The role of Asia in the origin and diversification of hystricognathous rodents

Abstract

In the absence of a comprehensive pre‐Oligocene fossil record, the origin and early evolution of hystricognathous rodents have long been the subject of much uncertainty. Baluchimyinae (Rodentia) were initially interpreted as a subfamily of the ctenodactyloid Chappatimyidae (sciurognathous), a group considered to be endemic to the Indian subcontinent and to be closely related to hystricognathous rodents. A newly discovered early Oligocene hystricognathous rodent, Bugtimys zafarullahi gen. n. et sp. n., described herein, from the Bugti Hills (Balochistan, Pakistan) sheds new light on the higher level taxonomy of the previously described Baluchimyinae. As a contribution to the phylogenetic debates regarding the origin of Hystricognathi, we present a cladistic assessment of the dental evidence for the Palaeogene hystricognathous rodent cladogenesis. Our phylogenetic results consistently support the monophyly of the Hystricognathiformes clade (including Tsaganomyidae plus Hystricognathi) of which baluchimyine rodents are clearly members. There is, however, no support for the monophyly of a baluchimyine clade. Nonetheless, ‘baluchimyines’ are for the moment reinterpreted as Hystricognathi incertae sedis. Hystricognathous rodents appear to be well diversified at least since the early Oligocene, both in Africa and South America (phiomorphs and caviomorphs, respectively), and also now in south Asia. Furthermore, our phylogenetic results support close relationships between early hystricognathous and Asian ‘ctenodactyloid’ rodents, which clearly points to an Asian origin for Hystricognathi. In this phylogenetic framework, ‘baluchimyines’ and tsaganomyids are representatives of an initial phase of diversification of hystricognathous rodents in Asia. Oligocene phiomorphs and caviomorphs (sister groups) seem therefore to share a common ‘Asian’ hystricognathous ancestor. This reinforces the possibility that the early dispersal of hystricognathous rodents to South America was not from Africa but from Asia.

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

“…We consider it likely that P. aegyptensis and Waslamys attiai are at least slightly older than the relatively poorly-dated P. algeriensis, because BQ-2 and nearby contemporaneous localities lack any evidence for the presence of the immigrant artiodactyl family Anthracotheriidae, a group that otherwise makes its first appearance in Afro-Arabia at Bir el-Ater. Furthermore, Jaeger et al noted that ''several species of [undescribed] (13) phylogenetic analysis of dental characters found the phiomorph-caviomorph clade to be more closely related to two Oligocene Asian baluchimyine lineages (Bugtimys-Hodsahibia and Lophibaluchia) than to Protophiomys. Their topology implies two independent dispersals of hystricognathous rodents into Afro-Arabia: one from within a paraphyletic ''Baluchimyinae'' that gave rise to Protophiomys, and another that gave rise to either phiomorphs alone or to a phiomorphcaviomorph clade.…”

“…The discovery of hystricognathous tsaganomyid (10) and ''baluchimyine'' (11)(12)(13) rodents in Paleogene deposits of Asia has been interpreted as supporting an Asian origin for the stem lineage of Hystricognathi (10,13,14), but because early phiomorphs and caviomorphs have strictly Afro-Arabian and South American distributions, respectively, the early biogeographic history of crown Hystricognathi remains a matter of persistent debate. 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).…”

Two New Taxa (Caviomorpha, Rodentia) from the Early Oligocene Tinguiririca Fauna (Chile)

“…The sudden mid-Cenozoic appearance of caviomorphs in South America's stratigraphic record is perplexing, given the continent's geographic isolation at the time and the "AfricanAsian" distribution of the group's nearest putative relatives, Phiomyidae and Baluchimyinae (Marivaux et al, 2000(Marivaux et al, , 2002Jaeger et al, 2010). The venerable notion of caviomorph monophyly (Wood and Patterson, 1959) has been corroborated repeatedly by molecular analyses (Nedbal et al, 1994;Huchon and Douzery, 2001;Opazo, 2005;Farwick et al, 2006;Poux et al, 2006;Huchon et al, 2007;Blanga-Kanfi et al, 2009;Churakov et al, 2010), but morphological evidence has remained more ambiguous.…”

“…An Asian origin for caviomorphs has been proposed on molecular and morphological grounds (Hussain et al, 1978;Flynn et al, 1986;Jaeger, 1989;Huchon and Douzery, 2001). Nevertheless, dispersal between Asia and South America via North America or Australia-Antarctica is contradicted by the lack of early Cenozoic hystricognaths in any of these locations (Hartenberger, 1985;Wood, 1985;Houle, 1999;Marivaux et al, 2002). South America's isolation during most of the Cenozoic produced highly endemic land mammal faunas.…”

“…Wyss et al, 1994 In his classic treatise Tullberg (1899) subdivided rodents into Sciurognathi and Hystricognathi, based on the angle between the mandibular ramus and the vertical plane of the incisors. Hystricognathous rodents were subsequently shown to form two subdivisions based on morphological (Luckett and Hartenberger, 1993;Marivaux et al, 2002Marivaux et al, , 2004, molecular (e.g., Huchon et al, 2000Huchon et al, , 2002Huchon et al, , 2007Huchon and Douzery, 2001;Murphy et al, 2001;Poux et al, 2006;Blanga-Kanfi et al, 2009), and endoparasitic (Hugot, 1999) evidence. These hystricognath subdivisions include the paraphyletic African Phiomorpha (Old World porcupines, cane rats, dassie rats) and the monophyletic South American Caviomorpha (chinchilla rats, pacas, chinchillas, capybaras, New World porcupines, agoutis, pacarana, spiny rats, tuco-tucos, cavies, hutias), a clade nested deeply within Hystricognathi.…”