Jurassic World: Facultative Bipedalism

In the new Jurassic World movie, the main movie monster is a critter that the movie characters called Indominus rex.  The dinosaur is a big guy, and its forearms are especially large, especially when compared to the tiny arms of Tyrannosaurus rex.  There were a few funky things going on with the Jurassic World dinosaur hands, but we can talk about that in a later post.  Today, we are going to talk about an interesting type of behavior exhibited by Indominus: facultative bipedalism.

Two baby Stegosaurus models on display at the Morrison Natural History Museum.  Stegosaurus individuals of all sizes would have been able to switch between walking on two and four legs, facultative bipedalism, which is the topic of this post.

Facultative bipedalism is an animal that can walk on both two or four legs, at least for a little bit.  For example, the gerenuk (Litocranius walleri), a type of African antelope, can rear up on their hind legs to nab plants off of some higher branches.  But they can't really walk on their hind legs, so they wouldn't really be considered facultative bipeds.  My little Djungarian hamster (Phodopus sungorus) will lean back on his hind limbs to manipulate food with his forepaws, as do many other types of rodents.  Meerkats (Suricata suricatta) often sit on their hind legs to observe their surroundings.  The extinct giant ground sloths would have reclined on their haunches to browse from the higher branches of trees.  But none of them would have moved around on their hind limbs, and therefore would not be classified as bipeds, facultative or otherwise.

Several gerenuk at Walt Disney World in Florida using their hind legs to eat some food off of the higher branches.  Photo Credit: Julie Neher

A little golden-mantled ground squirrel (Callospermophilus lateralis) using its forepaws to manipulate its meal at the Cheyenne Mountain Zoo in Colorado Springs.  Forepaw manipulation is something that many rodents can do. 

Another rodent manipulating an object with its forepaws. This North American porcupine (Erethizon dorsatum), also at the Cheyenne Mountain Zoo, is holding a primitive slingshot weapon.  Zookeepers have had a very difficult time controlling these animals.

A meerkat at the Cheyenne Mountain Zoo, using part of its termite mound as a lookout area.  It'll stand on its hind legs, but runs around on all fours. 

A Jefferson's ground sloth (Megalonyx jeffersoni) exaggerates the size of the fish it caught last summer at the Rocky Mountain Dinosaur Resource Center (RMDRC) in Woodland Park, Colorado.  Just like the gerenuk, the ground sloths would have reared up on their hind legs to consume vegetation off of a higher level.

A Glossotherium skeleton on display at the American Museum of Natural History in New York, walking quadrupedally.

The duck-billed hadrosaur dinosaurs and the iguanodonts are good examples of facultative bipeds.  They would have been capable of moving around on both two or four legs, depending on whether they were grazing lazily (quadrupedal) or moving more quickly (bipedal).

An Anatotitan skeleton on display at the American Museum of Natural History in New York.  You can see this skeleton is moving around on all fours....

....but the animal could also walk bipedally.

Stegosaurus was initially thought to be bipedal, and although most modern reconstructions show the armored dinosaur as a quadruped, fossil trackways at the Morrison Natural History Museum (MNHM) in Colorado demonstrate quite clearly that the baby Stegosaurus, tiny little six pound hatchlings, were entirely capable of moving around on their back legs!

Baby Stegosaurus model on display at the Morrison Natural History Museum, right next to the very first baby Stegosaurus track ever discovered by museum director Matthew Mossbrucker in 2007.

For stegosaur and hadrosaur dinosaurs, most of their weight was centered over their hips, and the same is true of some of the long-necked dinosaurs, such as Apatosaurus and Brontosaurus.  Fossil trackways of baby Apatosaurus at the MNHM show that the babies could run around on their hind legs, to keep up with their parents, and probably keep out of their way as well!  The little baby Apatosaurus tracks at the MNHM show the animal scooting along on its back legs, sort of like the modern basilisk lizard from South America.

Two trackways made by infant apatosaur dinosaurs, on display at the Morrison Natural History Museum.  The lower trackway has tracks from both the front and back feet, while the upper trackway has only hind foot tracks, and are spaced two to three times further apart than the ones in the lower trackway.  This shows that these baby dinosaurs would have been capable of running around on their hind legs!

Very few mammals are facultative bipeds, or even bipeds at all, with exceptions such as pangolins, jerboas, and kangaroo rats, as well as the regular old kangaroos.  Apparently, even cockroaches in the genus Periplaneta can run on their hind legs as well, if they get going fast enough!

A Parma wallaby at the Cheyenne Mountain Zoo, moving around on its hind limbs.

