THE FOSSIL DEPOSIT, VICTORIA CAVE, NARACOORTE, SOUTH AUSTRALIA

(Representatives of the South Australian Department of Environment and Conservation were unable to attend the Conference. Among material made available to the conference organisers was a copy of the generally available interpretive leaflet on the fossil deposits of the Victoria Cave, and in view of its interest, we have incorporated it in the proceedings)

The fossil chamber of Victoria Cave was discovered in 1969. The chamber is of worldwide importance because of its size and because of the variety and amount of fossil material that it contains. The largest known accumulation of fossils in a cave is a cave in the U.S.A. — Victoria Cave possibly ranks second in size in the world.

Victoria Cave is the only place in Australia, and one of the few in the world, where people can see a paleontological excavation in progress.

From the public viewing point, not all of the excavation can be seen, the more distant part of it is obscured by the overhanging rock. The silt deposit extends back for over 100 feet, is up to 50 feet wide, and is at least 10 feet thick (the depth was tested by putting down fine hollow bores). The silt is soft, except where it has been compressed on the pathway.

THE KINDS OF ANIMALS FOUND

All the medium sized and large animals in the deposit are marsupials, i.e. mammals with pouches. Many of them are now extinct. A comparison between two skulls illustrates some of the differences between one type of extinct kangaroo and a modern kangaroo. One skull is of a Sthenurine, which was dug from the fossil deposit, the other is of a recent kangaroo.

Consider firstly the modern kangaroo, which is a grazing animal. The palate, or roof of the mouth, is very long. It is long and narrow because the animal has a long, narrow tongue. Look at the lower jaw — the long front teeth point forwards. The tips of these teeth meet the upper front teeth, and the kangaroo is able to nip of small blades of grass. These are moved to the back of the mouth with the long slender tongue, and are swallowed.

The skull of the extinct kangaroo, the Sthenurine, is very different in shape. It had a shorter and wider palate. The tongue must have been broad and thick. It would have been completed unsuitable for moving small blades of grass, but would have been able to move more bulky food, such as leaves and small branches. The shape of the skull shows that the Sthenurine was a browsing animal, which ate quite different food from the grazing kangaroos.

The Sthenurine was about 5-6 feet tall, and because it had large bones, its body was bulky, and thick-set. It had a fairly short tail, which could not have acted as a balancer for hopping, as does the long tail of the modern kangaroo. The short tail and heavy body suggest that the animal lumbered along fairly slowly, but, as it was a forest dweller, lack of speed may have been no disadvantage to it.

The Sthenurine is only one of the several types of kangaroo found in the deposit. They range in size from small animals, smaller than the smallest living wallabies, to the giant kangaroo — Procoptodon, which was 8-10 feet tall (some idea of its size can be given by considering that the ceiling height above the viewing point is about 10 feet).

Another huge animal found in the deposit is Zygomaturus, a plant eating marsupial about the size of a rhinoceros (unlike the rhino, Zygomaturus probably had fur). Other animals found are giant koalas and a large type of emu. There are also kangaroos, wallabies, possums, bandicoots and marsupial cats which seem to be identical with animals living now.

HOW DID THE BONES GET INTO THE CAVE?

There are several possible ways in which the bones could have accumulated in the cave. One is that they could have been washed in by a creek. Another is that the bones may have been dragged into the cave by a predatory animal that used it as a den. This animal was the Thylacoleo, sometimes called the marsupial lion, although it is not related to the African lion, and probably did not much resemble it. It may have looked more like a long armed bear. Thylacoleo has been extinct for several thousand years . Although Thylacoleo is generally presumed to have been a carnivorous, flesh eating animal, its teeth differ from the teeth of any living animal.

The vegetable food of herbivorous animals must be chewed and broken up before it can be swallowed and digested; herbivorous animals therefore have big, strong, back teeth with grooves and transverse ridges, which grind up the food as the animal chews. On the other hand, flesh eating animals need sharp, pointed, interlocking teeth,with which they can firstly hold the prey and secondly tear off the flesh.

The teeth of the Thylacoleo differ from both typical carnivores and herbivores. It had two tusk-like front teeth, which did not interlock with the lower incisors, but met them tip to tip. The back teeth were not chewing teeth, but were more like shears. Along each side of the cheek was a massive razor edged tooth, which met a similar razor head tooth in the lower jaw. The muscles working the lower jaw were strong and powerful; hence the long, razor edged teeth would have been powerful shears.

The front teeth of the Thylacoleo would not have prevented the escape of a struggling victim. However, its forearms were disproportionately long, with heavy paws. Each toe had a claw, but one claw was very large, strong and sharp. Thylacoleo may have killed its prey with a swiping blow of its heavy paw.

We will not know how the bones came to accumulate in the cave until we have carefully studied many more of the bones, and also carefully studied the silt that surrounds them.

REMOVAL OF BONES FROM SILT

The bones are very old — we do not know for sure how old, but they are at least 10,000 years, and could be as old as 1 million years — 40,000 years would be a good estimate. The bones are therefore very fragile, and must be handled with extreme care.

After an excavation area has been selected, the silt is gently scraped from the surface with a small metal trowel or spatula, such as can be seen on the table. The silt is collected in buckets and later sieved so that tiny bones and single teeth can be recovered. When the scraping away of the silt reveals a small bone, that bone is taken out, and labelled with the position and depth at which it was found. Larger bones must be specially supported before they can be removed and this support is provided by a plaster casing.

The bone or skull to be encased is first partly freed of silt; the silt is carried away from the top, sides and partly underneath. Then it is packed with wet kleenex tissues and covered over and around with a piece of hessian that has been soaked in a slurry of fast drying plaster-of-Paris. This cast is allowed to dry. The encased bone now resembles a large plaster mushroom on an earthen stalk. When the cast is completely dry, the "stalk" is broken and the cast is flipped over. This turning over of the cast is the most difficult part of the process, as, if the stalk was too big, the entire contents may fall out through the hole in the cast. The hole is sealed with the more hessian and plaster-of-Paris, and, when this has dried the bone can be safely transported, protected by its hard, shockproof casing (a complete casing is on display, and also one that has been cut to show the jaw inside).

The bones that have been excavated are packed in boxes and carried back to the laboratory. After they have been allowed to dry for a day or two, they are gently brushed clean. Some that are encrusted with lime must be soaked in weak acetic acid and then thoroughly washed with water. All the bones are painted with a plastic hardener, which prevents them from drying excessively and cracking. Only after the bones have been thoroughly cleaned and protected can any attempts be made at re-assembling them into skeletons.