Top Ten Most Interesting Arboreal Mammals (Part 1)

Today, in honor of the birthday of Charlie Bowers, we are going to be taking a "Top Ten" approach to some pretty cool arboreal mammals.  FYI, for those of you who don't know, arboreal means an animal that lives in the trees!  So let's dive right in!  For Part 2 of this duology, click HERE.

10.  Squirrel - Although a fairly common animal and really not that exciting at first glance, the squirrel is actually quite the exciting animal!  Incredibly acrobatic, the squirrel is superbly adapted for an arboreal lifestyle.  Need more proof?  Click the link right HERE to be amazed!

One of the koalas at the San Diego Zoo in California.  Photo Credit: Julie Neher

9.  Koala -  Other than the kangaroo, the koala is probably the most iconic Australian marsupial.  Many myths abound in regards to the koala.  For example, many people believe that the koala is constantly "adjusting its altitude," so to speak, due to something in the leaves of the eucalyptus trees that they consume.  While it seems quite likely that the koala is constantly baked due to its lackadaisical attitude, it's not actually true: the koala just spends a great deal of its day asleep in order to digest the tough vegetation that composes its diet.  As a matter of fact, the 20-22 hours a day the koala sleeps makes it the sleepiest  mammal!  (For more information about the koala and its digestion, click HERE). 

8.  Primates - Perhaps the order of mammals that is most superbly adapted to a life in the trees, the primates include everything from the aye-aye to the orangutan, from the tarsier to us humans!  Thought to have started evolving in North America or Asia around 65 MYA or so, before even the dinosaurs died out, today there are over 200 extant species, with new ones still being discovered, like the lesula monkey that was discovered in the Democratic Republic of the Congo in 2012 (pictured above).

7.  Binturong - Often called the "Bear-cat," the binturong is the largest of the strange group of animals known as the civets.  (For more about civets and their relatives, click HERE).  Native to southeastern Asia, the binturong is omnivorous, but seems to consume fruit the most in its diet, and is particularly partial to figs.  Although the binturong is labeled as "Critically Endangered" in China, the IUCN labels the species as a whole as merely "Vulnerable."

6.  Sloth - When you hear the word "sloth," you might think of someone or something being lazy.  There is a very good reason for that association: the sloth is quite sloth!  As David Attenborough says in the excellent BBC production "Life of Mammals," "The sloth moves as if it's powered by the wrong sort of batteries."  Sleeping around 20 hours a day, the sloth is the second sleepiest mammal, right after the koala.  While it sleeps, the sloth hangs upside down from tree branches.  Sounds like a lot of work, right?  Actually, it really isn't: the sloth simply hooks its claws over the tree branch, and relaxes all of its muscles.  If a human hunter shoots a sloth hanging from a tree, it will usually simply remain hanging from the tree branch, anchored by its claws!  Then the hunter actually has to physically climb up into the tree to retrieve its prize!

Animal Spotlight: The Sloth

Today's "Animal Spotlight" is the arboreal South American three-toed sloth (Bradypus variegatus).  The three-toed sloth holds the record for the world's slowest mammal: in fact, it is so slow, that algae grows on its fur, giving it a greenish color.  The algae helps to camouflage the slow animal in the treetops of its rainforest home.  In the case that its camouflage fails it, then it will resort to taking a stab at its attacker with its incredibly large claws.  Definitely not something that you want to take a hit from.

After perusing a few sources, I have come up with a list of the top 10 sleepiest animals, as you can see below.  The numbers are all number of hours spent sleeping a day. 

1. Koala:            20-22
2. Sloth:             20
3. Armadillo:       19
4. Opossum:       19
5. Lemurs:          16
6. Owl Monkey:  17
7. Lion:              14-16
8. Hamster:        14
9. Squirrel:         13-14
10. House Cat:     11-12 

 HERE is a link to an earlier post about the koala, and why it is so sleepy.  The sloth apparently is so incredibly sleepy simply due to the fact that its leaves are so poor in nutrients, much like the predicament the koala finds itself in.

