When we meet a group of strangers, one of the first things we’ll do is to introduce ourselves by name. Nicola Quick and Vincent Janik from the University of St Andrews have found that groups of bottlenose dolphins do something similar. When they meet one another in the wild, they exchange “signature whistles”. These whistles are unique to each individual, and they’re strikingly similar to human names. And it seems that they’re a standard part of a dolphin’s meet-and-greet etiquette.

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On a grassy Ethiopian plateau, revolution and death are underway. The plateau is home to a group of geladas – shaggy, grass-eating, and occasionally terrifying relatives of baboons. They’re like a cross between a cow, Animal from the Muppets, and your nightmares.

Geladas live in units where a single dominant male lords over several related females, whom he monopolises as mates. It’s an enviable position, and males often have to fend off takeover bids by eager bachelors. If a newcomer ousts the chief monkey, it’s bad news for the group’s females. A wave of death sweeps through the unit, as the new male kills all the youngsters whom his predecessor fathered. Indeed, babies are 32 times more likely to die after a takeover than at any other time.

But that’s not all. Eila Roberts from the University of Michigan has found that the new male’s arrival triggers a wave of spontaneous abortions. Within weeks, the vast majority of the local females terminate their pregnancies. It’s the first time that this strategy has been observed in the wild.

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In the desert of the United Arab Emirates, there is an unusual series of flat discs imprinted in the sand.  Each one is about 40 centimetres wide, and they snake off into the distance in several parallel lines, for hundreds of metres.

They are tracks. They were made by a herd of at least 14 early elephants, marching across the land between 6 and 8 million years ago. The track-makers are long dead, but in the intervening time, nothing has buried their tracks or eroded them away. Today, their social lives are still recorded in their fossilised footsteps.

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“I can see its tail,” says David Attenborough, perched on a small boat. “It’s coming up… it’s coming up! There! The blue whale!” Ever since I first saw The Life of Mammals, I’ve always remembered Attenborough’s joy at seeing the “largest animal that exists or has ever existed”.

I now know how he felt.

On Monday, off the southern coast of Sri Lanka, my wife and I had the privilege of seeing five blue whales.

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The two apes above might look very similar to the untrained eye, but they belong to two very different species. The one on the right is a bonobo; the one on the left is a chimpanzee. They are very closely related but the bonobo is slimmer, with a smaller skull, shorter canines and tufts of lighter fur. There are psychological differences too. Bonobos spend more time having sex, and playing with one another. They’re less sensitive to stress. They’re more sensitive to social cues. And they are far less aggressive than chimps.

Many years back, a young researcher called Brian Hare was listening to the Harvard anthropologist Richard Wrangham expound on this bizarre constellation of traits. “He was talking about how bonobos are an evolutionary puzzle,” recalls Hare. “They have all these weird traits relative to chimps and we have no idea how to explain them.”

But Hare had an idea. “I said, ‘Oh that’s like the silver foxes!’ Richard turned around and said, ‘What silver foxes?’”

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A cat-like animal explodes from the long grass and leaps onto an antelope. Its huge bulk drags the target to the ground and its muscled forelegs pin it down. With two long sabre-shaped canine teeth, it stabs its victim in the throat, just the once, severing its blood vessels and windpipe. Death comes quickly.

The hunter could be Smilodon, a sabre-toothed cat that lived throughout North and South America, around one or two million years ago.

Or, it could be a nimravid, another group of hunters that looked like cats, but belonged to a separate, closely-related family. Some of them had sabre-teeth too, and they wielded these weapons between 42 and 7 million years ago, well before Smilodon or its relatives did.

Or, it could be Barbourofelis, a member of yet another group of sabre-toothed not-quite-cats, which lived between 16 and 9 million years ago. Its long sabres slipped into long grooves in its lower jaw, which looked like it was about to melt away.

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In the Battle of Rorke’s Drift, 150 or so British troops defended a mission station against thousands of Zulu warriors. At the Battle of Thermopylae, around 7,000 Greeks successfully held back a Persian army of hundreds of thousands for seven days. Human history has many examples of a small force defeating or holding their own against a much larger one.

Among animals too, the underdogs often become the victors. One such example exists in the rainforests of Panama. There, capuchin monkeys live in large groups, each with its own territory. The monkeys often invade each other’s land. Numbers provide an obvious advantage in such conflicts, but small groups can often successfully defend their territory against big ones. Unlike human underdogs, they don’t win because of superior tactics or weapons. They win because their rivals are full of deserters.

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It turns out that elephants have a sixth toe. They’ve adapted one of their wrist bones into a strut that supports their giant squishy feet. I wrote about this for Nature (excerpt below), but here’s my full interview with John Hutchinson, the man behind the discovery, and the owner of (probably) the world’s largest collection of frozen elephant feet.

Elephants walk on the world’s biggest platform shoes. Now, John Hutchinson at the Royal Veterinary College in London and his team have found that their footwear also contains hidden stiletto heels.

Even though an elephant’s leg looks like a solid column, it actually stands on tip-toe like a horse or a dog. Its heel rests on a large pad of fat that gives it a flat-footed appearance. The pad hides a sixth toe — a backward-pointing strut that evolved from one of their sesamoids, a set of small tendon-anchoring bones in the animal’s ankle.

This extra digit, between 5 and 10 centimetres long, had been dismissed as an irrelevant piece of cartilage. Almost 300 years after it was first described, Hutchinson finally confirmed that it is a true bone that supports the squishy back of the elephant’s foot. The ones on the hindfeet even seem to have joints.

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You enter a room with two cages. One contains a friend, who is clearly distressed. The other contains a bar of chocolate, which clearly isn’t. What do you do? While a few people would probably go for the chocolate first (and you know who you are), most would choose to free the friend. And so, it seems, would a rat.

Inbal Ben-Ami Bartal from the University of Chicago found that rats will quickly learn to free a trapped cage-mate, even when they get nothing in return, or when there’s a tasty chocolate distraction around. Bartal thinks that the rats conduct their prison breaks because they empathise with one another. This ability to understand and share the feelings of another individual is found in humans, apes, elephants, dolphins and other intelligent animals. It seems that rats belong in this club too.

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The naked mole rat must be one of the strangest mammals in existence. They live in underground colonies like those of ants and bees, with a fertile queen lording over sterile workers. They feel no pain in their skin, they live unusually long lives, they can cope with chokingly low levels of oxygen, and they seem to be immune to cancer. Their sight is poor, they can’t control their body temperature very well, and their teeth jut out beyond their lips. And they look like wrinkled sausages.

Now, just when you thought they couldn’t get any weirder, we can add another bizarre trait to the naked mole rat’s extensive list: they have really rubbish sperm.

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