Moenkopi and Lykins: The Mid-Triassic in Western North America

In this post, we continue with out exploration of the Mid-Triassic, 240 MYA.  In this post, we look at the Moenkopi and Lykins Formations of North America, and see what they can tell us about this ancient time.  We also delve a bit into the evolution of fin-backs and sails as display structures, like you can see in the picture below.

In the Moenkopi Formation of North America, we can gain a more complete understanding of the terrestrial fauna of this time period.  We already discussed the rauisuchian Ticinosuchus and the protorosaur Macrocnemus from Monte San Giorgio, as well as the large temnospondyl amphibian Eocyclotosaurus from Grès à Voltzia, but there were lots of other very exciting animals alive back then as well.  Arizonasaurus, a poposaurid archosaur, was likely one of the top predators, and had a back adorned by a Spinosaurus-like sail, similar to the sail seen in the more primitive German archosaur Ctenosauriscus.

We talked about the poposaurs in a recent post which you can read by clicking HERE.  The poposaurs, as well as the rauisuchians, were both members of a large group that many scientists refer to as "pseudosuchians."  These animals were crocodilian in nature, and fairly closely related to them.  But some pseudosuchians, including some rauisuchians and poposaurs, actually evolved a body design similar to some types of dinosaurs, where they could walk on either two or four feet.

Let's jump back to the sails on the back of Arizonasaurus, Ctenosauriscus, and Spinosaurus.  The first two are fairly closely related to each other, but Spinosaurus is not closely related at all, separated by around 150 MY of geologic time.  The question is, why would these animals have convergently evolved these sails on their backs?  The orthodox answer is that the sails help the animal thermoregulate, that by turning the sail towards or away from the sun, it would help the animal warm up or cool off.  Similar ideas have been proposed for other animals that feature similar anatomical structures, such as Stegosaurus with its double row of plates down its back, or the primitive synapsids Dimetrodon and Edaphosaurus.

A model of a juvenile Stegosaurus from the Morrison Natural History Museum.  Other stegosaurs that are very closely related, such as Kentrosaurus and Wuerhosaurus, have very different shaped plates, and a different amount of plates, as well.

This idea has some major flaws, however, as argued by paleontologist Dr. Robert Bakker in his excellent and influential book "The Dinosaur Heresies."  In the book, Bakker points out that very close relatives of these sail-animals don't have these strange fins on their back.  If the thermoregulation theory is accepted, then that would suggest that these very closely related animals had very different thermoregulatory needs.  For example, Bakker points out that the primitive synapsids Dimetrodon and Sphenacodon are very closely related to each other, and most of their anatomy is very similar, other than the fact that Dimetrodon has that enormous sail on its back, and Sphenacodon has only a very slight elongation of its vertebrae.  If we accept the thermoregulatory hypothesis at face value, it would imply that, despite being very similar in anatomy and lifestyle, for whatever reason Dimetrodon and Sphenacodon had drastically different thermoregulatory needs.  Below, we have a chart showing a sail-back on the left with a closely related animal on the right, this one lacking a sail.

So what do we propose instead?  Most likely a means of attracting a mate.  In animals today, it is display structures and behavior pertaining to courtship that changes the most.  An excellent example of this is the birds of paradise from New Guinea, which we discussed in greater depth in a post with a similar focus, in regards to the plates of Stegosaurus, which you can read HERE.

Sharks, such as the very strange-looking Hybodus, have also been discovered in the Moenkopi Formation.

Where I live in Colorado, the Lykins Formation is approximately contemporaneous with the Moenkopi Formation.  The Lykins Formation isn't the most exciting of Colorado's geologic formations (at least not for people interested in fossils or excitement), but stromatolites can be found in some areas of the formation.  Stromatolites are layers of wavy and convoluted cyanobacteria that sometimes form in areas of shallow water.  Cyanobacteria by themselves aren't very big, as they are simply single-celled photosynthetic bacteria.  However, together, the gelatinous secretions they produce is enough to trap the sediment that settles out of the water, forming visible laminations that sometimes fossilize.

