An Oligo-Miocene cricetid rodent from the Indus Group, NW Himalaya: Constraints on the age of initiation of continental sedimentation in the India–Asia collision zone

Journal Pre-proofs An Oligo-Miocene cricetid rodent from the Indus Group, NW Himalaya: constraints on the age of initiation of continental sedimentation in the India–Asia collision zone Varun Parmar, Supreem S. Jamwal, Guntupalli V.R. Prasad, Lobsang Palden PII: DOI: Reference:

S1367-9120(19)30542-5 https://doi.org/10.1016/j.jseaes.2019.104190 JAES 104190

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Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

28 November 2018 29 November 2019 7 December 2019

Please cite this article as: Parmar, V., Jamwal, S.S., Prasad, G.V.R., Palden, L., An Oligo-Miocene cricetid rodent from the Indus Group, NW Himalaya: constraints on the age of initiation of continental sedimentation in the India–Asia collision zone, Journal of Asian Earth Sciences (2019), doi: https://doi.org/10.1016/j.jseaes. 2019.104190

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An Oligo-Miocene cricetid rodent from the Indus Group, NW Himalaya: constraints on the age of initiation of continental sedimentation in the India–Asia collision zone

Varun Parmara,*, Supreem S. Jamwalb, Guntupalli V. R. Prasadc, Lobsang Paldena aPost

Graduate Department of Geology, University of Jammu, Jammu 180006, India

bDepartment

of Geology, School of Science, Cluster University, Jammu 180001, India

cDepartment

of Geology, Centre for Advanced Studies, University of Delhi, Delhi 110007, India

*Corresponding author. Telefax: +91 191 2452987 E-mail addresses: [email protected] (V. Parmar), [email protected] (S.S. Jamwal), [email protected] (G.V.R. Prasad), [email protected] (L. Palden).

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ABSTRACT The Indus Tsangpo Suture Zone representing the zone of collision between Greater India and Asian mainland comprises a variety of rock sequences, among which, the youngest sedimentary succession, the Indus Group, represents the first continental sedimentation in the India–Asia collision zone, the age of which, has been a subject of debate since long. Here we report a cricetid rodent from the basal part of the Indus Group exposed in the Indus Suture Zone near Taruche village, Leh district, Ladakh Himalaya, India. The newly recovered rodent tooth shows a combination of archaic cricetid traits and possesses a mesolophid concurrently with protolophid II. Based on the dental grade of evolution of the new tooth, an Oligo-Miocene age is assigned to the basal part of the Indus Group.

Keywords: Indus Group, Ladakh Himalaya, India, cricetid rodent, age implication OligoMiocene

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1. Introduction

The Cenozoic Era witnessed the India–Asia collision that led to slowing of northward drift of India, closing of the Neotethys Sea, and cessation of marine sedimentation in the collision zone. Hence geology and tectonic framework of the northwestern Himalaya have become a topic of active research in global tectonics as it leads to better understanding of major Cenozoic geological events in the collision zone. Though a general consensus places the initial timing of India–Asia collision around 55 ± 10 Ma (Powel and Conaghan, 1973; Le Fort, 1975; Molnar and Tapponnier, 1975; Patriat and Achache, 1984; Garzanti et al., 1987; Klootwijk et al., 1992; Beck et al., 1995; Rowley, 1996; Yin and Harrison, 2000; Wang et al., 2014; Zhuang et al., 2015; Hu et al., 2016, 2017 and references therein), the dating of this event has remained a subject of debate for long with estimates extending to as old as ~70 Ma and as young as ~25 Ma in some works (Yin and Harrison, 2000; Van Hinsbergen et al., 2012). This large variation in collision age is due to models suggesting collision of India with the intraoceanic island arcs and microcontinents prior to its final suturing with Asia (Van Hinsbergen et al., 2012; Bouilhol et al., 2013). Constraining the time of collision has remained a subject of prime interest for geoscientists. Consequently, extensive composite studies on Indus Tsangpo Suture Zone (ITSZ) rocks with respect to stratigraphic disposition, structure, sedimentology, paleontology and radiometric dating have been undertaken in the last three decades. ITSZ extends discontinuously over a distance of about 2500 km from Afghanistan in the west to Myanmar in the east in a NW–SE direction. It exposes a variety of rock sequences from deep sea sediments to flysch, ultrabasic and submarine volcanic rocks, plutonic intrusives and molasse deposits. Much of the debate is over the nature of sedimentary rocks (flysch vs molasse) 3

of the ITSZ (referred as Indus Basin Sedimentary Rocks (IBSR) in recent works viz., Henderson et al., 2010, 2011) and their age. The Cenozoic sequence of the ITSZ is divided into two groups, the older pre-syn-collision Tar Group and the younger post-collision Indus Group (Srikantia and Razdan, 1980; Garzanti and van Haver, 1988; Searle et al., 1990; Clift et al., 2002; Sinclair and Jaffey, 2001; Henderson et al., 2010). The Tar Group is a 1500 m thick, Middle Cretaceous to Early Eocene, mostly marine sequence, whereas the Indus Group is about 1200 m thick sedimentary sequence representing the depositional event immediately post-dating the collision of the Indian and the Asian plates. The Indus Group deposition is considered to have taken place in deltaic, alluvial fan, lake and riverine environments by most workers (Searle et al., 1990; Clift et al., 2001; Sinclair and Jaffey, 2001; Henderson et al., 2010), but in a relict sea in the form of an shallow embayment along the ITSZ that received sediments from rivers flowing from its north and south (Singh et al., 2015). The cessation of marine facies and accumulation of continental facies in the collision zone has been taken as the definition of onset of collision between India– Asia by some workers (Molnar and Tapponnier, 1977; Searle et al., 1987; Rowley, 1996; Aitchison et al., 2007). The Indus Group extends from west to east as discontinuous units all along the suture zone. Its western extremity in India terminates near Kargil town and eastwards it extends up to Nyoma and Hanle after passing through Basgo and Upshi near Leh (Fig. 1A). Sections of the Indus Group exposed west of Leh city, in the central part of the Ladakh region (J & K, India) near villages Taruche, Saspochey and Basgo, were prospected by us to find age diagnostic fauna in order to ascertain the age of the Indus Group following initial report of ostracods from here by Bajpai et al. (2004). As a result of our research work, gastropods, unionid bivalves, ostracods, fishes, rodents, ichno fossils, and plant remains have been recovered from this part of the Indus 4

Group among which, the findings of fishes and a cricetid rodent have already been published (Prasad et al., 2005; Parmar et al., 2013). In this paper, we describe another cricetid rodent tooth that we retrieved from the Indus Group near village Taruche and discuss its implication for assigning age to the Indus Group in the light of evolutionary grade of tooth morphology of the newly recovered specimen. The rodent specimen described here comes from a low lying mound not in direct contact with Ladakh batholith but separated from it by scree consisting of granite boulders and near to the base of a sequence consisting of alternating yellow and green coloured rocks representing the Temesgam Formation. The rodent yielding fossil locality Taruche (T–II) falls in Survey of India Toposheet No.52 F/3. It can be approached by Leh–Himis Sukpāchan road. The section is situated about 300 m southwest of Taruche village (Fig. 1B). The section comprises of 3 m thick, greenish, fine grained sandstone at the base, that in turn is overlain by fossil yielding 1.5 m thick yellowish-green soft sandstone, followed by 0.5 m thick dirty white silty clay layer, succeeded by pale yellow hard sandstone at top (Fig. 1C).

