by Becky Crew
The mongoose did not enter the water but at times approached within two metres (6.5 feet) of the mousedeer, which responded by flaring its throat and showing the white on its throat. The mountain mousedeer (or chevrotain) swam with only the upper half of its head out of the water and was completely submerged at times.
After fifteen minutes, the chevrotain emerged, only to be chased straight back in by the tenacious mongoose. “Investigation revealed that, similar to the Bornean specimen, this was also a pregnant female,” the team revealed.
The researchers also pointed out that while the chevrotains are not closely related to modern whales, their submerging behavior offers an analogue to another water-friendly hoofed mammal that lived millions of years ago.
Since Darwin speculated more than 150 years ago in On the Origin of Species, scientists have accepted that modern whales are the ancestors of terrestrial mammals, and over the past fifteen years, a number of intermediate fossils have been discovered that document this evolutionary journey from land to sea. One of the most significant of these discoveries occurred in 2007, when a team led by Hans Thewissen, a professor of anatomy from the Northeastern Ohio Universities Colleges of Medicine and Pharmacy, unearthed the 48-million-year-old bones of a genus of ancient, water-loving deerlike mammals called Indohyus. According to Thewissen, the fact that the chevrotain family Tragulidae had originally belonged to an ancient family of ruminants called Ruminantia indicated that aquatic escape is a behavior with very deep roots in hoofed land mammals.
A Poisonous Pelt
AFRICAN CRESTED RAT
(Lophiomys imhausi)
THE AFRICAN CRESTED RAT might look exactly like a kind of cuddly porcupine, but thanks to a neat little trick it’s learned, it’s a whole lot more dangerous.
No actual relation to rats, the African crested, or “maned,” rat can grow up to 21 inches from head to tail, and gives birth to fully furred young. Found in East African countries such as Ethiopia, Somalia, Kenya, and Tanzania, the crested rat is named after its distinctive coat of long, dense fur, silver and black tipped in color with a thick grey and white undercoat. Its fur features a long crest of coarse, black-and-white banded hairs running along its back from its nape to the base of its tail, and on either side of the crest are strips of shorter, chestnut-colored hairs that cover an area of glandular skin. When aggravated, the African crested rat will pull its head into its shoulders and use special muscles to part this peculiar area of fur and expose the skin beneath, pointing it toward a predator as if to say, “bite me.” This behavior is so unlike that of any other prey animal, who would either flee or try to at least protect its vulnerable flesh from a predator, that scientists have struggled to explain it since the species’ discovery in 1867.
Some scientists thought that the ability to draw attention to its striking black-and-white mane was a form of mimicry, the crested rat making itself appear like a porcupine or a zorilla—skunk-like polecats that emit foul-smelling secretions to make themselves seem less appetizing to predators. The crested rat’s apparent impersonation of the polecat was said to be a form of Batesian mimicry, a technique that describes a defenseless, naturally sluggish animal copying the defense mechanism of another animal in the face of danger. But then reports of dogs biting crested rats and then rapidly dying of heart failure began to surface, and it was clear that something else was in play.
In mid-2011, scientists from the University of Oxford published a paper in Proceedings of the Royal Society announcing that they had finally solved the puzzle of the African crested rat. They discovered that the species takes advantage of the highly toxic poison arrow tree (Acokanthera schimperi) by chewing on its bark and roots and smearing the toxins along its mane. African hunters use this toxin, called ouabain, to produce poison-tipped arrows that can bring down something as powerful as an elephant. According to the researchers, this particular defense technique is unique among the 4000 known species of placental mammals. A similar example of this behavior exists in the hedgehog, which chews on the poison glands of toads and slathers the venom on its spines. But the worst this can do is make a prick from its spines slightly more painful, and unlike the African crested rat’s poisonous fur, has never resulted in a recorded death.
