Mystacinid bats (Microchiroptera) from the Australian Tertiary

Journal of Paleontology, May 1998 by Hand, S J, Murray, P, Megirian, D, Archer, M, Godthelp, H

Based on the degree of crowding of the anterior dentition, Icarops aenae from Wayne's Wok is interpreted here to be the most plesiomorphic of Icarops species and (if it is adult) I. paradox from Neville's Garden probably the most derived. The Wayne's Wok and Neville's Garden assemblages are approximate contemporaries, both being early Miocene in age, and older than the middle Miocene Bullock Creek assemblages (Archer et al., 1989; Murray and Megirian, 1992; Creaser, 1997). Icarops breviceps and L paradox could represent separate branches of the Icarops lineage, both possibly derived from I. aenae or a closely related species. There is nothing known about Icarops aenae that would preclude it from ancestry of Quaternary species of Mystacina.

If species of Icarops and Mystacina are sister-groups, then the common ancestor of Australian and New Zealand mystacinids must be at least early Miocene in age. The plesiomorphic nature of the Australian fossils suggests that Australia was the source of New Zealand's mystacinids. New Zealand separated from the rest of Gondwana approximately 80 million years ago, carrying with it terrestrial vertebrates such as leiopelmatid frogs, tuataras, ratite birds, and possibly monotremes. Some 25-37 million years ago, in the Oligocene, much of New Zealand was submerged (Fleming, 1979) and any Gondwanan mammals it might have retained were evidently lost. In the early Miocene vulcanism and other tectonic activity recommenced and New Zealand began to rise. Since the mid-Tertiary the geographic relationship of Australia and New Zealand has changed little, a distance of 1600 km still separating the two landmasses. Isolated, wind-assisted dispersals by bats from Australia to New Zealand have been recorded during historic times (Daniel and Williams, 1984). There are no records of dispersals in the opposite, westerly direction, against the prevailing winds. It is likely that the first intrepid mystacinids arrived on the islands of New Zealand, from Australia, sometime after the late Oligocene.

The ultimate origin of the family Mystacinidae is less clear. Pierson et al.'s (1986) albumen data, which closely links mystacinids to noctilionoids, argue for a South American origin for the family. Recent phylogenetic analyses by Simmons (in press) using a "total evidence" approach, in which morphological, reproductive, behavioral, DNA, and other data are included in a single data set, suggest that mystacinids could represent the plesiomorphic sister-group of all other vespertilionoids sensu lato (i.e., vespertilionids, nataloids, molossoids, etc.). Based on the latter phylogeny, optimisation of biogeographic data (Simmons, 1996) suggests that the radiation of the Yangochiroptera (Vespertilionoidea Noctilionoidea; Koopman, 1985) took place in the New rather than Old World, possibly in the Neotropics. Hershkovitz (1972) and Pierson (1986) have argued for a Southern Hemisphere origin for the world's extant bat radiation on the basis of distributions of endemic bat families. Sige (1991) proposed that modern bat groups evolved from isolated immigrant archaic groups in the Southern Hemisphere in the early Eocene. Archaic bats are now known to have occurred in the Southern Hemisphere as well as the North by the early Eocene, and modern bat clades overlapped widely with more primitive bats, in both time and space (Sige, 1991; Beard et al., 1992; Ducrocq et al., 1993). There is yet no pre-Oligocene record of bats in South America, the oldest bat in the Southern Hemisphere being an archaeonycteridid from Australia (Hand et al., 1994).