Posts tagged as:

evolution

Goodfellow’s Tree Kangaroo (Dendrolagus goodfellowi)

by JR Kinyak on March 25, 2011

in Marsupials

I’m eager to introduce you to an enchanting tree kangaroo, but first let me remind you that starting Sunday, Coco and I will be selling original drawings of the mammals of Japan with all proceeds helping victims of the earthquakes and tsunamis. See yesterday’s post for the details!

Goodfellow's tree kangaroo (click image to enlarge)


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I have fallen in love with tree kangaroos. They are my new favorite animal. They’re magical; they sound like something someone made up for a children’s storybook. Like regular kangaroos, tree kangaroos are marsupials, and the two kinds of animals are related. It seems that all the kangaroos—tree and otherwise—evolved from a common ancestor. According to the 1947 book Furred Animals of Australia by Ellis Troughton (which, incidentally, has a most endearing dedication: “To my mother…to whom any originality of written thought is lovingly dedicated”),

“The tree-kangaroos are of particular interest in having undergone an unusual twist or secondary phase of evolution which is reflected in their appearance and habits. Originally descended like their fellows from primitive tree-dwelling stock, the adoption of a hopping means of progression resulted in marked lengthening of the hind-limb, with a corresponding loss of the possum-like clinging great toe, while the tail changed from a prehensile to a balancing implement. After the long period of terrestrial existence which moulded the kangaroo-like appearance, the animal reverted to the trees again for foraging and safety, with a corresponding reversal in general structure towards the arboreal type.”

In other words, in case you are not a natural at interpreting the words of early-20th-century naturalists like I am, Troughton’s saying that all the kangaroos descended from an early tree-dwelling mammal, then adapted to the plains through the evolution of big ol’ feet for hopping. They didn’t need to grasp trees with their back legs or prehensile tails, so they lost their handy big toes and their tails became big and sturdy—not agile for swinging through the branches but stable for balance. Then, the tree kangaroos re-evolved back into a treetop lifestyle among the branches of the cloud forest. That’s why they look, indeed, like kangaroos incongruously perched in the trees.

Troughton also says that this evolution—from treetops to the ground and back to the treetops—is an illustration of “the irreversible law of evolution wherein features lost owing to disuse cannot be regenerated.” The tree kangaroos’ ancient ancestors had prehensile tails; they evolved to have big balancing tails instead, and there’s no going back. If you’re a regular reader of this site, you know that I’m a fairly new student of evolution, and I believe this is the first time I read this “irreversible law,” or at least the first time it sunk in. What do you think of that idea?

There are 12 species of tree kangaroos, and they live in Australia and Papua New Guinea. This particular species, Goodfellow’s (and another question: why are some possessive scientific names spelled with two Is, like the other day’s finlaysonii and prevostii squirrels, but some only have one I, like today’s goodfellowi? I was expecting it to be goodfellowii) is endemic to Papua New Guinea and is endangered. Tree kangaroos have long been hunted for food by indigenous people, and their pelts are used in traditional ceremonies. Now they’ve been overhunted, and of course their habitats are also being destroyed because whose isn’t?

Another thing I like about tree kangaroos: if they jumped off a measly little boulder in an arroyo, they would not break their calcanea, the way I did two weeks ago. In fact, they routinely jump from the treetops to the ground 60 or more feet below without getting hurt! Isn’t that amazing? Here’s a remarkable video that includes footage of one of those jumps as well as “Crittercam” images from two tree kangaroos wearing cameras around their necks. (The beauties in the video are a different species, the Matschie’s tree kangaroo.)

I tell you, I adore them! I really do! And I’m not the only one. In fact, I found this lovely little story that says that before you judge someone else, think of the tree kangaroo, and remember that the other person loves the tree kangaroo just as much as you do. With that common foundation, can’t you find something else to agree on?

Tagged as: endangered, evolution, love, threats

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Wrinkle-faced Bat (Centurio senex)

by JR Kinyak on February 28, 2011

in Bats,Theme Weeks

wrinkle-faced bat

Wrinkle-faced bat (click image to enlarge)


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When I drew this guy, I was working on a Mammal Mating theme week, but that was several months ago, and now I can’t figure out what’s interesting about the wrinkle-faced bat’s mating habits, except that scientists speculate that the wrinkled face may be related to sexual selection. Only the males have big neck flaps, and they emit a musky odor from their chin regions, and why would males emit a musky odor from their chin regions if not to attract females?

The flaps at the male bats’ necks are so big that when they’re resting, they flip the flaps up to cover their entire faces. I thought it might be to keep light out so they could sleep better during the day, but then I learned that they have translucent patches over the eyes! Pretty amazing.

