A revision of the babbler genus Trichastoma and its allies (Aves: Timaliinae)

By means of a comparative analysis of 12 morphological and behavioural characters, the timaliine genus Trichastoma and its relatives in the tribe Pellorneini are revised to reflect new understanding of inter- and intrageneric relationships (cf. Mann et al. 1978). Trichastoma as constituted by Deignan (1964) is here subdivided into three unambiguously monophyletic genera, the Malayan Trichastoma and Malacocincla , and the African Illadopsis.
Evidence is presented indicating that the reconstituted Trichastoma should be considered the stem genus for the tribe. Reviewing the distribution of morphological and behavioural characters, the general implication is that the African forms share a recent common ancestor with those from Asia. Distributional data support the contention that the group originated in the Malayan region and colonized westward through southern Asia and Arabia to Africa (probably in early Quaternary) when humid and warm conditions fostered a continuous Afro-Asian corridor of tropical wooded habitats. The postulated greater age of the pellorneine assemblage in Malaysia, along with the region's insular geography, has fostered a larger species radiation than that in continental Africa. Recent desiccation of Arabia and central and northwestern India probably caused widespread regional extinction of linking forms and has isolated the Pellorneini into two humid forest refuges in equatorial Africa and eastern Asia.