Australia, land of placentals (part II)

I'd like to talk about the filming of long-eared jerboas Euchoreutes naso (after all, I covered them on ver 1 back here), about the reclassification of Brontornis (again, covered on Tet Zoo ver 1 here), about Aaron Filler's new paper on bipedality in hominoids (see the PLoS pdf here), and about astrapotheres, swimming giraffes, Loch Ness Monsters, British iguanodontians, proterosuchids and phytosaurs.. but right now I want to get this Australian murid thing finished. You'll need to have read part I before proceeding. Here we go, hold on to your hats...

Wurlies: time capsules of palaeoclimate and ancient DNA

Represented by one living species and one recently extinct one, stick-nest rats are well known for their habit of building a 'house' of piled-up sticks. The extant species, L. conditor [shown above], was until recently restricted to Franklin Island in South Australia, but - prior to 1921 - occurred widely across the Australian mainland. During the late 1990s the species was successfully reintroduced to South Australia (Moseby & Bice 2004), although colonies introduced elsewhere have not fared so well in the face of competition from cats, foxes and other predators.

The structures that stick-nest rats manufacture, dubbed wurlies, can be up to 1.5 m high, 2 m wide, and may serve as shelters for toads, snakes, bandicoots and even penguins. Normally manufactured around or above a burrow or small bush, some of the sticks used to make a wurlie might be 1 m long. Consolidated masses of faeces and urine (forming a material known as amberat) are often associated with the structures, and they also contain stores of leaves, seeds and other plant parts. More remarkable is that they also contain all manner of organic bits and pieces that the rats have collected from the local area, including bones, hairs, egg shell fragments, and the droppings of everything from insects and arachnids to bats, echidnas and dingoes. Consequently, old wurlies that were accumulated hundreds or thousands of years ago (and were added to constantly by generation of rats, in cases for over hundreds of years) have proved to be a major source of information on changing climatic and floral conditions, on the fauna of the area, and might even serve as repositories for ancient DNA (Head 1993, McCarthy et al. 1996, Pearson et al. 1999, Webeck & Pearson 2005). Built by co-operating colonies of the rats, wurlies were first discovered by European explorers in 1838 and were assumed to be created by aborigines for use in lighting signal fires (Hanney 1975) [adjacent image shows Peter Schouten's reconstruction of the extinct stick-nest rat L. apicalis together with faecal pellets and amberat: image borrowed from Murdoch University's ancient DNA lab page here].

Incidentally, landscaping is also practised by some species of native mice. Low mounds of pebbles, extending for perhaps a metre in diameter, are built up over the burrow system that the mice create. It's been suggested that these pebble mounds function as condensation traps, and apparently some farmers use the mounds for mixing concrete (Nowak 1999).

Water rats and false water rats

The water rats or beaver rats (Hydromys: of the five species only H. chrysogaster [shown in adjacent image] occurs on Australia) are big, streamlined murids with dense, water-repelling fur, broad, partially webbed feet, small ears and a flattened head with small, dorsally located eyes. Basin-shaped molar surfaces are thought to be a specialisation for its diet of aquatic invertebrates. Hydromys is able to break open small bivalves with these teeth, but it is reported to leave bigger ones out in the sun. As the bivalve heats up and dies, its valves gape, allowing the rat access to the interior.

Of the 60-odd Australian murids currently recognised, H. chrysogaster was - when named in 1804 - the first to be described. Only one other species entered the literature prior to 1830, but between then and 1860 an additional 18 were recognised, most of them by John Gould... but then Gould did name over 300 Australian bird species and 45 mammals. The period between 1880 and 1940 proved to be another period of extensive discovery (Watts & Kemper 1989).

Closely related to Hydromys is the very poorly known False water rat Xeromys myoides [shown in adjacent image], not to be confused with Xenomys, the peculiar Mexican Magdalena rat. Known only from a few specimens, its water-repellant fur and streamlined shape suggest amphibious habits but, in one detailed study involving thousands of hours of observation, the animal was never seen to enter the water (Magnusson et al. 1976). It inhabits the borders of swamps and mangroves and eats invertebrate and vertebrate prey, even being able to kill crabs larger than it is (head + body length = 115-127 mm).

Australia's lost murids

If you're familiar with Australia's small mammal fauna, you'll know that it most certainly has not fared well in the face of anthropogenic change. Amongst the marsupials, several species of potoroo, hare-wallaby, rat-kangaroo, wallaby and bandicoot have been lost. Several endemic rodents have also disappeared. The better known of these were discussed by Tim Flannery and illustrated by Peter Schouten in their book A Gap in Nature (Flannery & Schouten 2001). Flannery's accounts of some of the species are very sparse, but that's because virtually nothing is known about them.

A poorly known species known from only two specimens, the Big-eared hopping mouse Notomys macrotis of SW Australia was most recently collected in 1843, while the much larger White-footed rabbit-rat Conilurus albipes [shown in adjacent image] apparently became extinct some time around 1845 (though Flannery noted a possible eyewitness account of this species from the 1930s). A second hopping mouse, the Short-tailed hopping mouse N. amplus of Central Australia was last recorded in 1896, and a third - the Long-tailed hopping mouse N. longicaudatus - in 1901 (though a skull fragment collected in 1977 from a fresh owl pellet might indicate later survival of the species) [Schouten's reconstruction of this species is shown in the image below]. The Lesser stick-nest rat Leporillus apicalis is thought to have become extinct around 1933, and Flannery related the tale of how the capture of the last-observed specimens was caught on film. There is a possible record of the species from 1970.

