Riversleigh Leaf-nosed Bat

Introduction

Riversleigh Leaf-nosed Bat, Brachipposideros nooraleebus, an Old World leaf-nosed bat from the Australian Miocene, was the first Australian fossil bat named and the first Brachipposiderosspecies found outside of France. It was discovered at Riversleigh in northwest Queensland, where its bones have been found in the thousands. The Orange Leaf-nosed Bat Rhinonycteris aurantius, a close relative, still lives in caves in the area today.

Identification

All bats have forelimbs modified into wings, formed by a thin membrane supported by elongated finger bones (the second through fifth digits). The claw of the first finger (digit one, or the 'thumb') is free for grasping. Many microbats (Microchiroptera) have complex nose morphologies as part of their echolocation system. Hindlimbs were reduced.

Rhinolophids and hipposiderids both have unfused premaxillary bones in the upper jaw, a shared feature uniting them as Rhinolophoidea. Hipposiderids (Old World leaf-nosed bats) have elaborate, fleshy nose leafs that help focus ultra-high frequency pulses of sound emitted by the bats that help detect prey or obstacles while in flight. The sounds produced by these bats originate in the larynx ('voice box') and are emitted through the nose rather than the mouth. They also have large, specially grooved ears that receive the sounds deflected back off objects (prey or other objects encountered in their environment). However, unlike most bats, hipposiderids do not have a tragus, a pointed, fleshy extension of the external ear. The dental formula of hipposiderids is (like many bats): I1/2 C1/1 P1-2/2-3 M3/3 (I = incisors; C = canines; P = premolars; M = molars).

Habitat

Riversleigh during the early to middle Miocene was mainly forested, with more open areas near the forest edges and freshwater streams or lakes in a karst (limestone) environment. Caves formed in the limestone would have provided roosting sites for a diverse group of hipposiderids (eight genera so far described), including up to five species of Brachipposideros.

Distribution

Brachipposideros nooraleebus is known only from the Riversleigh World Heritage Fossil Site in northwest Queensland. Other Brachipposideros species are known from the Oligocene and Miocene of western Europe and northern Africa. Fossil hipposiderids are known from Europe, and living hipposiderids from Africa, Asia, Australia and the Pacific (west as far as Vanuatu).

Feeding and diet

There is no information on the diet of Brachipposideros nooraleebus, although most living hipposiderids are insectivorous (sometimes bringing their insect prey back to their roosts).

Life history cycle

The biology and lifestyles of hipposiderids are not well known. Female hipposiderids carry sperm over the winter, with the young being born later in the spring. Hipposiderids are known to congregate in caves in very large numbers (up to 5,000), as Brachipposideros nooraleebus did at Riversleigh.

Fossils description

The Miocene Riversleigh deposits are one of the richest areas in the world for bat remains. Thousands of fragile fossils of Brachipposideros species have been collected and prepared by acid preparation of the Riversleigh limestones. Many of these bat sites represent old limestone cave deposits. The fine preservation of many of the specimens suggests that fossilization was rapid and that it occurred at the roosting site (in situ).

One of the oldest bats in the world, Australonycteris clarkae, is also from Queensland (Murgon). Australonycteris is early Eocene in age (about 55 million years old) and was an archaic bat much like those from other Eocene sites (most of which are in the Northern Hemisphere).

Evolutionary relationships

Higher-level relationships of bats are the subject of much debate. The closest relatives of bats among mammals may be tree shrews (tupaiids), primates or colugos/flying lemurs (dermopterans); together, these four groups would form the grandorder Archonta. However, other ancestors have been proposed, including carnivores, insectivores and ungulates among others. Most scientists think that both fruit bats (megachiropterans) and 'insectivorous' (echolocating) bats (microchiropterans) are a natural group, descended from a common ancestor, although there are some that think the megabats are separately descended from a primate group. Due to the enormity of the task of sorting bat relationships (these generally tiny mammals make up about one-quarter of all living mammal species), a clear idea of the interrelationships of bats is probably well in the future. Bats in Australia also make up about one-quarter of native, non-marine mammal species.

Some have proposed that megabats and Rhinolophoidea (Rhinolophidae and Hipposideridae) are a natural group. This scenario, however, would require that echolocation, powered flight and many other bat characteristics evolved separately, a view that many do not subscribe to. Rhinolophidae and Hipposideridae are closely related, and are a fairly basal group within bats (in the same clade as Megadermatidae, or Ghost Bats, also known from Riversleigh and still living in the area today). The relationships of Hipposideridae, however, are not well resolved, although they are a very old group (the oldest fossils, from Europe, are middle Eocene in age). Brachipposideros species, all extinct, were early, specialized hipposiderids. The high number in Australia of such early members of the family may suggest that the early radiation of the group occurred here. Several new species (three to four) from Riversleigh are yet to be described.

References

• Bogdanowicz, W. and Owen, R. D. 1998. In the Minotaur's labyrinth: a phylogeny for the Hipposideridae. In Kuntz, T. (ed) Bats: Phylogeny, Morphology, Echolocation and Conservation Biology. Smithsonian Institution, Washington.
• Hand, S. J., 1997b. New Miocene leaf-nosed bats (Microchiroptera: Hipposideridae) from Riversleigh, Queensland. Memoirs of the Queensland Museum 41, 335-349.
• Hand, S. J. 1998. Riversleigha williamsi gen. et sp. nov., a large Miocene hipposiderid (Microchiroptera) from Riversleigh, Queensland. Alcheringa 22, 259-276.
• Hand, S, J. 2006. Bat beginnings and biogeography. Pp. 673-705 in Merrick, J. R., Archer, M., Hickey, G. M. and Lee, M. S. Y. (eds) Evolution and Biogeography of Australasian Vertebrates. Australian Scientific Publishing, Oatlands.
• Hand, S. J., Novacek, M. J., Godthelp, H. and Archer, M. 1994. First Eocene bat from Australia. Journal of Vertebrate Paleontology 14, 375-381.
• Hand, S. J. and Kirsch, J. A. W. 1998. A southern origin for the Hipposideridae (Microchiroptera)? Evidence from the Australian fossil record. In Kuntz, T. (ed) Bats: Phylogeny, Morphology, Echolocation and Conservation Biology.Smithsonian Institution, Washington.
• Hand, S. J. and Archer, M. 2003. A new hipposiderid genus (Microchiroptera) from an early Miocene bat community in Australia. Palaeontology 48, 371-383.
• Jones, K., Purvis, A., MacLarnon, A., Bininda-Emonds, O. R. P., and Simmons, N. B. 2002. A phylogenetic supertree of the bats (Mammalia: Chiroptera). Biological Reviews 77, 223-259.
• Sigé, B., Hand, S. J. and Archer, M. 1982. An Australian Miocene Brachipposideros (Mammalia, Chiroptera) related to Miocene representatives from France. Palaeovertebrata 12, 149-171,
• Sigé, B., Thomas, H., Sen, S., Gheerbrandt, E., Roger, J. and Al-Sulaimani, Z. 1994. Les chiroptères de Taqah (Oligocène inférieur, Sultanat d'Oman). Premier inventaire systématique. Münchner Geowissenschaftliche Abhandlungen A 26, 35-48.

Further reading

• Archer, M., Hand, S. J. and Godthelp, H. 1994. Riversleigh: The Story of Animals in Ancient Rainforests of Inland Australia. Reed Books, Chatswood.
• Long, J. A. et al. 2002. Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution. Johns Hopkins University Press, Baltimore, 240 pp.