Description of Propotamochoerus hysudricus Fossils from the Siwalik Beds of District Jhelum, Punjab, Pakistan

1. INTRODUCTION

Suids, classified as artiodactyl mammals, exhibit a significant presence inside the Siwalik region of northern Punjab, as well as several other areas situated amidst these mountainous terrains (Figure 1). From the nineteenth century and onwards, numerous scholars including [1–6] have excavated at diverse locations on the hills of the subcontinent, where they have found a large number of fossils. In this regard, [7–15] are among the most well-known palaeontological researchers that have conducted studies in this region. A few millennia ago, the family Suidae was among the most ubiquitous families in the Siwalik Hills of the Indo-Pak region and represented by a significant number of genera. It was due to the family's ability to produce many offsprings [16–18].

Figure 1. Map showing Different Fossil-Bearing Localities of the Potwar Plateau in Northern Punjab, Pakistan [19]

Even though many species from that time have left a significant number of fossil records discovered repeatedly, others exhibit significantly fewer fossils that represent them. As a result, the discovery of any additional examples of these ancient species is of utmost significance in order to understand the ecological part they played and where they stood during the evolution of this particular group. The five component formations, namely Soan, Dhok Pathan, Nagri, Chinji, and Kamlial are apparent in the region around Hasnot [10]. Out of these formations, the Dhok Pathan formation is vibrant for the fossils of even-toad ungulates including Suidae [20, 21].

The Siwalik Hills of Punjab, Pakistan have a reputation for housing vertebrate fossil sites at places like Hasnot, District Jhelum (Figure 1), and many others [22, 23]. Hence, a field survey was scheduled to be carried out to locate and examine any deceased remnants of previous life inside the study region. The objective was to describe the morphological features of these remains and categorize the retrieved material to the level of specific genera or species.

2. SYNTHESIS DETAILS

The tooth described above was found in the Nagri formation in Punjab, Pakistan in the general region of the Hasnot hamlet. During field visits, it was found partially exposed in the formations present around Hasnot. The tooth was excavated carefully with the help of field hammers, chisels, fine needles, and brushes. Then, it was transferred carefully to the Palaeontological Laboratory of GC University, Lahore, covered within several layers of cotton. There, once again, it was carefully cleaned and washed by using different brushes, needles, water, and cotton in order to make it ready for morphological identification. Currently, it is stored in the paleontological collection of the Department of Zoology at Government College (now known as GC University), Lahore, Pakistan. The measurements were obtained using a Vernier caliper calibrated in millimeters (mm) and the recorded data were expressed in this unit of measurement (Table 1). The morphometric features of the specimen under investigation were examined. The specimen in question was assigned a serial catalog number. The numbers associated with the specimen represent the serial number as well as the year the specimen was collected (the denominator and the numerator, respectively). For example, Government College Palaeontological Collection Number 370/2001 (where "Government College Palaeontological Collection Number" is abbreviated as "G.C.P.C. No."). The terminology used to describe the parts of the dental crown and the measurement methods is based on [6].

The following results were drawn after the detailed study of the recovered specimen from the study site, namely Hasnot village of District Jhelum, Punjab, Pakistan.

2.1. Systematic Account

Order      Artiodactyla          Owen, 1848

Family   Suidae                    Gray, 1821

Genus     Propotamochoerus Pilgrim, 1926

Species   P. hysudricus       Stehlin, 1900

2.2. Specimen under Study

G.C.P.C. No. 370/2001, an individual upper second molar located on the right side of the maxilla. It was obtained from Hasnot, a region situated in District Jhelum, Punjab, Pakistan.

3. RESULTS AND DISCUSSION

The morphological description of the material under study is given below.

3.1. Upper Dentition: Second Molar

The specimen is an isolated second maxillary molar. It was recovered from Hasnot, which is a village within the Jhelum District of Punjab, Pakistan. The presence of a pressure mark on both the front and posterior aspects of the tooth is indicative of its classification as a second molar. The crown view of the tooth shows all of its principal cusps, which are rounded and pyramidal and have pretty clear summits. The tooth is quadrangular in its general contour. The enamel layer is thick, shiny, and corrugated. The lingual surface of the tooth and the transverse valley both exhibit the presence of a thin layer of cement. The tooth exhibits a robust multituberculated cingulum, both at its anterior and posterior aspects. The development of this condition occurs at an early stage on both the labial and lingual surfaces of the tooth. On the whole, the tooth is well-preserved and is only slightly touched by wear. Its height-to-width index (Table 1) indicates that it is a brachyodont and broad crowned tooth. The tooth's prominent cones including the protocone, paracone, hypocone, and metacone are clearly distinct and readily identifiable. The protocone inhabits the frontal side of the specimen and is connected to the anterior accessory conule through a narrow channel of its anterior lobe. From its posterior and lingual sides, it is attached to the basal pillars present at the very entrance of the tooth’s transverse valley. The median lobe of the protocone exhibits continuity with the median accessory conule observed within the transverse valley of the tooth without complete obstruction.

