Revealing the brain of the Tasmanian tiger
Scans of thylacine brains held in museum collections hint at areas of the cortex involved in complex predatory behaviour.
VERY LITTLE IS known about the behaviour of the Tasmanian tiger. Although animals were kept in captivity at zoos in both Hobart and London, there were few systematic studies and most of the data we have are based on anecdotal reports from bushmen and hunters.
The thylacine was once common across Australia. It vanished from the mainland several thousand years ago, but persisted in Tasmania until the early 20th century. A government bounty scheme for hunters from 1830 to 1914 finally drove it to extinction there. Most reports say the last thylacine died in captivity in Hobart Zoo in 1936, but it may have survived in the wild until the 1940s.
With so little data from living animals, scientists have turned to the anatomy of museum specimens to make educated guesses about their behaviour. Although the thylacine had a stronger bite force than the dingo, the anatomy of its head and neck may have meant it was less suited to taking large prey. Its elbow joint suggests it was an ambush predator, and an analysis of its teeth hints it was a ‘pounce-pursuit’ predator that took prey in the 1–5kg range.
In an attempt to understand more about what it was capable of, researchers have now scanned two century-old thylacine brains – one at the Smithsonian Institution in the USA and the other at the Australian Museum. At least four brains are known from museums, but two others were in such poor condition they were not useful for analysis.
“The natural behaviour of the thylacine was never scientifically documented,” says Professor Gregory Berns, a neuroscientist at Emory University in Atlanta, USA, and the lead author of a paper about the research in the journal PLOS ONE. “Our reconstruction of its white matter tracts, or neural wiring, between different regions of its brain is consistent with anecdotal evidence that the thylacine occupied a more complex, predatory ecological niche versus the scavenging niche of the Tasmanian devil.”
To make their findings, Gregory and co-author Professor Ken Ashwell, at the University of New South Wales in Sydney, used a kind of MRI technique called ‘diffusion tensor imaging’ (DTI) to scan the preserved brains of the thylacines and two Tasmanian devils. A relatively new technique, DTI is more useful than conventional MRI for studying preserved brains – rather than those of living or recently dead animals. DTI collects data on how molecules move through body tissues, and in this case revealed the structure of the connective pathways, or white matter, of the brains. Compared with the brain of its relative the Tasmanian devil, the thylacine’s brain “may have had relatively more cortex devoted to planning and decision-making”, the authors write.
“While it is easier to study the brains of animals that have recently died, we’ve shown that we can successfully use our scanning techniques on specimens that are 100 years old,” Gregory adds.“We now have the technology available to make use of the treasure trove of museum collections around the world.”
Dr Bradley Smith, an expert on dingo psychology at Central Queensland University, says:“It is wonderful that technology and our understanding of brains has got us to the point where we can start to learn more about the Tasmanian tiger… This study has confirmed that, as a predator, they had to think differently than other marsupials, such as the devil. In essence, they thought more like a dingo.”
However, Bradley says it’s difficult to infer what thylacine behaviour was like based on looking at brains alone. “Results need to be combined with… studies looking at the shape of the skulls and bite forces, which tell us about diet.”
Gregory is now building an online database of digital scans of animal’s brains – ‘Brain Ark’ will include extinct species and will help researchers explore questions about brain evolution. Although the brains of rats and primates are well studied, most other mammals have not been looked at in detail.
“The Brain Ark is going to fill that gap,” he says.“We are living in a time when much of the planet’s megafauna is at risk of extinction. It’s important to gather as much data as we can.”
Look out for a feature on the Tasmanian tiger in the May/June edition!