Antlers Vs. Horns, Part 2: Horns

A horn, unlike an antler, is attached to an animal.  It consists of a bony core, a projection of the bone of an animal, and is covered by a layer of keratin (your fingernails are composed of keratin).  Also unlike an antler, that falls off easily and annually, a horn, if it is broken off, will never grow back the same way.  That is why poachers have to kill rhinos (who have horns) to actually take their horns, as opposed to just letting them fall off.

Many different types of animals have horns.  Let's take a look at a few of these creatures.

The members of the family "Giraffidae," which includes the giraffe and the okapi, both have horn-like things on their heads, called "ossicones."

The members of the family "Rhinocerotidae," or the rhinos, have horns that are composed solely of keratin, and do not have the bone core typical of many horns.  The horns of the rhinos also grow continuously.

Some of the members of the family "Chamaeleonidae," or the chameleons, often have horns projecting out of their skulls, which are covered in a layer of keratin.

And, of course, the members of the family "Ceratopsidae," a group of marginocephalian dinosaurs, have horns projecting out of their skulls. 
Below is a short list of some of the more famous Ceratopsian dinosaurs.

Famous examples of Ceratopsian Dinosaurs (or "Ceratopsians That I Have Heard Of):

1. Triceratops - (Colorado, Montana, and Wyoming, U.S.; Alberta and Saskatchewan, Canada)
2. Arrhincoceratops - (Alberta, Canada)
3. Torosaurus - (Montana, North Dakota, South Dakota, Utah, and Wyoming, U.S.; Saskatchewan, Canada)
   
4. Monoclonius - (Montana, U.S.; Alberta, Canada)
5. Chasmosaurus - (Alberta, Canada)
   
6. Centrosaurus - (Alberta, Canada)
7. Styracosaurus - (Montana, U.S.; Alberta, Canada)
   
8. Achelousaurus - (Montana, U.S.)
9. Pentaceratops - (New Mexico, U.S.)
10. Vagaceratops - (Alberta, Canada)
    
11. Diabloceratops - (Utah, U.S.)
12. Albertaceratops - (Montana, U.S.; Alberta, Canada)
13. Einiosaurus - (Montana, U.S.)
14. Anchiceratops - (Alberta, Canada)
15. Mojoceratops - (Alberta and Saskatchewan, Canada)
16. Pachyrhinosaurus - (Alaska, U.S.; Alberta, Canada)
17. Kosmoceratops - (Utah, U.S.)
18. Medusaceratops (Montana, U.S.)
19. Utahceratops - (Utah, U.S.)

Keep in mind that the tusks seen in elephants, mammoths, walruses, and hippos, despite being superficially similar to horns, are actually greatly enlarged teeth!

What REALLY Killed the Dinosaurs?

Today, almost all paleontologists believe in one of two scenarios that brought upon the downfall of the dinosaurs; the Silver Bullet Hypothesis, and the Blitzkrieg Hypothesis.  Proponents of the Silver Bullet Hypothesis consider the asteroid that hit Mexico 65.5 MYA to be the cause of the dinosaurs extinction, while fans of the Blitzkrieg Hypothesis believe that the asteroid worked in concert with other factors, like a number of extraordinarily large volcanic impacts and receding sea levels.  Although both of these hypotheses hold great weight, and stand up well to investigation, I find myself more in the Silver Bullet camp.  (If you are unsure, check out this video: http://www.youtube.com/watch?v=5gqq2rgOmi8 .  It's a bit long, but you can skip parts of it and still get the gist.  I was simply blown away after watching it, and landed smack-dab in the center of the Silver Bullet camp.)

However, this post is not to talk about the merits of the generally accepted dinosaur-death hypotheses; just like the post regarding the oddly named animals (http://thenaturalworld1.blogspot.com/2012/07/masiakasaurus-knopfleri-and-other.html), Scott Sampson's book Dinosaur Odyssey had another especially interesting tale, a tale about the many different hypotheses (over one hundred in all!) about how the dinosaurs died from over the years.  Here are some of the more interesting ones, quoted from Scott Sampson's book:

1.   Disease
2.   Slipped Vertebral Discs:  Because dinosaurs were so big
3.   Loss of Interest in Sex
4.   Poisonous Plants 1:  The consumption of these plants led to a deadly diarrhea amongst the dinosaurs
5.   Poisonous Plants 2:  The consumption of these plants led to a deadly constipation amongst the dinosaurs
6.   Fungal Invasions
7.   Climatic Change 1:  Global Warming
8.   Climatic Change 2:  Global Cooling
9.   Cosmic Radiation From a Supernova
10.  Egg-Eating Mammals
11.  Sunspots
12.  Nasty Aliens
13.  Not Enough Room on Noah's Ark
14.  The Racial Senility Hypothesis:  Dinosaurs, as a group, were young and restless when they first appeared in the Late Triassic Period.  During the Early Jurassic, the dinosaurs experienced "adolescence," as they expanded "in both form and diversity."  When they reached the Late Jurassic and Early Cretaceous, the dinosaurs had "reached their evolutionary peak;" they were middle-aged, and had nowhere to go but down.  Thus, in the Late Cretaceous Period, when the dinosaurs like Triceratops, Parasaurolophus, and Pachycephalosaurus grew interesting crests, frills and the like, these were "the result of hormones gone wild and certainly symbolic of a group on its way out."

