Siamotragulus (Tragulidae: Artiodactyla: Mammalia) from the Siwalik Group of Indian Subcontinent (Pakistan)
Muhammad Akhtar1*, Sayyed Ghyour Abbas2,3, Muhammad Wajid4, Muhammad Adeeb Babar4, Fizza Jaber1, Muhammad Akbar Khan1 and Shahzad Ahmed5
1Dr. Abu Bakr Fossil Display and Research Centre, Institute of Zoology, University of the Punjab, Quaid-i-Azam Campus, Lahore
2Department of Zoology, University of Sialkot, 1-Km Main, Daska Road, Sialkot
3Institute of Vertebrate Palaeontology and Palaeoanthropology, Chinese Academy of Sciences, Beijing 100044, China
4Department of Zoology, University of Okara, Okara
5Department of Zoology, Government College University, Faisalabad
ABSTRACT
The present study deals with the description of a right mandibular fragment having p2-m3 referred to the genus Siamotragulus. This specimen was recovered from the Chinji Formation outcrops (Middle Miocene) of Dhok Bun Ameer Khatoon, District Chakwal, Punjab, Pakistan. The dentition of this mandibular ramus under study is characterized by selenodonty, premolars with very sharp edges, molars with preproto- and premetacristids are longer than the postproto- and postmetacristids, lingual cusps are flat without any prominent bend or rib and lack Dorcatherium platform. These characters differentiate it from the genus Dorcatherium and help to associate the mandibular fragment with the genus Siamotragulus. Based on its size, being larger than S. nagrii and S. minimus, it is referred to as Siamotragulus nov. sp.
Article Information
Received 12 April 2025
Revised 25 May 2025
Accepted 01 June 2025
Published 24 October 2025
Authors’ Contribution
MA and MAK: Concept and Supervision
MA and MW: Data Acquisition
SGA, MAB and FJ: Data Analysis and Comparison
SA and FJ: Formatting and Graphics
Key words
Siamotragulus, Middle miocene, Dhok Bun Ameer Khatoon, Siwaliks, Dorcatherium, Chinji Formation
DOI: https://dx.doi.org/10.17582/sajz/2025/43.2.67.73
* Corresponding author: [email protected]
1013-3461/2025/0067 $ 0.00/0
Copyright 2025 by the authors.
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Introduction
The Siwalik Group of Indian subcontinent represents the fluvial sedimentation phase in the Himalayan Foreland Basin, which developed south of the rising Himalayan in response to the collision between the Indian and Eurasian tectonic plates which started 50 million years ago and even continues today (Nanda et al., 2022). Siwaliks are very famous for vertebrate fossils pertaining to almost all the major mammalian groups such as Rodentia, Artiodactyla, Perissodactyla, Proboscidea and Carnivora etc. (Colbert, 1935). Of these, the fossil artiodactyls are very well known in different formations of the Siwaliks. Artiodactyls are represented by a variety of suids, hippos, camels, cervids, giraffids, bovids and tragulids. There are four extinct genera of the family Tragulidae in the Siwaliks; Dorcatherium, Afrotragulus, Dorcabune, and Siamotragulus Among these, Dorcatherium, Dorcabune, Afrotragulus are known mostly by maxillary and mandibular fragments and isolated upper and lower teeth while the genus Siamotragulus is known only by postcranials except that have previously been described as Dorcatherium.
We describe here the Middle Miocene Siamotragulus from the Chinji Formation outcrops exposed west of village Dhok Bun Ameer Khatoon (DBAK), Chakwal district, Punjab, Pakistan. The specimen under study is a right mandible which provides the basis to discuss the taxonomic problems of the Siwalik tragulid allocated to the genus Dorcatherium. The geographic and geological settings of Dhok Bun Ameer Khatoon are given below.
The fossil site, Dhok Bun Ameer Khatoon (Lat. 32° 47’ 34.6” N: Long. 72° 55’ 36.1” E and altitude 1942.43 ft) is in the northeastern region of the Chua Saydan Shah town, district Chakwal, Punjab, Pakistan (Fig. 1) and about 50 km northeast of the Chinji stratotype, Chinji Formation. The studied deposits are located northwest of the Dhok Bun Ameer Khatoon village. Locally, the outcrops area in the west from where the specimen is collected is known as Jallowala. The exposed sediments cover a few hundred square meters, approximately 40 m thickness, bearing mammalian remains. The outcrops consist of shales, siltstones and sandstones deposited in a fluvial environment, mainly filled by unweathered igneous minerals (Cheema, 2003). Based on the faunal elements, the age is dated between 14 and 11.6 Ma.
