Extinct species of mammal
Tupaia miocenica is a fossil treeshrew from the Miocene of Thailand. Known only from a single tooth, an upper first or second molar, it is among the few known fossil treeshrews. With a length of 3.57 mm, the tooth is large for a treeshrew. At the back lingual corner (the side of the tongue), the tooth shows a small cusp, the hypocone, that is separated from the protocone in front of it by a narrow valley. The condition of the hypocone distinguishes this species from various other treeshrews. In addition, the presence of a well-developed but simple mesostyle (a small cuspule) is distinctive.
Taxonomy
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]
Description
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]
Range and ecology
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]