A chemical analysis of the crested rat’s hairs revealed that they are loaded with ouabain, which works by inhibiting the pump that controls the balance of sodium and potassium ions in the body’s cells. This causes the cells to be flooded with sodium and calcium ions, and even small doses of ouabain can lead to muscle contractions. Higher doses can lead to deadly respiratory or cardiac arrest. The researchers tested the reaction of the flank hairs when brought into contact with liquid, in this case red ink, under a microscope. They discovered that each shaft is covered in tiny holes that eagerly soaked up the ink, while the fine fibers loaded inside each shaft effectively hold the substance in place. Thanks to its specialized flank hairs, the African crested rat is a poison-soaking and storing machine. What remains a mystery is how it prevents itself from being poisoned as it chews the bark of the poison arrow tree, when a tiny amount can bring a hippo or an elephant to its knees.
“Look, I get it, African Crested Rat, but I just don’t think it’s going to work.”
“Can I show you my sketches?”
“Okay, show me your sketches.”
“So here’s African Crested Rat Man fighting a house cat in his underground lair.”
“What’s that?”
“That’s African Crested Rat Man’s utility belt.”
“What’s in it?”
“Nothing.”
“Pardon?”
“There’s nothing in it. That’s the point. We don’t have to do anything, we just have to stand there and show the predators our poison fur and that’s our superpower.”
“And you can also chew poison bark and not die.”
“We’d rather not reveal the source of our powers, thanks very much.”
“Okay, look, I’m going to be straight with you, African Crested Rat. I just don’t think a superhero whose superpower is to stand there and expose himself is going to take off. Now get the hell out of my office.”
What Big Eyes You Have!
GIANT AND COLOSSAL SQUID
(Architeuthis and Mesonychoteuthis)
“Hello?”
“Hey, it’s me.”
“Oh hey, Giant Squid. What do you want? I’m trying to get dressed for work over here.”
“I know, I’m watching you.”
“Argh, would you quit it with that stuff? You guys should have to apply for a license to see so far away. You’re all a bunch of creeps.”
“That’s a really ugly tie.”
WHILE THE DIMINUTIVE PHILIPPINE tarsier has the largest eyes relative to body size of all the mammals on Earth, the giant and colossal squid have the largest eyes of the whole animal kingdom. What scientists couldn’t figure out until recently was why.
With bodies that grow up to 33 feet long from head to tentacle tip, the giant and colossal squid don’t have a wealth of predators to keep watch for. Plus they share the pelagic depths—or “open sea” near neither the ocean floor nor the shore—with many animals who get by perfectly well with eyes that are a mere fraction of the size. While scientists could not figure out why these two types of squid would need eyes 10–16 inches in diameter, which is nearly three times the diameter of any other animal’s eye, they knew this enormous size would have to serve a very specific function.
In 2007, the largest intact squid ever dredged up from the ocean depths was netted in the Ross Sea, a deep bay just off Antarctica. The 26-foot-long, 1091-pound adult colossal squid (Mesonychoteuthis hamiltoni) had stunning 11-inch-wide eyes, and it was these that a team of scientists, led by biologist Sönke Johnsen from Duke University in the United States, investigated in order to discover the secret of these mighty sea creatures and their slightly smaller cousin, the giant squid (Architeuthis). “Compared to the next largest eyes, they’re three t
imes wider and have twenty-seven times the volume,” says Johnsen. “Like elephant trunks and the stars on star-nosed moles, you just can’t help wondering what they’re good for and why they look the way they do.”
The team used a mathematical model to figure out the value of basketball-sized eyes in terms of vision. “Most of the research was really an extended and complex mathematical argument. And I do mean argument, since we disagreed on many points at first,” says Johnsen. “A wonderful thing about studying vision in the ocean though is that the system is complex enough to give you interesting results, but simple enough that you can model it accurately.” What they discovered was that the enormous output of energy to grow and maintain the eyes significantly outweighed the general vision benefits. So assuming that giant and colossal squid do what everyone else in the ocean does at depths of 984–3281 meters below the surface, their eyes would be a waste, an evolutionary blunder. But what sets these squid apart from other creatures in the ocean, and what renders these eyes an evolutionary success, is that colossal and giant squid are a favorite meal of the 49-foot-long sperm whale, judging from several stomach content analyses.
