Dorcatherium (Mammalia: Tragulidae) from Lower Siwaliks of Dhok Bun Amir Khatoon, Punjab, Pakistan
Dorcatherium (Mammalia: Tragulidae) from Lower Siwaliks of Dhok Bun Amir Khatoon, Punjab, Pakistan
Muhammad Akbar Khan1,*, Sayyed Ghyour Abbas1, Muhammad Adeeb Babar1, Sabah Kiran1, Ayesha Riaz2 and Muhammad Akhtar1
1Dr. Abu Bakr Fossil Display and Research Centre, Department of Zoology, University of the Punjab, Quaid-e-Azam Campus, Lahore 54590, Pakistan
2Department of Zoology, GC Women University, Faisalabad, Pakistan
Extinct tragulids Dorcatherium minus and Dorcatherium sp. were recorded from the Chinji Formation of Pakistan. Furthermore, Dorcatherium minus is relatively rare in Middle Miocene site of Dhok Bun Amir Khatoon, Chakwal district, Punjab province, Pakistan. The referred specimens comprise isolated dental elements and mandible fragments. The presence of tragulids in Dhok Bun Amir Khatoon during Middle Miocene Chinji Formation of Pakistan suggests a humid habitat with abundant cover.
Received 28 march 2016
Revised 28 June 216
Accepted 14 January 2017
Available online 28 April 2017
MAK conceived and designed the study and analyzed and interpreted the data. SGA and MAB acquired the data. SK and AR drafted the manuscript.
Mouse deer, Tragulids, Chevrotains, Ruminantia, Miocene.
* Corresponding author: email@example.com
0030-9923/2017/0003-0883 $ 9.00/0
Copyright 2017 Zoological Society of Pakistan
Tragulidae is the most primitive family among existing ruminants (; ; ; ; ; ; ; ; ). The molecular data also showed evidence that these were the first offshoot of the extant ruminant radiation and the sister group of Pecora (). They are mostly present in South East Asia and Africa (). Previously, this family was only represented by two genera throughout Eurasia and Africa as Dorcatherium and Siamotragulus but recently Archaeotragulus from the late Eocene of Thailand has been added to this family (; ). Siamotragulus is known only from the Early Miocene of Bugti Hills (Pakistan) and Middle Miocene of the Pong Basin (Northern Thailand). Dorcatherium instead is known from several Early-Late Miocene localities and mainly from Africa, Europe (Austria, France and Germany) and Asia (Pakistan and India) ().
Dhok Bun Amir Khatoon is in Chakwal district, Punjab province, Pakistan (). It is located about 308 km far from Lahore, the capital of the province and 155 km far from Islamabad, the capital of the country. The locality is dominated by red coloured mud/ shale and sandstone that made up the basal part of the Chinji Formation, has a very abundant vertebrate fauna, including fishes, amphibians, reptiles (crocodile and alligator are dominant), birds and mammals (bovids are dominant in mammals). Based on the faunal elements, the locality can be divided into two parts: the first one is most familiar to many workers, locally known as Jallo Aala and dominated by fossils that represent bovids, tragulids and giraffids. The second one, at the opposite is not very familiar and locally known as Loharan Aala, dominated by fossils that represent suids. The tragulid fossils discussed in this paper were collected from both parts of Dhok Bun Amir Khatoon ().
Definitions: Dorcatherium fold refers to the fold occurring on the postmetacristid on the lower molars of some primitive ruminants and extant tragulids and the entoconidian groove refers to the two parallel folds (thus forming a groove) occurring on the mesial side of the entoconid (). Tragulus fold refers to the fold situated on the postprotocristid and basally linked to the prehypocristid (; ).
MATERIAL AND METHODS
The tragulid specimens have been collected in more than 20 visits occurred to this locality from April 2011 to February 2013. The surface collection was the basic methodology adopted. Measurements were taken through a digital Vernier caliper and provided in millimeters (mm).
Uppercase letter was used for upper dentition (e.g. M for upper molar) and lower case for lower dentition (e.g. m for lower molar). The catalogue number of the specimens is made up by three elements: the prefix PUPC (institutional abbreviation-Palaeontological Collection of University of the Punjab, Lahore, Pakistan), the collection year (numerator) and serial number (denominator) of that year. So, for example PUPC 12/117 reference the sample with serial number 117 collected in the year 2012. Samples are housed in Dr. Abu Bakr Fossil Display and Research Centre, University of the Punjab, Lahore, Pakistan. The terminology and measurements of teeth followed .
Family Tragulidae Milne Edwards, 1864
Genus Dorcatherium Kaup, 1833
Dorcatherium minus Lydekker, 1876
PUPC 13/08, right P2; PUPC 13/15, left M2; PUPC 13/13, partial left M2; PUPC 13/11, left p3; PUPC 13/18, right mandible fragment with m1; PUPC 13/17, right mandible fragment with m1; PUPC 13/16, right m1; PUPC 13/19, right mandible fragment with m2; PUPC 14/110, right mandible fragment with partial m3.
The P2 represents simple cone without styles (). The molars are broad crown, semiselenodont and rugose with shiny enamel (, ). The antero-lingual cingulum extends up to the base of hypocone. The entostyle is absent. The major cones are unfused occlusally and inclined towards the median longitudinal line of the molars. The parastyle is broad and thick. The mesostyle is thick, broad and directed anteriorly. The paracone has a strong rib with a vertical groove. The metastyle is weak. The pre- and post-fossettes are somewhat broad posteriorly. The postparacrista and premetacrista are not directly attached to the mesostyle.
