Hedley Herbert Finlayson, The Red Centre, 1935When it comes to how hard an animal can bite, size always matters. There may be no truer a case of this than the desert rat-kangaroo (Caloprymnus campestris), known as the ngudlukanta to the traditional custodians of its Country of origin, the Wangkangurru Yarluyandi people.This small, possibly extinct marsupial from the inhospitable Sturt Stony Desert may have had a solid skull built for hard biting. But not enough to bite through the kinds of foods biologists used to think it ate.We discovered the lack of chomping power in the skull of this rat-kangaroo while testing new approaches for analysing skull biomechanics.Our results, published today in the Journal of Experimental Biology, may help with ongoing searches for the elusive species. Declared extinct 30 years ago, there remains hope the critter might still emerge in some parts of its original home range.A difficult desertThe Sturt Stony Desert in the far north-east of South Australia is one of the world’s most inhospitable places. Few animals can make it their home. However, one small marsupial species was known to brave the heat, drought, and scarcity of food: the ngudlukanta. The desert rat-kangaroo, known as ngudlukanta to the Wangkangurru Yarluyandi people. Hedley Herbert Finlayson, The Red Centre, 1935 The species was previously thought to be long extinct, until mammal researcher Hedley Herbert Finlayson led the rediscovery of the animal in the 1930s.But soon after, it vanished again.Sadly, the tiny desert dweller was officially declared extinct in 1994. Weighing just under 1kg, it would have been a perfect snack for introduced predators like foxes and cats. It was further pushed towards extinction by competition with rabbits, overstocking with cattle and sheep, and poor fire management.Yet, exciting reports of possible sightings of the ngudlukanta still emerge sporadically. Descriptions of its distinctive compact size, combined with its short face and the hopping gait of a kangaroo, have sparked renewed interest in rediscovering this animal.In the quest to find this elusive little battler, information about its diet is key. It can help people to keep a closer eye on areas where its favourite foods would be found.From a bite to a dietTo better understand its diet and feeding behaviour, we turned to the animal’s skull.The ngudlukanta had a solidly built skull, with a short and wide face. This led researchers to suggest that it could eat harder desert foods like roots, nuts and seeds.But in our latest analysis, we showed that these assessments were probably incorrect. Instead, the animal’s diet was more likely restricted to softer materials, rather than the tougher foods eaten by some of its harder-headed relatives like the burrowing bettong.The reason for this? It all comes down to its size.Previous interpretations of its biting ability had drawn conclusions from comparisons of skull shape between species, but without considering size differences between them.Our results form part of a paper that addresses this issue in the methods that researchers use. We used a method called finite element analysis, which helps to predict how a structure – in this case, a skull – would handle the forces it experiences in the real world. But what we did differently to other researchers was to keep information about size differences between the skulls in the models.What did we find?The skull of the ngudlukanta is definitely efficient at biting, but it is also about one quarter smaller than the skull of the next smallest species in our sample, the northern bettong.When we included its smaller size in the analysis, the results suggested its relatively short face and robust jaw were unlikely to help it eat harder foods.Instead, its solid skull features mostly compensated for its small size, but would only allow it to support bites about as hard as those of the long-nosed potoroo – a larger species with a much less efficient skull at biting. Finite element models simulating the stress of each skull during biting with the front teeth. The stress in the desert rat-kangaroo is more similar to the hard food-eating burrowing bettong when not including its small size in the models. But its stress levels are more like the long-nosed potoroo when including its small size. Authors Early investigations of stomach contents from the 1930s tell us the ngudlukanta fed mostly on leaves and small amounts of insects. But little further detail exists. A more restricted range of softer, fresher plant materials, as suggested by our analysis, would narrow its range of preferred foods in the deserts it lived in.Our results therefore paint a picture of a species occupying a delicate position within the desert ecosystem.An unsolved mystery in a vast desertIn recent years, one of us (Karl Vernes) has mounted several expeditions into the ngudlukanta‘s habitat, hoping to find evidence of its continued existence.However, finding this tiny marsupial in a vast desert is a challenge – not just because it was probably always rare and elusive, but also because we still know precious little about its ecology.Eyewitness accounts, remote camera traps, analysis of predator scat (poo) for mammal remains, genetic testing of scats, and the expert ecological knowledge of Traditional Owners have all been used to investigate the possibility of the survival of the ngudlukanta. No definitive evidence has yet emerged.Whether the ngudlukanta is extinct or not, therefore, remains an unsolved mystery. But history is replete with examples of rediscovered species believed to be extinct, known as “Lazarus species”. The desert’s vast, inhospitable terrain means it is plausible for a small nocturnal species to be evading detection. The distinctive short face of the ngudlukanta, alongside its small size and hopping gait, have led eyewitnesses to argue for its persistence. Hedley Herbert Finlayson, The Red Centre, 1935 In fact, the desert rat-kangaroo was already a Lazarus species after its rediscovery in the 1930s. The story of the ngudlukanta therefore serves as a reminder that extinction declarations are not always the end of the story. If the species is still roaming the most inhospitable regions of the continent, the new knowledge gained from our analysis could help pinpoint areas where the ngudlukanta might persist.Who knows? The next chapter in the story of this desert-dweller may yet surprise us.Rex Mitchell has received funding from the Australian Research Council's Centre of Excellence for Biodiversity and Heritage (CABAH). Karl Vernes has received funding from the Australian Research Council, the Mohamed bin Zayed Species Conservation Fund, Experiment.com, the Hermon Slade Foundation and Parks Australia. He is a member of the Australian Mammal Society.Vera Weisbecker receives funding from The Australian Research Council. She is affiliated with The Australian Mammal Society and member of the Australian Greens Party.