This article from the Journal of Zoology (link is to a PDF) uses words like bizarre, extraordinary, unusual, exceptional, enigmatic, and dramatic in describing the bat’s strange face and head. The wrinkle-faced bat is frugivorous, meaning it eats fruit, and the article’s authors conclude that it’s likely that the shape of the head, anyway, is in service of the bat’s strong bite, which perhaps helps it eat harder fruits and therefore survive when weaker-jawed frugivores wouldn’t. Usually, when a bat has strange facial folds, it’s thought that the wrinkles help focus the bat’s sonar so it can better catch insects. But this fruit-eater obviously doesn’t need that kind of help. I read one theory speculating that the wrinkles could channel fruit juice into the bat’s mouth.

The scientific name Centurio senex means “100-year-old man.”

Tagged as: bat, evolution, mating, names

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Common Wombat (Vombatus ursinus)

by JR Kinyak on April 10, 2010

in Marsupials

Common wombat (click image to enlarge)

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Wombats are Australian marsupials, and the common wombat is, naturally, the most common of the three wombat species. Common wombats live along the coast of southeastern Australia, in alpine areas and sandy places. The wombats’ claim to fame is that they are the only known large, herbivorous burrowing mammals: all the other burrowing herbivores are small, and all the other large burrowers are carnivores or insectivores. That’s because being a herbivore requires a lot of time and energy spent on foraging (don’t I know it), and being a burrower requires a lot of time and energy spent on digging. Large herbivores usually don’t have that kind of free time.

And wombats are large! The common wombat ranges from about 50 pounds to nearly 90, or about the size of a pretty-big dog to about the size of a really big dog. They look like they’d be about rabbit-sized, or at least they do to me, but no, they’re humongous. However, they have extraordinarily slow metabolisms and really don’t need to eat much at all: only about half as much as a kangaroo does, and a kangaroo weighs about the same as a wombat. That means the wombat can nocturnally forage at its leisure and spend most of its time lazing underground.

Coco drew a wombat, too!

Common wombat by Coco, age 11 (click image to enlarge)

Tagged as: evolution

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Greater Mouse-Deer (Tragulus napu)

by JR Kinyak on July 13, 2009

in Ungulates

Greater mouse-deer (click image to enlarge)

Greater mouse-deer (click image to enlarge)


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The greater mouse-deer is a teeny-tiny little thing, more or less rabbit-sized with legs the size of pencils. (I drew this one’s front legs too big.) The deer, also called chevrotains, live in Brunei, Indonesia, Malaysia, Myanmar, and Thailand. They weigh about 11 pounds, and unusually for deer, they don’t have horns or antlers. They do have big ol’ upper canine teeth, though, that become tusk-like in males.

Here’s an alarming (to me) fact: female greater mouse-deer spend only about two hours between giving birth and becoming pregnant again! They’re pregnant their whole lives. This leads me to ask a question of my biologist readers: are the pregnancies of other mammals as uncomfortable as ours? I’m thinking of morning sickness, varicose veins, hemorrhoids, backache, swollen ankles, etc. Is this unique to humans, and if so, why?

A remarkable thing about greater mouse-deer (which are sometimes called “living fossils” because of how ancient they are as a species) is that they are amazingly good swimmers. Scientists have observed them fleeing predators—say, humans or mongooses—by jumping into the water and staying under for up to five minutes at a time. They’ll swim around for an hour to keep away from a threat. Another Asian mouse-deer species does the same thing, as does an African relative of the species. These observations have lent credence to the idea that whales evolved from deer-like mammals.

Supposedly, greater mouse-deer make good pets. I think they would look particularly cute paired up with an Italian greyhound.

BBC: “Aquatic deer and ancient whales”

Tagged as: deer, evolution

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Darwin Days: Giraffe (Giraffa camelopardalis)

by JR Kinyak on February 14, 2009

in Theme Weeks,Ungulates

click image to enlarge

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Tonight, we conclude our celebration of Charles Darwin’s 200th birthday with one last look at a mammal he wrote about in The Origin of Species.

Although Darwin’s work is widely available for free online (see The Complete Work of Charles Darwin Online, and you’re probably all set), I still find it easier and more satisfying to thumb through an actual book. It’s kind of like rewinding a cassette tape versus placing a needle on a record. For me, anyway. So I bought a Penguin edition of Origin. There were three different printings to choose from at my bookstore, and I picked the middle one, price-wise, which seemed to have decent paper. Turns out it’s a reprint of the first edition, and Darwin produced six editions total, each quite different from the previous. All this is to say that in the sixth edition, Darwin added a second chapter dealing with objections to his theory. In that chapter, he discusses the giraffe in great detail, discussing how and why it might be advantageous for a “nascent giraffe” to evolve a long, long neck.