Two other sloth facts struck me as pretty interesting.  The first one is the fact that, due to a few extra neck vertebrae, the sloth can turn its head 270 degrees, as you can see in the picture below.

The second interesting fact is that, despite the poor ability of the sloth to walk on the ground due to weak hind legs, they are actually surprisingly adept swimmers, as you can see in both of the videos below.

A Sloth Walking

A Sloth Swimming


According to the website of National Geographic, the three-toed sloth is labeled as "Endangered" by the IUCN.  Sloths live in Central and South America, and the three-toed sloth specifically inhabits the countries of Venezuela, Guyana, Suriname, French Guyana, and Brazil.

Finally, to learn a little bit more about the sloth, click on the link below.  The video is a short clip narrated by David Attenborough, and is also quite amusing.  Enjoy!

Saying "Boo!" To A Sloth

Digest This: Or Can You? A Koala Could

I've been reading some interesting things about the koala (Phascolarctos cinereus) that I thought you might be interested in hearing.  As we all know, koalas are one of the sleepiest animals, and can be found sleeping and resting around eighteen or nineteen hours a day.  That means that out of their thirteen year life span, they are sleeping for around ten of those years. By comparison, a human with a lifespan of seventy-five years that sleeps an average of eight hours a day would sleep around 25 years of their life.  While a lot more than twelve years for the koala, keep in mind that humans only sleep around 33% of their life, while koalas sleep around a whopping 75-80%. But why do they sleep so much? The answer lies in what they eat: Eucalyptus leaves.

The leaves of the Eucalyptus trees are incredibly hard to digest.  Not only are the leaves very fibrous, much like celery (think about how hard celery is to chew), but they are also chock-full of toxins that very few animals can digest, with especially high concentrations of volatile oils and phenolic compounds.  What does that mean in English?  Well, phenolics are a type of organic chemical that naturally occur in plants, where they can act as deterrents against predatory browsing at the hands (or rather the mouths) of herbivores.  As stated before, the concentration of phenolics in the Eucalyptus leaves are so high that most animals would simply be unable to digest the leaves.  The koala decided not to take this lying down (ironic, as that is most of what koalas do in a day), and have evolved in a few key ways to help them deal with these toxins.

A fascinating moment of a koala's life: being awake.  Quite the statistical anomaly.

The first is simple; they have teeth that are great for chewing.  The broad, high-cusped molars possessed by the koala help it to thoroughly mash the food in its mouth prior to further digestion.  In our own mouth, we also have molars, along with a wide assortment of other types of teeth. When you are chewing your dinner, you tear bite-sized chunks off with your front teeth, or incisors and canines. Then, you move the food to the back of your mouth for further processing, and you further chew the food with your molars. The cusps on our teeth make it so the food is crushed fairly thoroughly. However, the koala doesn’t eat food like lettuce that can be torn up fairly easily. Thus, the koala has higher cusps on their molars, allowing for the Eucalyptus leaves to be ground up quite nicely.

A koala skeleton on display at the American Museum of Natural History in New York, New York.  Note the molars in the back.

The second major evolutionary adaptation is that the koala has a very long cecum, a pouch of sorts that is considered to be the first part of the large intestine.  In fact, at four times its own body length, the cecum of the koala is proportionally longer than that of any other mammal on the planet! The bacteria in the cecum help to break down the tough tissues in plants, such as cellulose, an important structural component of the cell wall in plants.  This gives our fuzzy marsupial friend a whole lot more time and space for that tough plant material to be digested.  Apparently, it takes a whole lot of guts to be a koala.

Believe it or not, I don't have a picture of a koala cecum on file.  So instead, take a look at this other interesting adaptation of the koala.  Instead of having a single thumb like we humans have, it has two!  Its first two digits are both functional thumbs, and are opposable to the other three digits on their hand.  You can see part of the hand skeleton the picture above this one.