Here, you can see the same Parma wallaby, moving on all four legs.

A mounted skeleton of the Pleistocene kangaroo Simosthenurus at the American Museum of Natural History in New York.  As you can see, even though it looks like its twerking, it is on its hind legs, grabbing some vegetation.

Although Indominus was never shown really running on all four legs, and most of the time seemed like a biped, there were a few times where the beast would drop down to all four legs.  At those times, Indominus looked a bit like some of the earliest dinosaurs might have, as well as their close cousins.  Poposaurus and Postosuchus are both dinosaur cousins for whom the possibility of facultative bipedalism, or just regular bipedalism, has been suggested in the past.  Even if those specific critters weren't facultative bipeds, there were definitely cousins of theirs that were.


Works Cited:

Alexander, R. (n.d.). Bipedal animals, and their differences from humans. J Anatomy Journal of Anatomy, 321-330.

Weinbaum, J. (2013). Postcranial skeleton of Postosuchus kirkpatricki (Archosauria: Paracrocodylomorpha), from the Upper Triassic of the United States. Geological Society, London, Special Publications, 525-553.

Thorny Trees and 20 Inch Tongues: A Case of Coevolution

A few days ago, I saw a very spiky-looking tree on the Bird of Prey Route near my house.  A few weeks ago, I saw another tree, much larger than this one, along the banks of Boulder Creek that had some enormous thorns on its branches as well, some of them easily six inches long, and super sharp on the end!  I don't know for certain what kind of tree this, or the Boulder Creek tree, is, but a good candidate I think is the honey locust (Gleditsia triacanthos), or some other tree closely related to the honey locust.  Below is the picture of the tree that I took on the Bird of Prey Route.

And here is the picture that I took on my iPhone at Boulder Creek of this tree.  The thorns look pretty similar to those of the honey locust, and I think that the trunk of the tree looks pretty similar, too.

Now why do these trees have such huge thorns?  When it comes to nature, everything evolves with a purpose.  There is no reason why a living organism would evolve something without a purpose, especially something as involved as giant, six-inch long thorns.  The question is, what purpose do these thorns serve?  Well that's a darn good question, and I am very pleased you asked.  Much like the "thorns" that you can see on the tail of a Stegosaurus, they likely were to help keep the organism from being consumed.  We see similar thorns on the branches of some trees in the genus Acacia in Africa today.  There, the thorns help protect the tree from attacks from one of the largest plant predators alive today, the giraffe.  This tree....well, suffice it to say that you probably won't see many activists hugging this tree.

"Oh, maybe these thorns look deceptively big," you're thinking.  Wrong.  These thorns do not look deceptively big.  If anything, they look deceptively small.  These thorns are frickin' HUGE.

So the real question is, why the long thorns, Goldilocks?  Many paleontologists believe that, during the Pleistocene Epoch (which lasted from between around 2.5 MYA to about 12,000 years ago), many of North America's mega-herbivores, everything ranging from mammoths and mastodons, to giant ground sloths and the North American camel Camelops, could have been preying upon these trees.  Selective pressures slowly caused these trees to evolve protection against these mammalian mega-herbivores.  Mastodons especially had very robust teeth, which would almost certainly have made them excellent bark-munchers.

In Africa, the acacia tree, also known as the whistling thorn, the thorntree, or (my personal favorite) the wattle, has a very similar defense.  Unlike the honey locust of North America, however, the acacia tree still has to deal with intense predation today, and from a wide variety of herbivores, everything from gerenuk to giraffe, elephants to more giraffes.

You see, the giraffes love the acacia tree.  If giraffes had Facebook, then they all would like the "I <3 Acacia Trees" page.  I remember reading somewhere that they can eat up to 60 or 65 pounds of acacia leaves per day.  (To understand this, try imagining a large hunk of butter that weighs 60 or 65 pounds.  Now you have an idea of how many pounds that is.)  They love it so much that, if the acacia tree hadn't adapted to keep up with the continual browsing pressure, the giraffes might have loved the acacia trees to death!  In response, the acacia trees convergently evolved these sharp thorns, just like the honey locust tree in North America.  (We talk about convergent evolution quite a lot as it is one of my favorite topics, so click HERE to learn more about it!)  

The giraffes love the acacia, though.  They aren't going to give up on those lovely leaves, just like that!  So while these acacia trees evolved their thorns to protect their leaves, the giraffes evolved something spectacular: a prehensile tongue!  Don't believe me?  Well, one of my favorite things about the Cheyenne Mountain Zoo is that you can feed the giraffes there.  And guess what: their tongues are HUGE!  Below, I have a video of my good friend Masaki Kleinkopf also feeding the giraffes!  Check out my gangsta hoodie, yo.  

