These Wallabies Rock!

If you came here hoping for some material on the Australian Rugby team, my apologies; whether they rock remains to be seen in weeks to come... No, this is a tribute to one of my favourite marsupial groups - indeed, one of my favourite mammal groups - the elegantly beautiful rock-wallabies. 

It seems that their ancestors were small rainforest dwellers; as the land began to dry out in the last 20 million years, the general belief is one branch of the group remained in the shrinking rainforest and still survive as the pademelons, while the rockies adapted to the increasing aridity.

Red-necked Pademelons Thylogale thetis, Mount Clunie, northern NSW.

More recent, and surprising, chromosomal studies suggest that their most recent connections were in fact with the tropical tree-kangaroos.

Lumholtz's Tree Kangaroos Dendrolagus lumholtzi, Malanda, Atherton Tableland, Queensland.

Whichever was the last link with other kangaroos, the rock-wallabies now form a very distinct and coherent group of some 16 species, all in the genus Petrogale (ie 'rock weasel'!), superbly adapted to life on rock stacks and cliffs. Presumably it was in the inland ranges that conditions remained sufficiently amenable for their continued survival. They are scattered right across the country, so are - or were before the advent of foxes and probably dingoes - quite capable of crossing large tracts of open land.

One of the key adaptations is in the feet. Other kangaroos push off with a powerful elongated fourth toe and claw.

Agile Wallaby Macropus agilis, Cape Hillsborough National Park, Queensland.
The powerful long fourth toe and claw are quite visible.

This wouldn't work at all on rock faces, so rock-wallabies have short broad feet, with reduced claws. The gripping and pushing happens underneath; the soles of their feet are thick and spongy and the surfaces are rippled and ridged like sandshoes.

Black-footed (or Black-flanked) Rock-wallaby Petrogale lateralis, Alice Springs.
The shorter toes without protruding claws are evident.

The tail too isn't tapered, stiff and smooth like other kangaroos' (see again the Agile Wallaby above), but heavy, cylindrical, flexible and furry. When they run the tail is held high and swivels like a rudder, even helping them change direction in mid-leap.

Another 'unkangaroo-like' trait is in the nature of their care of youngsters newly emerged from the pouch. In other species the 'at foot' young simply follows mum about, suckling from the pouch as required and hopping back in as the mood strikes. Again this would be impractical on a cliff face - dangerous territory for inexperienced youngsters learning , and also for a pouch-carried baby likely to be banged on rocks when mum is hurrying - so the baby is parked in a convenient cave or crevice, to which the mother returns to feed it. When it is strong and confident enough, it embarks on a life on the rock faces. 

Black-footed Rock-wallaby, Alice Springs.
This baby will be left in a safe place while mother feeds, when it gets too big for her to continue to carry safely around.

All rock-wallabies had a common ancestor only 4 million years ago. The Short-eared Rock-wallaby P. brachyotis (and a couple of recently-recognised closely related species) from the north-west, the Proserpine Rock-wallaby P. persephone (a rare and threatened species from the tropical Queensland coast) and the southern inland Yellow-footed Rock-wallaby P. xanthopus, are the oldest and most distinct species.

Yellow-footed Rock-wallaby, Brachina Gorge, Flinders Ranges, South Australia, an 'old rocker'.
This lovely animal also demonstrates how colourful some rock-wallaby species are, relative to other kangaroos.

The most recently arisen are a group of species from the Queensland coast and ranges, whose ancestors came east from the drylands only in the last million years. Indeed some of them have only been recognised in the past 20 years or so, and several are virtually only distinguishable by chromosomes (not a generally useful field characteristic!) and range. 

A life on isolated outcrops has led to serious problems for several species, in combination with disruption and competition from feral goats, and ferocious predation from feral Red Foxes, especially when they are dislodged by the goats and try to cross open country. The once-abundant Brush-tailed Rock-wallaby P. penicillata has virtually gone from its south-eastern range, though captive breeding and re-colonisation programs are proceeding; animals bred at Tidbinbilla Nature Reserve have been released in Gariwerd (Grampians) National Park in Victoria.

Brush-tailed Rock-wallaby, Wollomombi Falls, northern New South Wales.
Only in small parts of north-eastern New South Wales and south-east Queensland
is this species still moderately common.

And while I try to hold my anthropomorphism in check, I have to confess that the sheer grace and beauty of the rock-wallabies biases me heavily in their favour. While the bigger Euro Macropus robustus, which often coexists with them, seems to power up the cliffs by sheer force, the rock-wallabies glide, like water improbably flowing uphill.

Euros, Broken Hill; powerful hill-climbing kangaroos.

Yellow-footed Rock-wallaby, Idalia National Park, south-west Queensland; all grace and poise, capable of flying up slopes where not even a toe-hold is obvious to us.
The range of the Yellow-foot is typical of the fractured remnant population of rockies; it is found in the Gawler and Flinders Ranges in South Australia, with a very few in the Barrier Ranges of western New South Wales, and a population in Idalia - all many hundreds of kilometres apart.

I've seen a couple of other species, but not with a digital camera; I intend to try to see more in the years to come. And every time I do, it's a good day.

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