When sperm whales dive up to 1640 feet below the surface, emitting sonar to locate the whereabouts of huge squid, they set off a wave of bioluminescence from smaller gelatinous animals such as plankton wherever they go. While the giant and colossal squid’s eyes don’t give them significantly better eyesight, they do allow these animals to take in much more light than animals with smaller eyes. This enables them to detect the subtle differences in contrast within the dim environment of the deep sea, such as that caused by a sudden path of light emitted by smaller creatures fluorescing when disturbed by something bigger. Johnsen explains:
The interaction of light with matter (for example a retina) is not continuous, but instead comes in discrete chunks we call photons. These arrive randomly over time, so you need a lot of them to get a sample accurate enough to see small differences in brightness between a target and the background. So having a huge eye (in particular a giant pupil) lets in more light so more photons arrive over a shorter period of time and give you a better image.
The ability to sense contrast in ocean light is not particularly useful to smaller sea creatures, who have to worry more about predators in their immediate area, but to be able to detect the presence of a giant object lurking more than 300 feet away is a matter of life and death for a giant or colossal squid. “The most likely explanation for the unusually large eyes in giant and colossal squid is the unique ability to detect large predators that trigger plankton bioluminescence as they move through the water,” the researchers reported in a 2012 issue of Current Biology. “A long detection range implies that a huge water volume around the squid can be monitored for predators.”
But being able to detect sperm whales up to 395 feet away doesn’t mean that the giant and colossal squid can easily slip away undetected. The sperm whale’s sonar, which the squid are incapable of hearing, will have already given away the squid’s location, leading Johnsen’s team to suggest that the squid’s large, powerful bodies are built for hauling them and their giant eyes away from a looming threat. So the main advantage of their huge eyes is not to spot the sperm whales before the sperm whales spot them, it’s to give them enough time to prepare an effective escape. “What a big eye gives you is the ability to see very low contrast objects in dim light. Where it really matters is when you are trying to see a very large object from far away underwater in dim light. Very few animals need to do this,” says Johnsen. He adds:
Whales would be the obvious choice, but they mostly use sonar and vision is relatively unimportant. So you’re left with animals that are preyed upon by large toothed whales. Most of these are too small to benefit from seeing the whale, but squid are big enough to take advantage of early detection, since they actually have a chance to jump out of the way.
According to Johnsen, the only other known evolution of huge eyes is in the ichthyosaurs—a group of large sea creatures not unlike swordfish that lived around 230–100 million years ago, from the mid-Triassic to mid-Cretaceous period. These are the only animals known to have eyes comparable to the giant and colossal squids’ in terms of size, which suggests that they were used to detect the presence of giant apex predators called pliosaurs. Just like the giant and colossal squids’ eyes, the ichthyosaur’s massive peepers would have given it the head start it needed.
Wolverine Frog
HAIRY FROG OF CAMEROON
(Trichobatrachus robustus)
“She left me.”
“Texas Horned Lizard? For whom?”
“A fucking frog. He’s got bone claws … I just can’t believe it’s over.”
“Wow, she’s really got a thing for species that weaponize their own skeletons, huh?”
A CREATURE THAT FLICKS claws made from its own bones through its fingers as a defense mechanism? Sure, Marvel revealed that Wolverine’s six retractable claws were made from his own bones in 1993, but the hairy frog of Cameroon has been using its own bones as weapons for way longer than that.
