Grès à Voltzia: Mid-Triassic French Lagerstätten

In our last post*, we got our first glimpse of some of the flora and fauna that inhabited the earth 240 MYA, in the Mid Triassic Period.  In that post, we mostly looked at the aquatic environments, fossils found at a fascinating place in Italy called Monte san Giorgio.  In good time, we will learn more about the terrestrial ecosystems and what lived on land.  But first, let us look between the aquatic and the terrestrial.  Let's look at the seashores of this ancient Earth.

To gain a better understanding of what lived on the margins of the oceans, we can look at Grès à Voltzia in France.  The importance of this site lies not just in the preservation of a large number of different organisms, but in the exceptional quality of said preservation.  Grès à Voltzia is considered a Lagerstätte, a German word referring to fossil sites that feature remarkable detail in the preservation of fossils, with famous examples including the Solnhofen Limestone in Germany and the Green River Formation in Wyoming.  The depositional environment that would one day become Grès à Voltzia featured deltas very close to the shore, and were home to many animals.  This prime habitat resulted in the burial of both terrestrial and marine animals, painting an even more complete picture of this ecosystem.

Here we have a picture lifted from my Instagram that shows three very different animals from the aforementioned Lagerstätten. What ties these three animals is their common ability to fly.  On the right, we have pictures of two fossil casts from the Solnhofen Limestone in Germany, deposited about 150 MYA.  Archaeopteryx, the primitive bird/dinosaur link, is on top, and Pterodactylus, a type of pterosaur, is on the bottom.  The picture on the right is of a bat from the Eocene of Wyoming, found in the Green River Formation, deposited approximately 50 MYA.  Despite its age, Icaronycteris was fairly similar to modern bats.  All three of these animals convergently evolved flight, and were not derived from a common ancestor.

Along the shores of these 240 MY old rivers, horsetails and and ferns grew in abundance, as well as several different types of gymnosperms.  Large amphibians such as Eocyclotosaurus made their home in these waterways, as they were tied to moist environments just like modern amphibians are today.

Horseshoe crabs like Limulitella, very similar to modern horseshoe crabs, are commonly found, as are many types of crustaceans, such as Antrimpos, a type of shrimp.

Insect larvae includes dipteran (true flies), odonatopteran (dragonflies and damselflies) and ephemeropteran (mayflies).  Annelids (segmented worms like the modern earthworm) have also been discovered here, as well as fish and a jellyfish.

The horsetails, such as Equisetites, grew along the edges of the water, while the gymnosperms grew further inland, probably reaching at least several meters in height.

A large number of insects, including the dipterans and ephemeropterans that we already mentioned, lived here.  Proto-cockroaches (blattopterans), beetles (coleopterans), and hemipteroids were all present, as well as myriapods (centipedes and millipedes), and spiders.  A strange mixture of modern and exotic looking animals to be certain!

Next time, we will be continuing our investigation regarding the flora and fauna of the Mid Triassic by learning about two North American geologic formations that might reveal a bit more about the terrestrial ecosystems.  Join us!

*As those of you who are familiar with myself and this blog, you are likely familiar with the fact that once I start talking, it takes a good deal to make me shut up.  The same is true for writing this blog.  When I originally came up with the idea to do a post about the flora and fauna that inhabited the Earth 240 MYA, flora and fauna that many people, myself included, are relatively unfamiliar with, it was supposed to be a relatively short post, maybe four or five paragraphs in length.  Instead, I ended up just writing and writing and writing.  I realized, as I often do, that A) so few people would be reading these posts to begin with, and B) those people who do wind up reading these posts would likely not have stuck around for an immense post that talks about everything from the ichthyosaurs of Italy, the stromatolites of Colorado, the insects of France, the communal latrines of Tasmanian devils, the lack of communal latrines of Maiasaura, the communal latrines of dicynodonts (yes, poop is cool), the heterodont condition of primitive whales, and everything in between, that it made more sense to split the post up.  This is the second installment of five (so far, at least) regarding the flora and fauna of the Mid Triassic Period, approximately 240 MYA.  It now occurs to me that I probably lost most of you in this long-winded exposition.  I don't want to just delete all this though, as future generations will find this fascinating glimpse into my thought processes an untapped reservoir of knowledge that is absolutely vital to an understanding of the ultimate being I shall become.  I think I will just make this whole thing an endnote.

