of the fossil vertebrate deposits in Victoria Fossil Cave:
The Fossil Bed and Ossuaries of Victoria Fossil Cave contain the remains
of tens of thousands of vertebrate animals, making it one of the richest
deposits of Pleistocene vertebrate fossils in the world (Wells 1975).
Represented are over 93 species of frogs, turtles, snakes, lizards, birds,
monotremes, marsupials and placental mammals. The remains include
skulls, jaws and complete skeletal remains which are often associated and,
in some cases, articulated.
The Fossil Bed is located in the Fossil Chamber, a cavern some 60 m long
and 20 m wide. The Bed covers an area of more than 70 sq m, is at
least 4 m deep, and is estimated to contain more than 5000 tonnes of bone-laden
silt. The accessible portion of the deposit consists of a cone and
fan deposit . The fossil-bearing beds are believed (Wells et al.,
1984) to have originated in a series of depositional stages comprising
two events: first, clay soil formation with bone and rock accumulating
with the soil products on the cone; and second, sandy soil formation with
fast sedimentation on the cone and periodic water flows onto the fan.
The lower part of this sequence is exposed in the 3 m deep stratigraphic
pit and consists of a sequence of poorly-sorted to partly-sorted quartz
sands containing variable quantities of clay, bone, charcoal and organic
remains. The bone in the deposit is bleached and mineralised and
appears to have been exposed sub-aerially for some time in a dry environment.
Bone orientation studies by Wells et al. (1984) show a predominent alignment
of large, long bones with the long axis of the cave, with large end downslope,
indicating low energy transport of bone and sediment. Partially articulated
material is found at the distal end of the fan or against the wall of the
cave. From the Fossil Bed, the remains of the complete range of animals,
from very small to very large, have been retrieved. The Upper and
Lower Ossuaries are located several hundred metres beyond the Fossil Bed
and are connected to each other by a short, very low crawlway.
bone bed inside Victoria Fossil Cave. The sheer amount of fossils
contained within this deposit will provide hundreds of years of excavation
work for palaeontologists. Courtesy: Sonny Vandevelde.
The deposit here consists of a thin veneer of sediment and bone spread
over the cave floor rather than a deep bed as in the Fossil Chamber.
The deposit is also notable for the apparent absence of small vertebrates,
suggesting either that the bone accumulated differently to that in the
Fossil Bed or alternatively, that water carried smaller material deeper
into the cave leaving behind only the larger bones (Wells et al. 1984).
The Ossuaries deposit appears to be of approximately the same age as the
Fossil Bed. In the Lower Ossuary, a low roof conceals the lateral
extent of the deposit while in the Upper Ossuary it covers an area of more
than 40 sq m.
For reasons outlined by Wells et al. (1984), a pitfall hypothesis for the
accumulation of the fossils is suggested. Studies of the age-frequency
distributions of one of the commonest animals in the fauna, the Red-necked
Wallaby (Macropus rufogriseus), suggest that individuals were trapped
at random. The depositional hypothesis proposed is that: 1, large
animals fell into the cave via a pitfall; 2, skeletons of those that perished
on the cone were buried by incoming sediment, redistributed and disarticulated
either by mass movement or gentle rafting when water washed down the cone,
or a combination of both; 3, skeletons of animals that perished on the
distal part of the fan were subject to even less water movement and hence
partial articulation was maintained; and 4, that in the absence of other
evidence the proportion of particular skeletal elements within a local
area of any sedimentary horizon is correlated with the ease of transport
of those elements.
The entrance through which the animals and sediment entered the Fossil
Chamber is now completely sealed but has been determined (by pneumatic
and hand augering) to have been a section of chamber exposed by partial
roof collapse (Wells et al. 1984). This was at the base of a doline
some 150 m wide, possibly caused by erosion of the limestone by water flowing
towards the entrance. Laterally, the entrance was steep to vertical
with an average width of 10 m, finishing in a drop of approximately 11
m to cave floor.
Although this was probably the mode of accumulation of the larger vertebrates
in the deposit, Smith (1971, 1972) suggests that many of the small animals
may have been brought into the cave by a predator, probably an owl.
It has been suggested that the entrance of the cave was possibly a roost
for predatory birds, though Van Tets & Smith (1974) believe that many
of the birds represented in the deposit were washed into the cave.
At least some of the animals (for example, some of the frogs, bats and
elapid snakes) probably lived in the cave, much as they do today.
of the deposits:
The bone-bearing sediments in Victoria Fossil Cave are estimated to have
accumulated between 15,000 and greater than 280,000 years before present
(BP). Preliminary racemisation of bone and uranium series dating
of bone from the upper levels of the Fossil Bed are, for uranium series,
125,000 years BP U/Th and 150,000 years BP U/Pa (Ayliffe and Veeh, 1988;
Wells et al., 1984) and, for racemisation, 50,000 years BP and 70,000 years
BP (plus or minus 20%) for the same levels (J. Bada pers. comm. in Wells
et al., 1984). Charcoal associated with fossil bone from the top
1.5 m of the Fossil Bed (Levels 1-10) has been dated at between 16,700
years BP for Level 1 and 35,000 for Level 10. For the Upper Ossuary,
carbon dating of bone gave a date of 36,500 years BP, while racemisation
of bone gave a date of 20,000 years BP for the same deposit. Preliminary
dating of apatite and collagen is equivocable, and Wells et al. (1984)
suggest that the deposit may be outside the range of this dating technique.
More accurate estimations of the deposits' ages are emerging from the dating
work using a variety of methods. These include uranium series analyses
in collaboration with Linda Ayliffe at the Australian National University
(ANU). TIMS dates on flowstones capping and/or sandwiching bone bearing
sediments are extending the age of these deposits to beyond 280,000 years
BP. Based on the dates from speleothems in the caves, it is possible
that some deposits may be found to be in excess of 500,000 years old.
Electron Spin Resonance (ESR) dating on tooth enamel in collaboration with
Rainer Grun of the Quaternary Dating Laboratory has confirmed a Middle
Pleistocene age for the Fossil Bed and Grant Hall. Dates range back
to 350,000 years BP, confirming results from the U-series dating.
Optically Stimulated Luminescence (OSL) dating of the associated quartz
in the bone beds by Richard Roberts of LaTrobe University is at a preliminary
stage. His dates are suggesting some sands entered the caves between
200,000 to 300,000 years BP.