Diatomyidae
Encyclopedia
Diatomyidae is a family of hystricomorphous, sciurognathous rodent
s found in Asia
. It is currently represented by a single known living species, Laonastes aenigmamus.
s. The family has a nearly continuous fossil
range from Early Oligocene
fossils of Fallomus from Lower Chitarwata Formation (32.5 Ma; Bugti Member, Bugti Hills
; Flynn et al., 1986) in Balochistan
, Pakistan
to Middle/Late Miocene
fossils (11 Ma) of Diatomys
.
Jenkins et al. (2004) reported the discovery of a wholly unique new species of rodent, Laonastes aenigmamus, for which they created a new family, Laonastidae. They suggested that it was a hystricognath
rodent, but basal
to all other hystricognaths. Dawson et al. (2006) re-evaluated the phylogenetic position
of Laonastes based on morphology
and included fossil taxa in their analysis. They determined that Laonastes is actually sciurognathous and that it belongs to the Diatomyidae.
Dawson et al. (2006) described the Diatomyidae as a Lazarus taxon
due to the 11 million year gap between the most recent diatomyid in the fossil record and the existence of Laonastes today. The only other comparable length of time for a mammal Lazarus taxon is the Monito del Monte
, which is part of a family (Microbiotheriidae) also most recently known from Miocene deposits. Mary Dawson described Laonastes as the "coelacanth
of rodents" http://msnbc.msn.com/id/11746910/.
in being simultaneously hystricomorphous and sciurognathous. The masseteric fossa in diatomyids is enlarged and extends to below the first cheek tooth (p4). The enamel
on incisor
s is multiserial (similar to the springhare
, Ctenodactylidae (gundis), and Hystricognathi
). The single premolar
on both the upper and lower toothrows is enlarged (unlike the reduced state in Ctenodactylidae). Most diatomyids have cheek teeth with four roots except for p4. In Laonastes, the lower molars have four roots, but upper cheek teeth have three roots including a U-shaped anterior root that may be derived from the merging of two roots.
Living diatomyids are only represented by the Laotian Rock Rat from the Khammouan region of Laos
. Fossil diatomyids have been recovered in Pakistan
, India
, Thailand
, China
, Japan
, and Saudi-Arabia.
was clear upon its initial discovery. The results of the phylogenetic analyses performed by Jenkins et al. (2004) were somewhat inconclusive and contradictory. Both morphological
and molecular studies suggested Laonastes is a member of the rodent suborder Hystricognathi
. The morphological analysis suggested that it is the most basal hystricognath. Fossil taxa were not included in the morphological analysis.
Analysis of mtDNA 12S rRNA and cytochrome b
sequence
, however, suggested that Laonastes might be related to such living African hystricognaths such as the Dassie Rat
and the Naked Mole Rat
. Another type of analysis on the cytochrome b sequence data produces the same result as morphology. Neither analysis, however, showed entirely robust statistical support for the position of Laonastes within the hystricognaths; altogether, it appeared to belong among the basal African radiation.
Dawson et al. (2006) refuted the notion that Laonastes is a hystricognath and instead argued that the mandible
is sciurognathous. They evaluated Laonastes in comparison to several fossil rodents and determined that it is closely related to the diatomyids, particularly Diatomys. Their results suggested that the Diatomyidae are a sister group to the Ctenodactylidae, and that this diatomyid/ctenodactylid clade (along with the Yuomyidae) is sister to the Hystricognathi.
Besides Laonastes, other diatomyids have also been placed in different families. Mein and Ginsburg (1986) and McKenna and Bell (1997) placed Diatomys in the Pedetidae
(the springhare family). Flynn et al. (1986) considered Fallomus to belong to the Chapattimyidae (a completely fossil group). Mein and Ginsburg (1997) erected the family Diatomyidae and considered it to be a member of the superfamily Ctenodactyloidea. Marivaux et al. (2004) united the two into a single family (Diatomyidae), but also suggested that this family might be related to the Pedetidae.
The fossil study of Dawson et al. was corroborated by the more comprehensive DNA sequence analyses of Huchon et al. (2007), which suggested a roughly Lutetian
(c.44 mya, Early/Middle Eocene
) divergence date between the ancestors of the Laotian Rock Rat and the African gundi
s (Ctenodactylidae), which are each other's closest living relatives. Considering the present-day distribution, the fossil record, and Eocene paleogeography, this divergence probably took place in one of three regions. Either the lineages split in Eurasia, somewhere in today's Zagros Mountains
or adjacent ranges of the Alpide belt
. These at that time formed a rugged and broken coastline with many offshore islands, as they emerged from the shrinking Tethys Sea. Alternatively, the entire Ctenodactyloidea might be of African origin, or the lineage split took place on India
as is joined the Asian mainland, the gundis reaching Africa via the Mascarene Plateau
's archipelagos and island continents. Each hypothesis would unite the paleontological, anatomical and molecular findings into a robust model. Which one is preferred depends on whether the Hystricomorpha
are considered Laurasia
n or Gondwana
n in origin.
