Humans are fascinated by extremes; just consider the popularity of the Guinness Book of Records. It’s also reflected by our fascination with huge dinosaurs; think Tyrannosaurus rex and Brachiosaurus. So it is not surprising that claims that ‘giant predatory lizards 11m long once roamed Ancient Australia’ would garner attention and intrigue. In fact the lizard was appropriately given the scientific name, Megalania, meaning ‘giant ripper’. But the search for the true size and nature of this giant reptile, reveals a story of misidentification, opposing ideas, inexact science and false assumptions.

The story begins in the 19^th Century, with a large number of fossils of a particular type being uncovered by land owners and naturalists. The size of the bones and teeth indicated that the animal was large. Many perceived the fossils to be of a dinosaur and others classified them as crocodilian. It was never dreamt of at the time that they could been the remains of a gigantic lizard (the Komodo dragon was unknown to science at that time). However, as fragments were combined and examined more closely, it gradually became clear that these were the remains of a giant extinct lizard living during the late Pleistocene, approximately 30,000-180,000 years ago.

Well actually, it wasn’t that clear. In fact the science was decidedly murky. Many of the remains were incorrectly labelled for a long time, and were actually the bones of giant land tortoises, giant flightless birds or even giant marsupials. The opposite also occurred, with many bones identified as belonging to these groups, actually being those of Megalania. Debate among palaeontologists over these matters ruffled a few feathers.

But the debate really got heated around the issue of the size of Megalania. Early estimates inferred a length of 3 m, but over time, the body length increased to 9, 10 and even 11 m—stupendously big for a lizard. It was almost as if a competition was being held: “my Megalania is bigger than yours”.

The variation in size estimates arises from assumptions that have to be made, largely due to the fragmentary nature of the evidence. For example:

• The ratio of claw length to body length from living goannas was applied to the fossil claws of Megalania. The only problem was that it is later discovered they were giant flightless bird claws – not Megalania.
• Determining the head length from skull remains, and then using the head-to-body length ratio of a lace monitor (alive today) to calculate a length of around 7-10 m. However, further research has identified that the ratio is much smaller in komodos and Megalania, so the size was a massive overestimate.

The confusion of the Megalania story intrigued Queensland Museum palaeontologist and Snr. Curator Geosciences, Dr.Scott Hocknull. He recognised that as a key predatory animal, gaining an accurate understanding of it’s biology is essential in understanding the ecology of prehistoric Australia. So Scott travelled the country and even overseas to examine every Megalania fossil he could find.  Meticulous measurements of the remains, and comparison with living goanna species, has helped test many of the assumptions previously made, and identified a total body length of between 5 and 6 m. This still makes it the largest lizard to have ever lived.

This situation is a prime example of one of the AC: Science learning descriptors within the strand ‘Science as a Human Endeavour’.  ‘Scientific understanding, including models and theories, are contestable and are refined over time through a process of review by the scientific community’ (Yr 9). Science is not always exact, assumptions are made and formulas applied. Scientists are also human and can become attached to particular theories.

So should scientists assume anything? It’s not a very rigorous and reliable methodology is it?  Assumptions are an inescapable and integral part of scientific research. In almost all cases when not everything is known about an object or topic, assumptions simply have to be made. The challenge is to minimise the number of assumptions, and when made, to ensure they are as valid as possible. Scientific investigation in one sense is all about testing assumptions and theories—by different people, using different approaches and as new evidence and material becomes available.

Palaeontology is one area of science particularly susceptible to forming assumptions due to the fragmentary nature and scarcity of evidence. Uncovering a single bed of fossils can overturn theories held for decades. In fact, this is just what is occurring at the moment with the discovery of an enormous fossil bed at South Walker Creek. Scott and his team from QM are investigating this site, and early results indicate that it will substantially expand and change our understanding of Ancient Australian megafauna, including our very own mega-lizard.