Mystacinid bats (Microchiroptera) from the Australian Tertiary

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

All cusps are connected by crests, except for the hypoconulid which is isolated. Because the protoconid is broken, it is difficult to assess the relative lengths of the paracristid and metacristid or their paraconid, protoconid and metaconid contributions. The cristid obliqua, in occlusal view, is uncurved and contacts the trigonid at a point directly below the junction of the components of the metacristid. In lateral view there is an inflexion along the cristid obliqua midway between the hypoconid and trigonid. The hypocristid extends from the hypoconid directly to the entoconid, almost perpendicular to the axis of the toothrow, isolating the small hypoconulid and thereby exhibiting the myotodont condition. The inflexion in the hypocristid occurs closer to the hypoconid than the entoconid, reflecting the almost vertical rise from the talonid basin of the hypoconid before lingually recurving only slightly. A pre-entocristid, straight and gently declining, links the entoconid to the trigonid at the base of the metaconid. The angle between the para- and metacristids is relatively acute, as might be expected in an M,, these crests being relatively transverse with respect to the toothrow. The cristid obliqua and paracristid are almost parallel to each other. There is a well developed, uniform, nonsinuous and continuous anterior, buccal and posterior cingulum, terminated anterolingually by notch for the hypoconulid of M, and, at its posterolingual end, well short of the hypoconulid thus providing a notch for the anterior cingulum of M3.

M3, represented in P895-14a, is described in so far as it differs from M2. It is a narrower, more rectangular tooth, being conspicuously longer than wide. It is shorter than M2. The trigonid is conspicuously wider than the talonid, and the talonid longer than the trigonid. The protoconid is the tallest and most massive cusp, the paracristid is longer than the metacristid, the protoconid contribution to the paracristid being particularly long. The anterior fossa in the talonid basin is not as deep and there is less inflexion in the cristid obliqua. Although M3 is reduced, remnants of all cusps are present, including the hypoconulid.

Etymology.-breviceps, Greek, short-headed. Holotype.-P895-14a, partial mandible preserving a fragment of left dentary with alveoli for I1, and C1 and right dentary containing M3 and alveoli for C1 P2,4, and M1,2. P895-14b, right M2 almost certainly from P895-14a.

Type locality and age.-Blast Site, Bullock Creek, Camfield Beds, Northern Territory, Australia (Murray and Megirian, 1992). Blast Site is topographically low in the fossiliferous freshwater limestone sequence at Bullock Creek but its stratigraphic relationship to other fossiliferous units is not known. The Camfield Beds are considered to be middle Miocene (approximately 12 million years old) on the basis of stage-of-evolution biochronology of marsupial taxa (Murray and Megirian, 1992).

Associated fauna and nalaeoenvironment.-The Bullock Creek Local Fauna contains teleosts, lungfish, hylid and myobatrachid frogs, pythons, madtsods, elapids, varanids, meiolands, chelids, crocodylids, dromornithids, casuards, anatids, dasyurids, thylacinids, peramelemorphians, thylacoleonids, diprotodontids, palorchestids, phalangerids, pseudocheirids, potoroids, and macropodids (Murray and Megirian, 1992). The geology and biology of the Bullock Creek assemblage indicate a fluvio-lacustrine environment with permanent or at least seasonally-abundant water. The fauna reflects a waterhole assemblage around which larger predators would be expected to congregate. Blast Site may represent point bar accumulations or low energy fluvio-lacustrine deposits in which minimal transport and dissociation has occurred (Murray and Megirian, 1992). ICAROPS AENAE new species Figures 1.6, 1.7, 2.1