So, yeah.  Suffice it to say, giraffes have frickin' long tongues.  And they use these TWENTY INCH LONG TONGUES to help circumnavigate through the acacia tree's poky and spiny maze of thorns to reach the leaves!  The acacia tree wasn't going to just take this lying down, though: no giraffe is going to be feeding on my leaves, yo!  So the acacia tree adapted again.  This time, by employing the use of tannins.

Long story short, tannins are used by humans in a variety of ways, including tanning, food processing, and making cocoa and wine.  They also apparently taste terrible.  Don't ask me, I've never tried it, but then again I don't have a 20 inch prehensile tongue, so it's a whole different ballgame.*

Not only do tannins taste terrible, but they inhibit the digestion of the leaf matter in a number of nasty ways, none of which would be all that fun for the giraffe.  So when a giraffe starts munching on the leaves of the acacia tree, that tree will release tannins to make the leaves taste like....well, leather I suppose.  (Again, haven't tried either.)  This tannin releasing is a pretty cool adaptation all on its lonseome.  The giraffe begins to move off to another acacia tree nearby.  However, if it's within 50 yards or so (especially downwind) of the original, now tanniny acacia, then the giraffe is out of luck: the nearby acacias react in turn, releasing their own tannins, and rendering their leaves almost indigestible to the giraffes, as well!  I would imagine that, because of this, giraffes have in turn developed the behavior of moving upwind as they eat, and a cursory glance over the Internet indicates that this does seem to be a behavior observed in giraffes!  Coevolution at its finest!

Make sure to check back soon for our next episode in our coevolution series, all about a very fun little squirrel!  See you then!  In the meantime, you can read about what coevolution actually is, by clicking HERE.

*The second baseball metaphor that I believe has been used on this blog.  Refer to "23-Fact Tuesday: Prairie Falcon, Red-Tailed Hawk, and Great-Horned Owl at the Dino Hotel" and "Eye Black: What Works for Football Players Works for the Cheetah" to learn more about this sport.  

Works Cited:

Making Yourself Taller

In life, things often seem as if they are out of reach.  Sometimes, this is true, and you need a ladder or something to help you.  In the wild, however, animals don't have access to conventional ladders.  So what do they do to get there?  Some animals become adapted to climbing, like those that live in forests (arboreal animals).  Other animals don't want to sacrifice a ground-dwelling life style for an arboreal one.  These animals must somehow make themselves taller.

Lots of different animals make themselves taller, by many different means.  Some animals simply grow bigger, like the giraffe and the long-necked dinosaurs (sauropods).  With their long necks, these animals can reach vegetation that is a great deal higher than most animals can reach.  Other animals put special things on their feet to make themselves taller called shoes.  Some of these shoes, known to scientists as "high-heels," are apparently designed to put the girl at optimal kissing height (a fact that I learned about from a friend of mine just a few days ago).  And finally, some animals simply stand up.

Like the gerenuk.  This interesting African antelope is one of my favorites!  As you can see in the picture below, the gerenuk, in order to access vegetation on a higher plane than most animals can, will rear up so it is supported solely by its back two legs, and feed from there.  Many paleontologists hypothesize that the sauropods could also do something similar, as supported by the fact that Apatosaurus babies would run solely on their back feet to keep up with the rest of the herd.

Gerenuk standing on their back legs to access higher vegetation at the Animal Kingdom park at Walt Disney World in Florida.  Photo Credit: Julie Neher

Animal of the Day: Beira Antelope

The Beira Antelope (Dorcatragus megalotis) is a small, 1.5 to two foot tall (at the shoulder) antelope that is native to the arid and mountainous regions of Djibouti, Somalia, and eastern Ethiopia.  The males have straight, short horns, and they are currently listed as "Vulnerable" by the IUCN.  The captive breeding program in Qatar, at the Al Wabra Wildlife Preservation center, reached its height in 2005 when it had 58 Beira Antelope.  The center has around 2,000 animals, including gerenuk, Somali wildass, sand cats, and cheetahs.  According to their posters on their website, they also have other felines, including the African wildcat, the caracal, the jungle cat, and even a king cheetah, which is a melanistic form of the regular cheetah.  As well as having many different types of felines, they do have lots of ungulates, as well as many types of birds, and some reptiles to boot.

HERE is the page on the Beira Antelope from the Al Wabra Wildlife Preservation center's website.