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Laotian rats (Family Diatomyidae)

The family Diatomyidae contains hystricomorphous, sciurognathous rodents found in Asia. There is one living species, Laonastes aenigmamus. Before this animal was discovered, the family was known only from fossils ranging from Early Oligocene fossils of Fallomus in Pakistan, 32.5 million years ago in the Early Oligocene (32.5 Ma; [2] ) to Middle/Late Miocene fossils of Diatomys dating back to 11 milion years ago. (11 Ma) of Diatomys.

Jenkins et al. (3) reported the discovery of a new species of rodent, Laonastes aenigmamus, for which they created a new family, Laonastidae. They suggested it was a hystricognath rodent, basal to all other hystricognaths. Dawson et al. (4) used morphology and fossil taxa to determine that Laonastes is sciurognathous and belongs to the Diatomyidae. They described the Diatomyidae as a Lazarus taxon as there was an the 11 million year gap between the most recent fossil diatomyid and the existence of Laonastes today. Mary Dawson called Laonastes the "coelacanth of rodents" [1].

The Diatomyidae are similar to the Ctenodactylidae and the Anomaluromorpha in being hystricomorphous and sciurognathous. The enlarged masseteric fossa in diatomyids extends to below the first cheek tooth (p4). The enamel on incisors is multiserial (similar to the springhare, gundis and Hystricognathi). The single premolar on both toothrows is enlarged (unlike the reduced state in gundis). 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.

The Laotian rock rat occurs in the Khammouan region of Laos. Fossil diatomyids lived in Pakistan, India, Thailand, China, Japan, and Saudi-Arabia.

Phylogenetic analyses by Jenkins et al. (3) were inconclusive and contradictory. 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.

Analysis of mtDNA 12S rRNA and cytochrome b sequence suggested that Laonastes may be related to living African hystricognaths, such as the dassie rat and naked mole rat. Analysis on the cytochrome b sequence data produces the same result as morphology. Neither analysis showed entirely robust statistical support for the position of Laonastes within the hystricognaths; it seemed to belong among the basal African radiation.

Dawson et al. (4) refuted the idea that Laonastes is a hystricognath and argued that the mandible is sciurognathous. They evaluated Laonastes compared 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 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 (5) and McKenna and Bell (6) placed Diatomys in the Pedetidae). Flynn et al. (2) placed Fallomus in the extinct family Chapattimyidae. Mein and Ginsburg (7) erected the family Diatomyidae asa member of the superfamily Ctenodactyloidea. Marivaux et al. (8) united the two into one family (Diatomyidae), but also suggested that this family might be related to the Pedetidae.

The fossil study of Dawson et al. (4) was corroborated by the more comprehensive DNA sequence analyses of Huchon et al. (9), which suggested a roughly Lutetian, about 44 million years ago in the Early/Middle Eocene divergence date between the ancestors of the Laotian rock rat and the African gundis, which are each other's closest living relatives. The present-day distribution, fossil record and Eocene paleogeography indicate that this divergence probably occurred in one of three regions. The lineages may have split in Eurasia, somewhere in the Zagros Mountains or adjacent ranges of the Alpide belt, which formed a rugged and broken coastline with many offshore islands, as they emerged from the shrinking Tethys Sea. Alternatively, the entire Ctenodactyloidea may be of African origin or the lineage split took occurred on India as it joined the Asian mainland; the gundis reached Africa via the Mascarene Plateau's archipelagos and island continents. Each hypothesis would unite the paleontological, anatomical and molecular findings into a robust model and depends on whether the Hystricomorpha are considered Laurasian or Gondwanan in origin.