Materials and Methods
The material includes a mandibular fragment with p2-m3 during the 2024 field visits. The specimen was found partially buried in the sediments (Fig. 1B) and recovered with the help of geological hammer and chisel in five pieces that were later glued with Elfy after preparation of the specimen. Fine needles and brushes were used to remove the sediments and clay. A hand lens was used for keen observations of very small and ambiguous morphological features of the teeth of the mandible under study. Photographs were taken with the help of DSLR camera (Canon 6D). The measurements of the specimen were taken millimeters (mm) with the help of digital Vernier caliper. The specimens collected show the collection year and the serial number of that year e.g., PUPC 25/34. The upper figure denotes the collection year and the lower one the serial number of the respective year.
Abbreviations: PUPC, Punjab University Palaeontological Collection; PG, Pong.
Systematic palaeontology
Mammalia Linnaeus, 1758
Artiodactyla Owen, 1848
Ruminantia Scopoli, 1777
Tragulina Flower, 1883
Traguloidea Gill, 1872
Tragulidae Milne Edwards, 1864
Genus Siamotragulus (Thomas et al., 1990)
Type species: Siamotragulus sanyathanai (Thomas et al., 1990)
Holotype
PG1, left mandible with p2 (partly broken) to m3 (Thomas et al., 1990).
Type locality and age
Pong, Phayao Province, Thailand and Middle Miocene in age (Thomas et al., 1990).
Diagnosis
Small Tragulidae with a size intermediate between that of Dorcatherium minus Lydekker and Dorcatherium minimus west. The lower premolars, in particularly the p3, are very pointed and sharp, differing thereby from those of Dorcatherium and Dorcabune. The p4 possess an elongate posteriorly directed metaconid but no other lingual feature which may correspond to the entoconid or entostylid. The p3, long, treanchant and strongly compressed, has a tall protoconid, a minute paraconid and a distinct hypoconid. No posterolingual ridge (metaconid) is present on p3. Upper canines of males (?) saberlike. The limb bones are relatively long and slender (Thomas et al., 1990).
Siamotragulus nov. sp.
(Fig. 2)
Referred specimen
PUPC 25/34, a right mandible bearing p3-m3, partially broken p2 and root of p1 (Fig. 2).
Locality and age
Dhok Bun Ameer Khatoon, Chakwal district, the Punjab province, Pakistan.
Description
PUPC 25/34 is a mandible having p3-m3, partially broken p2, and root of p1 (Fig. 2).
Corpus
The corpus though cracked at various places and thin, but it is extremely stout. The corpus is concave lingually and convex labially (Fig. 2A). It also preserves a small part of symphysis, diastema, angular process, and ascending ramus. A large mylohoid line is present at the base of the corpus stating under the p2 on the lingual side (Fig. 2B). There are two mental foramina: the anterior and larger under the diastema and a posterior and smaller under the p3 (Fig. 2C). The diastema is very small and has a length between mandibular symphysis and p2 is 6.5 mm. The depth of the corpus increases under the teeth from p1 to m3 and the vertical depth of the mandible below the m1 is about 13 mm and transverse width is about 6 mm. The antero-posterior length of mandible is 80 mm and of p2-m3 series is 62.36 mm. Length of premolar series 29.01 mm length of molar series 33.35 mm.
Premolars
The dentition is also well preserved except for the p1 and p2. Only the root of p1 is preserved. The p2 is in early stages of wear and partially broken anteriorly resulting in loss of paraconid and some part of the protoconid which is large and connected to the hypoconid and metaconid through its postcristid. A prominent valley is present between the metaconid and hypoconid. The p3 is also in early stage of wear and well preserved. It has a large paraconid which is connected to the large and bulbous protoconid through its postcristid. A shallow valley is present between the paraconid and protoconid lingually and small groove labially. The metaconid is large, more lingually and posteriorly oriented and is in contact with large and round hypoconid. A large groove is present between the protoconid and hypoconid and a large, lingually open valley is present between the metaconid and hypoconid. The p4 is most worn among premolars and is in the early middle stage of wear. It is slightly smaller than p3 (Table I) and is most developed. Most of its morphology is similar to p3 except the posterior half in which the posthypocristid is large the posterior valley is extremely narrow.