Stromatolites were much more common prior to the Cambrian Explosion approximately 500 MYA, as back then there wasn't really anything that could eat it.  Believe it or not, layers of cyanobacteria are notoriously bad at running away from herbivores, even something as slow as a snail or a slug.  Today, stromatolites are relatively rare, especially considering their past abundance, but you can still find them in isolated areas like Shark Bay, Australia, and Lake Salda in Turkey.  Most stromatolites form in areas that discourage herbivore grazing.  Shark Bay and Lake Salda are both hypersaline areas, places where most herbivores simply don't want to go (especially slugs and snails).  More recently, stromatolite-like growths were found living in an abandoned asbestos mine in Yukon, Canada.  This indicates to us that the parts of the Lykins Formation in which the stromatolites are found were likely not conducive to supporting herbivores, perhaps also due to hypersaline conditions.

Join us soon for our next post, in which we look at ancestors of both dinosaurs and mammals that were alive during this time!  We will also do a little investigating into different types of dentition, so stay tuned!

Works Cited:

Meet Marshosaurus, Morrison's Mysterious Meat Muncher!

If I were to tell you to picture the environment of the Morrison Formation 150 million years ago (MYA) in the Late Jurassic Period, most of you would probably have no idea what I was talking about.  For some of you, the words “Morrison” and “Late Jurassic” would trigger images of enormous sauropods like Apatosaurus and Diplodocus, with the occasional plated Stegosaurus, and the carnivorous Allosaurus.  For still fewer, images of the ornithopods Camptosaurus and Dryosaurus might appear, the theropods Ceratosaurus and the smaller Ornitholestes, and perhaps another sauropod or two.  Fewer still might picture the theropod Torvosaurus, the ankylosaur Gargoyleosaurus, and the ornithopod Othnielia.  However, very few people indeed would think of the medium sized, 20-foot long theropod Marshosaurus.

Marshosaurus bicentesimus was first named in 1976, and received the second half of its scientific binomial name (bicentesimus) from the fact that it was described during the bicentennial of the United States!  The first part of the name (Marshosaurus) honors the famous paleontologist Othniel Charles Marsh, one of two main participants in the extreme paleontological competition more than 100 years ago!  If you want to learn more about the Bone Wars, be sure to check out a song that I wrote about it below: to the tune of Carrie Underwood's "Two Black Cadillacs!"

Anyways, all silliness aside, I actually got to see what is widely considered to be the most complete Marshosaurus specimen ever discovered about a month back when my friend Sam Lippincott and I got to go on a behind the scenes tour of the Denver Museum of Nature and Science with paleontologist Dr. Ian Miller!  To be honest, even from a paleontologists perspective, the Marshosaurus specimen was definitely not the most exciting thing there, not by a long shot!  Overall, all of the known material attributed to Marshosaurus taken together, there sure isn't much: four fragmentary skeletons, composed of bits and pieces of the spine, skull, and pelvis.

One of two small trays of bones belonging to Marshosaurus that the Denver Museum has on display in the paleo lab for the time being.  Looks like we have some vertebrae and ribs!

One of two small trays of bones belonging to Marshosaurus that the Denver Museum has on display in the paleo lab for the time being.  This box contains the right maxilla of the specimen.  You actually have a right maxilla, too: just tap abut halfway between your nose and your mouth on the right side of your face: that's your right maxilla!

According to a brief article written by paleontologist Dr. Joe Sertich and published in the Denver Museum's magazine, the specimen of Marshosaurus held at the Denver Museum has "large portions of the skull....several vertebrae, bones from the back and neck, and ribs."  Although it doesn't give us a lot to work with, such fragmentary remains are often all that paleontologists have to work with!  It appears to have been enough for some scientists to come to the conclusion that Marshosaurus is a member of the megalosauroids, a distinct group of meat-eating theropod dinosaurs that includes the famous Megalosaurus, the very first dinosaur ever described!  (I would say discovered, but most people suspect that ancient races have been discovering dinosaur bones for hundreds of thousands of years: but more on that later!)  It is thought that Spinosaurus and its relatives are closely related to the megalosauroids as a group.

According to the article, the remains of the Denver Museum's Marshosaurus specimen were discovered at a site in Dinosaur National Monument that, due to a fluke of the law (I would say loophole, but I feel like that's too harsh of a word), allows the Denver Museum to collect fossils and take them back to their collections, as opposed to them going to the collections facility at the visitor's center.  At this particular site, the remains of "at least six other animals made their way back to Denver."  Amongst these remains  includes the small, plant-eating ornithopod Dryosaurus, and the very famous Stegosaurus, as well as a few bits and pieces of a crocodile!