It seems that the giraffe is still throwing people for a loop. When I was researching giraffe photos online for reference, I found one posted on Flickr that had a long, not overly polite discussion in the comments section about whether or not it was possible for a giraffe’s neck to evolve, or whether the very fact of the giraffe’s long neck was proof of the creation of the giraffe as a whole being, immutable and perfect. To me, it seems a textbook example of natural selection: the protogiraffes with the longest necks were able to eat more than the others. They lived longer because they ate longer. They reproduced more because they lived longer. More giraffes were born with long necks. And so on. But people still have problems with it because the giraffe seems unique, because it requires special structural adaptations in order to operate with such a long neck, or maybe because it looks like something someone like Dr. Seuss would have had to think up.

The giraffe reference I particularly like in Origin, though, is in my first-edition reproduction. After discussing the problem of the evolution of organs of seeming perfection (like the eye), Darwin addresses the problem of the evolution of “organs of little apparent importance.” In his charmingly open and self-effacing way, he writes, “I have sometimes felt much difficulty in understanding the origin of simple parts, of which the importance does not seem sufficient to cause the preservation of successively varying individuals.” Darwin goes on to point out that we shouldn’t be so arrogant as to presume we know what’s important and what’s not. And the example he uses is the giraffe’s tail:

“The tail of the giraffe looks like an artificially constructed fly-flapper; and it seems at first incredible that this could have been adapted for its present purpose by successive slight modifications, each better and better, for so trifling an object as driving away flies; yet we should pause before being too positive even in this case, for we know that the distribution and existence of cattle and other animals in South America absolutely depends on their power of resisting the attacks of insects: so that individuals which could by any means defend themselves from these small enemies, would be able to range into new pastures and thus gain a great advantage. It is not that the larger quadrupeds are actually destroyed (except in some rare cases) by the flies, but they are incessantly harassed and their strength reduced, so that they are more subject to disease, or not so well enabled in a coming dearth to search for food, or to escape from beasts of prey.”

First of all, don’t you love that 19th-century sentence structure, with endless commas, colons, semicolons, and then more commas? I love it. What Darwin is saying here* is that a fly-swatter is not as trivial as it seems. Fighting off flies saps a person’s energy, and so it makes sense that the best fly-flighters would have a reproductive advantage. I imagine this is why giraffes have such lovely eyelashes, too.

My husband Ted has a theory that sexual selection could play a part here (see my lion post of a couple days ago). In his theory, female giraffes would be more attracted to those male giraffes who coolly switched their tails, rather than those who itched and jumped because flies were crawling all over them. It makes sense to me.

*I should note that my mammalogy is completely self taught. Two of my worst teachers ever were my two biology teachers (7th grade and 8th grade). What knowledge I have of science is from my dad (a geologist and painter) and my own curiosity and love of animals. So if I’m telling you really, really obvious things about evolution, I apologize. I’m just learning it all myself.

Tagged as: books, darwin, evolution, sexual selection

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Darwin Days: American Mink (Neovison vison or Mustela vison)

by JR Kinyak on February 12, 2009

in Carnivores,Theme Weeks

click image to enlarge

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Welcome, readers of the Blog for Darwin blog carnival! (A blog carnival is a collection of posts from different blogs but on the same topic. I’m participating in one that compiles posts related to Darwin today through the 15th. Click the link above to read some of the other bloggers’ posts.) At the Daily Mammal, we’re celebrating Charles Darwin’s 200th birthday (today! happy birthday!) with a look at some of the mammals that Darwin mentions in his Origin.

Chapter Six of Origin is dedicated to answering some of the problems that Darwin anticipates people finding with his theory. One of these issues is the seemingly amazing perfection of certain natural structures, like the eye, and the incredulity with which people consider that such perfection could arise gradually through natural selection. Another is the apparent lack of transition species: if species are always changing one into another, why don’t we see all kinds of transition species, both now and in the fossil record? And how is it even possible that, for instance, a land animal could evolve into an aquatic one? How would the transitional species in between have lived?

That’s where this fellow, the American mink, comes in. Darwin writes:

“It would be easy to show that within the same group carnivorous animals exist having every intermediate grade between truly aquatic and strictly terrestrial habits; and as each exists by a struggle for life, it is clear that each is well adapted in its habits to its place in nature. Look at the Mustela vison of North America, which has webbed feet and which resembles an otter in its fur, short legs, and form of tail; during summer this animal dives for and preys on fish, but during the long winter it leaves the frozen waters, and preys like other polecats on mice and land animals.”