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240 MYA: Messing Around in the Mid-Triassic

People tend to think of the dinosaurs filling the dominant terrestrial ecological niches during the entirety of the Mesozoic Era, from the Early Triassic all the way to the Late Cretaceous.  This is an oversimplification, however, as the dinosaurs didn't really evolve until the Mid or Late Triassic, and still up against competition from other groups of animals until the Early Jurassic.  Today, we are going to travel back in time 240 MY, back to the Middle Triassic Period.  This slice of time is approximately 10 MY after the mysterious Permian Extinction, and is about 10-15 MY before the first undisputed dinosaurs start showing up.  We are in a time when many of the animals that lived on the land and swam in the seas looked similar to life that is more familiar to us, but much of it was distinctly different.

All of the Earth's continents were united in the supercontinent Pangaea, surrounded by the super-ocean Panthalassa.  The Tethys Sea was nestled into what would one day become the somewhat smaller supercontinents Laurasia (North America, Europe, and Asia) and Gondwana (pretty much all the rest).  Warmer conditions prevailed, and the poles were ice free all year round.  Although the coasts seemed to be more hospitable to life, the center of Pangaea was not quite as welcoming, receiving little rain and remaining fairly arid.

There are several important sites around the world that preserve fossils from this time period.  Let's start in the ocean and work our way onto the land, starting with Monte San Giorgio.  This site along the border between Switzerland and Italy gives us insight into the ecosystem that flourished beneath the waves of the Tethys Sea.

Sauropterygian reptiles such as the ten-foot long Ceresiosaurus cruised around, likely hunting smaller sauropterygians such as Neusticosaurus.  These reptiles resembled the more famous Nothosaurus and the later plesiosaurs, with their four limbs greatly resembling paddles, all of approximately equal length.

The dolphin-like ichthyosaurs such as Mixosaurus and Besanosaurus would have zoomed around, feeding on faster prey such as squid and fish.  Mixosaurus was pretty much your stereotypical ichthyosaur, but Besanosaurus was a bit odd-looking, with all four fins/limbs being fairly close to equal in length, unlike the shortened hind flippers that is more commonly seen in ichthyosaurs.  Besanosaurus also seems to not have had a dorsal fin.

The giraffe-like protorosaur Tanystropheus also probably hunted fish and squid, using its extraordinarily long neck to ambush unwary prey items, sneaking up on them while the rest of the animal was still four or five feet away!

A drawing of the protorosaur Tanystropheus by the talented young artist Sam Lippincott!  Photo Credit: Sam Lippincott

The turtle-like placodonts like Paraplacodus and Cyamodus possessed large, flat teeth perfect for crushing the shells of molluscs and crustaceans.  The teeth of these placodonts are similar to the molars that you can see in the mouth of the walrus, a marine mammal that has a diet fairly close to the placodonts of 240 MYA.

Thalattosaurs like Askeptosaurus also probably fed on molluscs and crustaceans, and likely fish as well.  Askeptosaurus had a long snout, and superficially resembled animals like Ceresiosaurus and Nothosaurus.  In the picture below, the snout is tucked towards the animals left armpit, almost like it's trying to figure out whether Triassic animals can get B.O.

Several terrestrial reptiles have been discovered at Monte San Giorgio as well, such as the rauisuchian Ticinosuchus and another protorosaur like Tanystropehus (albeit one with a much shorter neck), Macrocnemus.  We'll talk more about the terrestrial ecosystems of the Mid-Triassic later, with more talk of animals like Rauisuchians!  Check back for our next post, featuring the French site Grès à Voltzia!