The family includes the following species: Fallomus razae, ginsburgi and quraishyi; Diatomys shantungensis and liensis; Marymus dalanae; Pierremus explorator and ladakhensis; Willmus maximus; Laotian rock rat (Laonastes aenigmamus)

  • 1. López-Antoñanzas, R. (2010). "First diatomyid rodent from the Early Miocene of Arabia". Naturwissenschaften 98 (2): 117–123. doi:10.1007/s00114-010-0745-0. PMID 21136247. http://www.springerlink.com/content/v6p7631775881671/fulltext.pdf.
  • 2. Flynn, L. J., L. L. Jacobs, and I. U. Cheema (1986). Baluchimyinae, a new ctenodactyloid subfamily from the Miocene of Baluchistan. American Museum Novitates, 2841:1-58.
  • 3. Jenkins, Paulina D.; C. William Kilpatrick; Mark F. Robinson and Robert 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(4): 419-454. doi:10.1017/S1477200004001549 (HTML abstract). Erratum: Systematics and Biodiversity 3(3):343. doi:10.1017/S1477200005001775
  • 4. 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.
  • 5. Mein, P. and L. Ginsburg (1985). Les rongeurs miocènes de Li (Thailande). Compte Rendus de l’Académie des Sciences, Paris, Série II, 301:1369-1374.
  • 6. McKenna, Malcolm C. and Susan K. Bell (1997) Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8
  • 7. 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.
  • 8. 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.
  • 9. Huchon, Dorothée; Pascale Chevret; Ursula Jordan; C. William Kilpatrick; Vincent Ranwez; Paulina D. Jenkins; Jürgen Brosius and Jürgen Schmitz (2007): Multiple molecular evidences for a living mammalian fossil. PNAS 104(18): 7495-7499. doi:10.1073/pnas.0701289104 (HTML abstract)
  • Flynn, L. J. and M. E. Morgan. 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, [2]
  • Flynn, Lawrence J. (2007): Origin and evolution of the Diatomyidae, with clues to paleoecology from the fossil record. Bulletin of Carnegie Museum of Natural History 39(1): 173-181. doi:10.2992%2F0145-9058(2007)39%5B173%3AOAEOTD%5D2.0.CO%3B2 (HTML abstract)
  • Marivaux, L. & J.-L. Welcomme (2003). New diatomyid and baluchimyine rodents from the Oligocene of Pakistan (Bugti Hills, Balochistan): Systematic and paleobiogeographic implications. Journal of Vertebrate Paleontology 23:420-434.
  • Marivaux, L. J. L. Welcomme, M. Vianey-Liaud, and J.J. Jaeger (2002). The role of Asia in the origin and diversification of hystricognathous rodents. Zoologica Scripta, 31:225-239.
  • Nanda, A.C. & A. Sahni (1998). Ctenodactyloid rodent assemblage from Kargil Formation, Ladakh molasses group: Age and paleobiogeographic implications for the Indian subcontinent in the Oligo-Miocene. Geobios 31:533-544.
  • Other references
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Wikipedia

Diatomyidae

The Diatomyidae family of hystricomorphous, sciurognathous rodents, found in Asia, is represented by a single known living species, Laonastes aenigmamus.

"Lazarus effect"[edit]

Prior to the discovery of Laonastes, the family Diatomyidae was known only from fossils. The family has a nearly continuous fossil range from Early Oligocene fossils of Fallomus from the Lower Chitarwata Formation (32.5 million years ago, Bugti Member, Bugti Hills,[1][2]) in Balochistan, Pakistan, to Middle/Late Miocene fossils (11 Mya) of Diatomys.

Jenkins et al.[3] reported the discovery of a wholly unique new species of rodent, Laonastes aenigmamus, for which they created a new family, Laonastidae. They suggested it was a hystricognath rodent, but basal to all other hystricognaths. Dawson, et al,[4] re-evaluated the phylogenetic position of Laonastes based on morphology and included fossil taxa in their analysis. They determined Laonastes is actually sciurognathous and belongs to the Diatomyidae. They also 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" [2].

Characteristics[edit]

The Diatomyidae are similar to both the Ctenodactylidae and the Anomaluromorpha in being simultaneously hystricomorphous and sciurognathous. The masseteric fossa in diatomyids is enlarged and extends to below the first cheek tooth. The enamel on incisors is multiserial (similar to the springhare, gundis, and Hystricognathi). The single premolar on both the upper and lower tooth rows is enlarged (unlike the reduced state in Ctenodactylidae). Most diatomyids have cheek teeth with four roots except for the first. 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.