Figure 2. Crown View (2-A), Lingual View (2-B), and Labial View (2-C) of the Specimen

The paracone is conical in shape and all three characteristic suid grooves are clearly visible. It is surrounded by a thick cingulum forming a shelf-like structure, that is, the cingular ridge is present anteriorly to the paracone. The enamel is corrugated and somewhat rough, perhaps due to the process of weathering. The paracone is attached to the protocone through the longitudinal valley and blocks it to some extent, which is further disrupted by the presence of the median accessory conule. The hypocone is pyramidal in its present shape and it's all three characteristic suid grooves are easily visible. From its anterior end, it is attached to the median accessory conule. Posteriorly, it is attached to the posterior accessory conule, which is contiguous with the posterior cingulum. The metacone is the vertically highest cone of the tooth. It is posteriorly attached to the posterior accessory conule through a thick channel, which is contiguous with the wrinkled cingulum of the posterior side. The cingulum is thick lingually and gradually becomes thin towards the labial end. Unlike the anterior cingulum, the posterior cingulum shows comparatively straightforward cingular ridges which, due to wear, have become almost flat. The median accessory conule is fairly worn out but still shows characteristic suid grooves, such as the principal cones of the tooth.

Table 1. Measurements (in mm) of G.C.P.C. No. 370/2001

4. CONCLUSION

The specimen is an isolated upper, second molar of the right maxilla recovered from the outskirts of Hasnot hamlet of District Jhelum, Punjab, Pakistan. The tooth is quadrangular in appearance and has a rounded posterior part with rounded and low tubercles, which are the characteristics of pigs [24, 25]. The molar teeth are devoid of complications and there is no crowding on the crown [4].

The molar teeth of the genus Propotamochoerus exhibit a longer length as compared to their width. They possess robust anterior and posterior cingulum, while these features are not present on the lateral aspects, save for a small, significantly reduced, basal pillar located at the entrance to the transverse valley on the lingual and labial sides, specifically in the case of the second molar. Anterior accessory conules are very small. The size of the posterior auxiliary tubercle is greater than that of the anterior tubercle, although the median tubercle is the biggest. The median accessory tubercle is isolated from the primary tubercles of the tooth. Some additional suid grooves are also present on these tubercles, since these are the generic characters of the genus Propotamochoerus. So, the specimen may be referred to as the genus Propotamochoerus.

The genus Propotamochoerus was observed to have originated in the Siwalik Hills within the bunodont pigs. It is distinguished by its possession of simple molars consisting of two rounded tubercles. In the Siwalik Hills, four species of the genus Propotamochoerus are present. These are Propotamochoerus salinus, Propotamochoerus uliginosus, Propotamochoerus hysudricus, and Propotamochoerus ingens. Out of these four species, Propotamochoerus salinus is of small-sized suids, with rugose enamel on its molars and a small heal on the last tooth [4]. Propotamochoerus hysudricus is a large suid species characterized by its relatively intricate molar structure [3].

The species Propotamochoerus hysudricus was established by Pilgrim [4] based on the examination of a mandibular ramus (Ind. Mus. B. 30), previously described and illustrated as Sus hysudricus by Lydekker [26]. Subsequently, Stehlin [3] reclassified it under the genus Propotamochoerus. The type specimen was a mandibular ramus bear P₃-M₃. The premolars exhibit elongation and possess a substantial transverse thickness. The M¹ is elongated. Propotamochoerus uliginosus has similarities to Propotamochoerus salinus, with discernible variations observed mainly in dental characteristics. According to Colbert [5], the species resembles Propotamochoerus salinus and Propotamochoerus ingens very much, which is a related form of the genus Propotamochoerus. According to his perspective, there exists a resemblance between the species Propotamochoerus salinus and Propotamochoerus hysudricus, with the only discernible distinction being their respective sizes. The author is of the opinion that Propotamochoerus salinus is probably a variant of the species Propotamochoerus hysudricus [5].

The cranial dimensions of Propotamochoerus hysudricus and contemporary African Propotamochoerus specimens exhibit a notable similarity in size and morphology. The distinction between the two species is characterized by variations in the location and dimensions of the orbit, with Propotamochoerus hysudricus exhibiting a more centralized and comparatively smaller orbit [4]. The presence of the first upper premolar has been seen in Propotamochoerus hysudricus, although it is notably absent in the genus Potamochoerus [5]. Propotamochoerus is a sizable suid species characterized by its intricate molars, possessing smooth enamel together with vertical ridges and grooves [5].

Conclusion

The specimen has enamel that is about average in thickness, a crown structure that is straightforward, and tubercles that are round in shape. All of these are typical characteristics of the species Propotamochoerus hysudricus. So, the specimen may be refrred to as the species Propotamochoerus hysudricus.

CONFLICT OF INTEREST

The authors of the manuscript have no financial or non-financial conflict of interest in the subject matter or materials discussed in this manuscript.

DATA AVALIABILITY STATEMENT

Data availability is not applicable as no new data was created.