'Donts and 'Apsids: Ancestral Dinos and Mammals of the Mid-Triassic

When it comes to dinosaurs and mammals, neither had quite yet evolved yet.  Most people consider animals like Herrerasaurus and Eoraptor to be among the oldest known dinosaurs, but others now consider Nyasasaurus to be the oldest, originating from 240 MY old rocks from Tanzania.  Many dinosaurs looked very similar to other, closely related archosaurs, and only extensive research and more specimens will be able to shed light on these ancient critters.

Mammalian ancestors took the form of the now-extinct dicynodonts and the cynodonts, the latter of which include modern mammals, as well.  In modern mammals, you can see how the skull only has a single hole behind the eye (the space where the coronoid process sneaks in between the main part of the skull and the extruding zygomatic arch), making it a synapsid, or "one-holer."  In previous posts, we've talked about primitive, mammal-like animals such as Dimetrodon and Cotylorhynchus.  Both of these critters are synapsids.  Diapsids, or "two-holers" (remember from our recent Latin/Greek Roots post that the root "di" means "two" [click HERE to read that post]), is another large group, and includes everything from crocodiles to dinosaurs, lizards to snakes, and tuataras to birds.  It also includes the archosaurs, a subgrouping of diapsids that are characterized by an additional hole in the skull, bringing the total number of skull holes up to three.  So some diapsids are also archosaurs, such as birds, dinosaurs, and crocodiles.  There's also the anapsids, which are animals with no holes in the skull, such as amphibians and turtles.  Taxonomically, this can get a bit confusing (especially since sometimes an animals classification doesn't correspond to the number of holes that it has at that point in its evolutionary history), and maybe later we can go into greater detail about these different 'apsids, but below we have a nice picture that should help clear things up a little.

Holes in the skull.  On the top left, we have the prehistoric sea turtle Protostega, an anapsid, with no extra holes behind the eye socket.  Below Protostega, we have Prestosuchus, a type of archosaur.  Not only does Prestosuchus have the two holes in the skull behind the eye socket that characterize older diapsids, but it also has a third hole, in front of the eye socket, but behind the nose openings.  On the bottom right, we have Edaphosaurus, a primitive synapsid.  The largest hole in the skull, furthest on the right, is what will one day become the hole that the coronoid process sneaks through, between the zygomatic arch and the rest of the skull.  In the picture above Edaphosaurus, you can see what I'm talking about, with the extinct mammalian synapsid Hyaenodon.  Here, you can see the little nub of the coronoid process between the zygomatic arch and the skull.

As we talked about in that Latin/Greek post that I mentioned above, the name of the primitive, fin-backed synapsid Dimetrodon means "two measures of teeth," referring to the two different types of teeth this animal possesses.  This is a feature known as "heterodonty," a term that means "different teeth."  Most mammals are heterodonts, and most other animals like reptiles are not, but it doesn't always work that way.  Modern cetaceans such as the sperm whale, as well as orcas and dolphins, are homodonts, meaning that they only have one type of tooth in their mouth.  If you look at ancient ancestors of whales, such as Basilosaurus or Zygorhiza, you can see that they have different types of teeth in their mouth.  This condition can be traced all the way back to 50 MY old Pakicetus.

A trio of cetacean skulls.  On the top left, we have Pakicetus, a terrestrial ancestor of the cetaceans, that lived in Pakistan approximately 50 MYA.  Below Pakicetus, we have Zygorhiza, a more derived and fully aquatic cetacean.  In both Pakicetus and Zygorhiza, you can see how the front teeth and back teeth are different, with the front teeth more for gripping prey, and the back teeth perfect for slicing.  On the right, you can see the skull of the modern killer whale, or orca, which has only one type of tooth in their mouth, the conical, gripping teeth.

Then, of course, there are the heterodont reptiles and dinosaurs such as the Cretaceous crocodilian Malawisuchus, and the dinosaurs Heterodontosaurus (literally meaning "different-toothed lizard") and the oviraptorosaur Incisivosaurus.  We also talked about the primitive pterosaur Dimorphodon (two morphs of teeth) in the Latin/Greek post as well.  If you look at the skulls of any of these animals, you can clearly see the different types of teeth in their mouth.  Cynodonts were not merely an aberrant heterodont form amongst a vast sea of closely related homodonts, but instead were precursors to the default heterodont condition seen in mammals.

The skull of Heterodontosaurus, on display at the American Museum of Natural History in New York.  You can see the two different types of teeth in the skull, especially in the lower jaw.

Works Cited:

Top Ten Pokémon Inspired By Real Animals

Many of you are probably familiar with the popular video game and TV series "Pokémon."  While I myself never got into it, a few months ago, I did a post about the axolotl, a fascinating little salamander. While I was researching the post (which you can view by clicking HERE), I found that a Pokémon called Wooper was based off of the axolotl.  I thought this was pretty funny, as I thought that no one had ever really heard of the axolotl, much less based a video game character after it!  The more digging I did, the more I realized that this is a fairly common theme: a great many Pokémon are based off of real animals, both living and dead!  So I thought that for the birthday post of my good friend Masaki Kleinkopf, we could look at the Top Ten Pokémon Inspired By Real Animals!

1.  Farfetch'd - Duck

According to my Pokémon sources (AKA the Internet), the Farfetch'd is supposed to live in and around water, just like a real duck!  It's also supposed to taste pretty good: again, like a real duck!

2.  Lanturn - Anglerfish

Probably one of the freakiest animals in the animal kingdom, the deep-sea loving anglerfish bait other fish closer with the so-called "esca" on its head.  The little fish swim closer, attracted to the bioluminescence emanating from the esca, and then the anglerfish snaps them up.  The name of this Pokémon is clearly an homage to this glowing appendage.