The lower dental elements include premolars and molars (, ). The p3 have prominent parastylid and entostylid. The premolar lingually shows three valleys: anterior, median and posterior. The paraconid, metaconid and entoconid can be clearly differentiated. There is no entoconid complex. The premolars are two rooted. The anterior stylid is missing; the anterior conid, the posterolingual conid and the posterior stylid are partially broken in the 3rd premolar (). The mesolingual conid is well preserved. The antero and posterolingual cristids are thick. There is a small furrow with the posterolabial conid.
The mandible fragments are thin and shallow (). In lower molars, Tragulus fold and Dorcatherium fold are present at the protoconid and metaconid, directed posteriorly and representing prominent Σ shape structure. The Tragulus fold is present in the protocristid and the postmetacristid show the Dorcatherium fold (). The trigonid and talonid are not equal in size; the trigonid is narrower than the talonid. The protoconid and hypoconid are crescent whereas the metaconid and entoconid are transversally compressed. The hypoconid is projected forward, directed posteriorly and largest among the conids. The cingulid is present anterolabially. The postfossette is wider than the prefossette. There is a prominent ectostylid in the transverse valley.
Teeth are characterized by having strong cingulum, styles and labial ribs. The lower molars represent the M structure (Dorcatherium fold and Tragulus fold) and this reflects the affinity with the family Tragulidae and the genus Dorcatherium. Teeth were assigned to Dorcatherium according the buno-seleno-brachydonty with the M structure. The Siwalik Dorcatherium species are mainly differentiated by their size (; , , ; ; ; , ; ). The specimens are smaller than the material assigned to D. majus, and larger than D. nagrii and D. minimus that are common at Chakwal during the Middle-Late Miocene (; ; , , ; ; , ; ; ). The described teeth features coincide with the characters of the holotype of D. minus (; , ). Hence, the material is assigned to the Siwalik tragulid species D. minus.
|D. minus||PUPC 13/08*||rP2||7.60||3.90||0.51|
|D. sp.||PUPC 13/12*||rm3||7.66||4.00||
PUPC 13/12, partial right 3rd molar.
Description and comparison
PUPC 13/12 represents two unusual Dorcatherium folds and two Tragulus folds directed anteriorly (). These folds are located on the prehypocristid and preentocristid. The anterior folds are more prominent than the posterior one. The Tragulus fold is thicker than the Dorcatherium fold. The tooth has thick shelf like cingulid. The antero-transverse cingulid is broken whereas the postero-transverse cingulid is complete. The pre- and postfossettes are narrow and deep.
The molar shows peculiar structure with ∑/M structures directing anteriorly. The specimen looks to be a primitive member of the genus Dorcatherium, showing affinity with a primitive tragulid Archaeotragulus (), in having Dorcatherium fold, Tragulus fold and entoconidian groove. Anteriorly directed folds are present in genus Krabimeryx (), which is also a primitive member of tragulids.
The majority areas where Dorcatherium has been found indicate wetlands, dominated by pockets of dense forests (; ; ; ; ; , ; ). The presence of D. minus and D. sp. with D. nagrii, D. minimus and D. majus in the Chinji Formation suggests a strong connection to wet, forested habitats with dense understory, where the animals could hide from predators in vegetation or water (; ; , ; ; ). A significant representation of tragulids with adaptations to ecotonal wet and swampy habitats indicates humid conditions in Dhok Bun Amir Khatoon, Northern Pakistan.
The associated large mammals might suggest that a savanna-like environment could be present in the surroundings of Dhok Bun Amir Khatoon. Moreover the presence of large mammals (e.g. Chilotherium, Deinotherium) indicates that, open areas covered by grass, should also exist nearby the wetlands of Dhok Bun Amir Khatoon. This kind of environment was rather specific for the Chinji Formation of the Siwaliks () and might be interpreted as a representation of a more open habitats upward and more closed habitats to the lower level ().
Miotragocerus, Eotragus and Hypsodontus recorded from the lower level of the site (, ), might have been semi-aquatic in habit (; ), and the high abundance of Dorcatherium at the lower level of Dhok Bun Amir Khatoon might be indicative of wetlands. The lower level of the locality may have comprised relatively more humid and closed habitats, based on the ecomorphology of their dominant taxa, particularly Dorcatherium, which may have been an inhabitant of the wetlands (; ; ). The presence of Dorcatherium indicates more or less closed and humid habitats (; ; ). The faunal association suggests a humid habitat pocket with abundant cover indicating the dominance of forested landscapes during the Middle Miocene time of the Chinji Formation in the Lower Siwalik Subgroup (Pakistan).
Dorcatherium were discovered in the Middle Miocene site of Dhok Bun Amir Khatoon (Pakistan), including two species D. minus and D. sp. In Middle Miocene, there is a variety of Dorcatherium in the Lower Siwalik Subgroup, having the basic pattern of Dorcatherium fold and Tragulus fold, but these species differ in size. Palaeoenvironmental conditions coincide with wet and swampy habitats under a humid climate.
We are highly thankful to Mr. Iftikhar Hussain, Mr. Atif Mehmood, and Mr. Muhammad Khan, residents of DBAK for their guidance and help in the fieldwork.
Statement of conflict of interest
Authors have declared no conflict of interest.
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