Among native mice Pseudomys, several species have disappeared and been thought extinct, only to be rediscovered later on. This goes for the Heath rat P. shortridgei, discovered in 1906 and thought extinct for 56 years until its rediscovery in 1983 (Baynes et al. 1987), and the New Holland mouse P. novaehollandiae, rediscovered after supposed extinction in 1967. Other species have yet to be rediscovered, including the once widespread P. gouldii and P. fieldi of Northern Territory.

And finally...

So, ok, with a quarter of its native mammal fauna composed of placentals, it's not really accurate to describe Australia as a 'land of placentals': it's still a 'land of marsupials'. But hopefully we can put to rest the popular misconception that Australia lacks native placentals entirely.

Given that the Australian terrestrial mammal fauna is generally considered isolated from that of the rest of the world, what is it about murids that has allowed them to invade the continent from the north, and do so on several occasions? Presumably, the small size and fecundity of murids, their rapid generational turnover and resistance to inbreeding, and their sheer numbers and diversity all contribute to their ability to make accidental, but successful, sea voyages. There is an awful lot more than could be said about the subject of overseas dispersal of terrestrial animals, but I can't do that now. Indeed there are even indications that additional murid lineages once managed to colonise Australia, but have since become extinct. Archer et al. (1999) discussed unnamed dendromurine-like murids discovered at the Pliocene Rackham's Roose site. Dendromurines - the African climbing mice - are, as you'd guess from their name, limited to Africa today, but they occurred in Eurasia during the Late Miocene. If they did invade Australia then their past distribution was even more extensive.

So there we have it. As mentioned in the previous article, I've been promising the Australian murid stuff since May 2007. Strictly speaking, you can't do Australian murids without doing those of New Guinea as well, but I think that's enough murids for right now. Several ver 1 articles are devoted to murids though: for recently discovered South American murids and Lazarus rodents go here, and for the amphibious murids of Africa and South America, go here. Coming next: well, that would be telling wouldn't it. Ok: Loch Ness monsters!

Refs - -

Archer, M., Arena, R., Bassarova, M., Black, K., Brammall, J., Cooke, B., Creaser, P., Crosby, K., Gillespie, A., Godthelp, H., Gott, M., Hand, S. J., Kear, B., Krikmann, A., Mackness, B., Muirhead, J., Musser, A., Myers, T., Pledge, N., Wang, Y. & Wroe, S. 1999. The evolutionary history and diversity of Australian mammals. Australian Mammalogy 21, 1-45.

Baynes. A., Chapman, A. & Lynam, A. J. 1987. The rediscovery, after 56 years, of the heath rat Pseudomys shortridgei (Thomas, 1907) (Rodentia: Muridae) in Western Australia. Records of the Western Australian Museum 13, 319-322.

Flannery, T. F. & Schouten, P. 2001. A Gap in Nature. William Heinemann, London.

Hanney, P. W. 1977. Rodents: Their Lives and Habits. David & Charles, Newton Abbot, London, Vancouver.

Head, L. 1993. Stick-nest rat (Leporillus spp.) nests as sources of arid and semi-arid zone palaeoclimatic data: review and prospects. Quaternary Australasia 11, 38-42.

Magnusson, W. E., Webb, G. J. W. & Taylor, J. A. 1976. Two new locality records, a new habitat and a nest description for Xeromys myoides Thomas (Rodentia: Muridae). Australian Wildlife Research 3, 153-157.

McCarthy, L., Head, L. & Quade, J. 1996. Holocene palaeoecology of the northern Flinders Ranges, South Australia, based on stick-nest rat (Leporillus spp.) middens: a preliminary overview. Palaeogeography, Palaeoclimatology, Palaeoecology 123, 205-218.

Moseby, K. E. & Bice, J. K. 2004. A trial re-introduction of the Greater Stick-nest Rat (Leporillus conditor) in arid South Australia. Ecological Management & Restoration 5, 118-124.

Nowak, R. M. 1999. Walker's Mammals of the World, Sixth Edition. The Johns Hopkins University Press, Baltimore and London.

Pearson, S., Lawson, E., Head, L., McCarthy, L. & Dodson, J. 1999. The spatial and temporal patterns of stick-nest rat middens in Australia. Radiocarbon 41, 295-308.

Watts, C. H. S. & Aslin, H. J. 1981. The Rodents of Australia. Angus & Robertson, Syndey.

- . & Kemper, C. M. 1989. Muridae. In Walton, D. W. & Richardson, B. J. (eds). Fauna of Australia. Surrey Beatty and Sons, Chipping Norton.

Webeck, K. & Pearson, S. 2005. Stick-nest rat middens and a late-Holocene record of White Range, central Australia. The Holocene 15, 466-471.