimeyer's Bucapra might be an immature female Proamphibos.

CONCLUSIONS

The main characters defining the new fossil skull are: the wide posterior tuberosities of the basioccipital, the large bullae, and the absence of horn cores (according to the plesiomorphic shallow temporal fossae, weak temporal lines, parietals in the dorsal plane). These same characters are documented on the crania of Hemibos and Proamphibos (to name two bovine taxa with horn cores that are not shifted far posteriorly).

The described opisthocranium (PUPC 71/57, Fig. 2) corresponds fairly with the referred specimen GSI 817 of P. kashmiricus and the holotype BMNH 36677 of Bucapra daviesii described by Pilgrim (1939) from the sediments of the Tatrot. The opisthocranium is massive than those of P. kashmiricus and B. daviesii, nevertheless, it defines sufficient similarity with the female P. kashmiricus regarding skull anatomy. Comparing the referred specimen GSI 817 of P. kashmiricus and the holotype BMNH 36677 of Bucapra daviesii with the studied opisthocranium PUPC 71/57, it is clear that the differences should be credited to intraspecific variability. The strong resemblance of the studied skull with P. kashmiricus and B. daviesii suggest synonymy of Bucapra genus with Proamphibos. The size and morphology of the studied specimen and Bucapra allow us to regard them local races of Proamphibos. Nevertheless, the material is insufficient and more material will be required for the confirmation.

ACKNOWLEDGEMENTS

We thank Prof. Dr. M. Sarwar for access to the material. We wish to thank Maia Bukshianidze for providing us with fruitful comments on this manuscript. We could not come off the taxonomic complication without her help. We thank Dimitris S. Kostopoulos, George Iliopoulos (Greece) and Faysal Bibi (USA) for their useful comments on previous versions of this manuscript. Mr. Adeeb Baber and Nadeem Fazal prepared the plate and the map. Mr. Sajjid Shah and Mr. Razzaq helped in the fieldwork. The work was supported by the University of the Punjab, Lahore, Pakistan.

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Muhammad Akbar Khan and Muhammad Akhtar Department of Zoology, Government College University, Faisalabad, Pakistan Palaeontology Laboratory, Department of Zoology, University of the Punjab, Lahore-54590, Pakistan Corresponding author: akbaar111@yahoo.ca 0030-9923/2011/0004-0615 $ 8.00/0 Copyright 2011 Zoological Society of Pakistan.
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Publication:Pakistan Journal of Zoology
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Geographic Code:9INDI
Date:Aug 31, 2011
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