3.  Shieldon - Ceratopsian

The ceratopsians are a large group of dinosaurs containing one of the most famous dinosaurs of all time: Triceratops.  Although most sources state that Shieldon is based off of Triceratops, the Pokémon differs in that it has no horns.  This makes a more likely candidate for the origin of Shieldon another, more primitive ceratopsian called Protoceratops.  If you click on the link to a post HERE and scroll down to the second picture, you can see a picture of the skull of Protoceratops.

4.  Sandslash - Pangolin

The Pokémon called Sandslash is clearly based off of a funny, but quite fascinating, animal called the pangolin.  Sandlash features the dermal armor of the pangolin (a fancy way of saying "armor formed from hardened skin, akin to the armadillo"), as well as the massive claws.  The claws, in both the pangolin and, apparently, Sandslash, can be used to attack potential threats, as well as burrowing.  The pangolin uses its claws to burrow into termite mounds, consuming them by the thousands.  Sandslash can also roll into a ball to defend itself from attack, just like the pangolin: however, I don't think that the pangolin can roll away from its attacker while in "ball mode."  For a song about dermal armor that features, amongst many other things, the pangolin, click HERE!

5.  Relicanth - Coelacanth

Relicanth is based off of a very unassuming, but entirely fascinating, fish called the coelacanth.  For many, many years, conventional wisdom had dictated that the coelacanth went extinct at the end of the Cretaceous Period, along with the non-avian dinosaurs, the pterosaurs, and the massive marine reptiles. This assumed extinction was backed up by the fact that no fossils had been discovered, at least none that had been positively attributed to the coelacanth.  It wasn't until 1938, when a live coelacanth was pulled up off the coast of Madagascar, that scientists realized that perhaps the coelacanth wasn't quite as dead as they thought it was.  Since then, other sites along the coast of Africa, as well as in Indonesia, have yielded live coelacanths, giving the prehistoric fish a title it very much deserves: a living fossil.  According to the Pokédex in the game (a sort of encyclopedia that talks all about the different Pokémon), the Relicanth was also recently discovered, and is also labeled as a "living fossil."

6.  Tirtouga - Archelon

So apparently, some Pokémon can evolve, which is another cool and clever way of adding science into video games without making the video games dumb and boring.  Apparently, the Pokémon Tirtouga isn't necessarily based off of the massive sea turtle Archelon, but Tirtouga actually evolved into another Pokémon called Carracosta that is based off of Archelon.  Tirtouga appears to be based off of either the extant (still living, opposite of extinct) leatherback sea turtle, or perhaps another extinct sea turtle called Protostega.  Either way, all three sea turtles look pretty much the same!

7.  Archen - Archaeopteryx

It's in the name: clearly, the name Archen is based off of the name Archaeopteryx, a fossil bird that is widely considered to be the missing link (at least the first in a long line of links) between dinosaurs and birds.  First discovered in the 1800s, the feathered fossil of Archaeopteryx helped famed naturalist Charles Darwin and his followers to promote his ideas about evolution and natural selection.  According to the Pokédex, Archen is not able to fly, leading people to speculate that Archen is also based partly off of other, non-flying feathered dinosaurs, such as Velociraptor or Deinonychus.

8.  Lileep - Crinoids

Up until last week, I'd never devoted a whole lot of thought to the evolutionary relationships of a fascinating group of creatures called crinoids.  In my mind, if they look like plants, they're probably plants!  Well, I was wrong: the crinoids are actually echinoderms, just like sea urchins and sea stars, and are actually animals!  I also didn't realize that crinoids were still around today: I knew that there were a ton of them in the past, but I didn't realize that some of them had survived to the present day!  Many people believe that Lileep is based off of these strange animals, and it's not too hard to see the resemblance!

9.  Cranidos - Pachycephalosaurus

Of all of the pachycephalosaurs, Pachycephalosaurus seems like the most likely candidate for the inspiration of the strange Pokémon called Cranidos.  The main means of attack of this Pokémon is by head-butting its opponents, a means of combat long attributed to the pachycephalosaurs.  This head-butting is currently under a lot of scrutiny, with some paleontologists saying that yes, of course pachycephalosaurs head-butted each other, in the same fashion that bighorn sheep do today.  On the other hand, some paleontologists say that there is no way these guys could head-butt each other, as their necks would simply snap after a few impacts.  Other paleontologists believe that they did use their heads for head-butting, but not in the way that the previous two groups were hypothesizing: instead of getting a running start and then cracking heads, bighorn sheep style, they would instead just lock heads without the running start, like many types of deer and elk that spar today.  Still others propose that maybe these dinosaurs were smacking each other in the side or in the flank.  Like many facets of paleontology, we may never know what, exactly, they did with their craniums. 

10.  Anorith - Anomalocaris

This is the Pokémon that really inspired me to do a post like this.  Anomalocaris is one of my favorite animals because it is just so weird looking!  Living in the Cambrian Period, about 500 million years ago (MYA), Anomalocaris is definitely one of those animals that does not get a lot of the limelight.  Often found amongst the various and assorted crazies from the Burgess Shale in Canada, Anomalocaris is definitely something that I never expected to be in a video game!  Nevertheless, here it is!

This was the birthday post of Masaki Kleinkopf! Happy birthday, Masaki! If you have a birthday coming up, just email me the date at cuyvaldar123946@gmail.com with the date and your favorite animals, and I will do my best to get a post in! And if you like what you are reading, please feel free to follow us here or via Facebook!