Koalas aren't born with those important cecum bacteria, though, and to my knowledge no animals really are.  After five months of suckling from mom, the koala joey starts to enjoy the "partially digested leaf material produced from the female's anus" (MacDonald, 1984), or, as I like to call it, "Mom's Butt Leaves."  This delicious meal is actually thought to come from the cecum, giving the joey those essential bacteria and microbes, not to mention a delightful, pre-digested meal of Mom's Butt Leaves.  (Check out our other post about butt bacteria and eating poop HERE.)

Get yours at your local King Soopers today!

A fourth innovation of the koala is simply the exorbitant amount of time that the marsupial spends sleeping.  When you sleep, you are burning fewer calories than you would be if you were running around or hunting, or moving through a Eucalyptus tree browsing on its leaves.  Therefore, the more time the koala spends sleeping, the more energy it saves in exchange.  (The popular myth that the koala gets "stoned" by the Eucalyptus leaves is nothing more than that: a myth.)  The koala is able to delicately walk the line that we all desire to find: the maximum amount of sleep that one can get without dying.  It's truly a marvelous achievement, one which the koala handles with much grace and aplomb.

During the Pleistocene, there existed a larger species of koala, Phascolarctos stirtoni, a slightly larger koala than the modern species, P. cinereus.  Based on dentary measurements of both species from Price et. al., I came up with an approximate size increase of 1.4.  That is, take the length of a body part of P. cinereus, the modern koala, and multiple that value by 1.4, and you should get the approximate length of the same body part for the robust koala, P. stirtoni.  Not exactly the most precise method, but one that'll work for our purposes.  Below, you can see an approximate size comparison that I made of the two koalas, our modern species in gray and the extinct species in brown.

An approximate size comparison between the modern Phascolarctos cinereus (right) and the extinct P. stirtoni, with a can of Mom's Butt Leaves for scale.

More recently, scientists have realized that there is actually no evidence that does not support the idea that the hypothetical Laser-Eyed Koala (Phascolarctos oculaser) could have maybe possibly existed.  Scientists have been quoted as saying "We have never found it but that's not to say that who's to say that we aren't all koalas."  Below is the first unrefuted photographic evidence of the Laser-Eyed Koala in action.

That incredible, hands-on natural history museum in scenic Morrison, Colorado never stood a chance against that koala.  Fortunately, repairs to the facility should be completed on time for tomorrows 10:15 AM tour, which is included with your admission fee and well worth the time.  Talk about great free advertising, am I right?

Works Cited:

Hättenschwiler, S., & Vitousek, P. (2000). The role of polyphenols in terrestrial ecosystem nutrient cycling. Trends in Ecology & Evolution, 238-243.

Logan, M., & Sanson, G. (2002). The effect of tooth wear on the feeding behaviour of free-ranging koalas (Phascolarctos cinereus, Goldfuss). Journal of Zoology, 63-69.

Macdonald, D. (1984). The Encyclopedia of mammals. New York, NY: Facts on File.

Nagy, K., & Martin, R. (1985). Field Metabolic Rate, Water Flux, Food Consumption and Time Budget of Koalas, Phascolarctos Cinereus (Marsupialia: Phascolarctidae) in Victoria. Australian Journal of Zoology Aust. J. Zool., 655-655.

Piper, K. (2005). An early Pleistocene record of a giant koala (Phascolarctidae: Marsupialia) from western Victoria. Australian Mammalogy Aust. Mammalogy, 221-221.

Price, G. (2008). Is the modern koala (Phascolarctos cinereus) a derived dwarf of a Pleistocene giant? Implications for testing megafauna extinction hypotheses. Quaternary Science Reviews, 2516-2521.

Price, G., Zhao, J., Feng, Y., & Hocknull, S. (2009). New records of Plio-Pleistocene koalas from Australia: Palaeoecological and taxonomic implications. Records of the Australian Museum Rec. Aust. Mus., 39-48.