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s found in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
. It is currently represented by a single known living species, Laonastes aenigmamus.
"Lazarus effect"
Prior to the discovery of Laonastes, the family Diatomyidae was known only from fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s. The family has a nearly continuous fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
range from Early Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
fossils of Fallomus from Lower Chitarwata Formation (32.5 Ma; Bugti Member, Bugti Hills
Bugti Hills
Bugti Hills are a range of hills in eastern Balochistan, Pakistan. It includes the tribal tract called Bugti country.30 million years ago the Haplorrhinies: Bugtipithecus inexpectans, Phileosimias kamali and Phileosimias brahuiorum, similar to today's lemurs, lived in rainforests on the Bugti...
; Flynn et al., 1986) in Balochistan
Balochistan (Pakistan)
Balochistan is one of the four provinces or federating units of Pakistan. With an area of 134,051 mi2 or , it is the largest province of Pakistan, constituting approximately 44% of the total land mass of Pakistan. According to the 1998 population census, Balochistan had a population of...
, 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...
to Middle/Late Miocene
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...
fossils (11 Ma) of Diatomys
Diatomys
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 .- Specimens :...
.
Jenkins et al. (2004) reported the discovery of a wholly unique new species of rodent, Laonastes aenigmamus, for which they created a new family, Laonastidae. They suggested that it was a hystricognath
Hystricognathi
Hystricognathi is an infraorder of rodents. Hystricognaths are distinguished from other rodents by the bone structure of their skulls. The masseter medialis passes partially through the infraorbital foramen and connects to the bone on the opposite side...
rodent, but basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
to all other hystricognaths. Dawson et al. (2006) re-evaluated the phylogenetic position
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
of Laonastes based on morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and included fossil taxa in their analysis. They determined that Laonastes is actually sciurognathous and that it belongs to the Diatomyidae.
Dawson et al. (2006) described the Diatomyidae as a Lazarus taxon
Lazarus taxon
In paleontology, a Lazarus taxon is a taxon that disappears from one or more periods of the fossil record, only to appear again later. The term refers to the account in the Gospel of John, in which Jesus raised Lazarus from the dead...
due to the 11 million year gap between the most recent diatomyid in the fossil record and the existence of Laonastes today. The only other comparable length of time for a mammal Lazarus taxon is the Monito del Monte
Monito del Monte
The Monito del Monte The Monito del Monte The Monito del Monte (Spanish for "little mountain monkey", Dromiciops gliroides, is a diminutive marsupial native only to southwestern South America (Chile and Argentina). It is the only extant species in the ancient order Microbiotheria, and the sole New...
, which is part of a family (Microbiotheriidae) also most recently known from Miocene deposits. Mary Dawson described Laonastes as the "coelacanth
Coelacanth
Coelacanths are members of an order of fish that includes the oldest living lineage of Sarcopterygii known to date....
of rodents" http://msnbc.msn.com/id/11746910/.
Characteristics
The Diatomyidae are similar to both the Ctenodactylidae and the AnomaluromorphaAnomaluromorpha
Anomaluromorpha is the name given to a clade that unites the anomalures with the springhare. It has alternately been designated as either a suborder or infraorder...
in being simultaneously hystricomorphous and sciurognathous. The masseteric fossa in diatomyids is enlarged and extends to below the first cheek tooth (p4). The enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
on incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s is multiserial (similar to the springhare
Springhare
The springhare , or springhaas, is not actually a hare, but a member of the order Rodentia. It is one of a number of species in the genus Pedetes, and is native to southern Africa. Synonyms are P. caffer or P...
, Ctenodactylidae (gundis), and Hystricognathi
Hystricognathi
Hystricognathi is an infraorder of rodents. Hystricognaths are distinguished from other rodents by the bone structure of their skulls. The masseter medialis passes partially through the infraorbital foramen and connects to the bone on the opposite side...
). The single 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...
on both the upper and lower toothrows is enlarged (unlike the reduced state in Ctenodactylidae). Most diatomyids have cheek teeth with four roots except for p4. In Laonastes, the lower molars have four roots, but upper cheek teeth have three roots including a U-shaped anterior root that may be derived from the merging of two roots.
Living diatomyids are only represented by the Laotian Rock Rat from the Khammouan region of 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...
. Fossil diatomyids have been recovered in 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...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, 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...
, 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...
, and Saudi-Arabia.
Relationship to other rodents
The uniqueness of the 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...
was clear upon its initial discovery. The results of the phylogenetic analyses performed by Jenkins et al. (2004) were somewhat inconclusive and contradictory. Both morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and molecular studies suggested Laonastes is a member of the rodent suborder Hystricognathi
Hystricognathi
Hystricognathi is an infraorder of rodents. Hystricognaths are distinguished from other rodents by the bone structure of their skulls. The masseter medialis passes partially through the infraorbital foramen and connects to the bone on the opposite side...