2. Stratigraphic setting

The Indus Group, variously referred as Ladakh Molasse Group (Tewari, 1964; Bhandari et al., 1977), Wakka River Formation (Tewari and Dixit, 1972), Kargil and Tharumsa facies (Raiverman and Mishra, 1975), Kargil Formation (Shah et al., 1976; Thakur, 1981), Indus Molasse/Hemis Conglomerate (Frank et al., 1977), Karroo Formation (Pal and Mathur, 1977), Liyan Formation/Kargil Molasse (Shanker et al., 1982), Upshi Molasse (Frank et al., 1977; Brookfield and Andrews-Speed 1984a), Wakka Chu Molasse (Brookfield and Andrews-Speed, 5

1984b), Indus Clastics (Garzanti and van Haver, 1988), Liyan Molasse (Tiwari 2003) lies within the ITSZ. The ITSZ runs along the entire length of the Himalaya between the Karakorum block to the north and the Tethys Himalaya in the south. It is divided into southern Indus Suture Zone (ISZ) and the northern Shyok Suture Zone (SSZ) (Thakur, 1990). The Indus Group falls within the ISZ, unconformably overlying the Ladakh Batholith on its northern edge and Precambrian– Eocene Zanskar passive margin sediments and or Tar Group sediments on its southern side Srikantia and Razdan (1980) divided the Indus Group into Skinding, Kuksho, Maklishun and Karit formations, in an order of ascendance. Searle et al. (1990) redefined the Indus Group based on their study of Zanskar Gorge section and divided it into Nurla and Choksti formations. Sinclair and Jaffey (2001) added two more formations to the Indus Group atop the Choksti Formation, namely Hemis Conglomerate and Nimu formations based on geological investigation of three cross-sections in central Ladakh close to Leh. In a latest work, Henderson et al. (2010) mapped the IBSR along the Zanskar Gorge between the villages Sumda and Nimu. They characterized the different formations of the Indus Group. However, in order to avoid confusion they retained the formational names given earlier as Nurla, Choksti and Nimu formations (Henderson et al., 2010) and compared the existing Indus Basin stratigraphies (Fig. 2). Henderson et al. (2011) extended their study to the Indus Group exposed east of Leh between Lato and Upshi, wherein they subdivided the group into different formations and equated them with the Zanskar Gorge section. Singh et al. (2015) too studied Lato–Upshi and Zanskar Gorge sections, in addition to Karu, Hemis Gompa, Basgo and Chiktan Nala sections. Our study area falls west of Leh town near the village Taruche. The Indus Group exposed in this region has been studied by van Haver (1984), van Haver et al. (1984), and Garzanti and van Haver (1988). Garzanti and van Haver (1988) while discussing the sedimentary history of 6

the Indus Basin opined that the pre-collision sedimentation was not homogenous across the basin. The southern side of the basin developed marine terrigenous carbonate succession whereas the continental clastic sediments characterized its northern side, though, after collision the sedimentary succession was uniform throughout the basin. The Taruche section falls on the northern side of the basin wherein the Indus Group has been divided (see Fig. 2) into Basgo, Temesgam, Gonmaru La, Hemis Conglomerate, Nurla, Choksti, and Nimu formations, in this order of superposition (van Haver, 1984; van Haver et al., 1984; Garzanti and van Haver, 1988). The Basgo Formation, basal member of the northern sequence of the Indus Group rests unconformably over the Ladakh Batholith. It shows considerable lateral facies variation from alluvial fan conglomerates to braid-plain sandstones to lacustrine marls and limestone (Garzanti and van Haver, 1988). Overlying the Basgo Formation is the Temesgam Formation, a sequence of fine-grained, yellow coloured pelites alternating with reddish sandstone (Garzanti and van Haver, 1988). Though there is considerable lateral variation in the stratigraphy of the Indus Group from west to east, the occurrence of the similar fossil assemblage comprising fishes, gastropods, unionid bivalves, and charophytes all along the ISZ point towards the homotaxial nature and freshwater fluviatile-lacustrine depositional environment for the Indus Group (Parmar et al., 2013). Recently, Singh et al. (2015) studied the Basgo and Temesgam formations on Leh– Kargil road near village Basgo (not the same site as ours) and opined that the Basgo Formation was deposited in a braid-plain with quickly shifting channels that debouched sediments into a shallow sea, whereas deposition of the overlying Temesgam Formation took place in a shallow sea, mostly in tidal flat areas.

3. Materials and methods 7

The rodent tooth described in this paper was obtained along with fish remains and charophytes following sorting of screen-washed residue under stereoscopic binocular microscope. About 100 kg of the rock sample collected from Taruche II was disintegrated employing water–oil immersion method to release fossils. Following disaggregation, the sample was washed under running water using 0.25 mm sieve. The residue so obtained was dried and then sorted under stereozoom scopic zoom microscope DZ–240 for recovery of microfossils. The cricetid specimen described in this paper is housed in the Vertebrate Paleontology Laboratory of the Department of Geology, University of Delhi, under the acronym DUGF/IM/43 (Delhi University Geology Fossil/Indus Molasse/Catalogue number). Photomicrographs of the tooth were obtained with Zeiss Scanning Electron Microscope Model MA15 at the Department of Geology, University of Delhi. The basic dental terminology followed here to describe the tooth is that given by Lindsay (1988), Maridet and Ni (2013), and Lindsay and Flynn (2016).

4. Biota and age of the Indus Group

The Indus Group is known to be scantly fossiliferous in contrast to other Cenozoic contemporary and younger deposits (viz., Subathu, Murree, Siwalik, etc.). Meager fossils have been reported from a few sporadic localities across the Indus Group viz., near Kargil town, west of Leh city, and near Nyoma village (Table 1). Some of the reported biota has been utilized by different workers to constrain the age of the Indus Group resulting in diverse views on age from Upper Cretaceous to Late Pliocene (see Table 1), with more recent works favouring Late Oligocene–Early Miocene age for the basal part of the Indus Group.

