Of all the adjectives you could use to describe a crocodile’s face, “sensitive” might not be an obvious one. But their huge jaws, pointed teeth and armoured scales belie a surprising secret. Their faces, and possibly their entire bodies, are covered with tiny bumps that are far more sensitive than our own fingertips.
The bumps are obvious if you look carefully. Each one is a small dome, barely a millimetre wide, surrounded by a groove. There are around 4,000 of them on an alligator’s jaws and inside its mouth. Crocodiles and gharials also have the bumps on virtually every scale of their bodies, giving a total of around 9,000. (All of these animals are called crocodilians.)
The thing in the photo above, I’m sad to say, is a penis. It belongs to the male seed beetle. And just in case you’re holding out hope that appearances are deceiving, I can assure you they are not. Those spikes are hard and sharp, and they inflict heavy injuries upon the female beetles during sex. Why would such a hellish organ evolve?
This isn’t just about beetles. The animal kingdom is full of bafflingly-shaped penises adorned with spines, spikes, and convoluted twists and turns. In some animal groups, like certain flies, penis shape is the only clue that allows scientists to distinguish between closely related species.
For a male, sex isn’t just about penetration. After he ejaculates inside a female, his sperm still have to make their way to her eggs to fertilise them and pass on his genes. If she mates with many suitors, her body becomes a battleground where the sperm of different males duke it out. Females can influence this competition by being choosy over mates, storing sperm in special pouches, or evolving their own convoluted genital passages. Males, meanwhile, have evolved their own tricks, including: guarding behaviour; self-castration; barbed sperm; chemical weapons in their sperm; mating plugs; ‘traumatic insemination’; and having lots of sperm.
And spiky penises. That too.
Four years ago, I wrote about a group of African frogs that remind me of the Marvel Comics character Wolverine, who fights with three retractable claws in each arm. The frogs, belonging to the family Arthroleptidae, also have bone claws in their feet. They use these in defence, as many naturalists discovered to their dismay.
They’re not alone. On another continent, Noriko Iwai from the University of Tokyo has studied a different species – the Otton frog – that carries a similar bony spike in its foot. It’s large for a frog, growing to around 12 centimetres in length. The males use their spikes as anchors to latch onto females, and flick-knives for duelling with rival males.
Stranger still, the Otton frog houses its spike in a “thumb”, which other frogs lack. Frogs have five toes on their hind legs, just like us, but most species have just four on their front legs. There are exceptions, though, and the Otton frog is one of them. It has a fifth front toe – a “pseudothumb” – which houses its spike.
Our intelligence clearly surpasses those of our primate relatives, even though other apes and monkeys also rank within the highest tiers of animal smarts. Likewise, the corvids – the group of birds that includes crows, ravens, rooks, magpies and jays – have very sophisticated brains for birds, but one species reputedly outclasses the rest. It’s the New Caledonian crow.
Found in a Pacific island, this crow wields tools in a way that none of its relatives can match. It uses sticks to “fish” for grubs buried in dead wood, and can chosen the right tool for different jobs, combine tools together, and improvise from unusual materials. These abilities have fuelled the New Caledonian crow’s reputation as the top of the corvid class – an unusually intelligent member of an already intelligent family.
But what if it just has the right face?
If I wanted to fish for a grub, I can use my dextrous hands while moving my face around so I can see what I’m doing. The crow only has its beak, which is attached to its face. But Jolyon Troscianko from the University of Birmingham has shown that it has two features that make the job easier: an unusually straight bill, and an extreme overlap between what both eyes can see. These physical traits set it apart from other crows and corvids, and give it an edge when using tools.
When Marvel Comics created a short superhero who could heal horrific injuries, perhaps instead of “Wolverine”, they should have named him “African spiny mouse”. These tiny rodents can jettison strips of skin from their own hides when captured by predators, and heal those same wounds with extraordinary speed.
Healing powers are common in the animal world. Salamanders and starfish can regrow lost limbs, while some flatworms can regenerate their bodies from a single cell. But mammals lag behind – while some species can grow back a lost tail, when most of us lose our body parts, we do so permanently. The spiny mice are an exception.
