Multiple molecular evidences for a living mammalian fossil

Abstract

Laonastes aenigmamus is an enigmatic rodent first described in 2005. Molecular and morphological data suggested that it is the sole representative of a new mammalian family, the Laonastidae, and a member of the Hystricognathi. However, the validity of this family is controversial because fossil-based phylogenetic analyses suggest that Laonastes is a surviving member of the Diatomyidae, a family considered to have been extinct for 11 million years. According to these data, Laonastes and Diatomyidae are the sister clade of extant Ctenodactylidae (i.e., gundies) and do not belong to the Hystricognathi. To solve the phylogenetic position of Laonastes, we conducted a large-scale molecular phylogeny of rodents. The analysis includes representatives of all major rodent taxonomic groups and was based on 5.5 kb of sequence data from four nuclear and two mitochondrial genes. To further validate the obtained results, a short interspersed element insertion analysis including 11 informative loci was also performed. Our molecular data based on sequence and short interspersed element analyses unambiguously placed Laonastes as a sister clade of gundies. All alternative hypotheses were significantly rejected based on ShimodairaHasegawa tests, supporting the idea that Laonastes does not belong to the Hystricognathi. Molecular dating analysis also supports an ancient divergence, Ϸ44 Mya ago, between Ctenodactylidae and Laonastes. These combined analyses support the hypothesis that Laonastes is indeed a living fossil. Protection of this surviving species would conserve an ancient mammalian family.Laonastes aenigmamus ͉ molecular phylogeny ͉ rodent ͉ retroposons

Fossil and molecular evidence constrain scenarios for the early evolutionary and biogeographic history of hystricognathous rodents

“…S3, Fig. 4) are about 15% younger that those presented in a recent analysis (19), but are remarkably congruent with the fossil record. The divergence of Caviomorpha and Phiomorpha is estimated to have occurred at 36.1 Ma (95% credibility interval 33.4-39.0 Ma), very close to Opazo's (22) previously published estimate of 36.6 Ϯ 2.5 Ma.…”

“…This hypothesis is further supported by the lack of morphological diversity observable among the hystricognathous rodents represented at BQ-2. This scenario is clearly not consistent with molecular estimates for the time of origin of crown Hystricognathi that range in age from Ϸ85 to Ϸ43 Ma (9,18,19,23,34). The temporal and phylogenetic evidence provided by these fossil discoveries, combined with younger molecular estimates for basal divergences within crown Hystricognathi, suggests that the key events determining the distribution of Oligocene-to-Recent hystricognathous rodents occurred between Ϸ40 and Ϸ34 million years ago.…”

“…Some have argued that phiomorphs and caviomorphs are likely to have shared a common Afro-Arabian ancestor (15)(16)(17), while others have suggested that the phiomorph-caviomorph split might have occurred in Asia, and that caviomorphs dispersed to South America either through Afro-Arabia or via a southern Gondwanan route (13,18). One critical issue that has hindered understanding of the group's historical biogeography is the phylogenetic position of the family Hystricidae, which has been placed as either the sister group of a phiomorph-caviomorph clade or as the sister group of Caviomorpha, in recent molecular phylogenetic analyses (9,(19)(20)(21). Temporal and tectonic constraints on competing biogeographic hypotheses have also been limited by radically different molecular estimates of the phiomorph-caviomorph split, which range in age from Ϸ85 Ma to Ϸ36 Ma (9,18,19,22,23).…”

“…One critical issue that has hindered understanding of the group's historical biogeography is the phylogenetic position of the family Hystricidae, which has been placed as either the sister group of a phiomorph-caviomorph clade or as the sister group of Caviomorpha, in recent molecular phylogenetic analyses (9,(19)(20)(21). Temporal and tectonic constraints on competing biogeographic hypotheses have also been limited by radically different molecular estimates of the phiomorph-caviomorph split, which range in age from Ϸ85 Ma to Ϸ36 Ma (9,18,19,22,23).…”

Mosaic retroposon insertion patterns in placental mammals

“…In strong contrast to most of the mammalian branches that we and others investigated previously with this method (e.g., Nishihara et al 2005Nishihara et al , 2006Huchon et al 2007;Möller-Krull et al 2007;Xing et al 2007;Warren et al 2008), we found a rare example of virtually equal support for three competing hypotheses ( Fig. 2B; Supplemental Table S1; .…”