Late Pliocene rodents from the Irrawaddy sediments of central Myanmar and their palaeogeographical significance

Yuichiro Nishioka,Masanaru Takai,Takeshi Nishimura,Thaung Htike,Zin-Maung Maung-Thein,Naoko Egi,Takehisa Tsubamoto,Maung Maung

doi:10.1080/14772019.2014.909537

Yuichiro Nishioka, Masanaru Takai + Show 6 more

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https://doi.org/10.1080/14772019.2014.909537

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Abstract

The Upper Pliocene Irrawaddy sediments in the Gwebin area of central Myanmar recently yielded a rodent assemblage that contains nine species belonging to four families: four species of Muridae, three of Hystricidae, one of Spalacidae, and one of Sciuridae. The murids consist of Hapalomys cf. longicaudatus, Maxomys pliosurifer sp. nov., Rattus jaegeri and cf. Rattus sp. indet., which include both extinct and extant forms. Maxomys pliosurifer is relatively similar to Maxomys surifer that lives in South-East Asia in terms of tooth morphology but retains plesiomorphic features shared with the ancestral rat, Karnimata, and possible sister genera of Maxomys, such as Ratchaburimys and Millardia. The three hystricids belong to the genus Hystrix and consist of two extinct brachydont species (Hystrix paukensis and Hystrix sp. indet.) and one hypsodont species similar to living form (Hystrix cf. brachyura). This finding indicates that primitive brachydont species and derived hypsodont species of Hystrix had likely coexisted in the locality, but the brachydont species are significantly more common amongst specimens collected from the Gwebin area. The spalacid species is Cannomys cf. badius and the sciurid species is Menetes sp. indet. These two rodents are similar to living species in continental South-East Asia although they show minor differences in tooth characteristics compared to the living forms. Some species and genera of the fossil rodent assemblage from the Gwebin area also occur in Upper Pliocene localities of Thailand, suggesting chronological correlation between these two faunas. Moreover, these fossil rodent assemblages are composed primarily of the species distributed endemically in continental South-East Asia. Late Pliocene rodents of continental South-East Asia were affected by river barriers that formed during the Mio-Pliocene, and they were probably not able to disperse from South-East Asia into South and East Asia.http://zoobank.org/urn:lsid:zoobank.org:pub: 0171B3BE-02D4-433C-A5CE-4729C537FAF8

Highlights

Rodents (Mammalia) are one of the most diverse orders in South-East Asia, and their distribution is affected stronglyby geographical barriers such as seas, high mountains and rivers
The absence of H. paukensis from Mg1/2 is probably due to a taphonomic or collecting bias rather than age differences between localities; the fossil rodents discovered from the Gwebin area comprise a single fossil assemblage
The Gwebin rodent assemblage is characterized by the coexistence of primitive species that survived from the Late Miocene or Early Pliocene, and members of the earliest lineages directly linking to extant rodents in SouthEast Asia (Table 3)

Summary

Introduction

Rodents (Mammalia) are one of the most diverse orders in South-East Asia, and their distribution is affected stronglyby geographical barriers such as seas, high mountains and rivers. The zoogeographical region of continental South-East Asia is included in the Indochinese Division that is a part of the Indomalayan Region, or Oriental Region (Corbet & Hill 1992). The Brahmaputra and Ganges Rivers in the west, the Kra Isthmus in the Malay Peninsula in the south, and the mountain ranges or rivers of southern. There are many endemic genera and species of mammals living in South-East Asia mainland. There are eight main rivers in continental South-East Asia: the Brahmaputra, Irrawaddy (or Ayeyarwady), Salween, Chao Phraya, Mekong, Red, Pearl and Yangtze Rivers. The past flow and channel shifts of these rivers are important factors that have controlled the distributional patterns of some mammals

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