So how likely is it that Marshosaurus will become as famous as Tyrannosaurus and Triceratops?  Not very likely at all!  But it's a cool animal, and I definitely hope we find the remains of more of these guys sometime in the future!

The Purpose of the Plates of Stegosaurus (Stegosaurus Week)

The horns and frills of Triceratops.  The tube-like crest of Parasaurolophus.  The two crests of bone on Dilophosaurus.  The sail on Spinosaurus.  What function do these various bells and whistles that adorned these so-called "Terrible Lizards" serve?  For years, most paleontologists assumed that they were for the sole purpose of combat, be it against predators, or the inter-specific variety.  But now, more and more paleontologists are looking to birds to answer the question of functionality when it comes to these bony dinosaurian protuberances.

But what, specifically, about birds is it that is helping paleontologists figure out the purpose of these structures?  It all boils down to an interesting phenomenon called "sexual selection."  Most people are familiar with the term "natural selection."  Popularized by Charles Darwin, natural selection essentially states that animals that are unfit to survive and reproduce in a given environment will die, and will be unable to add their genes to the genepool.  (Certainly an oversimplified definition, but you get the picture.)  Sexual selection, on the other hand, is a mode of natural selection, and introduced by Charles Darwin, as well.  Sexual selection states that some individuals in a given population will be more likely to breed than other individuals will because they will stand out above the rest of the population.  There are many ways of doing this, and birds are but one example.  Horns and antlers are one instance: typically, if an animal has larger horns or antlers, they will be able to not only fend off predators better (i.e. natural selection), but they will be more likely to be able to fend off other males, and be more likely to be picked for the females (i.e. sexual selection).  In many animals, form overcomes functionality in this endless quest for a mate, especially on insular (or island) populations.  One of my favorite examples of this is the birds of paradise from New Guinea, as you can see in the video below.

That's all well and good, but how does that apply to the dinosaurs that we were talking about above?  Well, for years, paleontologists assumed that dinosaurs like Triceratops and its relatives were using their horns and frills to fight off predators.  Well, for Triceratops, that makes sense: with forward-facing horns and a two-inch thick frill, fighting off Tyrannosaurus doesn't seem that far out of the realm of possibility.  However, upon examination of many of the other relatives of Triceratops (collectively called ceratopsian dinosaurs), you can see that, perhaps, not all of these frills and horns evolved to fight off predators.  Below we have just one example.  The picture you see is of a skull that below belongs to a ceratopsian dinosaur called Einiosaurus.  As you can see, it does not seem anywhere near as well equipped for fighting off predators as Triceratops does.  For example, its frill has a pair of massive holes in it.  Furthermore, of its three horns, one points downwards, and two point towards the sky at about a forty-five degree angle.  Unless Einiosaurus was being attacked by giant woodchuck-like, burrowing dinosaurs, or being dive-bombed by Tyrannosaurs in F-14s (as seen in Calvin and Hobbes!), it is difficult to see how Einiosaurus might have defended itself against its predators using its frill and horns.  Another analogy I like to make is this: if you are a knight going into battle, you don't necessarily want to have a pair of giant holes in your shield, and your sword bent and pointing towards the ground.

So how does this all tie in to Stegosaurus?  Well, a same sort of discussion has centered around Stegosaurus for many years.  Were the plates used for defense?  Or were they used for something else?  First let's address the idea of defense.  IN THE PREVIOUS POST, we discussed the thagomizer, the group of tail spikes, on the rear end of Stegosaurus.  These tail spikes were almost certainly used to fend off enemies, and seemed to have done a very good job, too.  So, if you think about it, if you were to cover a stegosaur in these spikes, it would be almost impervious to attack, right?  Well, what's interesting is that, early in stegosaur evolution, many of these animals actually did have a lot more spikes than Stegosaurus did.  As a matter of fact, the plates of Stegosaurus are nothing more than heavily modified spikes!  Below, we have a few more primitive stegosaurs, all of whom demonstrate the fact that, prior to Stegosaurus, many of the plates were actually spikes!