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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!

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When Is A Turtle Not A Turtle?

When it's a placodont!  All right, so they're technically not turtles.  Instead, they are a classic example of the fascinating phenomenon known as "convergent evolution," as we shall soon see!

Placodonts were a fascinating group of marine reptiles that lived during the Triassic Period in the Mesozoic Era, between around 235 and 200 million years ago (MYA), and thought to have a common ancestor with the long-necked plesiosaurs and the long-necked nothosaurs, all of which are in the large group called the saruopterygians.  As a group, the placodonts are sometimes referred to as "walrus turtles," due to their diet of molluscs and other shelled invertebrates and, of course, their general appearance.

Like the turtles and tortoises of today, the placodonts would not have been all that quick and nimble.  Their weight would have made them negatively buoyant, akin to the manatees and sea cows of today, meaning that they would have had no trouble swimming along the bottom of the ocean, snapping up molluscs and other shelled invertebrates, and using their large, flattened cheek and palatal teeth to crush them down.  It's also possible that they scraped algae off of marine rocks and swallowed it whole, letting it slowly digest in their massive guts!  Like modern sea turtles, the placodonts are thought to have been amphibious, spending most of  their time (sleeping, chillaxing, and other activities) on land, but dipping into the water to feed, akin to the extant marine iguana of the Galápagos Islands.

Although younger placodonts would have been especially vulnerable to predation from many different types of animals, many paleontologists puzzle over why the ponderous adult placodonts would have needed this armor, as there don't seem to be any marine predators capable of making a meal out of them that lived at the same time.  Of course, as we mentioned before, they probably spent much of their time on land and, as we also mentioned before, their awkward build would have left them particularly vulnerable to attack.  So to counter this, some of the placodonts started to evolve in a very turtle-like appearance. 

Placodus, the animal whose name is lent to the entire group, displays a single row of dermal ossifications above its neural spines down its back.  This dermal armor (a fancy way of saying "skin armor," in which the skin hardens into an armor like structure, as seen in the armadillo) would have helped to protect the animal from attack.  Earlier, more primitive genera, such as Paraplacodus, lack this dermal ossification.  However, other, more derived placodonts take this ossification of the dermals to a whole new level.

Remember Henodus, the first picture in this post? Henodus is one of those dermal armorers (I don't think that's actually a word) that took the ossification of the dermals to a whole new level.  Outwardly similar to the turtle shell, the placodont armor was composed of a number of polygonal ossicles, while the shells of turtles are composed of large plates.  Two other placodonts that were extremely well armored include Cyamodus, as well as the VERY turtle-looking creature, Placochelys. 

Like many other animals, the placodonts became extinct at the end of the Triassic Period.  Many groups did survive, however, and one of those groups that survived through to the Jurassic Period was actually the turtles!  220 MYA, the placodonts were sharing the seas with what would one day become the hard-shelled reptiles adored by so many people! 

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

Animal of the Day: Coelophysis

Today's Animal of the Day is Coelophysis!  The picture of the cast you see off to the left (taken by me at the Denver Gem and Mineral Show a few months back) is from the AMNH (American Museum of Natural History) in New York.  I actually know a little bit more about this particular specimen of Coelophysis than I believe was labeled there, as I remembered seeing this specimen in my Dinosaur Atlas book from DK Publishers.  One of around 500 or so individual Coelophysis specimens discovered at a place called Ghost Ranch in New Mexico, this particular specimen was once thought to reveal something interesting about the species: Coelophysis was once thought to probably be a cannibal, as the remains of a baby Coelophysis were found in the area of the stomach!