Biologists have noted that these rodents have very weak skin, which seems to slough off easily when they are handled. Led by these anecdotal reports, Ashley Seifert from the University of Florida has studied the skin-shedding ability in greater depth, focusing on two species: Kemp’s spiny mouse (Acomys kempi); and Percival’s spiny mouse (Acomys percivali).
In 2010, an article in Rolling Stone likened the investment bank Goldman Sachs to “a great vampire squid wrapped around the face of humanity, relentlessly jamming its blood funnel into anything that smells like money.”The creature it was referring to does exist – it’s not a true squid, but one of their close relatives. But despite its terrifying name and appearance, it’s not a vampire. It doesn’t suck blood. It doesn’t have a “blood funnel”.
In fact, thanks to newly published observations, we now know that the vampire squid is a garbage-eater. It extends living fishing lines from its body to snag a rain of rubbish falling from the surface, getting fat on a menu of faeces and corpses.
The Goldman Sachs metaphor still works, doesn’t it?
The vampire squid belongs to the cephalopods, the group that includes squid, octopuses and cuttlefish. But it’s an evolutionary relict that appeared well before any of these more familiar animals. Its body is gelatinous and blood-coloured, as if the internal organ of a larger animal had broken free. It swims with two wing-like flaps, sees with opal-blue eyes, and lights up the surrounding water with flashing organs found all over its body, and especially at the tips of its arms.
Two of these arms have been modified into white thin filaments, which coil up into special pockets, and can extend to 8 times the animal’s length. The other eight arms are connected by a cloak-like web that can be inverted over the vampire squid’s body to reveal a muddy charcoal interior, lined with fleshy spines. You can see where the name comes from.
The vampire squid lives all over the world, but we know very little about what it does. That’s partly because it lives at incredible depths – 600 to 900 metres below the surface, in pitch blackness. This level is known as the oxygen minimum zone (OMZ) and unlike the vampire squid, it’s well-named. While a few animals thrive here, most are choked off by the lack of oxygen.
The vampire squid copes by having an incredibly slow metabolism, blood proteins that hug oxygen molecules with an unyielding grip, and a body that so closely matches the density of water that it neither floats nor sinks. It rarely wastes energy on unnecessary movements. It simply hangs in the darkness.
But even though it lives life in the slow lane, the vampire squid needs food, and that’s in short supply in the oxygen minimum zone. What does it eat? To find out, Hendrik Hoving and Bruce Robison from the Monterey Bay Aquarium Research Institute (MBARI) analysed footage of 170 vampire squids, taken over the last decade by the institute’s submersibles.
The videos, along with feeding experiments on captive vampire squids, revealed that they use their filaments like mobile spider webs. They extend these into the surrounding water to ensnare particles of food falling from above. The filaments are covered in tiny hairs, probably for catching these particles. They also have neurons that connect to a particularly large part of the creature’s brain, presumably so it can sense what’s stuck to its fishing lines.
When the time is right, it retracts the filaments, transfers the food to its other arms, and coats them in mucus secreted from its arm tips. It then conveys these delicious balls of mucus-bound detritus into its mouth, possibly with the help of the spines within its cloak.
This strategy is very different to that of other cephalopods, most of which are active hunters that attack and kill their food. Vampire squids are definitely not that, as Hoving and Robison confirmed by checking the stomachs of captured specimens. They found eggs, algae, pellets of faeces, bits of jelly, crustacean body parts—antennae, eyes, some shells, whole copeopods—and flesh from another deep-sea squid. In both kind and quantity, these remnants don’t reflect the diet of a hunter.
Instead, Hoving and Robison think that the vampire squid is mainly a ‘detritivore’ – a rubbish-eater. With few predators in the oxygen minimum zone, it can afford to sacrifice powerful swimming muscles or a high metabolism. Instead, it leads a relatively passive lifestyle, collecting the plentiful snowing debris with its two modified arms. With these adaptations, it can greatly extend the reach of its mouth, while its body—and its life—literally hangs in the balance.
Reference: Hoving & Robsion. 2012. Vampire squid: detritivores in the oxygen minimum zone. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2012.1357
All images from Hoving and Robison
More on cephalopods
The cheetah’s spots look like the work of a skilled artist, who has delicately dabbed dots of ink upon the animal’s coat. By contrast, the king cheetah – a rare breed from southern Africa – looks like the same artist had a bad day and knocked the whole ink pot over. With thick stripes running down its back, and disorderly blotches over the rest of its body, the king cheetah looks so unusual that it was originally considered a separate species. Its true nature as a mutant breed was finally confirmed in 1981 when two captive spotted females each gave birth to a king.