So if the spikes were better than plates were at defending an animal against predators (which is the only logical conclusion that I think people can draw from the data at hand), then why did some of the stegosaurs change?  For many years, paleontologists thought that they had a pair of answers to this interesting dilemma.  The first was the idea that perhaps Stegosaurus used its plates as a thermoregulaton device.  If the animal was too cold, then it could turn its body so that its plates faced the sun, maximizing its surface area that was facing the sun, and enabling it to warm up quicker.  The reverse would have also worked: when it became to hot, Stegosaurus could turn perpendicular to the sun, minimizing the surface area that was absorbing the sun.  Another theory was that Stegosaurus could flush blood to the plates, turning them a brighter color.  This could have either frightened off enemies, or instead it could have been used to attract a mate.

These two ideas seem fairly good in theory: however, much like the skull of Einiosaurus, there are a few massive holes in this logic.  If Stegosaurus used its plates as a thermoregulatory device, why do close relatives of Stegosaurus have very different plate shapes, or sometimes fewer plates altogether?  If there was one design that these animals used to warm up or cool down, one would imagine they would all converge on the same design.  But they didn't, which casts some serious doubt on the whole thermoregulatory idea.

There are two theories that seem to hold the most water today.  The first one has the same general idea that the "flushing the plates full of blood" idea has: make yourself more noticeable, as these plates were very impressive looking structures.  And, since they alternated down the back (SEE THE FIRST STEGOSAURUS WEEK POST HERE), then a side-on look of Stegosaurus would have been a very impressive sight, indeed!  Other stegosaurs of the opposite sex would undoubtedly think so, and these plates probably served a large role in attracting a mate!  Predators might have thought that the side-on view was impressive, too, and this might have caused them to think twice about attacking Stegosaurus.  It also might have caused other members of the same species to back down, too, in cases where inter-specific combat might have otherwise come into play.  As Matt Mossbrucker, the director and curator at the Morrison Natural History Museum likes to say, "think a skinny kid in a puffy coat."

Finally, the plates might have helped stegosaurs to differentiate from one another.  This is a tactic often used in animals today (again, the birds of paradise and many other birds: see the last paragraph of our post on the cichlids of the Great African Rift Lakes HERE), and is thought to have been a tactic used by many extinct animals, as well.  For example, the various horns and frills of the ceratopsian dinosaurs (like Triceratops and Einiosaurus that we were talking about before) are now thought by many paleontologists to have been used to tell each individual species apart, and its possible that that is what the stegosaurs were doing, too. 

Want to learn more about Stegosaurus?  Well, check out the Homebase for Stegosaurus Week HERE to partake in more of the festivities! 

Top 10 Favorite Dinosaurs by Zack Neher (Part 1)

Just a few days ago, we had our first ever guest blog post by David Church.  Mr. Church did his top ten favorite dinosaurs, which got me thinking about what my favorite dinosaurs were, and inspired me to do this post!  So here is my top ten favorite dinosaur list!

10. Argentinosaurus

Inhabiting South America during the Late Cretaceous Period, the enormous sauropod Argentinosaurus is the heaviest known terrestrial animal and, according to BBC, also has the record for being the longest land animal.  It was, of course, discovered in Argentina, and would have been a contemporary of Giganotosaurus.  

A picture of Argentinosaurus (background) under assault from a Giganotosaurus (foreground) with my parents off to the left at the Fernbank Museum in Atlanta, Georgia, United States

Another shot of the Argentinosaurus at Fernbank

9. Allosaurus

Allosaurus was a thirty or so foot long carnivorous dinosaur from the Late Jurassic Period.  Discovered in the Morrison Formation of Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming, this dinosaur (or one quite like it) was also likely found in the Tendaguru Beds of Tanzania.  The Cleveland-Lloyd Dinosaur Quarry near Price, Utah holds the remains of more than forty individual Allosaurus bones.

Assorted Allosaurus bones from our visit to the Cleveland-Lloyd Dinosaur Quarry

8. Spinosaurus

Spinosaurus is an enormous carnivorous dinosaur that we have talked about on multiple occasions, both in our "Biggest Carnivorous Dinosaur" trilogy of posts awhile back, but also in Mr. Church's Top Ten list.  Spinosaurus, despite the fact that it is easily the largest known carnivorous dinosaur, with an estimated length of almost sixty feet, did not eat meat like the other enormous dinosaurs: instead, Spinosaurus was a piscivore, or a fish eater.  This giant creature lived in Africa during the Cretaceous Period.