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The age of the Indus Group has also been ascertained by radiometric and or fission track dating of detrital zircons or mica. The topmost unit of Tar Group, the Nummulitic Limestone underlies the basal unit of the Indus Group, the Nurla Formation in the Zanskar Gorge Section. Green et al. (2008) proposed an age of 50.5 Ma for the Nummulitic Limestone, whereas Henderson et al. (2010) favoured an age range of 50.8 to 49.4 Ma and Singh et al. (2015) suggested an age of 55.8–51 Ma for the Nummulitic Limestone. The sediments underlying the Nummulitic Limestone belonging to Chogdo Formation were dated between 51–50.8 Ma based on 206Pb/238U method (Henderson et al. 2010), whereas the age of Choksti Formation overlying the Nurla Formation based upon 206Pb/238U of detrital zircon was placed at 41+ 0.3 Ma (Wu et al., 2007). A fission-track age of 35.7 Ma was provided by Clift et al. (2002) for the top most unit of Indus Group, the Nimu Formation. Clift et al. (2002) further observed that no material from Higher Himalaya is present in the Indus Group, which was exposed around 20–23 Ma (Walker et al., 1999), which implies that the upper age limit of the Indus Group sediments cannot be younger than 20 Ma. Recently, Singh et al. (2015) based on the occurrence of a carbonate pebble containing foraminifera of early Eocene age in the Hemis Conglomerate suggested that the Indus Group may be of middle Eocene to early Miocene age.

5. Systematic Paleontology

Order Rodentia Bowdich, 1821 Family Cricetidae Rochebrune, 1883 Cricetidae gen. et sp. indet. Fig. 3A–F 9

Referred Material DUGF/IM/43, a well preserved first right lower molar. Horizon and Locality Yellowish-green sandstone of the Indus Group exposed southwest of Taruche village. Description DUGF/IM/43 is a fully preserved first right lower molar (Length=1.33 mm, Width=0.92 mm). In occlusal view, the crown is lozenge-shaped, longer than wide, and wider posteriorly. It comprises five major cusps, namely, anteroconid, metaconid, protoconid, entoconid and hypoconid, increasing in size posteriorly and all with a conical outline. The lingual cusps are higher and more anteriorly placed than the labial cusps. The anteroconid is the smallest of all the cusps. It is uni-cusped, mesiodistally compressed and lies a little more labial to the longitudinal axis of the tooth. In lateral view anteroconid is lower than the four other main cusps. It has an oblong wear facet that slopes labially. The labial anterolophid (anterior labial cingulum) descends from the anteroconid as a narrow ridge and meets the protoconid at its anterolabial base enclosing a deep, crescent-shaped basin, the protosinusid, between the anteroconid and the protoconid. The protosinusid is an anterolabially–posterolingually directed valley which is closed posterolingually by the labial margin of the metalophid II and anterolabially by the labial branch of the anterolophid. However, the anteroconid lacks the lingual branch of the anterior cingulum (the lingual anterolophid). The anteroconid is lingually separated from the metaconid by a narrow, shallow, small notch-like valley, the anterosinusid. A short, narrow and high ridge, the metalophid I connects the posterolingual tip of the anteroconid to the anterolabial base of the metaconid. The metaconid is located at the anterolingual angle of the crown. Its apex is slightly elongated transversely. The wear facet of the metaconid is somewhat oval and slants towards the posterolabial direction. Although not as voluminous as the protoconid, the metaconid is higher than the former. A relatively long, posteriorly sloping 10

metalophid II joins the metaconid to the protoconid at its posterolingual base. The protoconid has tear drop apex and a wear facet that slants posterolingually with its narrow end pointing in the same direction as well. The protoconid lacks the anterior arm. The connection between the protoconid and the anteroconid is lacking and thus the anterolophulid is absent. However, the protoconid extends posterolingually as a loph (protoconid posterior arm) connecting with the posterior end of the metalophid II and extending posteriorly parallel to the long axis of the tooth forming the anterior mure (anterior part of the ectolophid). The ectolophid is relatively long, straight, and medial in position that meets the anterior base of hypoconid forming the posterior mure (posterior part of the ectolophid). A small, low, very short ectomesolophid (called as ectolophid by Lindsay, 1988; Lindsay and Flynn, 2016) extends transversely from the central part of the mure (longitudinal crest/ectolophid) into the labial valley, the sinusid, present between the protoconid and the hypoconid. The sinusid is deep, wide and square. It is enclosed labially by a curved, thick, labial cingulum. The anterior cingulum and the labial cingulum are not continuous. The ectostylid is absent. Lingual to the ectolophid, a sub-rectangular wear facet of the mesoconid is present. The mesoconid lies in the center of the tooth, and is low. A short, low, transverse loph (but longer than ectomesolophid) extends lingually from the mesoconid towards the middle of the mesosinusid. This small loph lies closer to the entoconid than to the metaconid but is anterior to ectomesolophid. Since the tooth has posterior arm of protoconid (protolophid II of Lindsay and Flynn, 2016 and second mesolophid of Maridet et al., 2009), the posterior loph is identified as mesolophid. However, the protoconid posterior arm is short and oriented posterolingually to join metalophid II rather than being transverse and free. The mesosinusid is a wide, deep valley, nearly squarish in outline. It is slightly smaller than the labial sinusid. A small mesostylid is present beyond the lingual margin of the 11

mesosinusid between the metaconid and the entoconid. The mesostylid It is conical in outline with a very small oval wear facet. It is connected to the posterolingual end of the metaconid by an ascending, narrow crest, the metaconid ridge (or metaconid spur of Lindsay and Flynn, 2016). This ridge forms the lingual margin of the tooth. Posterior to the mesosinusid lays the entoconid. The entoconid is the largest of all the cusps of the tooth. Its apex has a tear drop wear facet who’s pointed end slants anterolabially. A short, wide crest, hypolophid, extends anterolabially from the entoconid and joins the mesoconid medially. No entoconid spur is present. Posterior to and labial to the entoconid is hypoconid. The hypoconid, though more voluminous than the entoconid, is lesser in height. The hypoconid has a tear shape wear facet that slopes posterolingually. The hypoconid is connected to the posterior end of the mesoconid by a short anterior arm. Posteriorly the hypoconid joins the posterior cingulum (posterolophid). Its hind arm is absent. A shallow posterolabial sulcus is present at the union of hypoconid and posterolophid. The posterolophid is long and thick but low in height than any of the cusps. It extends to the posterolingual margin of the tooth up to the posterior base of the entoconid, enclosing a crescent, long, narrow and deep valley, the posterosinusid. The labial branch of posterolophid is absent and no additional distal cingulid is present. The roots of the tooth are not preserved. Remarks The rodent family Cricetidae is characterized by the presence of three cheek teeth in the form of molars in which, the cusps are joined by lophs (Lindsay, 1994). The cricetids, considered as the stem of the muroid clade represented by 716 modern genera (Hartenberger, 1984) lack premolars. However, a few primitive forms like Pappocricetodon antiquus (Wang and Dawson, 1994) and P. schaubi Zdansky, 1930 (Dawson and Tong, 1998) from the Eocene of China were shown to have incomplete loss of P4 (or dP4). Flynn et al. (1985), Lindsay (1994), and Lindsay and Flynn (2016) identified primitive and derived 12

