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:

Baby Prairie Dogs and Birdwatching on the Bird of Prey Route!

Today, with the summer weather and the lack of school, I decided to take my car over to what I like to call the "Bird of Prey Route," a little dirt road in between Superior and Boulder about ten minutes from my house here in Colorado.  You can usually see at least one or two different types of raptors there, and there are a number of other awesome animals that I have spotted there, as well!  Today, I saw a lot of really cool birds, as well as some baby prairie dogs, as you can see below!

This particular species of prairie dog is the black-tailed prairie dog (Cynomys ludovicianus).  Like the other species of prairie dog, the black-tail is a highly social little rodent.  Below you can see two pups "kissing" each other, a type of interaction that members of the same family group will employ.  I think this is just to help solidify familial bonds, but I'm not sure if anybody knows for certain.

Today, the bird of prey route did not disappoint!  Perched in the tree in the picture below is the red-tailed hawk (Buteo jamaicensis), definitely the raptor that I see most often when on the route.

I also saw a pair of American kestrels (Falco sparverius), the species of raptor that I see second most often.  I don't usually see the kestrels so close together, however, so perhaps this was a mated pair.  I did see one of them fly into a hollow in a tree, which might be where a nest is hidden away!

As I was watching the hollow in the tree where the American kestrel swooped off into, I noticed several European starlings (Sturnus vulgaris) flying into other hollows on the tree.  Then I realized that the angle of one of the hollows was just right, and that I could actually see the adult starling feed its young!  If you zoom in on the picture, you can see that the baby already looks pretty big, maybe even as big as the parent!

Black-billed magpies (Pica hudsonia) are especially abundant in the area, and I saw several of them as well.

This magpie looks like it is molting!

Now this particular tree presents a particularly provocative puzzle, as it is almost completely covered in some very sharp looking thorns.  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.

Here is a picture of the thorns of the honey locust tree.

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?  That's a really good question.  I started answering (or at least trying to answer) the question here in this blog post, but everything rapidly started spiraling out of control and off focus as I started talking about giraffes, tiny squirrels, cheetahs, and extinct North American elephants.  For those of you who know me, it should come as no surprise that I spiraled so quickly off topic.  But regardless, what I had written ended up having enough material for at least three or more posts, so I have moved the answer to a different post, which I will hopefully be publishing soon.  Keep an eye out for that!  In the meantime, back to the future birds!  Here, we see a pair of barn swallows (Hirundo rustica) perched on a wire.

I'm not quite as sure about the identity of this particular bird.  Also a swallow, I am thinking that it might be a violet-green swallow (Tachycineta thalassina).

I believe this to be a vesper sparrow (Pooecetes gramineus).

A western kingbird (Tyrannus verticalis), another bird that I see all the time here, at least in the summer!

At last, we have one of the most exciting birds that I saw on the route today, the blue grosbeak (Passerina caerulea), a bird that I don't remember ever seeing before!

Remember to check back soon to learn all about those massively spiky trees!

Works Cited:

Robbins, C. S., Bruun, B., & Zim, H. S. (1983). Birds of North America. New York: Golden Press.

Stokes, D. W., & Stokes, L. Q. (2010). The Stokes field guide to the birds of North America. New York: Little, Brown.

Birdwatching at the Morrison Natural History Museum!

Last Monday, a snow storm hit Colorado....in the middle of May.  Although it snowed even as much as sixteen inches in some places, it melted pretty quickly afterwards, leaving an excellent opportunity for many birds that rely on insects for their meals.  After a rain, you can often see birds like the American robin or flicker foraging around (click HERE to read more), using the soft ground to their advantage to try and catch insects that were washed up out of the ground.  After the snow, it seems like a number of birds were attempting to do the same thing.  As I was closing up, I looked out behind the Morrison Natural History Museum, and noticed a bonanza of birds!  I ran downstairs and grabbed my camera, and tried to get some good shots.  Here, we have a male western bluebird (Sialia mexicana), perching on one of the blocks of sandstone from the historic Quarry 5 in Morrison.  This block contains dinosaur bone, making it ironic that the bluebird, a dinosaurian descendant itself, perched upon the block.

There were plenty of American robin (Turdus migratorius) running around, and got a few shots of them!

As we talked about in a PREVIOUS POST, winter causes many birds, including the American robin, to decrease their territoriality, and flock together.

There were several lark bunting (Calamospiza melanocorys) hopping around.  The lark bunting is actually the state bird of Colorado!

A European starling (Sturnus vulgaris) probes the ground.

There were several more male and female western bluebirds flitting around, and I got some pictures of them that I really like!  Below is a female perched on the fence next to the Jurassic Garden!

A male perched on a fence.  Notice the sexual dimorphism displayed here; the male displays much more vibrant plumage than does the female.

A female perched near my car!

Sometimes, I am really, really bad at identifying birds.  Below are two pictures of birds that I think I have identified correctly, but am not positive.  The first I think is a picture of a pair of chipping sparrows (Spizella passerina).

This one gave me a bit more trouble.  I think this bird is either a western wood-pewee (Contopus sordidulus) or a least flycatcher (Empidonax minimus).