. The morphological analysis suggested that it is the most basal hystricognath. Fossil taxa were not included in the morphological analysis.
Analysis of mtDNA 12S rRNA and cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
, however, suggested that Laonastes might be related to such living African hystricognaths such as the Dassie Rat
Dassie Rat
The dassie rat, Petromus typicus, is an African rodent found among rocky outcroppings. It is the only living member of its genus, Petromus, and family, Petromuridae. The name "dassie" means "hyrax" in Afrikaans, and the two animals are found in similar habitats...
and the Naked Mole Rat
Naked Mole Rat
The naked mole rat , also known as the sand puppy or desert mole rat, is a burrowing rodent native to parts of East Africa and the only species currently classified in the genus Heterocephalus...
. Another type of analysis on the cytochrome b sequence data produces the same result as morphology. Neither analysis, however, showed entirely robust statistical support for the position of Laonastes within the hystricognaths; altogether, it appeared to belong among the basal African radiation.
Dawson et al. (2006) refuted the notion that Laonastes is a hystricognath and instead argued that the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
is sciurognathous. They evaluated Laonastes in comparison to several fossil rodents and determined that it is closely related to the diatomyids, particularly Diatomys. Their results suggested that the Diatomyidae are a sister group to the Ctenodactylidae, and that this diatomyid/ctenodactylid clade (along with the Yuomyidae) is sister to the Hystricognathi.
Besides Laonastes, other diatomyids have also been placed in different families. Mein and Ginsburg (1986) and McKenna and Bell (1997) placed Diatomys in the Pedetidae
Pedetidae
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...
(the springhare family). Flynn et al. (1986) considered Fallomus to belong to the Chapattimyidae (a completely fossil group). Mein and Ginsburg (1997) erected the family Diatomyidae and considered it to be a member of the superfamily Ctenodactyloidea. Marivaux et al. (2004) united the two into a single family (Diatomyidae), but also suggested that this family might be related to the Pedetidae.
The fossil study of Dawson et al. was corroborated by the more comprehensive DNA sequence analyses of Huchon et al. (2007), which suggested a roughly Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...
(c.44 mya, Early/Middle Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
) divergence date between the ancestors of the Laotian Rock Rat and the African gundi
Gundi
Gundis are a group of small, stocky rodents found in Africa. They live in rocky deserts across the northern parts of the continent. The family comprises 4 living genera and 5 species , as well as numerous extinct genera and species...
s (Ctenodactylidae), which are each other's closest living relatives. Considering the present-day distribution, the fossil record, and Eocene paleogeography, this divergence probably took place in one of three regions. Either the lineages split in Eurasia, somewhere in today's Zagros Mountains
Zagros Mountains
The Zagros Mountains are the largest mountain range in Iran and Iraq. With a total length of 1,500 km , from northwestern Iran, and roughly correlating with Iran's western border, the Zagros range spans the whole length of the western and southwestern Iranian plateau and ends at the Strait of...
or adjacent ranges of the Alpide belt
Alpide belt
The Alpide belt is a mountain range which extends along the southern margin of Eurasia. Stretching from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic, it includes the Alps, the Carpathians, the mountains of Asia Minor and Iran, the Hindu Kush, the Himalayas,...
. These at that time formed a rugged and broken coastline with many offshore islands, as they emerged from the shrinking Tethys Sea. Alternatively, the entire Ctenodactyloidea might be of African origin, or the lineage split took place on India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
as is joined the Asian mainland, the gundis reaching Africa via the Mascarene Plateau
Mascarene Plateau
The Mascarene Plateau is an submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately 2000 km, from the Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km² of shallow water, with depths ranging from...
's archipelagos and island continents. Each hypothesis would unite the paleontological, anatomical and molecular findings into a robust model. Which one is preferred depends on whether the Hystricomorpha
Hystricomorpha
The term Hystricomorpha has had many definitions throughout its history. In the broadest sense it refers to any rodent with a hystricomorphous zygomasseteric system. This includes the Hystricognathi, Ctenodactylidae, Anomaluridae, and Pedetidae...
are considered Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n or Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n in origin.
Species
- †Fallomus
- †Fallomus razae
- †Fallomus ginsburgi
- †Fallomus quraishyi
- †DiatomysDiatomysDiatomys 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 .- Specimens :...
- †Diatomys shantungensis
- †Diatomys liensis
- †Marymus
- †Marymus dalanae
- †Pierremus
- †Pierremus explorator
- †Pierremus ladakhensis
- †Willmus
- †Willmus maximus
- Laonastes
- Laonastes aenigmamus - Laotian Rock Rat