Friday, 25 October 2019

Musk Deer from the Miocene of Mongolia.

Musk Deer, Moschidae, are small Artiodactyls closely related to True Deer, Cervidae, but differing from them in the absence of antlers; instead the males have enlarged, tusk-like canine teeth which are used in conflict with other males. Musk Deer also lack the facial glands of True Deer, instead the males have a musk gland in their genital area. Unfortunately this musk gland is highly prised in the perfume industry and Chinese medicine, with the effect that six of the seven extant species of Musk Deer are now classified as Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species, with the remaing species being classed as Vulnerable. All extant species of Musk Deer are placed in a single genus, Moschus, found within wooded areas of Asia. The group is represented by twenty seven fossil species, split into fourteen genera, dating from the Miocene onwards, with the oldest known specimens coming from Serbian strata dated to about 17 million years ago. However, almost all known fossil specimens assigned to the group are from Europe, with fossil Musk Deer only reported from two Miocenesites in China, Silong in  Jiangsu Province, and Damiao in Hebei, with the Sihong specimens being lost.

In a paper published in the journal Palaeontologica Electronica in August 2019, Bastien Mennecart of the Naturhistorisches Museum Wien and the Naturhistorisches Museum Basel, Manuela Aiglstorfer of the Staatliches Museum für Naturkunde Stuttgart, and Ursula Göhlich and Gudrun Daxner-Höck, also of the Naturhistorisches Museum Wien, describe a serious of isolated Musk Deer teeth from Loh Formation at the Miocene Ulan Tolgoi locality in the Valley of Lakes Region of Mongolia.

The locality Ulan Tolgoi is situated in the northeast of the Taatsiin Tsagaan Nuur Basin, which is part of the Valley of Lakes in Central Mongolia. From bottom to top, the basin is filled with Mesozoic and Cenozoic continental sediments. From 1995 to 2012, the Mongolian Academy of Sciences and the Natural History Museum of Vienna carried out an extensive program of field work in Oligocene and Miocene deposits of the Valley of Lakes region in Mongolia. This project’s output included several scientific publications, the identification of about 19 000 fossils, the description of 175 fossil Mammal species (including 32 newly erected species), and the first precise integrated stratigraphy of the Mongolian Oligocene and Miocene combining biostratigraphy and radiometric dating. 

Geographic position (1) of Mongolia (black) in Asia (light grey) and (2) of the Ulan Tolgoi locality (black square). (3) Photo of the Ulan Tolgoi locality taken by Gudrun Daxner-Höck during fieldwork in August 2015. Mennecart et al. (2019).

A 50 m thick sediment sequence of the Loh Formation is exposed along a southwest to northeast striking ridge at Ulan Tolgoi. From bottom to top, the beds are: (1) reddish-brown sandy siltstone, followed by (2) whitish-grey sandstone and siltstone with gravel lenses (scattered bones included). The sandy whitish part is locally covered by (3) a reddish-brown silty claystone, followed by (4) a rose-grey siltstone layer Towards the top of the sequence (5) brown silt, and (6) quaternary gravels follow.

The age of the Ulan Tolgoi fauna can only be inferred from biostratigraphic data, because no Miocene basalt is exposed in this region, and no magnetostratigraphic data are available so far. Comparisons of the Ulan Tolgoi fauna to Mammals from early and middle Miocene faunas from Inner Mongolia in China show that most genera listed from Ulan Tolgoi have their lowermost occurrences in the early Miocene and beginning of the middle Miocene.

The Ulan Tolgoi fossil collection is composed of small and large Mammals. Small Mammals were selected from three screen washed samples, and scattered large Mammal remains were collected from surface in the vicinity of the sample places. Though the fauna comprises 21 genera, though species identification is almost impossible, because the taxa are represented by only one or a few specimens.

Very few Ruminant species and specimens were described from the Ulan Tolgoi Miocene deposits during the course of the project, with those that were assigned to the genera Eotragus (a Bovid) and Lagomeryx (a member of the Lagomerycidae, or Rabbit Deer, an extinct group that may have been ancestral to both the True Deer and Musk Deer). 

