The wolfish thylacine

The extinct Tasmanian tiger, or thylacine (Thylacinus cynocephalus), remains one of Australia’s most iconic and mysterious native species nearly 90 years after the last confirmed sightings.

Largest of the dasyurids (marsupial carnivores) and related to Tasmanian devils, quolls and antechinus, the thylacine had a kangaroo’s pouch and tiger-like stripes, but in body shape and size it most resembled dogs and wolves.

Snapshot: Tasmanian tigers

• Thylacines were the largest carnivorous marsupial in modern times
• They had 1–1.3 m long bodies and tails of 50– 65 cm, and weighed 15–30 kg
• They are believed to have emerged about 4 million years ago and were once widespread across Australia before disappearing everywhere except Tasmania
• Excessive hunting combined with habitat destruction and disease led to their extinction. “Benjamin”, the last known thylacine died in 1936 at Beaumaris Zoo, in Hobart

Now, a team of Australian researchers has found there are more similarities between the thylacine and the grey wolf (Canis lupus) than were previously thought. They’ve discovered that thylacine pups are also extraordinarily similar to wolf pups– despite them last sharing a common ancestor over 160 million years ago.

“We know that the thylacine and wolf look similar as adults, but we don’t know when they started to exhibit their remarkable similarities during development,” says lead author Axel Newton, from Monash University.

Using Micro-CT scanning and digital reconstructions, the team compared thylacine and wolf skulls of different ages, stages and sizes, from newborn through to fully grown adults.

They then were able to generate digital models for comparison to determine when the similarities arose between thylacine and wolf.

“Remarkably, the Tasmanian tiger pups were more similar to wolf pups than to other closely related marsupials,” says Andrew Pask, from the University of Melbourne.

The team suggest the thylacine and grey wolf are an example of convergent evolution – where organisms that are not closely related independently evolve similar traits.

While scientists know that different animals will evolve to look the same because they have similar places in ecosystems, they are yet to explain how animals converge and more specifically, the forces that drive their early development.

In the case of the thylacine and wolf, researchers suggest evolution of nearly identical skull shapes may have been in response to shared carnivorous and predatory ecologies.

The researchers say that next steps to understanding probably lead to the realm of biochemistry – specifically, molecular genetics. They say that looking at what genes are being used inside specific cell tissue could shed insights into why animals look the same, despite millions of years of divergence.

“By comparing entire growth series from newborns to adults, we were able to visualise tiny differences in development that pinpoint when and where in the skull adaptions to carnivory arise on a cellular level,” says Christy Hipsley from Museums Victoria.

The research is published in the journal Communications Biology.

Related reading: Climate killed thylacine on mainland Australia