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

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

deposits in

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...

, and

Thailand Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...

. The fossil range 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 is a coastal Provinces of China, province in East China. Shandong has played a major role in Chinese history since the beginning of Chinese civilization along the lower reaches of the Yellow River. It has served as a pivotal cultural ...

province, China,

Jiangsu Jiangsu is a coastal Provinces of the People's Republic of China, province in East China. It is one of the leading provinces in finance, education, technology, and tourism, with its capital in Nanjing. Jiangsu is the List of Chinese administra ...

province in China,

Kyūshū is the third-largest island of Japan's four main islands and the most southerly of the four largest islands (i.e. excluding Okinawa and the other Ryukyu (''Nansei'') Islands). In the past, it has been known as , and . The historical regio ...

in Japan, the

Siwaliks The Sivalik Hills, also known as Churia Hills, are a mountain range of the outer Himalayas. The literal translation of "Sivalik" is 'tresses of Shiva'. The hills are known for their numerous fossils, and are also home to the Soanian Middle Pale ...

in northern Pakistan, and Li Basin in Lamphun Province, 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, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

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 Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

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 Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

for ''Diatomys'' is . Incisors display multiserial enamel. The structure of the Hunter-Schreger bands is very similar to ''Laonastes''. The root of the incisor is shortened. The

cheek teeth Cheek teeth or postcanines 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 The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone toot ...

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

horseshoe A horseshoe is a 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 toenail, altho ...

shape. Cheek teeth have four roots on both the upper and lower jaws. The

infraorbital canal The infraorbital canal is a canal found at the base of the orbit that opens on to the maxilla. It is continuous with the infraorbital groove and opens onto the maxilla at the infraorbital foramen. The infraorbital nerve and infraorbital artery t ...

is enlarged, presumably allowing for the passage of the medial masseter muscle as with other hystricomorphs. The

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

is sciurognathous. As with other diatomyids, ''Diatomys'' has no coronoid process 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 that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...

, 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 ...

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

terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...

Relationship

Several authors have suggested that ''Diatomys'' might belong to the family

Pedetidae The Pedetidae are a family (biology), family of rodents. The two living species, the springhares, are distributed throughout much of Southern Africa and also around Kenya, Tanzania, and Uganda. Fossils have been found as far north as Turkey.McKen ...

(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, officially the Lao People's Democratic Republic (LPDR), is the only landlocked country in Southeast Asia. It is bordered by Myanmar and China to the northwest, Vietnam to the east, Cambodia to the southeast, and Thailand to the west and ...

. 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 Ctenodactylomorphi Extinct animals of Japan Fossils of China Miocene mammals of Asia Miocene rodents Prehistoric rodent genera Fossil taxa described in 1974 Fossils of Japan