Mystacinid bats (Microchiroptera) from the Australian Tertiary

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

ICAROPS PARADOX new species Figures 1.4, 1.5, 2.3

Diagnosis.-Smaller than L breviceps and I. aenae, and with P2 larger and P4 more transversely oriented than L aenae. Unlike other Icarops species, I. paradox lacks the area of attachment for digastric muscle(s).

Description.-This species is known only by the holotype QMF20808 a partial mandible preserving fragments left and right dentaries with alveoli for L I1 C1, and P2 and R C1 P2,4 and Ms. A ventral mandibular shelf extends posteriorly only to the alveolus for the anterior root of P4. The site for attachment of the digastric muscles is not clear in this specimen. The small, dorsally directed mental foramen occurs below the alveolus for P2. The area between the canines is damaged anterodorsally. Foramina posteroventral to the midline and just dorsal to the level of the mental foramen are probably homologous with the foramina found in other Icarops species, other foramina in this area evidently being for the incisors. Given the similarity in morphology and available space in this region of the mandible a single pair of incisors was probably present. The canine alveolus is large and oval. The single alveolus for P2 is larger than in . aenae but much smaller than the canine alveolus. There is evidence of crowding of teeth with overlapping of the alveoli. P4 has two roots oriented slightly obliquely with respect to the toothrow; the anterior alveolus is significantly smaller than the posterior one and displaced towards the buccal margin of the toothrow. The anterior alveolus for M1, is also slightly buccally displaced.

Etymology.-paradox, in reference to its curious mixture of primitive and derived features.

Holotype.-QMF20808, partial mandible preserving fragments of left and right dentaries with alveoli for L I1 C1, and P2 and R C1 P2,4 and Mi.

Type locality and age.-Neville's Garden Site occurs on the northern edge of the D Site Plateau, Riversleigh World Heritage Property, Lawn Hill National Park, Queensland, Australia (Archer et al., 1989, 1994). On the basis of stratigraphy and faunal assemblages, the Neville's Garden deposit has been interpreted (Archer et al., 1989, 1994) to be part of Riversleigh's System B, and as such early Miocene in age. It is topographically higher and therefore possibly slightly younger than the Wayne's Wok deposit (Creaser 1997). The palaeoenvironment of the deposit has been discussed by Archer et al. (1994) and Hand (1997), but is interpreted to represent a deep pool, associated with a limestone cave, surrounded by forest. The associated fauna includes numerous aquatic vertebrates, diverse amphibians, reptiles, birds, marsupials, and at least seven bat species.

Measurements of the types of Icarops breviceps, L aenae and L paradox are given in Table 1.

COMPARISONS

Comparison of the three new species.-Based on size and morphology, three species appear to be represented by the Australian specimens. Icarops breviceps from Bullock Creek and I. aenae from Wayne's Wok are similar in size but very different in morphology, with I. breviceps having a deeper dentary but slightly shorter toothrow than I. aenae. Both species are about 20 percent larger than 1. paradox from Neville's Garden. In 1. aenae there is little crowding of alveoli of the anterior dentition (C1-M1,), the alveoli for P4, for example, being oriented longitudinally in the toothrow (Fig. 2). In L paradox, crowding of the anterior alveoli is conspicuous with the anterior root of P4 (and M,) buccally displaced with respect to the toothrow and the alveoli tend to be transversely flattened rather than rounded as in 1. aenae. This condition appears to be intermediate in 1. breviceps, although P2 was evidently very large in both 1. breviceps and 1. paradox. The I. paradox specimen does not appear to represent a juvenile animal; for example, there are no alveoli for the deciduous dentition. However, the ventral mandibular shelf border is not as well developed as in other Icarops specimens and a digastric scar is not evident; this condition occurs in juvenile Cheiromeles torquatus which later develop extensive ventral mandibular shelves.