characters in muroids. The synapomorphies in the Cricetidae suggested by these authors include myomorphy, anterior union of metaconid and protoconid, large anteroconid, biliobed anterocone, reduction or loss of mure, presence of lingual accessory cusps in upper molars and labial accessory cusps in lower molars, loss of protocone and protoconid posterior spur, reduction and loss of metacone in M3 and entoconid in m3, posterior orientation of metaloph in M1–2, and increase in height of the crown. Among the characters listed above, DUGF/IM/43 possesses almost all primitive cricetid traits, like posterior union of the protoconid and the metaconid, small anteroconid, welldeveloped mure, presence of protoconid posterior spur (protolophid II), and absence of labial accessory cuspule. However, the tooth also has a mesolophid simultaneously with the protolophid II (protoconid posterior spur) that characterize Late Oligocene–Early Miocene generation of cricetid rodents (Lindsay and Flynn, 2016). This transitional state among the cricetids from primitive to modern forms is represented by taxa such as Paracricetodon and Heterocricetodon of Europe, Eucricetodon of Asia, and Leidymys of North America. Primus is also part of this transition. The transition gets nearly completed with the appearance of Democricetodon in Eurasia and Copemys in North America (Lindsay and Flynn, 2016). In the Indian subcontinent, Pseudocricetodon nawabi and Atavocricetodon paaliense, from the Lower Oligocene Nari Formation of Bugti Hill (Fig. 4), Baluchistan, Pakistan, are the oldest known cricetids (Marivaux et al., 1999). Freudenthal et al. (1992) while presenting a classification for European Oligocene cricetids gave the following diagnosis for Pseudocricetodontinae. The first lower molars of Pseudocricetodontinae nearly always possess the protoconid hind arm that is nearly always connected to the metaconid. However, the anterior metalophulid (=metalophid) in the m1 is usually absent. The posterolophid extends straight 13

towards the entoconid rather than curving towards it. The posterior branch of the hypoconid is hardly ever present. The m1 mostly has a strong ridge descending from the metaconid, along the border of the tooth, into the mesosinusid, without reaching the entoconid, and the mesolophid is frequently double. The lower first molar of Pseudocricetodon nawabi (Marivaux et al., 1999) has a well-developed metalophulid II like the other members of the genus Pseudocricetodon; however, it differs from all the other taxa of the Pseudocricetodon on account of having less pronounced anteroconid and general retention of pleisomorphic characters (Marivaux et al., 1999). Our specimen when compared to the Pseudocricetodontinae show affinities in terms of possession of protoconid hind arm that is connected to the metaconid by way of metalophulid II, absence of hypoconid hind arm, and presence of metaconid ridge along the border of the tooth that doesn’t reach the entoconid. However, it differs from the members of the Pseudocricetodontinae as the former has a well-developed metalophid I and a curving rather than a straight posterolophid. Based upon this comparison, DUGF/IM/43 can’t be attributed to any of the members of Pseudocricetodontinae. In addition to Pseudocricetodon nawabi, Marivaux et al. (1999) described a second cricetid taxon, Atavocricetodon paaliense, from the Early Oligocene Paali Nala C2 locality of Bugti Member (Fig. 4). The genus Atavocricetodon was erected by Freudenthal (1996) for the Eucricetodon atavus–group. Atavocricetodon cheek teeth are low crowned, with relatively small cusps, and long crests. The analysis of character states of Atavocricetodon carried out by Freudenthal (1996) shows that the first lower molars of the Atavocricetodon have complete anterolophulid and metalophid, the protoconid hind arm is low or free, that is frequently connected to the metaconid, the mesolophid is better developed, the mesoconid, ectomesolophid and the hypoconid hind arm may or may not be present. The first lower molar of 14

Atavocricetodon paaliense (Marivaux et al., 1999) described from the Early Oligocene Paali Nala C2 locality, Bugti Hill, Pakistan has a well-developed anterolophulid. Its posterolophid is wide and curved and the mesolophid very low or absent. The new specimen recovered from Ladakh matches Atavocricetodon in maintaining connection between the protoconid hind arm and the metaconid, presence of mesolophid, mesoconid, ectomesolophid and the absence of hypoconid hind arm. However, the presence or absence of most of these characters viz., mesoconid, ectomesolophid and hypoconid hind arm in Atavocricetodon are variable (Freudenthal, 1996; Marivaux et al., 1999), such that these characters are not helpful in determining the affinities of the new specimen. But the absence of anterolophulid in DUGF/IM/43 refutes its attribution to any of the known species of Atavocricetodon as all its members have a complete development of an anterolophulid. Other members of the Subfamily Eucricetodontinae reported from the Tertiary deposits of the Indian subcontinent are represented by Eucricetodon, Primus and Spanocricetodon. The taxon Eucricetodon sp. listed in the faunal list of Z113 and Z126 localities of the Upper Oligocene–Lower Miocene Chitarwata Formation, Dalana, Zinda Pir Dome (Fig. 4), Pakistan (Downing et al., 1993) was neither described nor illustrated. Moreover, Lindsay and Downs (1998) in their list of identified cricetid taxa from the Zinda Pir Dome did not enlist the taxa Eucricetodon. However, the genus Eucricetodon is well represented in Central Asia and as such warrants a comparison with the present material. The new specimen from India possesses few common characters of Eucricetodon such as bunodont teeth with voluminous cusps, a single anteroconid and short connections between the main cusps (Dienemann, 1987; Li et al., 2016; Freudenthal and Martín-Suárez, 2016). From the Oligocene–Early Miocene of Central Asia (China, Kazakhstan and Mongolia) nine species of Eucricetodon have been reported. These 15