Finally, a yellow-rumped warbler (Dendroica coronata)!

Works Cited:

Robbins, C. S., Bruun, B., & Zim, H. S. (1983). Birds of North America. New York: Golden Press.

Stokes, D. W., & Stokes, L. Q. (2010). The Stokes field guide to the birds of North America. New York: Little, Brown.

Top Five Extinct Crocodilians

As a reward for winning our Winter Trivia Contest, Carla has requested a "Top Five Extinct Crocodilians" post, and I was all too happy to oblige (but sorry it took so long)!  Let's face it: living crocodilians are pretty awesome, and their extinct cousins?  Even MORE so!  And although some of the creatures that we will look at in this Top Five list may not be crocodilians by the strictest sense of the term, those that don't entirely fit the bill are very closely related.  These "almost crocodilians," as well as the actual crocodilians, are all from a group of reptiles that we call the archosaurs.  Archosaurs include many fascinating animals, including the crocodilians, pterosaurs, dinosaurs, and birds, as well as their extinct ancestors.  Some of the members of this list are critters that look a whole lot like crocodilians, but just weren't quite there yet, as most sources state that modern crocodiles did not evolve until the Late Cretaceous.  Some people refer to this large group of crocodile-like creatures, as well as the crocodilians and their ancestors, as "pseudosuchians," which is what is used to describe the first few animals that we are looking at today!

1.  The phytosaurs are the first of these "pesudosuchian" groups.  Although at a glance they look pretty similar to the modern day Indian gharial, the phytosaurs lived in the Late Triassic, right around the time that dinosaurs were first evolving too, about 200-220 MYA.  We still have nearly 150 million years before the appearance of modern crocodiles!  As you can see below, the phytosaurs definitely resembled the later crocodilians in many ways, but they were different, too.  Just look at how far back on the skull those nostrils were!

2.  Our next pseudosuchian is one of my favorites, named Desmatosuchus.  A member of the extinct group called the aetosaurs, Desmatosuchus was actually an herbivore!  As you can see on the back of this animal, Desmatosuchus is yet another one of those fascinating creatures that has evolved dermal armor, similar to the armadillo and the ankylosaurs!  The giant shoulder spikes of Desmatosuchus definitely look a whole lot like those of the ankylosaurs, and served a similar defensive purpose.  If you traveled back to the Late Triassic period, you would have been able to find Desmatosuchus in the southern United States.

3.  While Poposaurus definitely looks a lot like a dinosaur, just like Desmatosuchus and the ankylosaurs, this is simply another fascinating example of convergent evolution!  Poposaurus, just like Desmatosuchus and the first dinosaurs, lived during the Late Triassic Period, about 225 million years ago.  For whatever reason, it was the poposaurs and not the dinosaurs that went extinct at the end of the Triassic Period.  Apparently, the Triassic town wasn't big enough for these two groups of bipedal reptiles.

4.  Postosuchus, a member of another group of pseudosuchians called the rauisuchians, looked a lot like Poposaurus, as this critter also is thought to have been able to walk on its hind legs.  Postosuchus and Poposaurus also both lived at the end of the Triassic, and both disappeared in the mass extinction event that jumpstarted the Jurassic.  Apparently, when it was first discovered, Postosuchus was thought to be a tyrannosaur ancestor, an understandable mistake once you look at the skull of this creature!

5.  This next crocodilian seems like a bizarre medley of different animals and, in some ways, it kind of is!  Meet Dakosaurus, a member of a group of extinct crocodilians called the metriorhynchids.  The metriorhynchids display numerous physiological adaptations that suggest they were quite comfortable in marine environments, such as paddle-like front limbs, hypertrophied nasal salt glands (presumably to help keep the body from getting an excess of salt), and a hypocercal tail.*  Unlike many other crocodilians, the metriorhynchids evolved sharp, serrated teeth, similar to those seen in terrestrial predatory dinosaurs.  These marine crocodilians also lost their dermal armor over the course of evolution, the tough, bony scales and scutes on the backs of modern day crocodiles that help defend them against attack from predators or other crocodilians.  Presumably, this lack of dermal armor would have helped make the metriorhynchids even more hydrodynamic.  Dakosaurus has been discovered in Europe, South America and Mexico, and lived during the Late Jurassic and Early Cretaceous.

*As you can probably tell from the complicated words used in these descriptions, the "hypertrophied nasal salt glands" and "hypocercal tail" are both direct quotes from the paper describing Dakosaurus (click HERE to check it out).  I had a tough time determining the exact meaning of the term "hypocercal," but as I understand it, it is a condition seen in many extinct fish and other marine creatures, in which the vertebral column bends downwards in the tail, (as you can see in the picture of Dakosaurus above), as opposed to where the vertebral column bends upwards, or simply doesn't protrude very far into the tail to begin with.  Amongst other creatures, the ichthyosaurs seem to have a very similar tail design, as you can see below.  I'm not certain what, if any, the distinction is between hypocercal and reversed heterocercal; either way, this sort of tail definitely seems like it would be a good adaptation for swimming!

Works Cited: