''Diatomys'' is an extinct rodent genus known from

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

deposits in

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...

, and

Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...

. The

fossil range A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

is from the late Early Miocene to the Middle Miocene (22.5–11 Ma).

Specimens

Specifically the strata and regions from which ''Diatomys'' has been collected are: Shanwang series in

Shandong Shandong ( , ; ; alternately romanized as Shantung) is a coastal province of the People's Republic of China and is part of the East China region. Shandong has played a major role in Chinese history since the beginning of Chinese civilizati ...

province, China,

Jiangsu Jiangsu (; ; pinyin: Jiāngsū, Postal romanization, alternatively romanized as Kiangsu or Chiangsu) is an Eastern China, eastern coastal Provinces of the People's Republic of China, province of the China, People's Republic of China. It is o ...

province in China,

Kyūshū is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surround ...

in Japan, the

Siwaliks The Sivalik Hills, also known as the Shivalik Hills and Churia Hills, are a mountain range of the outer Himalayas that stretches over about from the Indus River eastwards close to the Brahmaputra River, spanning the northern parts of the Indian ...

in northern Pakistan, and Li Basin in

Lamphun Province Lamphun ( th, ลำพูน, ; Northern Thai: ) is one of Thailand's seventy-six provinces (''changwat''), lies in upper northern Thailand. Neighboring provinces are (from north clockwise) Chiang Mai, Lampang, and Tak. Geography Lamphun is ...

, Thailand. Li (1974) described ''Diatomys shantungensis'' on the basis of two moderately complete specimens from Shandong. This material had good preservation of dental characters, but much of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

was difficult to interpret due to flattening. Dawson ''et al.'' (2006) reported the finding of another ''D. shantungensis'' fossil from Shandong that showed much improved preservation of cranial and skeletal characters. Impressions of hair and whiskers were observable in the specimen. Mein and Ginsburg (1985) described ''Diatomys liensis'' from Thailand, and considered it distinct enough to warrant recognition as separate from ''D. shantungensis''. ''D. liensis'' was found to be smaller overall, with a higher molar crown height and distinctions in cusp morphology in the

premolar The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...

and first molar.

Characteristics

Head and body was about . The overall appearance of ''Diatomys'' was thought to be very similar to the extant

Laotian rock rat The Laotian rock rat or ''kha-nyou'' (''Laonastes aenigmamus'', Lao: ຂະຍຸ), sometimes called the "rat-squirrel", is a species of rodent found in the Khammouan region of Laos. The species was first described in a 2005 article by Paulina ...

. The dental formula for ''Diatomys'' is . Incisors display multiserial enamel. The structure of the

Hunter-Schreger bands Hunter-Schreger bands, commonly abbreviated as HSB, are features of the enamel of the teeth in mammals, mostly placentals.Line and Bergqvist, 2005, p. 924 In HSB, enamel prisms are arranged in layers of varying thickness at about right angles ...

is very similar to ''Laonastes''. The root of the incisor is shortened. The

cheek teeth Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and ...

are bilophodont, displaying two transverse ridges that are each slightly curved into a mild

horseshoe A horseshoe is a fabricated product designed to protect a horse hoof from wear. Shoes are attached on the palmar surface (ground side) of the hooves, usually nailed through the insensitive hoof wall that is anatomically akin to the human toen ...

shape. Cheek teeth have four roots on both the upper and lower jaws. The infraorbital canal is enlarged, presumably allowing for the passage of the medial masseter muscle as with other hystricomorphs. The

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

is sciurognathous. As with other diatomyids, ''Diatomys'' has no

coronoid process The Coronoid process (from Greek , "like a crown") can refer to: * The coronoid process of the mandible, part of the ramus mandibulae of the mandible * The coronoid process of the ulna The coronoid process of the ulna is a triangular process proj ...

and the masseteric fossa extends far forward to below the fourth premolar. The postcranial skeleton does not appear to have any unique specializations that might be associated with a

fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric eviden ...

, arboreal, or

saltatorial This glossary of entomology describes terms used in the formal study of insect species by entomologists. A–C A synthetic chlorinated hydrocarbon insecticide, toxic to vertebrates. Though i ...

way of life. This has led researchers to assume ''Diatomys'' was terrestrial.

Relationship

Several authors have suggested that ''Diatomys'' might belong to the family Pedetidae (McKenna and Bell, 1997) or be related to the pedetids (Mein and Ginsburg, 1997; Marivaux ''et al.'', 2004). Li (1974) also noted the possibility that it was related to geomyoids based on the bilophodont tooth. Dawson ''et al.'' (2006) determined that the closest known relative of ''Diatomys'' is the extant Laotian rock rat, a unique rodent first described in 2005 (Jenkins ''et al.'', 2004) from Khammouan,

Laos Laos (, ''Lāo'' )), officially the Lao People's Democratic Republic ( Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, French: République démocratique populaire lao), is a socialist ...

. The remaining diatomyid in their analysis, '' Fallomus'', was determined to be more distant.

References

*Dawson, M. R., L. Marivaux, C.-k. Li, K. C. Beard, and G. Métais. 2006. ''Laonastes'' and the "Lazarus effect" in Recent mammals. Science, 311:1456–1458. *Flynn, L. J. and M. E. 2005. An Unusual Diatomyid Rodent from an Infrequently Sampled Late Miocene Interval in the Siwaliks of Pakistan, Palaeontologia Electronica Vol. 8, Issue 1; 17A:10p, *Jenkins, P. D., C. W. Kilpatrick, M. F. Robinson, and R. J. Timmins. 2004. Morphological and molecular investigations of a new family, genus and species of rodent (Mammalia: Rodentia: Hystricognatha) from Lao PDR. Systematics and Biodiversity, 2:419–454. *Li, C.-k. 1974. Vert. PalAsiatica, 12:43. *Marivaux, L., M. Vianey-Liaud, and J.-J. Jaeger. 2004. High-level phylogeny of early Tertiary rodents: dental evidence. Zoological Journal of the Linnean Society, 142:105–134. *McKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York, 631 pp. *Mein, P. and L. Ginsburg, L. 1985. Les rongeurs miocènes de Li (Thailande). Compte Rendus de l’Académie des Sciences, Paris, Série II, 301:1369–1374. *Mein, P. and L. Ginsburg. 1997. – Les mammifères du gisement miocène inférieur de Li Mae Long, Thaïlande : systématique, biostratigraphie et paléoenvironnement. Geodiversitas 19 (4) : 783–844. {{Taxonbar, from=Q905010 Extinct animals of Japan Fossils of China Miocene mammals of Asia Miocene rodents Prehistoric monotypic mammal genera Prehistoric rodent genera Fossil taxa described in 1974 Fossils of Japan