Molars
Except the extreme wear, the molars are also well preserved. The m1 is the most worn and smallest among the molars. The metaconid is partially broken resulting in loss of the enamel in the center. It is in the late stage of wear resulting in loss of both anterior and posterior fossette. However, the distinction between the cusps is still possible. A large ectostylid is present in the median valley. The Tragulus fold has been lost due to wear, but the Dorcatherium fold is still recognizable. The m2 is less worn and it is also in late stage of wear. The anterior posterior side of the anterior fossette is preserved rest is lost due to wear. It is a selenodont and brachydont tooth. The preprotocristid is longer than the postprotocristid and premetacristid which is longer than the postmetacristid. Similarly, the prehypocristid is longer than the posthypocristid and preentocristid while postentocristid is extremely reduced. The Dorcatherium fold present on the postmetacristid is large and prominent while a small part of the Tragulus fold is preserved. The median valley is blocked by a moderate sized ectostylid. The posterior cingulid is present at the posthypocristid that runs posterotransversly. The m3 is least worn, most preserved in terms of its morphology and trilobed. It is extremely selenodont. The cusp morphology is similar to the m2. Both fossettes are well preserved and these are narrow and crescentic especially the posterior fossette. The M/Σ structure is complete and pronounced as both the Dorcatherium fold on the postmetacristid and Tragulus fold on the postprotocristid are intact and complete. The median valley has a weak ectostylid and a small cingulid is present at the base of postprotocristid. The postentoconid groove is open. The third lobe is composed of hypoconulid and very small entoconulid. The hypoconulid has prominent pre- and postcristids while a small entoconulid completely closes the prominent back fossette of m3 lingually. The posthypocristid is bifurcated and makes a small fold which is in contact with the hypoconulid. Dorcatherium platform is completely absent. The lingual walls of the metaconid and entoconid are flat. The enamel is extremely rugose.
Table I. Comparative measurements of the lower cheek teeth of middle miocene tragulids.
|
Taxa/Catalog No. |
Position |
Length |
Width |
References |
|
Siamotragulus nov. sp. |
||||
|
PUPC 25/34 |
p1 |
- |
- |
This study |
|
p2 |
8.71 est. |
2.95 |
||
|
p3 |
9.46 |
3.51 |
||
|
p4 |
8.84 |
3.80 |
||
|
m1 |
8.87 |
6.57 |
||
|
m2 |
9.81 |
7.11 |
||
|
m3 |
14.67 |
7.14 |
||
|
Siamotragulus nagrii |
||||
|
VPL/AS/H/101 |
p2 |
5.2 |
2.3 |
Gaur, 1992 |
|
p3 |
7.0 |
2.6 |
||
|
VPL/AS/H/102 |
p4 |
8.2 |
3.3 |
|
|
m1 |
5.8 |
3.4 |
||
|
m2 |
7.1 |
4.2 |
||
|
m3 |
11.0 |
4.3 |
||
|
Siamotragulus sanyathanai |
||||
|
PG1 |
p3 |
9 |
3 |
Thomas et al. 1990 |
|
p4 |
8 |
3 |
||
|
m1 |
6.7 |
4 |
||
|
m2 |
8 |
5 |
||
|
m3 |
11.7 |
5.1 |
||
|
Dorcatherium minus |
||||
|
SNSB-BSPG 1956 II 2489 |
p3 |
12.0 |
3.5 |
Guzmán- Sandoval and Rössner, 2021 |
|
p4 |
10.0 |
4.4 |
||
|
m1 |
10.5 |
6.2 |
||
|
m2 |
11.4 |
6.6 |
||
|
PUPC 68/313 |
m1 |
8.95 |
5.60 |
Khan and Akhtar, 2013 |
|
m2 |
10.25 |
6.70 |
||
|
m3 |
15.65 |
7.40 |
||
|
GSI-B 594 |
p4 |
10.0 |
4.8 |
Pilgrim, 1915 |
|
m1 |
10.8 |
6.8 |
||
|
m2 |
12.5 |
7.5 |
||
|
m3 |
16.7 |
8.3 |
||
|
Dorcatherium guntianum |
||||
|
SNSB-BSPG1956 II 2554 |
m1 |
7.7 |
4.3 |
Guzmán- Sandoval and Rössner, 2021 |
|
m2 |
9.1 |
5.0 |
||
|
m3 |
14.5 |
6.6 |
||
|
SNSB-BSPG 1881 IX 737 |
m1 |
8.6 |
5.5 |
|
|
m2 |
10.0 |
6.1 |
||
|
m3 |
14.7 |
6.4 |
||
Comparison
The studied specimen proves strongly its inclusion in the family Tragulidae, based on the selenodont pattern, rugosity of enamel and the presence of M/Σ structure. The family Tragulidae in the Siwalik hills are represented by two extinct genera Dorcatherium and Dorcabune, with many species. The Dorcabune is a large extinct tragulid of the Siwaliks and very close to anthracotheriids having bunodont molars. The paraconus rib is more conspicuous in Dorcabune than in Dorcatherium (Colbert, 1935; Farooq et al; 2007; Farooq et al., 2008; Khan and Akhtar, 2013). The specimen studied differs from Dorcabune having more selenodont cusp pattern.