The hairy frog of Cameroon belongs to the Arthroleptidae family of “screecher frogs” from sub-Saharan Africa, so-called because of the distinctive high-pitched call that runs through all seventy species in this group. The hairy frog is a dark-colored, almost black species with blush-pink and white colorings on its underside. At 4 inches long from snout to toe, it is among the larger of the Arthroleptidae frogs, and was named because of the odd, hair-thin skin fibers that form a thick, shaggy fur across the thighs and flanks of the males during the breeding season. Because these fibers are highly vascularized, which means they’re packed with blood vessels to aid the supply of blood and oxygen, scientists have suspected that the male’s hirsute coat increases respiration while it sits submerged in a stream for long periods of time on clutches of eggs laid by its mate.
While the males’ hairy legs might be the most obvious physical feature of the hairy frog of Cameroon, their bone-claws are certainly the strangest. Observations have been made about claw-wielding frogs since the 1930s, the most famous of which was made by British naturalist, zookeeper, and author Gerard Durrell, who in his 1954 book The Bafut Beagles describes in painstaking detail the process of catching one of these nimble amphibians. And the even bigger challenge? Holding on to it.
He was not going to give up his liberty without a fight, and he uttered a loud screaming gurk, and kicked out frantically with his free hind leg, scraping his toes across the back of my hand. As he did so, I felt as though it had been scratched with several needles, and on the skin of the back of my hand appeared several deep grooves which turned red with the welling blood. I was so astonished at this unexpected attack from a creature which I had thought to be completely harmless, that I must have relaxed my hold slightly. The frog gave an extra hard kick and a wriggle, his moist leg slid through my fingers, there was a plop as he hit the water and the ripples danced. My Hairy Frog had escaped.
The hairy frog of Cameroon shares the bone-claw trait with another species from Cameroon called Scotobleps gabonicus, and eleven species in the closely related Astylosternus, or “night frogs,” genus. But despite the fact that several species of frogs wield claws, for years scientists could not explain the anatomical mechanism that causes it, because very few observations had been made using live specimens. This was until evolutionary biologist David Blackburn from the University of Kansas Biodiversity Institute traveled to Cameroon in 2006. “I was working in Cameroon on dissertation research when I also had the experience of collecting these frogs and having them rake their claws against my skin. It’s definitely enough to give you a bloody scratch and certainly can cause you to drop the frog, especially if you’re not expecting it!” Blackburn says of his first encounter with the frogs.
When he returned to Harvard’s Museum of Comparative Zoology, where he was based at the time, Blackburn discovered that the very claws that made him bleed in Cameroon were protruding cleanly
through the toe flesh of the museum’s preserved hairy frog specimens. “When discussing this with my friend and colleague [and Harvard paleontologist] Farish Jenkins, it struck us as strange that no one had ever investigated how it was that these toe bones could come to protrude through the skin,” he says.
It took almost a year before Blackburn had access to enough live specimens to rule out the possibility that the hairy frog’s toe claws are formed by bones that grow so long over an extended period of time that they eventually poke through the tips of the skin. Rather, he says, it seems to occur suddenly to cause a traumatic wound to the toe. “We thought it noteworthy that most vertebrates do a perfectly good job of keeping their skeletons on the inside of their bodies, and yet these frogs seemed to have evolved some mechanism for getting the last bone in their toe to pop through the skin,” he says, adding that if you take a moment to look down at your own fingertips or toes and imagine somehow pushing your bones right through them on command, you can understand how strange and difficult to explain this situation was.
What he discovered is that the hairy frog of Cameroon has a small piece of bone beyond the end of the toe bones in its hind feet. There is a soft tissue connection made of collagen that connects this little piece of bone to the end of the toe bone. It appears that when these frogs flex a particular muscle in their toe, the toe bone breaks free of this little piece of bone and pierces through the bottom of the toe. “These frogs have evolved a suite of very unusual anatomical structures at the ends of their toes. Imagine having another bit of bone beyond the last bone in your finger or toe … a very unusual situation!” he says, having published his findings in a 2009 issue of Biology Letters.