include Oligocene forms, Eucricetodon asiaticus Matthew and Granger, 1923, E .caducus Shevyreva, 1967, E. deploratus Shevyreva, 1967, E. occasionalis Lopatin, 1996, E. bagus Gomes Rodrigues et al., 2012, E. jilantaiensis Gomes Rodrigues et al., 2012 and E. wangae Li et al., 2016, and Early Miocene taxa E. youngi Li and Qiu, 1980 and E. sajakensis Bendukidze, 1993. The newly recovered tooth is distinctive in size and morphology from almost all the known Oligocene–Early Miocene species of Eucricetodon such as in absence of hypoconid posterior arm and wide transverse valleys (Dienemann, 1987; Li et al., 2016; Freudenthal and Martín-Suárez, 2016) baring Eucricetodon bagus. The later first reported from several late Early Oligocene–Late Oligocene localities in Ulantatal, Inner Mongolia, China (Gomes Rodrigues et al., 2012) has recently been added from Taatsiin Gol and Taatsiin Tsagaan Nuur areas of Central Mongolia (López-Guerrero et al., 2017). DUGF/IM/43 and Eucricetodon bagus lower first molars have a relatively similar shape and size. In both, the anteroconid, and metaconid spur are well developed, the hypolophid is short and connected to the posterior mure (ectolophid), whereas the anterior mure (ectolophid) is joined to the posterior arm of the protoconid, ectomesolophid though small is distinguishable, mesoconid is small, sinusid is wide with mesial and distal parts equally developed, mesosinusid is wide, and the hypoconid hind arm and entoconid spur are absent (Gomes Rodrigues et al., 2012; López-Guerrero et al., 2017). DUGF/IM/43 however possess metalophulid I and II, which in few specimens of E. bagus may be absent, however when present, metalophulid II is always connected to the posterior arm of the protoconid as in DUGF/IM/43 (Gomes Rodrigues et al., 2012; López-Guerrero et al., 2017). The anterior border of E. bagus lower molar is angular (Gomes Rodrigues et al., 2012) while in DUGF/IM/43 it is round. Even the mesolophid is variable in E. bagus, being weakly developed or absent to long in one specimen (López-Guerrero et al., 2017). The mesolophid however when 16

present is directed obliquely in E. bagus as its ectomesolophid (Gomes Rodrigues et al., 2012), whereas, in DUGF/IM/43, both mesolophid and ectomesolophid are transversely oriented. Anteroconid in E. bagus is pinched and situated on the longitudinal axis of the tooth (Gomes Rodrigues et al., 2012; López-Guerrero et al., 2017), whereas in DUGF/IM/43 anteroconid is broad and is located slightly labial to the longitudinal axis of the occlusal surface. The labial anterolophid is well developed in E. bagus and connects the anteroconid to the labial part of the protoconid (vide López-Guerrero et al., 2017) as in DUGF/IM/43, however, the lingual anterolophid that connects the anteroconid to the base of the metaconid in some of the specimens of E. bagus (vide Gomes Rodrigues et al., 2012) is absent in DUGF/IM/43. Even in some of the lower molars of E. bagus, anterolophulid and a weak hypoconulid is present (Gomes Rodrigues et al., 2012; López-Guerrero et al., 2017), which in DUGF/IM/43 are absent. The posterosinusid is wide, enclosed lingually by posterolophid whereas the sinusid is either open or closed by a small cingulid in E. bagus (Gomes Rodrigues et al., 2012; López-Guerrero et al., 2017). In contrast, posterosinusid though enclosed lingually by posterolophid is narrow in DUGF/IM/43 and the sinusid is closed labially by a cingulum. Based upon the above comparison of DUGF/IM/43 with Eucricetodon bagus it is apparent that the two show many resemblances, however due to subtle yet important morphological differences between the two it is not wise to assign DUGF/IM/43 to Eucricetodon bagus or to a new species of Eucricetodon, especially based upon a single tooth. de Bruijn, Hussain and Leinders (1981) erected a new genus Primus with Primus microps its type species from the dental material recovered from the Lower Miocene Murree Formation at locality H–GSP 116, situated in the Banda Daud Shah region of Kohat (Fig. 4) in Pakistan and suggested Primus to be in or near the ancestry of the Muridae. Downing et al. (1993) too listed 17

the presence of Primus sp. at Oligocene locality Z113 within the Chitarwata Formation at Zinda Pir Dome, Pakistan though Lindsay and Downs (1998) in their revised list of cricetid taxa from the Zinda Pir Dome did not enlist the presence of Primus there. But recently, representatives of the genus Primus were described by Lindsay and Flynn (2016) from several Late Oligocene– Early Miocene localities lying within the Chitarwata and Vihowa formations in Zinda Pir Dome, Pakistan. These include Primus microps de Bruijn, Hussain, Leinders 1981 and a new species Primus cheemai Lindsay and Flynn 2016. In addition, an isolated left upper second molar of Primus microps was also described by Kumar and Kad (2002) from the Lower Miocene Lower Murree Group rocks exposed at Sialsui in Kalakot (Fig. 4), Rajauri district, Jammu and Kashmir, India. Lindsay and Flynn (2016) presented an emended diagnosis for Primus microps as: a small cricetid with simple dental pattern, its lower molars with slight offset between lingual and labial cusps, the lingual cusps opposite to the anterior margin of the labial cusps, anteroconid small, low and wide, located on the continuous anterior cingulum, protolophid II short or absent, metalophid usually joining protoconid, and a long entolophid (hypolophid of other workers) that joins the posterior mure and/or hypoconid arm. In contrast the molars of Primus cheemai described by the same authors from the same localities as P. microps, are larger in size than P. microps, have more robust and wider teeth and the anteroconid on m1 is larger, wider and more symmetrical than that of P. microps (Lindsay and Flynn, 2016). Additionally, the lower first molars of both P. microps and P. cheemai have anterolophulid and protoconid anterior arm; a mesolophid that is short or absent; no mesostylid and ectostylid; both lingual anterior cingulum and lingual cingulum are present. The ectomesolophid is absent in P. microps and usually absent or short in P. cheemai. In contrast, the specimen described herein from Ladakh has lingual cusps 18