Dentition in PUPC 25/34 is characterized by selenodonty, premolars with very sharp edges, molars with preproto- and premetacristids are longer than the postproto- and postmetacristids, lingual cusps are flat without any prominent bend or rib and lack Dorcatherium platform. These characters differentiate it from the genus Dorcatherium and help to associate the mandibular fragment with the genus Siamotragulus. Table I and Figure 3 show that the dentition in PUPC 25/34 is larger than Siamotragulus sanyathanai and the range in the size previously described as Dorcatherium guntianum from the Siwaliks. Hence, it became evident that measurements of PUPC 25/34 match with most of the classically described material of Siwalik species Dorcatherium minus while the tooth morphology is like that of Siamotragulus and size is like that of guntianum. Such morphometric analysis is
convincing enough that PUPC 25/34 can be associated with the genus Siamotragulus as well as most of the material previously described as Dorcatherium guntianum. Hence, based on its morphology and size, it is referred to as Siamotragulus nov. sp. awaiting more material and in-depth study of all the Siwalik tragulid material.
Discussion
The genus Dorcatherium was created by Kaup (1833) based on the material from the Germany. Since the wide geographic acceptance of the genus, most of the tragulid material from Miocene to Pliocene deposits was allocated to this genus without any detailed study (Rössner, 2007; Sánchez et al., 2010, 2015). This led the status of the genus to a potpourri or waste bucket for most of the tragulid material and such a status of this genus was partly compromised by Thomas et al. (1990) by the creation of a new genus, Siamotragulus, for the tragulid material from Thailand. However, despite this study, the genus Dorcatherium remained a primary choice of researchers for the description of their tragulid material until the work of Sánchez et al. (2010) who identified the genus Siamotragulus from Africa after the indication of (Rössner, 2007). Further work was carried out by Barry (2014) who reported the presence of the genus Siamotragulus from the Siwalik Group based on the postcranial material. The next work was done by Sánchez et al. (2015) who identified yet another tragulid genus, Afrotragulus, from the material that was previously described as member of the genus Dorcatherium. This further shows the waste bucket nature of the genus Dorcatherium. Finally, such nature is also shown in Barry (2025) who described Dorcatherium nagrii as Siamotragulus nagrii and Dorcatherium minimus as Siamotragulus minimus and identified two more species of this genus. Such a nature also applies to the Siwalik tragulids and the description of PUPC 25/34 is an example to demonstrate it.
PUPC 25/34 is morphologically shows the characteristics of the genus Siamotragulus similar to the specimen AMNH 19365, right mandibular fragment with m2-m3. Even in the AMNH 19365, the preprotocristid is longer than the postprotocristid and premetacristid which is longer than the postmetacristid. Even the lingual walls of the metaconid and entoconid are flat and it is also selenodont like PUPC 25/34. However, the illustration of AMNH 19365 shows the Dorcatherium platform but this could be due to the illustration bias. Similarly, most of the material described as Dorcatherium minus by Khan and Akhtar (2013), Khan et al. (2005, 2010, 2012a, b, 2013, 2017), Batool et al. (2014), Samiullah et al. (2015, 2021), and Draz et al. (2020, 2021) shows similar features as in PUPC 25/34 including the measurements. Hence, all such material can be allocated to the genus Siamotragulus without any hesitation.
Conclusions
We are describing a tragulid mandible collected from the Chinji Formation deposits of Dhok Bun Ameer Khatoon, Chakwal, Punjab, Pakistan. The teeth in the mandible show the characteristics of the genus Siamotragulus (selenodonty, premolars with very sharp edges, molars with preproto- and premetacristids are longer than the postproto- and postmetacristids, labial cusps are flat without any prominent bend or rib and lack Dorcatherium platform) while the measurements are in the range of previously described material as Dorcatherium guntianum. Further, most of the material previously described as Dorcatherium clearly shows the characteristics of the genus Siamotragulus. Hence, we are describing this mandible as Siamotragulus nov. sp. until more material is recovered and/or comprehensive study of all the Siwalik tragulid material is done.
Declarations
Acknowledgement
University of Okara is acknowledged for facilitating in field and University of the Punjab, Lahore is acknowledged for Laboratory facility.
Funding
The study received no external fundings.
Generative AI or AI-assisted technology statement
No AI technology is used in this manuscript.
Statement of conflict of interest
The authors have declared no conflict of interest.
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