Laotian rock rat Laonastes aenigmanus, a relictual member of the Hystricomorpha from south-east Asia. Photo from here.

Belongs within: Rodentia.
Contains: Ctenodactyloidea, Hystricognathiformes.

The name Hystricomorpha has been used for a supposed clade of rodents characterised by a large infraorbital foramen, allowing for the passage of the M. masseter medialis, as well as a tendency to develop a complete hypolophid and anterior displacement of the entoconid on the lower molars (Jaeger 1988). However, it is uncertain whether rodents showing this feature form a monophyletic clade, and it has possibly evolved more than once. Early myomorphs, in particular, had a hystricomorph-like infraorbital foramen (Jaeger 1988). The molecular analysis of mammals by Meredith et al. (2011) supports a clade of Ctenodactylidae, Diatomyidae and Hystricognathi, but places the 'hystricomorph' Anomaluromorpha elsewhere among the rodents.

The Diatomyidae are a family of rodents originally described as fossils from the early Oligocene to late Miocene. However, the Laotian rock rat Laonastes aenigmanus, only described in 2005, has subsequently been identified as a living member of the Diatomyidae (Naish 2010).

<==Hystricomorpha [Ctenohystrica]
    |--+--Yuomys [Yuomyidae] MJ11
    |  `--+--+--Tataromys MJ11
    |     |  `--Protataromys MJ11
    |     `--+--Ctenodactyloidea MJ11
    |        `--Diatomyidae MJ11
    |             |--Diatomys J88
    |             |--Laonastes [Laonastidae] N10
    |             |    `--L. aenigmanus MJ11
    |             `--Fallomus MJ11
    `--+--Chapattimyidae J88
       `--+--Hystricognathiformes MJ11
          `--Downsimys [Baluchimyinae] J88

*Type species of generic name indicated


[J88] Jaeger, J.-J. 1988. Rodent phylogeny: new data and old problems. In The Phylogeny and Classification of the Tetrapods, vol. 2. Mammals (M. J. Benton, ed.) pp. 177-199. Clarendon Press: Oxford.

[MJ11] Meredith, R. W., J. E. Janečka, J. Gatesy, O. A. Ryder, C. A. Fisher, E. C. Teeling, A. Goodbla, E. Eizirik, T. L. L. Simão, T. Stadler, D. L. Rabosky, R. L. Honeycutt, J. J. Flynn, C. M. Ingram, C. Steiner, T. L. Williams, T. J. Robinson, A. Burk-Herrick, M. Westerman, N. A. Ayoub, M. S. Springer & W. J. Murphy. 2011. Impacts of the Cretaceous terrestrial revolution and KPg extinction on mammal diversification. Science 334: 521-524.

[N10] Naish, D. 2010. Tetrapod Zoology: Book One. CFZ Press: Bideford (UK).

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