Mystacinid bats (Microchiroptera) from the Australian Tertiary

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

ABSTRACT.-A new genus and three new species of the microchiropteran family Mystacinidae are described from Miocene freshwater limestones in northern Australia. The type species, Icarops breviceps new genus and species, is from the middle Miocene Bullock Creek deposit, Northern Territory; I. aenae new species and I paradox new species are from the slightly older (early Miocene) Wayne's Wok and Neville's Garden Sites at Riversleigh, northwestern Queensland. Fossil mystacinids are rare in each deposit and represented so far only by lower teeth and dentary fragments. They are characterized by a suite of apomorphies shared only with Quaternary mystacinids endemic to New Zealand. The family Mystacinidae has no pre-Pleistocene record and its relationships to other groups of bats remain unclear. Possible sister-groups include South American noctilionoids and the cosmopolitan molossoids and/or vespertilionoids. The presence of plesiomorphic mystacinids in the Australian Tertiary suggests an Australian origin for the family.

INTRODUCTION

THE FIRST pre-Pleistocene record for New Zealand's only endemic mammal family, the Mystacinidae, has been found in Australia. Previously, the family was known only from the living Mystacina tuberculata and the larger, recently extinct M. robusta, as well as subfossil and late Pleistocene remains of these species. All records were from New Zealand, the oldest being 17-18,000 year old remains from Hermit's Cave, near Charleston, West Coast, South Island (Worthy and Holdaway, 1994). Three species of this bat family have now been identified from early to middle Miocene limestone deposits at Bullock Creek in the Northern Territory and Riversleigh, Queensland. The Australian fossil mystacinids are represented so far only by isolated teeth and dentary fragments but these exhibit a combination of apomorphies shared only with M. tuberculata and M. robusta. The Australian fossil taxa were previously regarded by Hand et al. (1995) as molossids.

The vespertilionid Chalinolobus tuberculatus, New Zealand's only other endemic mammal, has been demonstrated to be most closely related to Australian species of that genus (Dwyer, 1962), but the origins and relationships of mystacinids have remained obscure. Taxonomists have placed the family in three of the four microchiropteran superfamilies (Miller, 1907, p. 23940). The issue appeared resolved when Pierson et al. (1986) used albumen immunology to suggest that Mystacina tuberculata is a basal member of the South American superfamily Noctilionoidea (=Phyllostomoidea), with dispersal to New Zealand from South America interpreted to have occurred more than 35 million years ago. Recent phylogenetic analyses, based on morphological, anatomical, physiological, and molecular data, suggest mystacinids are basal members of either the superfamily Molossoidea (i.e., molossids plus tomopeatinids) or Noctilionoidea, or the plesiomorphic sister-group of all other vespertilionoids sensu lato (Simmons, in press).

In this paper, Australian fossil mystacinids are described and their paleogeographic significance discussed. Taxonomy and dental terminology follows Legendre (1985) and Hand (1990). Stratigraphic nomenclature for the Riversleigh region follows Archer et al. (1989, 1994). The prefix P refers to specimens held in the fossil collections of the Northern Territory Museums and Art Galleries, Darwin; QM F refers to specimens held in the fossil collections of the Queensland Museum, Brisbane.

SYSTEMATIC PALEONTOLOGY

Order CHIROPTERA Blumenbach, 1779 Suborder MICROCHIROPTERA Dobson, 1875 Superfamily incertae sedis Family MYSTACINIDAE (Gray, 1843)

Type species.-Mystacina tuberculata Gray, 1843 Familial assignment.-The bats described here share with mystacinids (Mystacina species) the unique condition in which two lower incisors are lost but P2 is large, though single-rooted, and M3 is only moderately reduced. Other shared apomorphies include the robust dentary with fused dentary symphysis, ventral mandibular shelf, tall ascending ramus and deep masseteric fossa, myotodont lower molars, and M2 trigonid not much wider than talonid.

ICAROPS new genus

Type species.-Icarops breviceps new species

Diagnosis.-Species of this genus differ from other mystacinids (i.e., species of Mystacina) in having less procumbent lower incisors, canines and anterior premolars, a more anterodorsallysituated mental foramen (mid-dentary depth beneath P2), and a shorter, more robust dentary relative to tooth size. Additionally, Icarops species differ from M. robusta in their smaller size.

Etymology.-From Icaros, the mythological Greek who flew towards the sun, in reference to the ancient mystacind that flew eastwards from Australia to New Zealand.

Referred species.-Icarops aenae n. sp.; Icarops paradox n. sp.

Age and distribution.-Early to middle Miocene of northern Australia.

ICAROPS BREVICEPS new species Fieures 1.1-1.3. 2.2

Diagnosis.-Deeper dentary than in l. aenae and with P4 roots more transversely oriented. Larger than L paradox and with anterior teeth less crowded. Broader ventral mandibular shelf than both I. aenae and I. paradox.