Arthur the Aardvark

Almost everybody has heard of Arthur Read from the popular PBS show "Arthur."  What a lot of people don't realize is that Arthur is an aardvark.  And even more people don't usually even know what an aardvark is.

A fossorial (burrowing, like terrestrial or marine), nocturnal mammal from Africa, the aardvark is an insectivore, its favorite food being termites, and is labeled as "Least Concern" by the IUCN.  The aardvark, as you can see below, inhabits an incredibly large portion of Africa, including South Africa, Ethiopia, Kenya, Tanzania, Uganda, Mozambique, the Democratic Republic of the Congo (DRC), Burundi, Somalia, Angola, and many others.

The aardvark has several important adaptations for its burrowing, insectivorous life style.  Perhaps the most important are the large claws on its front limbs.  These claws enable the aardvark to not only dig out immense burrows for habitation use, but also to dig into termite mounds to extract a meal.  Interestingly, when the aardvark leaves its burrow to dig a new one, the old burrow is often taken up by the African wild dog, where the pups shelter until they are old enough to leave the protection of the burrow.

The aardvark also has thick skin, which keep the termites from biting it, allowing it to feast in relative peace.  A further adaptation to keep insects (as well as dust) out is in its nose: it can close its nose, preventing both bugs and dust from invading its breathing passages.  Finally, another very important insectivorous adaptation is the tongue of the aardvark.  The long, sticky tongue of the aardvark is usually about 12 inches long, equivalent to about one-sixth the length of the animal!  Long, sticky tongues are a fairly common adaptation for termite-eaters such as the numbat (Myrmecobius fasciatus), pangolins (Manis sp.), and the giant anteater (Myrmecophaga tridactyla) among them.

A southern tamandua (Tamandua tetradactyla) shows off its extraordinarily long tongue during an animal demonstration at one of Denver Zoo's teen career days.  Tamanduas are also insectivorous, and clearly also possess an amazing tongue.

Smilodon Vs. Thylacosmilus: The Saber-Toothed Marsupial

Two million years ago, a saber-toothed predator stalked the landscape of South America.  Possessed with long, dagger-like teeth, Thylacosmilus was undoubtedly a terrifying predator of the plains of Patagonia.  This saber-toothed predator would have given even the saber-toothed cats pause, despite the fact that (to paraphrase Obi-Wan Kenobi), "He's more kangaroo now than cat."  Despite superficial similarities, Thylacosmilus was not a saber-toothed cat.  Instead, it was a six foot long, 500 pound saber-toothed marsupial.

A reconstruction of Thylacosmilus by the talented young artist Sam Lippincott.  Interestingly, the super-sized canines of Thylacosmilus grew continually throughout its life, unlike those of Smilodon or Xenosmilus (see below), two of the actual saber-toothed cats.  Photo Credit: Sam Lippincott

The immense canines possessed by Thylacosmilus had previously evolved in both the cat-like Nimravids and the various saber-toothed cats (amongst others), and is a classic example of convergent evolution, a topic, in my opinion, that is one of the most interesting happenstances in nature.  We will hopefully talk about convergent evolution sometime next week.

A mounted skeleton of Xenosmilus, a type of saber-toothed feline, at the Mace Brown Museum of Natural History at the College of Charleston in South Carolina.  I got to visit here in July of 2014, and it was a very nice little museum.  Compare the skull of Xenosmilus with that of Thylacosmilus (below).

Anyways, Thylacosmilus lived during the Miocene and the Pliocene Epochs, from 10-2 MYA.  Up until 2 MYA, South America had been its own, separate land mass, not connected to any other continents since some time during the Cretaceous.  2 MYA, however, something extraordinary happened: the Isthmus of Panama was formed, connecting the two continents.  With this connection, came something scientists have dubbed the "Great American Interchange."  Animals from both continents could move, and spread out into the other continents.  For some creatures, like the saber-toothed cats, this was a good thing; they moved down into South America from North America and dominated the landscape.  For other predators, like the terror-bird Titanis(again, a topic for another time), it was good, for a while; after moving into the southern part of North America, however, Titanis was outcompeted by other predators.  For Thylacosmilus, it was down-right disastrous.  Shortly after the Great American Interchange, fossil evidence of Thylacosmilus entirely disappears, similar to the competition between the dingo and the thylacine that drove the thylacine to extinction on mainland Australia.

The skull of Thylacosmilus on display at the American Museum of Natural History in New York.  Got to see this sucker in person in August 2014, when I visited with my good buddy Zach Evens! 

This is a partial post for the "Convergent Evolution" series.  That means that this post is partially included, but was not made specifically to be a part of that series.  HERE is a link to the Homebase for this series.  

Animal Spotlight: The Mountain Pygmy Possum

You've probably never heard of the mountain pygmy possum (Burramys parvus); few people have, it being one of Australia's many lesser known marsupials.  One of five extant (opposite of extinct, or still living today) species of pygmy possum, the mountain pygmy possum has a very interesting story about its discovery, a story that we will now look at.

The genus Burramys, the genus the mountain pygmy possum is a part of, also contains three extinct species of possum.   In fact, prior to 1966, the mountain pygmy possum had been described solely from fossils dated from the Pleistocene Epoch.  (The Pleistocene Epoch dates from around 2.5 million years ago to around 10,000 years ago, when the last Ice Age ended.)  It was first described from these Pleistocene fossils by the famous geologist/zoologist/paleontologist Robert Broom in the year 1896, and was assumed to be extinct, just like the other three members of the genus Burramys.  That is until 1966, when one showed up in a ski hut on Mount Hotham, a mountain in New South Wales, southern Australia, and home to the Hotham Alpine Resort.

Since this surprising discovery, scientists have located three populations of the Mountain Pygmy Possum in different spots in southern Australia.  Although it is exciting to discover a species that was previously thought to be extinct, it is saddening to find out that this animal has a wild population of a mere 2,000 individuals, and is labeled "Critically Endangered" by the IUCN.  Means have been taken to protect the mountain pygmy possum, including the so-called "Tunnel of Love," a little possum-path that granted the males better access to the female habitat, and helping to reduce fatal encounters with automobiles.

Works Cited:

Mountain Pygmy Possum. (n.d.). - Just another global2.vic.edu.au weblog. Retrieved June 29, 2012, from http://teacherrsc.global2.vic.edu.au/

Dinner Plain on Dwellable

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.