Monitor lizards, additionally recognized in Australia as goannas, are a number of the most iconic reptiles on the continent. Their lineage not solely survived the mass extinction that ended the reign of non-avian dinosaurs, but in addition gave rise to the most important dwelling lizards on Earth.
Right now, these formidable creatures tempo by means of forests and scrublands, flicking their tongues as they go.
A brand new examine revealed within the Zoological Journal of the Linnean Society seems to be beneath their pores and skin. For the primary time, it reveals hidden bone constructions which will maintain the important thing to the evolutionary success of goannas in Australia.
An important organ
The pores and skin is an organ important for survival. In some animals, it features a layer of bone plates embedded among the many pores and skin tissue. Consider the armour-like plates in crocodiles or armadillos: these are osteoderms.
Their measurement ranges from microscopic to huge, with the again plates of the stegosaurus as essentially the most spectacular instance.
A mounted stegosaurus skeleton on the Pure Historical past Museum, London.
Jeremy Knight/Wikimedia Commons, CC BY
We have now solely simply began to know these enigmatic constructions. Osteoderms could be present in animal lineages that diverged as much as 380 million years in the past. This implies these bone plates would have developed independently, similar to energetic flight did in birds, pterosaurs and bats.
However what’s their function? Whereas the benefit of flight is undisputed, the case is just not as clear for osteoderms.
The obvious potential could be for defence – defending the animal from accidents. Nonetheless, osteoderms might serve a far broader function.
In crocodiles, for instance, they assist with warmth regulation, play a component in motion, and even provide calcium throughout egg-laying. It’s the interaction of those poorly understood features that has lengthy made it tough to pinpoint how and why osteoderms developed.
Sand displays, also called sand goannas, are widespread by means of most of Australia.
Ken Griffiths/Shutterstock
A cutting-edge method
To assist resolve this enigma, we had to return to the start.
Surprisingly, up to now science has not even agreed on which species have osteoderms. Subsequently, we assembled a world workforce of specialists to hold out the primary large-scale examine of osteoderms in lizards and snakes.
We studied specimens from scientific collections at establishments such because the Florida Museum of Pure Historical past, the Pure Historical past Museum in Berlin, and Museums Victoria.
Nonetheless, we quickly learnt that this got here with challenges. Firstly, the presence of osteoderms can fluctuate dramatically between people of the identical species. Secondly, there isn’t a assure that osteoderms are sufficiently preserved in all specimens.
Most significantly, they’re buried deep inside pores and skin tissue and invisible to the bare eye. Historically, discovering them meant destroying the specimen.
As a substitute, we turned to micro-computed tomography (micro-CT), an imaging method much like a medical CT scan, however with a lot increased decision. This allowed us to review even the tiniest anatomical constructions whereas maintaining our specimens intact.
Micro-CT-based, computer-generated 3D mannequin of Rosenberg’s goanna (Varanus rosenbergi), with the left half displaying osteoderms and endoskeleton.
Roy Ebel
Utilizing computer-generated 3D fashions, we then digitally explored the our bodies of lizards and snakes from all elements of the world. Incorporating information from prior literature, we processed nearly 2,000 such samples in our seek for osteoderms.
As an example our outcomes, we devised a method referred to as radiodensity heatmapping, which visually highlights the areas of bone constructions within the physique.
For the primary time, we now have a complete catalogue displaying the place to search out osteoderms in a big and various group; it will inform future research.
Radiodensity heatmapping reveals newly found osteoderms (yellow to purple) within the limbs and tail of the Mexican knob scaled lizard (Xenosaurus platyceps).
Roy Ebel
Not simply anatomical curiosity
What we discovered was sudden. It was thought solely a small variety of lizard households had osteoderms. Nonetheless, we encountered them practically twice as typically as anticipated.
In truth, our outcomes present practically half of all lizards have osteoderms in a single type or one other.
Our most astonishing discovering involved goannas. Scientists have been learning monitor lizards for greater than 200 years. They had been lengthy thought to lack osteoderms, besides in uncommon circumstances such because the Komodo dragon.
So we had been all of the extra shocked after we found beforehand undocumented osteoderms in 29 Australo-Papuan species, rising their general recognized prevalence 5 occasions.
Examples of newly found osteoderms (magenta) in Australo-Papuan monitor lizards.
Roy Ebel
This isn’t simply an anatomical curiosity. Now that we all know Australian goannas have osteoderms, it opens up an thrilling new avenue for additional research. It is because goannas have an attention-grabbing biogeographic historical past: after they first arrived in Australia about 20 million years in the past, they needed to adapt to a brand new, harsh surroundings.
If osteoderms in goannas confirmed up round this time – probably owing to new challenges from their surroundings – we’d acquire essential insights into the perform and evolution of those enigmatic bone constructions.
Not solely might we simply have discovered the important thing to an untold chapter within the goanna story, our findings may enhance our understanding of the forces of evolution that formed Australia’s distinctive reptiles as we all know them immediately.