of the tooth placed much more anterior to the labial cusps than any of the known species of Primus; the anteroconid is small, low and wide and placed more labially rather than symmetrically. The new tooth has short hypolophid, it lacks anterolophulid, protoconid anterior arm, lingual anterior cingulum and lingual cingulum; it possess mesostylid, mesolophid and ectomesolophid. These characters differentiate DUGF/IM/43 from Primus and thus do not favour its attribution to this genus. de Bruijn, Hussain, Leinders (1981) were the first to describe Spanocricetodon species, S. khani and S. lii, from the Tertiary rocks of Indian subcontinent. They were reported from the H– GSP 116 locality in the Lower Miocene Murree Formation near Banda Daud Shah, Kohat, Pakistan. Additional report of S. lii was made from Lower to Middle Miocene Lower Manchar Formation locality GAJ 81.06 (Gaj river section), Pakistan by de Bruijn and Hussain (1984) and Spanocricetodon sp. from localities Z113 (Oligocene Chitarwata Formation), Z126 (Miocene Chitarwata Formation), and Z122 (Miocene Vihowa Formation) from Dalana, Zinda Pir Dome, Pakistan by Downing et al. (1993) without providing any illustrations or description. Lindsay and Downs (1998) placed the Spanocricetodon taxa reported by these earlier workers in quotation marks (‘Spanocricetodon’ khani, ‘Spanocricetodon’ lii) considering its morphology to be distinct and primitive to that of Spanocricetodon reported earlier from Middle Miocene of China by Li (1977). They also cited presence of “Spanocricetodon” khani at locality Z135 (Miocene Chitarwata Formation) in Dalana, Zinda Pir Dome, Pakistan (Lindsay and Downs, 1998) along with ‘Spanocricetodon’ n. sp. large from localities Z113, Z135, Z126 and Z122 of Zinda Pir Dome. ‘Spanocricetodon’ n. sp. large was also documented by these authors at locality Y721 of the Kamlial Formation in Potwar region (Fig. 4), Pakistan. Recently, Lindsay and Flynn (2016), following Maridet et al.’s (2011) observation that some species previously assigned to 19

Spanocricetodon actually belong to other genera, reassigned ‘Spanocricetodon’ khani to Democricetodon khani. Maridet et al. (2011) also provided a thorough review of Democricetodon and Spanocricetodon. The lower first molar of Spanocricetodon has small, compressed and narrow anteroconid; no mesolophid; strongly curved ectolophid; oblique sinusoids; no protoconid hind arm; extremely short and crescentic ectomesolophid; very anteriorly connected hypolophid; transverse metalophid; and the cuspids located closer to the margins of the tooth than in any other cricetids (Li, 1977; Maridet et al., 2011). In DUGF/IM/43, the anteroconid is small but broad, the ectomesolophid is very short but not crescentic rather transverse, mesolophid is present, ectolophid is straight, sinusoids are not oblique, protoconid hind arm is present and metalophid is not transverse. These differences in crown morphology do not allow referral of the present tooth to Spanocricetodon either. Among all the described cricetid taxa, crown morphology of DUGF/IM/43 is very close to that of Democricetodon, e.g., short and broad undivided anteroconid, short posterior arm of protoconid, a well-developed mure, alternating lingual and labial gracile cusps and metalophid directed anteriorly (Lindsay and Downs, 1998). Democricetodon khani is the first representative of the diverse and long-lived Democricetodon group that is characteristic of later Siwalik faunas of the Indian subcontinent. D. khani is known from Lower Miocene Murree Formation of Banda Daud Shah, Kohat and Chitarwata and Vihowa formations of Zinda Pir Dome, both in Pakistan (de Bruijn et al., 1981; Lindsay and Flynn, 2016). In fact, D. khani from 22 Ma old rocks of Pakistan is the oldest record of Democricetodon in the Indian subcontinent that even rivals the antiquity of the genus in Turkey and China (Lindsay and Flynn, 2016). D. khani displays a mix of archaic and modern muroid features as in Primus, for example, the transition in development of 20

lophs on cheek teeth, the protocone–protoconid posterior spur vs. the mesoloph or mesolophid (Lindsay and Flynn, 2016). D. khani retains primitive feature like small anteroconid, welldeveloped mure, and posterior protoconid spur on lower first molar as do our specimen DUGF/IM/43. However, DUGF/IM/43 in addition possess the primitive trait of posterior union of the protoconid and the metaconid, i.e., metalophid II which is usually absent in D. khani (Lindsay and Flynn, 2016). Moreover, D. khani possess the protoconid anterior arm, lingual anterior cingulum and lingual cingulum (Lindsay and Flynn, 2016), which are absent in DUGF/IM/43. D. khani has a long entolophid (hypolophid), whereas mesostylid and ectomesolophid are absent in D. khani. In contrast DUGF/IM/43 has a short entolophid, and mesostylid and ectomesolophid is present in it. DUGF/IM/43 thus retains more primitive cricetid traits than the oldest known Democricetodon, D. khani. Other Democricetodon species reported from the Miocene deposits of Pakistan comprise D. kohatensis, Democricetodon n. sp. X, Democricetodon sp. A, Democricetodon B–C, Democricetodon E, Democricetodon F, Democricetodon G, and Democricetodon H (Wessel et al., 1982; Lindsay, 1987, 1994; Lindsay and Downs, 1998). However, detailed descriptions and illustrations are lacking for these forms except D. kohatensis, and hence no comparisons are possible with these forms. D. kohatensis has been reported from Lower to Middle Miocene Lower Manchar Formation exposed in Sehwan Sharif and Gaj River (Fig. 4) sections (de Bruijn and Hussain, 1984) and Middle–Upper Miocene age Siwalik Group rocks exposed in Kohat, Jalalpur, and Potwar Plateau (Fig. 4) in Pakistan (Wessel et al., 1982; Cheema et al., 1983, 2000; Lindsay, 1987, 1994; Lindsay and Downs, 1998). In lower first molars of D. kohatensis, the anteroconid is unicuspid and the labial anterolophid is long as in DUGF/IM/43. However, D. kohatensis also possess protoconid anterior arm, that is absent in DUGF/IM/43. The mure in D. 21

kohatensis is a semicircular ridge whereas in DUGF/IM/43 it is straight. In addition, the anteroconid in D. kohatensis is connected to the antero-lingual top of the metaconid by a high anterolophid. No such connection is present in DUGF/IM/43. The new specimen thus differs from D. kohatensis in all the above mentioned characters. Comparisons of DUGF/IM/43 with the rest of the Democricetodon taxa reported from Pakistan as listed above is based on brief descriptions and line drawings of these available in Lindsay and Downs (1998). Democricetodon n. sp. X reported from Vihowa and Manchar formations (de Bruijn and Hussain, 1984; Lindsay and Downs, 1998) has very low crowned and narrow m1 (Lindsay and Downs, 1998) unlike in DUGF/IM/43. Democricetodon sp. A reported from Vihowa and Manchar formations (de Bruijn and Hussain, 1984; Lindsay and Downs, 1998) is a small-sized and a low-crowned species (Lindsay and Downs, 1998) unlike DUGF/IM/43 which is comparatively high-crowned. In lower first molars of Democricetodon B–C described from Kamlial, Chinji and Nagri formations exposed in Daud Khel (Fig. 4), Potwar Plateau, and Jalalpur (Hussain et al., 1977; Hussain et al., 1979; Cheema et al., 1983; Lindsay and Downs, 1998; Cheema et al., 2000), the anteroconid is elongate with moderate development of labial and lingual arms (Cheema et al., 2000). In contrast, DUGF/IM/43 has a short and broad anteroconid with well-developed labial arm and absence of lingual arm. Democricetodon E known from Chinji, Nagri and Dhok Pathan formations (Hussain et al., 1977; Hussain et al., 1979; Cheema et al., 1983; Lindsay and Downs, 1998) is similar to D. kohatensis but larger in size (Lindsay and Downs, 1998). Since DUGF/IM/43 differs morphologically from D. kohatensis as discussed above, DUGF/IM/43 can’t be attributed to Democricetodon E. Democricetodon F reported from Chinji, Nagri and Dhok Pathan formations (Cheema et al., 1983; Lindsay and Downs, 1998) is a large-sized, slender species in contrast to DUGF/IM/43, which is small in size and the tooth is 22