Dinosaur cannibalism is not unheard of, and almost certainly occurred in the Late Cretaceous Abelisaur Majungasaurus from Madagascar.  However, this was disproven in 2002 by Rob Gay, when he showed that the baby Coelophysis were either crushed by the smaller ones, or that they weren't even baby Coelophysis!  Instead, many of them were found to be other, small reptiles, such as the archosaur Hesperosuchus, a member of the same group as the crocodilians, dinosaurs, and pterosaurs, amongst others.  So for now, it looks like Coelophysis was probably not a cannibal, but future discoveries may force us to change our minds once again!

Another picture of Coelophysis that I took, at the DMNS

Coelophysis is one of the oldest known dinosaurs, inhabiting North America around 220 million years ago (MYA), during the Late Triassic Period.  The site at Ghost Ranch is interesting, because there are just so many different specimens all clumped together.  Some paleontologists have suggested that a flash flood drowned a huge herd of these animals, or perhaps that they died while trying to cross a river.  We might never know what, exactly, killed these dinosaurs, or why so many of them died in such close proximity.  

Some Like It Hot....Radioactive Hot

Today was quite an eventful day, for many reasons!  Went to the Zoo Lights at the Denver Zoo with some good friends of ours; learned that Ray Wise is not in X-Men Origins: Wolverine, but is actually in X-Men: First Class; and learned that the building off the highway called "Quaker Steak and Lube" is actually a restaurant, and not a car repair place.  Also, on my way to the Morrison Museum this morning, I saw what I am pretty sure was a peregrine falcon, as well as a number of red-tailed hawks and kestrels, and the great-horned owl that I have seen a few times recently perched on the "speed limit" sign on the highway!  It was pretty awesome!  Oh, and did I mention that one of my fossils might be radioactive?

One of the Zoo Lights was this tiger, but I'm pretty sure he's supposed to go around something a little thicker....

I was talking to Dr. Bob today at the museum, and we were talking about fossil hunting in Texas, chiefly the fossils that I got down there when we went to visit my gramma last Christmas, as well as the fossil dig-site that he has down there.  As we were talking, I thought back to the fossilized wood (top picture, the thing with the penny on it and everything to the right and above that piece) that I had picked up in Santa Rosa, New Mexico, on one of the first nights of our trip.  I had never been able to figure out what formation or what geologic time period it came from, so I asked Dr. Bob.  He said that there are a lot of different aged rocks from throughout the Mesozoic Era (the time of the dinosaurs), from the Triassic to the Cretaceous.  Then, as a sidenote, he mentioned that some of the fossilized wood down there tends to be radioactive, sometimes dangerously so.  Well then!  I am currently sorting this out, but I feel like I don't really have enough to worry about.  Famous last words, right?

Top Ten Favorite Dinosaurs by Zack Neher (Part 4.5)

As some of you may know, right now, we are in the midst of a lis of my  top ten favorite dinosaurs.  However, on December 7th, a new dinosaur was announced, and it has immediately made my top ten list if it is, in fact, a dinosaur, which is currently being debated.  Therefore, I have decided to make this guy number 4.5 on my list, as if this creature is a dinosaur, it may very well be one of the most important finds in the history of dinosaur paleontology, as the find, named Nyasasaurus, may be the ancestor of all dinosaurs! Since this fossil dates to the Middle Triassic Period and is estimated to be about 10-15 million years older than the previously-oldest known dinosaurs like Eoraptor and Herrerasaurus, if this animal is not, in fact, a dinosaur, it resides very close to the base of the dinosaurian family tree!  People around the world eagerly await more remains of this animal from being discovered in Tanzania (where the original fossils were discovered in the 1930s) or somewhere else in the world, in the hopes that some more light can be shed upon this controversy.

 TO BE CONCLUDED IN PART 5

Proterosuchus....or Should I Say "Broterosuchus?"