Obviously, some of these solutions are more interesting than others, but all of them are, at this point in the study of dinosaurs, outdated.  But who knows: perhaps, someday soon, someone will discover proof that it was aliens, and not an asteroid, that ultimately did-in the dinos.

The Thagomizer of Stegosaurus

Stegosaurus is a very famous dinosaurs, one of the most famous, along with Triceratops and Tyrannosaurus.  All three of these dinosaurs have been found in Colorado; in fact, the first Triceratops bones were actually found in Denver, and Stegosaurus is the state dinosaur of Colorado!  Stegosaurus has also been found in Wyoming and Utah, in the Morrison Formation, as well as in Portugal.  The row of plates along its back make it very interesting looking, as do the spikes on the end of its tail, nicknamed a "thagomizer."  Holes in the vertebrae of a potential predator of Stegosaurus, Allosaurus, fit exactly with the size of one of the spikes on the tail of the Stegosaurus, showing that there was almost certainly a predator-prey relationship between the two, as was previously suspected.  Studies have shown that the tail end of Kentrosaurus, a close relative of Stegosaurus, also with a thagomizer on its tail, could have been brought around to the side of the dinosaur, potentially swatting at enemies trying to attack the Stegosaur from the side.

Finally, discoveries of articulated Stegosaurus skeletons show that the spikes were actually horizontal from the ground, as opposed to held at an angle, as you can see in the outdated and incorrect picture below.

It's an interesting word, though, isn't it: "thagomizer."  It certainly doesn't sound like a very sciency name; in fact, when I first heard it, I immediately thought it sounded like something out of one of my favorite comic strips, Calvin and Hobbes, by Bill Watterson.  Well, if you thought that as well, then you were actually surprisingly close to the mark, as the term did in fact come from a comic strip, another one of my favorites: The Far Side.

The term wasn't used scientifically until the year 1993, at the annual meeting of the Society of Vertebrate Paleontology, by the one-time Curator of Paleontology at the Denver Museum of Nature and Science Ken Carpenter.  The name has been used multiple times since then, in different mediums; books and television shows (including another personal favorite, BBC's Planet Dinosaur), as well as places such as the Smithsonian Institution and Dinosaur National Monument.  Although an informal name, it is popular, and has amusing origins.

Gary Larson created a great number of hilarious The Far Side cartoons covering all sorts of topics.  However, it seems like a large number of them featured animals, or were in some way nature related.  You will undoubtedly see a great many of them in this blog as time goes on, but here are a few other amusing dinosaur ones.

Fossil Hunting 6/30

Yesterday, my friend Masaki Kleinkopf and I went to check out a fossil site that I had found with another friend a couple of days ago. It looks to be Laramie Formation (towards the end of the death of the dinosaurs, in the Late Cretaceous), and a river seems to have been in this area. The most exciting fossilized things we found was a bunch of fossilized wood, as you can see below.

Fossilized wood

More fossilized wood

However, the most exciting that we saw of the day was definitely a wolf spider, probably three inches across. We saw the web first, and I was going to try and get the spider to come out with a long piece of grass (didn't want to get too close!) when I accidentally startled a grasshopper into the web. It couldn't get out, and suddenly the wolf spider appeared, and attacked it. It ran up probably ten or fifteen times, stabbing the grasshopper with its mandibles (I think that's what it was doing, anyways) and with its two front legs held up in the air. After awhile, the grasshopper was still alive, and the wolf spider retreated back down its hole. When we came back fifteen or so minutes later, the grasshopper was gone; probably dragged down by the wolf spider into its burrow to be devoured. I took a pic of the spider, but I think the  spider moved when it saw my phone, so all you can see is a blurry shot of the burrow.

Wolf spider burrow.  I think that the darker black in the burrow might be the  spider.

Besides wood, the Laramie Formation has yielded a number of dinosaur remains as well, among them being Edmontosaurus, Ornithomimus, Thescelosaurus, Triceratops, and Tyrannosaurus.  But first, here is a map of where the Laramie Formation is in Colorado.  Many of the dinosaurs that I mention below were found up in the north, near Fort Collins I believe.