relatively wide. Democricetodon G recovered from Chinji, Nagri and Dhok Pathan formations (Hussain et al., 1977; Hussain et al., 1979; Cheema et al., 1983; Lindsay and Downs, 1998; Cheema et al., 2000) is large in size with wide and very robust molar, whereas DUGF/IM/43, is small, though wide, is less robust than Democricetodon G. Democricetodon H known from Chinji, Nagri and Dhok Pathan formations (Lindsay and Downs, 1998) is a medium-sized taxon and thus differs from the new, small-sized specimen from Ladakh Himalaya. Democricetodon sp. reported from India comes from the Basgo and Mansar formations. The cricetid from the Basgo Formation was found from a locality about 3 km west of the site yielding DUGF/IM/43 (Fig. 4), District Leh, Jammu and Kashmir (Prasad et al., 2005). Being an upper first molar, comparisons of DUGF/IM/43 with the former is not possible. The Mansar Formation (equivalent of Chinji Formation) cricetid was found near Ramnagar (Fig. 4), Jammu Himalaya (Singh et al., 2018). The lower first molar has a small and wide anteroconid, slightly alternating opposing cusps with smaller anterior cusps compared to posterior cusps, a short mesolophid, and a very weak development of the metaconid posterior mure (Singh et al., 2018). Since the description provided for the tooth of Democricetodon sp. recovered from Ramnagar area is brief and not diagnostic, the detailed comparisons of our material with it cannot be made. Moreover we fail to understand the character described by the authors, ‘very weak development of the metaconid posterior mure’. Recently, a new species of Democricetodon, Democricetodon fejfari was described by Lindsay (2017) from the Siwalik deposits of Pakistan, ranging in age between about 13.8 to 8.7 Ma. D. fejfari is the latest species to be recorded from the Siwalik deposits of Pakistan among the cricetid rodents. D. fejfari bears protoconid anterior arm and lingual anterior cingulum but the mesostylid, hypolophid, and metalophid II are absent (Lindsay, 2017). In contrast, 23

DUGF/IM/43 lacks protoconid anterior arm and lingual anterior cingulum but possess esostylid, hypolophid, and metalophid II thus differentiating it from D. fejfari. Additionally in D. fejfari, the protoconid posterior spur terminates freely (Lindsay, 2017), whereas in DUGF/IM/43 the protoconid posterior spur is connected to metalophid II. Hence, DUGF/IM/43 is not the first lower molar of D. fejfari. Three more cricetid subfamilies, megacricetodontinae, myocricetodontinae and dendromurinae are known to occur in Miocene rocks of Pakistan. Taxa belonging to megacricetodontinae have been reported from the Kamlial, Chinji, and Nagri formations (Wessel et al., 1982; Lindsay, 1988; 1994; Lindsay and Downs, 1998); members of the subfamily Myocricetodontinae have been recovered from the Chitarwata, Vihowa, Manchar, Kamlial, Chinji and Nagri formations (Hussain et al., 1977; Hussain et al., 1979; de Bruijn and Hussain, 1984; Wessels et al., 1987; Lindsay, 1988; Downing et al., 1993; Wessels, 1996; Lindsay, 1987, 1994; Lindsay and Downs, 1998; Lindsay and Flynn, 2016), whereas dendromurines have been described from the Vihowa, Manchar, Kamlial, Chinji and Nagri formations (Hussain et al., 1977; Hussain et al., 1979; de Bruijn and Hussain, 1984; Wessel et al., 1982; Cheema et al., 1983; Wessels et al., 1987; Lindsay, 1988, 1994; Wessels, 1996; Lindsay and Downs, 1998; Cheema et al., 2000; Lindsay and Flynn, 2016). From the Miocene counterparts in India, the reports of these families are very few. Megacricetodontinae and Myocricetodontinae have been reported from Chinji equivalents rocks from Ramnagar (Fig. 4), Jammu (Sehgal and Patnaik, 2012; Parmar et al., 2015, 2016), whereas, a Dendromurinae, ?Dakkamys nagrii has been described from rocks coeval of the Nagri Formation in Haritalyangar (Fig. 4), Himachal Pradesh (Vasishat and Chopra, 1981). The youngest known fossil cricetid from the Indian sections is

24

Kilarcola kashmiriensis, an arvicoline (Microtinae) described from the Late Pleistocene Karewa Formation (Fig. 4) of Jammu and Kashmir (Kotlia, 1985). The dentition of Megacricetodontinae, Myocricetodontinae and Dendromurinae reported from the Indian subcontinent is derived. In these forms, there is an anterior union of anteroconid and protoconid in lower first molars (Lindsay, 1988). Dental characters of Myocricetodontinae are more derived than those of Megacricetodontinae in terms of reduction of the mure and absence of the mesolophid (Lindsay, 1988, 1994; Lindsay and Downs, 1998). The mure is also weakly developed to absent in Dendromurinae with the absence of mesolophid (Lindsay, 1988, 1994; Lindsay and Downs, 1998). Moreover, in dendromurines, labial accessory cuspules are present, which is considered as a derived trait (Lindsay, 1994). DUGF/IM/43, as discussed earlier has retained many primitive traits. It lacks the anterior union of anteroconid and protoconid, the mure is well developed, mesolophid is present and the labial accessory cuspules are absent. These traits differentiate DUGF/IM/43 from any of the known species of Megacricetodontinae, Myocricetodontinae and Dendromurinae. The comparison of morphology of the newly recovered tooth, DUGF/IM/43 recovered from the Ladakh Himalaya, India with various cricetid taxa reported from the Indian Subcontinent and contemporary Eucricetodon fauna known from Central Asia shows DUGF/IM/43 to be more closely affiliated to either Democricetodon or Eucricetodon. However, due to paucity of material the exact generic and species identification of DUGF/IM/43 is deferred and for the time being it is referred as Cricetidae gen. et sp. indet. However, if future research work ratifies DUGF/IM/43 to be a Democricetodon then it will be the oldest known representative of the group from the Indian Subcontinent, since it possess more archaic traits in contrast to the presently known oldest representative of the group, Democricetodon khani. 25

Additionally the recognition of DUGF/IM/43 as Democricetodon would firmly establish the Indian Subcontinent as the place of origin of Democricetodon lineage that later migrated to other parts of Eurasia. However, if the later research work places DUGF/IM/43 as Eucricetodon then this will be the first representative of Eucricetodon to reach Indian Subcontinent most probably from Central Asia or alternatively from Europe as has been suggested for other taxa recovered previously from the coeval deposits of Indus Group within Ladakh Himalaya such as Tragulids: Lophiomeryx and Iberomeryx (Cryptomeryx) (Nanda and Sahni, 1990; Kumar et al. 1996), Rhinocerotid: Juxia sharmurense (Tiwari, 2003), Ostracod: Dongyingia (Bajpai et al., 2004), and Palm: Trachycarpus ladakhensis (Lakhanpal et al., 1984).