Before we learn about Proterosuchus, it will be helpful to discuss where this creature comes from.  Proterosuchus is an archosaur, and to understand what an archosaur is, we must first travel back 320 million years into Earth's history: back....to the middle of the Carboniferous Period.  To travel back to that period of Earth's history, click HERE TO SEE A POST I JUST MADE ABOUT THE EVOLUTION OF THE ANIMALS THAT WE ARE TALKING ABOUT RIGHT NOW.  Unless, of course, you are fine with just accepting the idea that the archosaurs are relatives of the dinosaurs, pterosaurs, and crocodilians, in which case you can just skip that post.  I think it's interesting, though, so it might be worth checking out!

Well, that was confusing.  So how does all of this evolutionary rig-a-ma-roll pertain to Proterosuchus?  Well, in his excellent book entitled "Gorgon," paleontologist Peter D. Ward actually talks about that.  Here is that passage from his book:

"During the Triassic a whole new suite of vertebrates populated the land.  The oldest true "ruling reptiles," the stock that would ultimately give rise to the dinosaurs, are found in the oldest rocks of the Triassic.  The most ancient of these is Proterosuchus.  Yet within several million years, there was a variety of these predinosaurs, belonging to a group known as the archosaurs.  From these ancestral stocks the successful lines of crocodiles and crocodile-like animals known as phytosaurs evolved.  From other members of this group came lizards, snakes, and, by the middle of the Triassic, the first true dinosaurs."  

Well, that certainly sums it up quite nicely, don't you think!  Anyways, Proterosuchus was around the size of the extant Komodo dragon, and was one of the largest reptiles alive during its time, in the Early Triassic Period.  Similar in appearance to the modern day crocodiles, it has been theorized that this animal would lie in wait much like the crocodilians, ambushing its prey when it came down to bodies of water to drink.  One bit of evidence that causes some scientists to believe that Proterosuchus hunted like the crocodilians was that the eyes of Proterosuchus were were located on top of its head, again like the crocodilians.

Remains of Proterosuchus are known from both China and South Africa, where it was first discovered by Robert Broom, a famous South African paleontologist, in 1903.  This specimen was discovered in the Karoo Basin, an enormous desert in South Africa where large numbers of fossils have been discovered. 

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Top Ten: Extinct Sea Monsters (Part 5 of 5)

Our final edition of "Top Ten:  Extinct Sea Monsters!

9.  Tanystropheus - Living during the Middle Triassic Period, Tanystropheus is somewhat of a misfit amongst this group, as he is not really a sea-monster, and was, at most, a semi-aquatic animal (think otters).  Purportedly piscivorous, Tanystropheus fossils are usually found in semi-aquatic sites.  Its neck has been likened to that of the Plesiosaurs, like Elasmosaurus.  They would all use their necks to surprise a group of fish, long before the fish would be able to see the body of the reptile. Remains have been discovered throughout France, Germany, and Italy, amongst other places. 

10.  Tylosaurus - Interestingly enough, the closest living relative of the extinct mosasaurs, of which Tylosaurus is a member, are the monitor lizards, like the Komodo dragon.  Both the monitor lizards and the mosasaurs have a third eye on the top of their heads, although it just looks like a little white dot on the top of the head of the monitor lizard.  It doesn't work in the same fashion as their other eyes, however.  Look towards a light (not the sun, because apparently that can actually be harmful) and close your eyes.  You can still still some light, right?  Now, move your hand back and forth in front of your face, between your eyes and the light.  Can you see how the light changes?  You can't see anything more distinct than the fact that something moved between you and that light.  That is what the third eye of monitor lizards and mosasaurs would have been like.  Tylosaurus also inhabited the Western Interior Seaway during the Late Cretaceous.  Remains, amongst other places, have been discovered in Alabama and Kansas, amongst other places.

So that concludes our "Top Ten:  Extinct Sea Monsters" edition!  Unfortunate that we had to break it up into five parts, to be sure, but hey, that's life!

This post is part of the "Top Ten: Extinct Sea Monsters" series.  For the rest of the posts in this series, click HERE.  

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.