I've been thinking – as one does – about marsupial lions. Of all the species that became extinct after people first arrived in Australia, between 40 and 50,000 years ago, this is the one that intrigues me most.

Even more, that is, than the spiny anteater the size of a pig; a relative of the wombat the size of a rhinoceros; a marsupial tapir as big as a horse; a ten-foot kangaroo; a horned tortoise eight feet long and a monitor lizard bigger than the Nile crocodile. The lost Australian megafauna looks like a science fiction film directed by an acid casualty.

But it's the marsupial lion (which was unrelated to the placental lions that remain alive today) that intrigues me most. It was big but, by Pleistocene standards, not huge: probably halfway between a leopard and an African lion.

Morphologically, in some respects it more closely resembles the bipedal carnivorous dinosaurs than any mammalian predator. It could walk and run on four legs, but it also seems to have possessed the ability to stand, with great stability, on two. We know this because, like the kangaroos and some of the heavier dinosaurs, it had chevron bones in its tail. These turned the tail into a stout prop, the third arm of a tripod when the animal stood up.

But unlike, say, tyrannosaurs and velociraptors, marsupial lion species (the biggest of which was Thylacoleo carnifex) also possessed enormous, highly muscled forelimbs. These were equipped with vast hooked claws. It seems to have been the only marsupial with the ability to retract its claws, which allows them to remain sharp. (Think of the difference between a cat's claw and a dog's, which is blunted as it scrapes on the ground). It had an extraordinary dentition - huge fused teeth like knife blades – and, the musculature suggests, the strongest bite for its size of any known mammal.

All this we know from the fossil bones. There's also a suggestion that it was striped. That, at least, is what the one ghostly image of this beast in an ancient rock painting, discovered in 2008, suggests.

Adaptations like this don't happened by accident. This was a specialised predator, which seems to have been equipped for a strategy unlike that of any carnivore alive today. But what was the strategy?

Skeleton of an extinct marsupial lion (Thylacoleo carnifex) casts a large shadow on the cave wall at an archaeological dig in Naracoorte Caves National Park, Australia. Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/Corbis

There are, I admit, more pressing matters. But once I started thinking about this, it was not easy to stop. So I spent a few hours in an academic library, reading all the available papers on Thylacoleo carnifex. The first thing I noticed was how few there are. While the dinosaurs have been studied from every imaginable angle, and their habits and strategies endlessly debated, the extinct giant mammals (which, being much more recent, tend to be better represented in the fossil record) have been, by comparison, neglected.

For example, a couple of years ago I spent three days in the library looking for papers which mention the ecological legacy of elephants in Europe. The legacy looks pretty obvious to me. Trees which can coppice and hedge, understorey trees (box, yew, holly) which – though they carry less weight and are subject to lower shear forces from the wind – are stronger and tougher than the big canopy trees. The black and white reticulations of birch bark look as if they might have evolved to confuse a bark-stripping beast with limited colour vision.

But though our forests were recently inhabited by a creature so monstrous that it made the African elephant look like a ballet dancer (the straight-tusked elephant, Elephas antiquus) all I could find was a throwaway sentence in one scientific paper. Look up trees and elephants in Africa, by contrast, and you'll encounter a large and interesting literature on their co-evolution.

There was once a lively academic discussion about marsupial lions, but it stopped at the end of the 19th century, long before modern analytical methods were available. More recently, a couple of sources have proposed that this beast might have been arboreal (living and hunting in trees). But an analysis of its scapula suggests "walking and trotting, rather than climbing ... the pelvis similarly agrees with that of ambulators and cursors [walkers and runners]".

These bones indicate that Thylacoleo was a slow- to medium-paced runner, which is likely to mean it was an ambush predator. That fits with the stripes: camouflage of the kind you need for stalking and hiding in a largely forested habitat (like tigers) rather than chasing across open spaces (like lions).

But that still doesn't get us very far. Sure, tigers have big forearms, but nothing (in comparison to their hindquarters) like those of Thylacoleo. Or such remarkable claws or – formidable as they are – such a terrifying bite. And they are top-heavy and unable to stand on their hindlegs for long. The marsupial lion did something that no living predator did, and nowhere in the papers I've read is a full explanation attempted.

I found one study, published in 1985, which takes us halfway there. It notes that the bones of the marsupial lion are most frequently associated with two genera of kangaroos, Macropus and Sthenurus, including giant kangaroos. The bones of extinct giant kangaroos bearing marsupial lion toothmarks, found in the Lancefield Swamp in Victoria, suggest that, like the sabretooth cats of the northern hemisphere, it fed largely on the internal organs of its prey.

But all this tells us is that kangaroos featured in its diet. I believe we might be able to go further, and speculate that Thylacoleo carnifex was a highly specialised kangaroo hunter.

Kangaroos, some of which are much bigger and heavier than the marsupial lion, seek to escape by leaping. An animal that can stand on its hind limbs and reach with its elongated forelimbs has a better chance of grabbing one than an animal that's strictly quadrupedal.

Because kangaroos are so tall, Thylacoleo couldn't go straight for the throat. Even standing on its hind paws it wouldn't have been high enough, especially if it were hunting giant kangaroos. But what it could have done was to hook onto the kangaroo's belly or chest and use those tremendous forelimbs to pull itself up.

A cast of a Thylacoleo carnifex skeleton, an extinct giant marsupial, Adelaide, Australia. Photograph: Amy Toensing/NG/Corbis Photograph: Amy Toensing/NG/Corbis

Attached to a very large, very powerful animal, with no purchase on the ground, the marsupial lion would then find itself in a perilous position. It had to bring down its prey quickly, or find itself thrown from pillar to post. The need to deliver sudden death might explain those extraordinary teeth and that powerful bite.

This is, of course, speculation, and it's quite possible that I've missed some papers that clear the matter up. If anyone can take the story forward, I'd be delighted to hear from them – please use the comment thread. But if this line of reasoning holds up, doesn't it invoke an astonishing image? A striped beast with formidable weapons, launching itself at much larger prey, sinking its grappling irons into the flesh and clinging on like a demon in a medieval manuscript.

I'm getting carried away again. That's the effect thinking about these animals has on me. Like the elephants and rhinos, hippos, lions, giant deer and scimitar cats of Europe, the elephant-sized rhinos of the Russian steppes, the moa-hunting giant eagles of New Zealand, the elephant birds of Madagascar, the giant ground sloths, giant sabretooths, bear-sized beavers, nine-foot salmon, mastodons and mammoths of the Americas, the Australian megafauna lived, in ecological terms, just a moment ago. And, like most of these beasts, the evidence strongly suggests that it was wiped out by people.

The sense of loss and the sense of wonder cannot be easily disentangled. You can keep your dinosaurs. The Pleistocene megafauna is just as interesting, and our ancestors knew it and fought it.

Monbiot.com