 7. Parasaurolophus

Parasaurolophus is another one of those dinosaurs that overlaps from Mr. Church's list to my own.  Parasaurolophus is certainly an interesting creature!  A member of the hadrosaurs, or duck-billed dinosaurs, Parasaurolophus, as Mr. Church discussed, is the only dinosaur I know of where paleontologists know with a high degree of accuracy what they sounded like.  The large crest on the back of the head of Parasaurolophus is full of hollow tubing, similar in shape and structure to the trombone, as well as similar in sound, too.  Unfortunately, I could not find a sound file or video of the call, so if anyone has access to a scientifically reconstructed call, let me know!

TO BE CONTINUED IN PART 2

The Denver Gem and Mineral Show Part 2: The Piscivores (Excepting Penguins)

As we started talking about a few weeks ago, my friend Masaki Kleinkopf and I were able to visit the Denver Gem and Mineral Show at the Denver Merchandise Mart.  Last time, we talked about the giant ammonites, the baby eryops that Dr. Robert Bakker was working on, the gliding Indonesian lizards of the genus Draco and the pterosaurs that evolved from creatures purportedly much like this millions of years ago.  Today, we are going to talk about all of the piscivorous animals that we saw there, except for the fossil penguin that I saw there.  Knowing me, that would easily take up one whole post of its own there.  Keep in mind throughout this post that I'm not certain for all of these animals that they actually eat fish, I just know that the large groups that they belong to often eat fish.  Today, we are going to be looking at the mosasaurs, crocodilians, pterosaurs, sea lions, other fish, sharks, and the dreaded piscivorous dinosaur Spinosaurus.  

MESSAGE FROM ZACK FROM THE FUTURE:  Hello, everyone.  This is Zack Neher.  I have travelled to this post from the future.  I wanted to give you a link to the Homebase for these posts.  I am like Rose Tyler, leaving clues in the form of Bad Wolf.  Except this is not quite like that at all really.  Anyways.  The Homebase for the series is HERE.

Myself next to a gigantic mosasaur skull

I am pretty sure that this is the skull of a mosasaur , anyway.....it looks more like a mosasaur skull than the skull of a crocodilian, if you ask me

A mosasaur jaw, from Morocco by the looks of it

A mosasaur skull (Platecarpus, if memory serves, but it is entirely possible that I am wildly off) in front of a fossil ray

Another huge mosasaur skull

We also got to see the teeth of a piscivorous pterosaur.  The teeth of a piscivore are usually different from those of other carnivorous animals due to their conical shape.  The teeth of the fish eaters, like those of crocodilians and dolphins, are usually conical in shape, to prevent prey from struggling out of their grasp.

The teeth of a piscivorous pterosaurs

Below are the skulls of various crocodilians.

 

 

The skulls of these dudes seem like they should be out of a cartoon or something, they are so weird and comic looking!

Here are a pair of photos of fossilized sea lion teeth, both from the extinct sea lion Imagotaria sp., from the Miocene to Pliocene in the Atacama region of Chile.

Imagotaria sp., from the Miocene to Pliocene in the Atacama region of Chile

Imagotaria sp., from the Miocene to Pliocene in the Atacama region of Chile

Next, a picture of a pair of fossil jellyfish!

Fossil jellyfish!

Next are the teeth of the gigantic, fifty to sixty foot long carnivorous (or actually, piscivorous) dinosaur: Spinosaurus.  Also in the picture are the teeth of another enormous carnivorous dinosaur that lived in the same area of Northern Africa as Spinosaurus at this time of the Cretaceous Period: Carcharodontosaurus, who was not a piscivore, at least not primarily a piscivore, like a penguin, or as Spinosaurus is purported to
be.  (Did you see that alliteration?  My language arts teacher would be most impressed).  I discuss both Spinosaurus and Carcharodontosaurus in two previous posts, which you can look at HERE FOR SPINOSAURUS and HERE FOR SPINOSAURUS AND CARCHARODONTOSAURUS.