Relationship to other rodents[edit]

The uniqueness of the Laotian rock rat was clear upon its initial discovery. The results of the phylogenetic analyses[3] were somewhat inconclusive and contradictory. Both morphological and molecular studies suggested Laonastes is a member of the rodent suborder Hystricognathi. The morphological analysis suggested 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 Laonastes might be related to living African hystricognaths such as the Dassie rat and the naked mole rat. Another type of analysis on the cytochrome b sequence data produced 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.[4] also 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 it is closely related to the diatomyids, particularly Diatomys. Their results suggested the Diatomyidae are a sister group to the Ctenodactylidae, and this diatomyid/ctenodactylid clade (along with the Yuomyidae) is sister to the Hystricognathi.

Besides Laonastes, other diatomyids have also been placed in different families. Some [5][6] placed Diatomys in the Pedetidae (springhare) family. Others[7] considered Fallomus to belong to the Chapattimyidae (a completely fossil group). The family Diatomyidae was erected and considered to be a member of the superfamily Ctenodactyloidea.[5] Marivaux et al.[8] united the two into a single family (Diatomyidae), but also suggested this family might be related to the Pedetidae.

Dawson's fossil study[4] was corroborated by more comprehensive DNA sequence analyses,[9] which suggested a roughly Lutetian (about 44 Mya, Early/Middle Eocene) divergence date between the ancestors of the Laotian rock rat and the African gundis, 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.[10] Alternatively, the entire Ctenodactyloidea might be of African origin, or the lineage split took place on India as is joined the Asian mainland, with the gundis reaching Africa via the Mascarene Plateau's archipelagos and island continents.[11] 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 Laurasian or Gondwanan in origin.

Species[edit]

References[edit]

  1. ^ Marivaux, L. & Welcomme, J.-L. 2003. New diatomyid and baluchimyine rodents from the Oligocene of Pakistan (Bugti Hills, Balochistan): Systematic and paleobiogeographic implications. Journal of Vertebrate Paleontology 23:420-434.
  2. ^ Flynn, L. J., L. L. Jacobs, and I. U. Cheema. 1986. Baluchimyinae, a new ctenodactyloid subfamily from the Miocene of Baluchistan. American Museum Novitates, 2841:1-58.
  3. ^ a b Jenkins, Paulina D.; Kilpatrick, C. William; Robinson, Mark F. & Timmins, Robert J. (2004): Morphological and molecular investigations of a new family, genus and species of rodent (Mammalia: Rodentia: Hystricognatha) from Lao PDR. Systematics and Biodiversity 2(4): 419-454. doi:10.1017/S1477200004001549 (HTML abstract). Erratum: Systematics and Biodiversity 3(3):343. doi:10.1017/S1477200005001775
  4. ^ a b c 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.
  5. ^ a b 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.
  6. ^ McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8
  7. ^ Flynn, L. J. and M. E. Morgan. 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, [1]
  8. ^ 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.
  9. ^ Huchon, Dorothée; Chevret, Pascale; Jordan, Ursula; Kilpatrick, C. William; Ranwez, Vincent; Jenkins, Paulina D.; Brosius, Jürgen & Schmitz, Jürgen (2007): Multiple molecular evidences for a living mammalian fossil. PNAS 104(18): 7495-7499. doi:10.1073/pnas.0701289104 (HTML abstract)
  10. ^ Marivaux, L. J. L. Welcomme, M. Vianey-Liaud, and J.J. Jaeger. 2002. The role of Asia in the origin and diversification of hystricognathous rodents. Zoologica Scripta, 31:225-239.
  11. ^ Nanda, A.C. & Sahni, A. (1998). Ctenodactyloid rodent assemblage from Kargil Formation, Ladakh molasses group: Age and paleobiogeographic implications for the Indian subcontinent in the Oligo-Miocene. Geobios 31:533-544.
  12. ^ López-Antoñanzas, R. (2010). "First diatomyid rodent from the Early Miocene of Arabia". Naturwissenschaften 98 (2): 117–123. doi:10.1007/s00114-010-0745-0. PMID 21136247. 
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