Diatomys
Encyclopedia
Diatomys is a hystricomorphous sciurognathous rodent known from Miocene
deposits in China
, Japan
, Pakistan
, and Thailand
. The fossil range is from the late Early Miocene to the Middle Miocene (22.5-11 Ma).
series in Shandong
province, China, Jiangsu
province in China, Kyūshū
in Japan, the Siwaliks 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
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
and first molar
.
.
The dental formula for Diatomys is 1/1 I
, 0/0 C, 1/1 P
, 3/3 M
= 20. Incisors display multiserial enamel. Structure of the Hunter-Schreger bands is very similar to Laonastes. The root of the incisor is shortened. The cheek teeth are bilophodont, displaying two transverse ridges that are each slightly curved into a mild horseshoe
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
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
, arboreal, or saltatorial way of life. This has led researchers to assume Diatomys was terrestrial
.
(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
. The remaining diatomyid in their analysis, Fallomus, was determined to be more distant.
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
deposits in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, and Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
. 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: ShanwangShanwang
The Shanwang National Geology Park is located in central Shandong province, People's Republic of China, about from Linqu County. It has an area of about . The Park is well known for its fossil bearing diatomitic deposits, one of only a few such deposits in China...
series in Shandong
Shandong
' is a Province located on the eastern coast of the People's Republic of China. Shandong has played a major role in Chinese history from the beginning of Chinese civilization along the lower reaches of the Yellow River and served as a pivotal cultural and religious site for Taoism, Chinese...
province, China, Jiangsu
Jiangsu
' is a province of the People's Republic of China, located along the east coast of the country. The name comes from jiang, short for the city of Jiangning , and su, for the city of Suzhou. The abbreviation for this province is "苏" , the second character of its name...
province in China, Kyūshū
Kyushu
is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....
in Japan, the Siwaliks in northern Pakistan, and Li Basin in Lamphun Province
Lamphun Province
Lamphun is one of the northern provinces of Thailand. Neighboring provinces are Chiang Mai, Lampang and Tak.-Geography:Lamphun is located in the river valley of the Ping River, surrounded by mountain chains....
, 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
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
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
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
and first molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
.
Characteristics
Head and body was about 25 cm (9.8 in). The overall appearance of Diatomys was thought to be very similar to the extant Laotian Rock RatLaotian rock rat
The Laotian rock rat or kha-nyou , sometimes called the "rat-squirrel", is a rodent species of the Khammouan region of Laos. The species was first described in a 2005 article by Paulina Jenkins and coauthors, who considered the animal to be so distinct from all living rodents that they placed it...
.
The dental formula for Diatomys is 1/1 I
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
, 0/0 C, 1/1 P
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
, 3/3 M
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
= 20. Incisors display multiserial enamel. Structure of the Hunter-Schreger bands is very similar to Laonastes. The root of the incisor is shortened. The cheek teeth are bilophodont, displaying two transverse ridges that are each slightly curved into a mild horseshoe
Horseshoe
A horseshoe, is a fabricated product, normally made of metal, although sometimes made partially or wholly of modern synthetic materials, designed to protect a horse's hoof from wear and tear. Shoes are attached on the palmar surface of the hooves, usually nailed through the insensitive hoof wall...
shape. Cheek teeth have four roots on both the upper and lower jaws.
The infraorbital canal
Infraorbital canal
Not to be confused with the infraorbital groove and infraorbital foramen, which are on opposite ends of the canal.One of the canals of the orbital surface of the maxilla, the infraorbital canal, opens just below the margin of the orbit...
is enlarged, presumably allowing for the passage of the medial masseter muscle as with other hystricomorphs. The mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
is sciurognathous. As with other diatomyids, Diatomys has no coronoid process
Coronoid process
The Coronoid process can refer to:* The coronoid process of the mandible, part of the ramus mandibulae of the mandible...
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
Fossorial
A fossorial organism is one that is adapted to digging and life underground such as the badger, the naked mole rat, and the mole salamanders Ambystomatidae...
, arboreal, or saltatorial way of life. This has led researchers to assume Diatomys was terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
.
Relationship
Several authors have suggested that Diatomys might belong to the family PedetidaePedetidae
Pedetidae is a family of mammals from the rodent order. 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. Together with the anomalures, Pedetidae forms the suborder...
(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
Laotian rock rat
The Laotian rock rat or kha-nyou , sometimes called the "rat-squirrel", is a rodent species of the Khammouan region of Laos. The species was first described in a 2005 article by Paulina Jenkins and coauthors, who considered the animal to be so distinct from all living rodents that they placed it...
, a unique rodent first described in 2005 (Jenkins et al., 2004) from Khammouan, Laos
Laos
Laos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...
. The remaining diatomyid in their analysis, Fallomus, was determined to be more distant.