How Scientists Reconstructed the Brain of a Long-Extinct Beast

This dog-like marsupial went extinct 80 years ago, but its preserved brains help us glean how its mind worked

Two thylacines at the Smithsonian National Zoo around 1905. A thylacine brain from the Smithsonian Institution was scanned as part of a study to learn more about the extinct marsupial, but it is unclear whether that brain belonged to one of the animals pictured. (Smithsonian Institution)
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In 1936, an animal named Benjamin died neglected and alone in an Australian zoo, and a perplexing species met its end.

Besides a longer tail and stripes across his furry body, Benjamin resembled a dog in many ways. But he was no dog. He was a marsupial called a thylacine, the last known member of his kind on Earth. Though the thylacine has been extinct now for 80 years, that hasn’t stopped enthusiasts from searching; Ted Turner once offered a $100,000 reward for any proof of a living thylacine.

"Many people are just fascinated with this creature,” says Greg Berns, a neuroscientist at Emory University. “It was iconic."

But even if humans will never see another living thylacine, that doesn’t mean we can’t get into their heads. Thanks to the continued fascination with these creatures and new techniques in brain imaging, Berns has now reconstructed how this animal likely thought.

Berns has spent most of his career studying dog cognition—he's trained dogs to sit awake and unrestrained in MRI machines to study their neural patterns when responding to commands or food. About three years ago, he came across the thylacine, and was fascinated by how dog-like the animals appeared, despite having a completely different evolutionary background. Its similar appearance to other mammals inspired its two main nicknames: the Tasmanian tiger and the Tasmanian wolf.

The thylacine is a likely example of convergent evolution, nature’s version of independent invention, Berns says. On the Australian mainland and later on the nearby island of Tasmania, the thylacine was a top-level predator, and thus evolved traits to help it hunt. These traits, including a long snout, large ears, sharp teeth and a sleek body. Wolves, another apex predator, would later evolve those same traits separately.

Roughly 2,000 years ago, the thylacine was likely driven to extinction on Australia's mainland by indigenous human hunting and competition from dingoes (wild dogs). By the time Europeans arrived in Australia, the marsupial was found only Tasmania, and not in large numbers. The thylacine was seen as such a nuisance and risk to livestock farmers, that the government even paid bounties for hunters to cull them. Competition from non-native wild dogs and the diseases they brought, as well as habitat destruction, also likely contributed to their demise.

As thylacine sightings grew rarer, authorities began to consider protecting the species. In July 1936, the Tasmanian government declared the thylacine a protected species, but it was too late: Two months later, the species went extinct.

Like many others, Berns was drawn to the thylacine and its strangely dog-like features. To get a peek into its mind, he first tracked down a thylacine brain preserved in formaldehyde at the Smithsonian Institution. That brain, which had belonged to a male Tasmanian tiger that lived at the National Zoo until its death in 1905, was joined in the study by another from Sydney's Australian Museum, according to the study published yesterday in the journal PLOS One.

Berns used MRI scans and a relatively new technique called diffusion tensor imaging, which maps the brain's areas of "white matter"—the tissue that carries nerve signals to and from neurons in different parts of the brain. For comparison, he did the same scans on two preserved brains of Tasmanian devils, the closest living relative of the thylacine.

Tasmanian Devil
The Tasmanian devil is the closest living relative to the thylacine, but it stands on the brink of extinction from habitat loss and disease. (Wayne McLean / Wikimedia)

Compared to its devil cousins, Berns says, the thylacine had a larger and more complex-looking frontal lobe. This would allow the animals a grasp of complex planning, which would be necessary for an apex predator that must constantly hunt for its food. This is in contrast to the Tasmanian Devil, Berns says, which usually scavenges its meals and wouldn’t necessarily need the same planning and hunting skills.

"When the thylacines were alive they were dismissed as stupid animals," Berns says. "[These results] would suggest otherwise."

Like the rest of an animal's body, the brain evolves as necessary to fill a certain environmental niche, Berns says. However, how exactly this process works outside of primates and lab animals has remained largely unstudied. "One of the things that I hope comes out of this is a better understanding of an animal's relationship between its environment and its brain," he says. "Not many people study the brains of wild animals.”

To remedy that, Berns launched a project called the "Brain Ark" two months ago in collaboration with Kenneth Ashwell, a neuroscientist at the University of New South Wales. Ultimately, the Ark seeks to create a digital archive of animal brain scans that scientists can study from anywhere in the world. So far, he's scanned about a dozen brains, he says.

Ashwell is particularly interested in seeing how the neural evolutionary tree can be mapped with more data from other species, living and extinct. Scans his team has done of Australia's short-beaked echidna show a similar neural architecture to the thylacine, meaning that the brain circuits of these two animals could have evolved in a common ancestor more than 200 million years ago. He also hopes that further scans could help scientists learn more about the poorly understood social behavior of the thylacine, and how it compares to living marsupials.

But the insights these scans could provide go beyond rare and fascinating animals long dead. Leah Krubitzer, an evolutionary neurobiologist at the University of California at Davis who was not involved in the study, says that similar studies of living and extinct and species will allow scientists to not only help map how animal brains have evolved—but also shed new insights on how the human brain evolved, and what exactly makes it so unique.

"I can't think of a better thing that could be funded," Krubitzer says. "This is part of our own history."

Correction, January 23, 2017: This article initially stated that Benjamin was a marsupial, but not a mammal. Marsupials are mammals that are typically born before they are fully developed, and continue developing in their mother's pouch.

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