6. Conclusions

The termination of marine deposition and beginning of continental sedimentation as manifested by Indus Group in the ITSZ provides a constraint for timing of initial collision of India and Asia (Molnar and Tapponnier, 1977; Searle et al., 1987; Rowley, 1996; Aitchison et al., 2007). Based upon several criteria, the age of deposition of the Indus Group has been proposed to extend from Upper Cretaceous to Late Pliocene by different workers. The discovery of a rodent molar from the basal part of the Indus Group helps in resolving this dilemma. The new tooth has an archaic dental grade of evolution that characterizes Late Oligocene to Early Miocene cricetid rodents. This indicates that the fossil yielding horizon of the Indus Group is Late Oligocene–Early Miocene in age which further implies that the continental sedimentation in India–Asia collision zone initiated during this time period.

26

Acknowledgments

We thank the anonymous reviewers and the editors of the journal for critical and constructive comments that greatly improved the paper. GVRP acknowledges research grant for this work from the JC Bose National Fellowship, Science and Engineering Research Board, Government of India. The research was also supported with funds from Council of Scientific and Industrial Research, Government of India in the form of Junior Research Fellowship to LP.

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FIGURE CAPTIONS

Fig. 1. A. Geological Map of the Ladakh Himalaya (after Singh et al., 2007). B. Location Map of the Fossil Yielding Site. C. Lithocolumn of the Fossil Yielding Site.

Fig. 2. Comparison of stratigraphic units of the Indus Basin Sedimentary Rocks and their depositional environment (slightly modified from Henderson et al., 2010:fig. 2). The continental clastic Indus Group sedimentation in the northern Indus Basin margin had its inception prior to that of the southern Indus Basin margin (Garzanti and van Haver, 1988).

Fig. 3. Right first lower molar of Cricetidae gen. et sp. indet. (DUGF/IM/43), A, occlusal view, B, line drawing of A, C, labial view, D, antero-occlusal view, E, posterior view, F, lingual view.

Fig. 4. Location map of various cricetid yielding fossil localities of the Indian Subcontinent mentioned in the text. The locations are general positions for multiple fossil sites of a region.

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Table 1 Contrastingly diverging ages proposed for the Indus Group exposed in western, central and eastern sectors of Ladakh Himalaya, India are presented. The western sector localities are in the vicinity of Kargil town, the central sector localities are west of Leh town near village Taruche and the eastern sector localities are in the surrounding of Nyoma village (see Fig. 1A). The letters w, c, e, in parentheses stands for western, central and eastern sectors, respectively.

Age

Taxa and Region

References

Middle Miocene–

Molluscs: Indonaia bonneaudi, I. glyptica,

Mathur, 1983

Late Pliocene

I. mittalli, Melanoides tuberculata (w)

Early–Middle

Rodent: Democricetodon sp. (c)

Prasad et al., 2005

Anthracotherid: Hyoboops of Dixit et al.

Savage et al., 1977

Miocene Lower Miocene

(1971) that was later identified as Hyoboops palaeindicus (w) Miocene

Palm: Trachycarpus ladakhensis (e)

Lakhanpal et al., 1984

Miocene

Anthracotherid: Hyoboops (w)

Dixit et al., 1971

Late Oligocene–

Rodents Fallomus razae and F.

Nanda and Sahni,

Early Miocene

ladakhensis (w)

1998

Oligocene–Lower

Anthracotherid: Hyoboops of Dixit et al.

Tewari and

Miocene

(1971) (w)

Sharma, 1972

42

Oligocene–Miocene

Rodents: Fallomous razae, F. ladakhensis,

Kumar et al., 1996

Wakkamys hartenbergeri, Zindapira; and Tragulid: Cryptomeryx of Nanda and Sahni (1990) = Iberomeryx Kumar et al. (1996) (w) Oligocene–Miocene

Hyoboops Dixit et al. (1971), and Fishes,

Sahni et al., 1984

Molluscs (e) Late Oligocene

Ostracod: Dongyingia (c)

Bajpai et al., 2004

Late Oligocene

Tragulids: Lophiomeryx and Cryptomeryx

Nanda and Sahni,

(w)

1990

Mollusc: Subzebrinus gudei (w)

Tewari and Dixit,

post Middle Eocene to Pliocene

1972

Late Eocene

Rhinocerotid: Juxia sharmurense (e)

Tiwari, 2003

Eocene

Molluscs: Melania kargilensis, Viviparus

Sahni and

sp., Palm: Sabal or Tachycarpus (w)

Bhatnagar, 1962

Nannofossils, Palynofossils (w)

Bhandari et al.,

Middle Palaeocene– Miocene Upper Cretaceous

1977 Ostracods: Bhythoceratina sp. and

van Haver et al.,

Platycytheris sp. (c)

1984; Garzanti and van Haver, 1988

Cretaceous

Palynofossils (w)

Ghosh and Lukose, 1967

43

44

45

46

47

48

49

Graphical abstract

50

Highlights 

A cricetid rodent is described from near Taruche village, Ladakh Himalaya, India from the basal part of the Indus Group that marks the beginning of continental sedimentation in the India–Asia collision zone.



The newly recovered tooth largely displays archaic cricetid traits along with the possession of a mesolophid.



The dental grade of evolution of the tooth proposes Late Oligocene–Early Miocene age to the basal part of the Indus Group.

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Author contributions

Varun Parmar: Conceptualization, Investigation, Writing - Original Draft, Review & Editing Supreem Singh Jamwal: Investigation, Resources, Writing - Review & Editing, Guntupalli V. R. Prasad: Conceptualization, Investigation, Resources, Data Curation, Writing Review & Editing, Funding acquisition Lobsang Palden: Investigation, Writing - Review & Editing, Funding acquisition.

52