Research website of Dr Gilbert Price

Archives for April 2012

Sifting through 80 thousand years of owl spew

Dr Julien Louys at the Colosseum Chamber excavation

This definitely isn’t the most glamorous title that I’ve ever come up with, but it’s certainly one of the most accurate! Situated at the Capricorn Caves tourist park, about 20 minutes north of Rockhampton in central eastern Queensland, lies one of the most important Quaternary-aged cave fossil deposits in Australia. The deposit, situated in Colosseum Chamber, is 2 m deep and contains numerous bones of small-bodied vertebrates such as rodents, dunnarts, antechinuses, bats, frogs and quails. By ‘numerous’, I mean ‘ridiculously abundant’- there are literally hundreds of thousands of bones in the deposit.

So how did they all get there? Well, that’s what the title of this post is all about! Owls, believe it or not, play a major contribution to the formation of fossil deposits. They are typically nocturnal, so conduct most of their feeding activities at night time. Being relatively small-bodied predators, they can only take relatively small-bodied prey. During the daytime, they commonly roost in caves, venturing out at night time to hunt,

Excavating at Colosseum Chamber

but will later return to the caves to consume their feast. In most cases, they will rip their prey apart using their tough beaks and strong claws before they swallow it. The smaller prey chunks will be partly digested in the stomach. The bits that aren’t digested, which normally include things like teeth, bone, fur and feathers, are regurgitated into pellets and drop to the floor of the cave. If you have enough owls out there using caves, hunting, digesting, and regurgitating, overtime they’ll accumulate a huge amount of bones, and if palaeontologists are lucky enough, they’ll often be incorporated into the cave fossil record.

That is exactly what we see in the Colosseum Chamber fossil deposit. So how do we know that the bones got there via owls? Well, most of the bones that we have identified are those from small-sized vertebrates, mostly less than about 500 grams- just the right size to be easily carried by an owl. Most of the fossil bones are relatively intact- we have an incredible amount of well-preserved teeth, jaws, and skeletal elements. Had the chief predator been a toothed mammal, such as a quoll, the bones would typically be all crunched up and we would see tooth marks all over them… but we don’t. Another key sign is that the bones belong to animals that are typically most active at night themselves. So, unfortunately for them, they were in the wrong place at the wrong time to become owl chow… but right place and right time to be incorporated into the fossil record.

PhD student Jonathan Cramb sifting through the sediment in search of fossils

The deposit was originally identified by Dr Scott Hocknull from the Queensland Museum back in the mid-2000s. Working alongside Scott, we conducted preliminary excavations and realised the potential for the site. Our initial dating study, supported in part by the Australian Research Council, as well as the Australian Institute of Nuclear Science and Engineering, has shown that the deposit spans roughly the last 80 thousand years.

Most recently, the project was passed onto my colleague Dr Julien Louys from The University of Queensland. Julien, Scott and I were successful last year in obtaining some generous funding from the Ian Potter Foundation to conduct a more extensive study on the Colosseum Chamber deposit. Julien was also awarded a post-doctoral fellowship from The University of Queensland which will not only support Julien’s salary, but also help towards costs for fieldtrips and laboratory analyses. We have a fieldtrip coming up in mid-April, so I will be sure to provide an update to the new work soon!