Tupaia miocenica

Tupaia miocenica was described in 1997 by French paleontologists Pierre Mein and Léonard Ginsburg in a report on the fossil mammals of Li Mae Long, a Miocene site in Thailand.[1] The animal is known from a single tooth, which according to Mein and Ginsburg's comparisons most closely resembles the living treeshrews of the genus Tupaia.[2] The specific name, miocenica, refers to the animal's occurrence during the Miocene.[1] Only a few other fossil treeshrews are known, and T. miocenica is the only fossil species from Thailand.[3] When it was described, it was the only Miocene representative of Tupaia,[1] but a second species, Tupaia storchi, was named from the Late Miocene of Lufeng, China, in 2012.[4]

The single known tooth, a worn left upper molar known as T Li 175, is large for a treeshrew, with a length of 3.57 mm and width of 4.79 mm.[1] Although Mein and Ginsburg described it a second upper molar (M2), Ni and Qiu argued in 2012 that it is more likely a first upper molar (M1).[5] It is dilambdodont (with a W-shaped chewing surface) and the labial surface (the side of the cheeks) is concave and bears a cingular crest. A well-developed small cusp, a mesostyle, is present on the labial side. The presence of the mesostyle distinguishes the animal from Ptilocercus,[1] the only member of the treeshrew family Ptilocercidae.[6] The lingual (tongue) side is narrow. A large cusp, the protocone, is on the front lingual corner. Two crests descend from it; one reaches the paracone on the front labial side and another approaches the metacone to the back of the tooth. A smaller cusp, a hypocone, is on the back lingual corner. This feature distinguishes T. miocenica both from the treeshrew genera Dendrogale, Prodendrogale, and Palaeotupaia, which lack the cusp entirely, and from Anathana and Urogale, which have a large hypocone. In T. miocenica the back and lingual sides of the hypocone are straight and form a right angle with each other.[1] The tooth most closely resembles Tupaia species with a simple mesostyle, such as the common treeshrew (Tupaia glis). However, this species is smaller and unlike in T. miocenica, the hypocone is not isolated from the protocone by a narrow valley.[2]

Li Mae Long, the collection site of T. miocenica, is dated to the latest Early Miocene, corresponding to the European zone MN 4,[1] around 18 mya.[7] It is in the Thai province of Lamphun.[1] The fossil fauna encompasses 34 species of mammals,[8] including the tarsier Hesperotarsius thailandicus, the rodent Diatomys liensis, the slow loris ? Nycticebus linglom, and the metatherian Siamoperadectes. Mein and Ginsburg conclude that the fauna represents a tropical forest environment close to a shallow lake.[9]

• Helgen, K.M. 2005. Order Scandentia. Pp. 104–109 in Wilson, D.E. and Reeder, D.M. (eds.). Mammal Species of the World: a taxonomic and geographic reference. 3rd ed. Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. ISBN 978-0-8018-8221-0
• Mein, P. and Ginsburg, L. 1997. Les mammifères du gisement miocène inférieur de Li Mae Long, Thaïlande : systématique, biostratigraphie et paléoenvironnement. Geodiversitas 19(4):783–844 (in French). Abstract in French and English.
• Ni, X. and Qiu, Z. 2012. Tupaiine tree shrews (Scandentia, Mammalia) from the Yuanmou Lufengpithecus locality of Yunnan, China (subscription required). Swiss Journal of Palaeontology 131(1):51–60.
• Sargis, E.J. 2004. New views on tree shrews: The role of Tupaiids in primate supraordinal relationships (subscription required). Evolutionary Anthropology: Issues, News, and Reviews 13(2):56–66.