Does size matter? Misidentification of, and assumptions about, the world’s largest lizard

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.

Megalania skull replica
Megalania skull replica

The story begins in the 19th 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”.

Estimated sizes of the extant monitor lizards Komodo dragon and Perentie, compared to different estimated sizes of the "Megalania" (Varanus prisca).
Estimated sizes of the extant monitor lizards Komodo dragon and Perentie, compared to different estimated sizes of the “Megalania” (Varanus prisca).

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.

Snr. Curator Geosciences, Scott Hocknull, describes some fo the features of a Megalania skull.
Snr. Curator Geosciences, Scott Hocknull, describes some of the features of a Megalania skull replica.

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.

Teaching kids to be scientifically discriminative

It’s the school holidays in Queensland and the seconded teachers at QM are taking a well-earned break. This provides me with an opportunity to pen a few words whilst our teaching experts are away!

Coral Reef damage in neigbouring Indonesia

Science has been at the forefront of local news lately, particularly in relation to conservation issues. The Courier Mail had a headline Reef at Risk blazed across the front page on 21st June highlighting a United Nations report declaring Australia’s failure to properly protect the  World Heritage listed Great Barrier Reef (GBR).  Scientists have reiterated their concerns at the 12th International Coral Reef Symposium held at Cairns. Dredging in close proximity to the GBR is a contentious issue.

The day before on the inside pages of the Courier Mail, the headline declared, “Red List shows world biodiversity in crisis as animals and plants vanish”The article referred to the declaration made prior to the UN Summit on Sustainable Development in Rio that, of 63,837 species assessed, 31% (19,817) are threatened with extinction. 2000 of the species listed live in Australian habitats. Queensland’s northern hairy-nosed wombat, mahogany gliders and cassowaries are among the animals whose numbers in the wild have been reduced to vulnerable levels.  

The Northern-Hairy-Nosed wombat is critically endangered

Happily, the news is not all bad on the conservation front as the Australian federal government announced in June the creation of a very large network of marine reserves. Perhaps mindful of presenting a balanced picture about successful conservation efforts, on 29th June the Courier Mail showed photos of a newborn Sumatran rhino calf born in Way Kambas National Park in Lampung, Indonesia.  Andatu, as he was named, was only the fifth calf born in captivity; there are estimated to be fewer than 200 Sumatran rhinos in the wild. Video footage of the baby rhino can be viewed from this link as Reuters syndicated this good news story around the world.

Andatu – a rare Sumatran Rhino calf born in captivity

A question posed in my mind about this concentrated and contrasting coverage of local and international conservation matters is how should we go about sharing and discussing the implications of these stories with our children, as parents or teachers, in a balanced and non-biased way? Many children and young people have a passion for animals and are keenly aware of, and participants in, local initiatives such as litter collection around our parks and creeks and caring for injured wildlife. Their sources of information about conservation issues are likely to be gleaned from social media, ABC3 and the Discovery Channel as well as news digests tailored for young people.

So how do we teach kids to be scientifically discriminative about what they read and hear from secondary sources? At what stage do school students begin to understand that the adult world is full of contrasting viewpoints based on a similar set of facts or events?  The term discriminative is defined as being “capable of making fine distinctions and expressing careful judgment.”  We would argue that many students form an ability to discriminate right from wrong, and weigh up fact from fiction, and rhetoric from reality, far earlier than they are given credit for.

Interestingly the new Australian Curriculum for English which is being trialled in QLD this year has several references to developing  discriminatory reading skills from an early age. For example, under sub-strand “Texts in Context”, Year 3 children should be able to “identify the point of view in a text and suggest alternative points of view”. And under the literature and content sub-strand, Year 4 students should be able to “make connections between the ways different authors represent similar storylines.”

A close scrutiny of ACARA’s Australian Curriculum: Science document reveals similar discriminatory expectations, albeit at a higher level. For example, under Science Inquiry Skills, Year 9 and 10 students should be able to “evaluate conclusions, including identifying sources of uncertainty and possible alternative explanations.

Science and conservation news is an ideal “real world’ information source for children and young people to develop their knowledge and understanding as well as powers of discrimination. And this approach is not new.  As a young teacher, I vividly recall facilitating several enjoyable and highly engaging lessons which were based around a courtroom setting. The class was split into two, character roles were assigned and the “defence and prosecution” were expected to present different views and interpretations of the evidence. Young children love role play and dressing up; the research the children undertook (with the help of parents) in presenting their case was deep and impressive.

Many children are capable of weighing up the merits of a debate

There is plenty of current (and often politically controversial) material in the news that lends itself to debate and raising student’s awareness of the complex, inter-weaving nature of science and conservation issues. For example, exploring the United Nation’s concern about protection of the GBR versus the federal and state government’s need for mining revenue and plans for QLD port and rail expansion; the protection of old-world growth forests in Tasmania advocated by conservationists versus the need to generate new forestry and wood processing jobs in a state with high unemployment.

As a conversational stimulus around the kitchen table or in your classroom, I wonder whether the world-wide depiction of a cute newborn Sumatran rhino is designed primarily to make the general population “feel better” about our efforts to ameliorate the alarming depletion of the world’s endangered wildlife and their habitats?  To discuss.