So, taking this mink as an example, if certain traits that lent themselves to living in the water began to be an advantage in the struggle for survival—say, water levels rose or predators pushed the minks out of their normal territory into one more waterlogged—the minks that were better adapted to aquatic living would be more likely to survive and reproduce their genes. And with successive generations, these characteristics would be strengthened, and as more and more minks were born with these adaptations, they would through greater numbers eventually take over, and perhaps we would have a new species. At least that’s this laywoman’s interpretation of the idea. Another example:

“In North America a black bear was seen by Hearne swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.”

Another thing to ponder is the way humans, through hunting, for instance, are creating unnatural selection. A recent study found that as bighorn sheep are hunted for their gigantic, beautiful, curling horns, those with smaller, less impressive horns are more likely to survive and reproduce. The result seems to be a decrease in horn size across the population. And since it seems that those bighorns with the biggest horns are also the most healthy and strongest, hunters are creating a weakened population. Some are calling it “evolution in reverse.” Perhaps we would have seen something like this in the minks if fur farms hadn’t overtaken the hunting of wild minks, and if trappers and mink hunters could selectively trap and hunt only the minks with the lushest coats.

Mink are fairly solitary and fairly nocturnal. They live in burrows beside rivers and they dine on crayfish and frogs in the summer, as Darwin noted, and small mammals like shrews and rabbits in the winter. Sometimes they use fur from their prey to line their dens. They are good at swiming, diving, and climbing.

Tagged as: books, darwin, evolution

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Darwin Days: Lion (Panthera leo)

by JR Kinyak on February 11, 2009

in Carnivores,Theme Weeks

click image to enlarge
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It’s quite fashionable to equate the theory of evolution with Charles Darwin himself. Science magazines and books sell with covers blaring “Darwin Was Wrong,” “Was Darwin Wrong?,” and “What Darwin Got Wrong.” Meanwhile, intelligent-design and creationism proponents attack “Darwinism,” and the New York Times publishes “Darwinism Must Die So That Evolution May Live” and “Let’s Get Rid of Darwinism.” By creating an -ism, the New York Times pieces suggest, “Darwinists” devalue their own arguments, putting them on the same level as, for instance, creationism.

The fact, as far as I can tell, is that Darwin was right about many, many things, and most of those things that he was wrong about (mainly because things like genetics and continental drift hadn’t yet been discovered, and the man couldn’t do it all!) have nevertheless been built on his foundation. Many of the articles celebrating Darwin’s bicentennial point out how remarkable it is that after 150 years, On the Origin of Species is still relevant. Today we’ll talk about one of the ideas Darwin had before his time and that is still being studied and proven: sexual selection.

Basically, sexual selection refers to the favoring of certain traits solely because they are attractive to mates. As Darwin says in Chapter 4 of Origin, “This depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring.” To attract females, males develop showy traits like bright feathers, big antlers, or electric guitars. The reasons why females are attracted to these things in the first place are not fully known; it could be that a male with big horns, for instance, has good genes in other ways; another theory holds that if a male can thrive despite the “handicap” of a huge tail or something, he must be pretty strong.

The lion’s mane has long been a puzzle. In 1859, in Origin, Darwin wrote, “The males of carnivorous animals are already well armed; though to them and to others, special means of defence may be given through means of sexual selection, as the mane of the lion, and the hooked jaw to the salmon; for the shield may be as important for victory, as the sword or spear.” The going theory for many years was that manes protected male lions from the claws and teeth of their rivals, but now it doesn’t appear that’s true because fighting lions don’t tend to go for the head and neck in particular.

Studies in the past several years have focused on the variations in mane length and color. Researchers found that the luxuriousness of a lion’s mane depended on its climate: lower, hotter, and more humid climates meant skimpier, lighter-colored manes because it can get hot under all that hair. The researchers were also surprised to learn that manes continue developing after the lion’s sexual prime has come and gone. In the hottest places, older males are the only ones with manes to write home about. It makes me wonder if there could be a reverse sexual selection going on there: if you don’t have a mane in a hot place, does it indicate that you’re younger and therefore more virile? I don’t know.

Scientists also fooled around with trying to lure both male and female lions with fake dummy lions of varying mane lengths. They found that males approached the shorter-maned dummies 9 out of 10 times, and females approached the longer-maned ones 13 out of 14 times. The males that intrigued the females intimidated the other males, in other words.

Here’s a book I read part of once that postulates that all human creative culture—from art to architecture to comedy to writing books, etc.—is the result of sexual selection. In other words, men do cool things because chicks dig it: The Mating Mind by Geoffrey Miller.

Tagged as: books, cat, darwin, evolution, sexual selection

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