The first specimen discussed by Mennecart et al. is a right lower second premolar with preserved roots, measuring 5.8 x 2.9 mm. The enamel of this specimen is slightly pleated on the lingual side (inner side, literallty the side towards the tongue). The anterior conid (front cust of a lower premolar) is located anteromedian (in front of the midline), forming a pointed anterior part of the tooth. The straight anterolabial cristid (front outside ridge) starts from the apex of the mesolabial conid (outside middle cusp) and joins the anterior conid (back cusp) on its posterolabial (outside back) side. The anterior conid is low and does not form any labial relief. The large mesolabial conid is the highest cuspid. It is located central and median. It possesses a broad posterior part. Since the posteriolingual conid is labiolingually oriented, it forms a narrow and deep posterior valley. The posterolingual conid is long, reaching to the lingual side of the tooth, forming a small protrusion. On its labial face (outside, towards the lips), we can observe a vertical depression. The posterolabial cristid (boack outside ridge), reaching from the mesolabial conid apex to the labial part of the posterolingual conid, is curved. The posterolabial conid (back outside cusp) is quite distinct. It forms the posterolabial corner of the tooth. As there is no posterior stylid (ridge running vertically down the middle of the tooth), the back valley is widely open. The posterolingual conid (back inside cusp) is higher than the anterior conid. There is no cingulid (ridge that runs around the base of the crown of a lower tooth).

Right lower second premolar from the Ulan Tolgoi Miocene deposits in labial (7), occlusal (8), and lingual (9) views. Mennecart et al. (2019).

The second specimen described is a fourth lower premolar with preserved roots measuring 8.6 x 4.9 mm,  which was formerly assigned to Lagomeryx, but which they consider to be an indeterminated Musk Deer. This specimen is a little worn, high crowned, and the enamel is slightly wrinkled. There is a short anterolabial cingulid (ridge running around the front and exterior surfaces) and a vestigial anterolingual cingulid (ridge running around the back and interior surfaces). The mesolabial conid (medium outside cusp) is located median (in the middle). It is smaller than the mesolingual conid (middle inside cusp). The latter is slightly shifted to anterior (front) and is laterally compressed (flattened sideways). It is the highest conid. The very deep anterior valley is closed by the connection of the anterolingual cristid (front inside ridge) and an enlarged anterior conid (front cusp). The anterior conid shows an additional minute anterior bifurcation. The anterior stylid (central ridge) forms the anterolingual (front inside) edge of the tooth. The oblique transverse cristid (diagonal ridge crossing the tooth) fuses with the posterior end of the posterolingual cristid (back inside ridge) building the posterior wall of the anterior valley. Transverse cristid and posterolingual conid (inside back cusp) are oriented parallel, as are posterior and back valley. The valleys are both deep and oriented obliquely. The posterior valley is open lingually. The posterior cristid turns posteriorly at the base and almost reaches the posterolingual edge of the tooth closing the back valley basally. The posterolabial cristid is very short, and the posterolabial conid is well-marked. There is a distinct labial depression anterior to it. The posterior stylid (back central ridge) is very weak. The posterior interdental contact surface implies that the fourth premolar was considerably intruded by the first premolar.

Right fourth premolar from the Ulan Tolgoi Miocene deposits in labial (4), occlusal (5), and lingual (6) views. Mennecart et al. (2019).