The teeth of Spinosaurus.  Actually in this shot, it looks as if most or all of these teeth belong to Spinosaurus.

And now for some pictures of the teeth of Megalodon, the largest shark that is ever known to have lived!  I have talked about Megalodon in the past, click HERE to learn more.

 

Now for some random ones.

It's a fish eat fish world out there

A pair of shark jaws.  I am not certain as I don't remember at all and they are unlabeled, but I believe them to be jaws of sand tiger sharks.  Again, I could be totally off on this!

The Biggest Carnivorous Dinosaur Part 3: Spinosaurus, The World's Largest Penguin

Spinosaurus quickly smashed its way to the top (literally!) following the success of Jurassic Park III.  At up to 56 feet (17 meters) in length, Spinosaurus (found in Egypt and Morocco) is unquestionably the longest carnivorous dinosaur that has ever been discovered, and by a significant margin, too.  But how could Spinosaurus be so successful when another carnivorous monstrosity, Carcharodontosaurus, lived in such close proximity?  The answer lies in what it ate; in fact, Spinosaurus appears not to have been as carnivorous as we once thought, and seems to in fact have been more piscivorous.  Essentially, it is thought that Spinosaurus might have survived on a diet consisting a great deal upon fish.

There is a great wealth of information that indicates the staple diet of Spinosaurus was fish.  Here we will take a more in-depth look at this evidence.

A picture of Spinosaurus drawn by the talented young artist Sam Lippincott.

1.  POSITION OF THE NOSTRILS:  Spinosaurus, unlike most other theropod (meat-eating) dinosaurs had nostrils situated very high up on its skull.  By contrast, most other theropods, like Tyrannosaurus, had nostrils very close to the front of the skull.  The nostril placement in Spinosaurus would have allowed it to stick its nose into the water quite deep, enabling it to hunt fish more effectively.

2.  SENSORY ORGANS ON THE TIP OF THE SNOUT:  Along with the high placement of the nostrils, Spinosaurus also had a number of small sensory organs at the front of the snout, revealed by CT scans.  These greatly resemble those of the crocodile, who uses them to sense where prey is by "seeing" tiny movements in the water.  Thus, a crocodile can attack its prey without ever seeing them with their eyes.  Spinosaurus appears to have been able to do much the same thing, making its hunting method of choice quite obviously effective, given its immense size.

3.  ISOTOPIC EVIDENCE:  A study of the isotopes in the skull of a Spinosaurus specimen revealed something quite interesting.  Spinosaurus shares a great deal of isotopic overlap with crocodiles, fairly aquatic animals.  By contrast, other carnivorous dinosaurs like Tyrannosaurus have very different isotopic readings, indicating a terrestrial lifestyle.  Given the great deal of overlap possessed by Spinosaurus and crocodiles, it appears that Spinosaurus spent much of its life like a crocodile; semi-submerged in rivers and streams.

4.  THE TEETH TELL THE TALE:  Spinosaurus, unlike most other carnivorous dinosaurs like Tyrannosaurus, Allosaurus, or the famous Velociraptor, possess conical, round teeth.  These other carnivores possess thin, blade-like teeth, made for slicing, crushing or tearing into other animals.  Spinosaurus has teeth much like a crocodile; round and conical.  These teeth are made for gripping and making sure that an animal does not escape. 

5.  THE TEETH TELL THE TALE....AGAIN:  Yet again, we come to the issue of teeth, and this is one of the most damning pieces of evidence of all.  During the time that Spinosaurus lived in North Africa, another inhabitant of these streams and rivers was a saw-toothed fish called Onchopristis.  Two fossils involving Onchopristis have been discovered in conjunction with the remains of Spinosaurus.  One was the skull of a Spinosaurus; imbedded in one of the tooth sockets was a vertebrae from an Onchopristis.  The other discovery was the barb of an Onchopristis embedded in the jaw of the Spinosaurus.

6.  PLUS:  We only ever seem to find Spinosaurus in shallow aquatic environments, where fishy prey would be abundant.

All in all, it seems like an inevitable conclusion to draw that Spinosaurus was, in fact, a piscivore, at least much of the time.  A fascinating example of the crazy turns evolution can take.