Two teams of scientists, led by Greg Barsh from the HudsonAlpha Institute for Biotechnology and Stanford University, and Stephen O’Brien from the Frederick National Laboratory for Cancer Research have discovered the gene behind the king cheetah’s ink-stains. And it’s the same gene that turns a mackerel-striped tabby cat into a blotched “classic” one.
Back in 2010, Eduardo Eizirik, one of O’Brien’s team, found a small region of DNA that seemed to control the different markings in mackerel and blotched tabbies. But, we only have a rough draft of the cat genome, they couldn’t identify any specific genes within the area. The study caught the attention of Barsh, who had long been interested in understanding how cats get their patterns, from tiger stripes to leopard rosettes. The two teams started working together.
Every whale and dolphin evolved from a deer-like animal with slender, hoofed legs, which lived between 53 and 56 million years ago. Over time, these ancestral creatures became more streamlined, and their tails widened into flukes. They lost their hind limbs, and their front ones became paddles. And they became smarter. Today, whales and dolphins – collectively known as cetaceans – are among the most intelligent of mammals, with smarts that rival our own primate relatives.
Now, Shixia Xu from Nanjing Normal University has found that a gene called ASPM seems to have played an important role in the evolution of cetacean brains. The gene shows clear signatures of adaptive change at two points in history, when the brains of some cetaceans ballooned in size. But ASPM has also been linked to the evolution of bigger brains in another branch of the mammal family tree – ours. It went through similar bursts of accelerated evolution in the great apes, and especially in our own ancestors after they split away from chimpanzees.
It seems that both primates and cetaceans—the intellectual heavyweights of the animal world—could owe our bulging brains to changes in the same gene. “It’s a significant result,” says Michael McGowen, who studies the genetic evolution of whales at Wayne State University. “The work on ASPM shows clear evidence of adaptive evolution, and adds to the growing evidence of convergence between primates and cetaceans from a molecular perspective.”
Look up any dinosaur, and chances are you will soon come across an estimate for how long it was. And chances are that estimate is wrong. That’s because, as Dave Hone from University College Dublin points out, our knowledge of dinosaur tails is woefully inadequate.
After searching through papers, museum collections, photos, and the minds of his colleagues, Hone found that among the thousands of dinosaur specimens that have been found, there are “barely two dozen complete tails”. These range from animals like Spinosaurus, where virtually no tail fragments have been found, to others where skeletons are missing an unknown number of vertebrae from the tips. Even in complete skeletons, Hone’s research showed that closely related species, and even individuals, can vary greatly in the length and number of bones in their tails.
This matters since tails are factored into estimates of the animals’ lengths, and lengths are often used to estimate mass. As I wrote in my Nature piece on Hone’s work, “If tails are telling tall tales, other important measures could be inaccurate.” Head over there for the rest of the story.
Image by Ballista
Here’s an amazing fact: Adult robins have a magnetic compass in their right eye that allows them to sense the direction of the Earth’s magnetic field, and navigate when all other landmarks are obscured. Here’s an even more amazing fact: Baby robins have two such compasses, one in each eye. They lose the left one as they grow up.
Robins kick-started the study of magnetic senses in the first place. In the 1950s, a German biologist called Hans Fromme showed that robins would always try to escape from a cage in the same direction when it came time to migrate. Even though they had no visual bearings, they headed south-west, as if sunny Spain lay just beyond their cages. In 1966, the husband and wife team of Wolfgang and Roswitha Wiltschko showed that a powerful magnet could disrupt this constant vector, sending them skittering in all sorts of directions.
The Wiltschkos have been studying the magnetic sense of robins ever since. In the 1980s and 1990s, they showed that their compass depends on light. They need some of it, and blue-green wavelengths in particular, to find their way. And in 2002, they showed that the compass lies in just one eye – the right one. If they wore a one-sided goggle that blocked their left eye, they could navigate just fine within their featureless cages. If their right eye was blocked, they headed in random directions. It’s not just robins. They right-eye compasses that the Wiltschkos discovered also exist in Australian silvereyes, homing pigeons and domestic chickens.