The next specimen is a medium-sized molar has a fully developed The medium-sized molar has a fully developed selenodonty (form suited to herbivory, with a low crown and cresent-shaped cusps). The enamel is slightly wrinkled. The lingual side of the tooth is flattened. The conids (cusps) are not fully aligned, comprising an intermediate situation between the condition of Bovids and Cervids/Palaeomerycids, as observed in some Moschid taxa. All cristids (ridges) are more or less straight. The preprotocristid and prehypocristid (front ridges) are parallel and oriented obliquely to the main axis of the tooth. The same applies to internal postprotocristid and posthypocristid (back ridges). The prehypocristid is lower and terminates in the posterior wall of the internal postprotocristid. It does not meet the connection between internal postprotocristid, preentocristid, and postmetacristid. A well-developed, long and  slender, external postprotocristid starting from the apex of the protoconid forms a deep 'Palaeomeryx fold'. The metastylid is weak and the entostylid is absent. Postentocristid and posthypocristid are fused and close the posterior wall. The ectostylid is very well-developed. The anterior cingulid is weakly developed. Due to the strong 'Palaeomeryx fold' and the still marked anterior cingulid, Mennecart et al. consider the tooth to be a first.

First molar from the Ulan Tolgoi Miocene deposits in labial (1), occlusal (2), and lingual (3) views. Mennecart et al. (2019).

The final specimen is a right third molar measuring 11.1 x 5.4 mm, formerly identified as Lagomeryx sp., but considered to be assignable to the genus Micromeryx and probably the species Micromeryx primaevus, a species previously described from the Miocene of Europe and China. The specimen is selenodont. The enamel is slightly wrinkled. The lingual wall is more bulgy than in the first molar, and the lingual cuspids are less aligned. The and the lingual cuspids are less aligned. The metastylid (ridge in front of the middle cusp) is very strong. The prehypocristid nearly meets the connection between internal postprotocristid, preentocristid, and postmetacristid. A well-developed, long, and bulky external postprotocristid, starting from the apex of the protoconid, forms a deep 'Palaeomeryx fold' with the internal one. There is a quite distinct entostylid (inside ridge) sitting lingual on the developed entoconulid (on the toungeward side of the inside cusp). The preentoconulidcristid connects the posthypocristid and the entostylid. The back fossa (depression) of the molar is oblique. The selenodont and quite large hypoconulid forms the posterolabial corner of the molar. The ectostylid and the posterior ectostylid are very well developed. The anterior metastylid is weakly developed.is very strong. The prehypocristid nearly meets the connection between internal postprotocristid, preentocristid, and postmetacristid. A well-developed, long, and bulky external postprotocristid, starting from the apex of the protoconid, forms a deep 'Palaeomeryx fold' with the internal one. There is a quite distinct entostylid sitting lingual on the developed entoconulid. The preentoconulidcristid connects the posthypocristid and the entostylid. The back fossa of the mollar is oblique. The selenodont and quite large hypoconulid forms the posterolabial corner of the molar. The ectostylid and the posterior ectostylid are very well developed. The anterior cingulid is weakly developed.

Micromeryx. cf. primaevus: left third molar fromthe Ulan Tolgoi Miocene deposits in labial (10), occlusal (11), and lingual (12) views. Scale bar is 10 mm. (13) dental nomenclature of the lower molar: Ci, anterior cingulid; Ec, ectostylid; En, entoconid; End, entoconulid; Hy, hypoconid; Hyd, hypoconulid; Me, metaconid; Med, metastylid; PF, “Palaeomeryx fold”; Pr, protoconid. (14) dental nomenclature of the lower premolar: AC, anterior conid; AS, anterior stylid; MaC, mesolabial conid; Mic, mesolingual conid; PaC, posterolabial conid; PiC, posterolingual conid; PS, posterior stylid; TC, transverse cristid. Mennecart et al. (2019).

See also...

https://sciencythoughts.blogspot.com/2019/07/charging-bison-injures-nine-year-old.htmlhttps://sciencythoughts.blogspot.com/2019/06/muntiacus-gigas-new-specimen-of-giant.html
https://sciencythoughts.blogspot.com/2018/03/giraffe-tracks-from-late-pleistocene-of.htmlhttps://sciencythoughts.blogspot.com/2016/08/lightning-kills-323-reindeer-in.html
https://sciencythoughts.blogspot.com/2016/01/ammotragus-lervia-diet-of-barbary-sheep.htmlhttps://sciencythoughts.blogspot.com/2015/12/capreolus-constantini-roe-deer-from.html
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