Jurassic World: Facultative Bipedalism

In the new Jurassic World movie, the main movie monster is a critter that the movie characters called Indominus rex.  The dinosaur is a big guy, and its forearms are especially large, especially when compared to the tiny arms of Tyrannosaurus rex.  There were a few funky things going on with the Jurassic World dinosaur hands, but we can talk about that in a later post.  Today, we are going to talk about an interesting type of behavior exhibited by Indominus: facultative bipedalism.

Two baby Stegosaurus models on display at the Morrison Natural History Museum.  Stegosaurus individuals of all sizes would have been able to switch between walking on two and four legs, facultative bipedalism, which is the topic of this post.

Facultative bipedalism is an animal that can walk on both two or four legs, at least for a little bit.  For example, the gerenuk (Litocranius walleri), a type of African antelope, can rear up on their hind legs to nab plants off of some higher branches.  But they can't really walk on their hind legs, so they wouldn't really be considered facultative bipeds.  My little Djungarian hamster (Phodopus sungorus) will lean back on his hind limbs to manipulate food with his forepaws, as do many other types of rodents.  Meerkats (Suricata suricatta) often sit on their hind legs to observe their surroundings.  The extinct giant ground sloths would have reclined on their haunches to browse from the higher branches of trees.  But none of them would have moved around on their hind limbs, and therefore would not be classified as bipeds, facultative or otherwise.

Several gerenuk at Walt Disney World in Florida using their hind legs to eat some food off of the higher branches.  Photo Credit: Julie Neher

A little golden-mantled ground squirrel (Callospermophilus lateralis) using its forepaws to manipulate its meal at the Cheyenne Mountain Zoo in Colorado Springs.  Forepaw manipulation is something that many rodents can do. 

Another rodent manipulating an object with its forepaws. This North American porcupine (Erethizon dorsatum), also at the Cheyenne Mountain Zoo, is holding a primitive slingshot weapon.  Zookeepers have had a very difficult time controlling these animals.

A meerkat at the Cheyenne Mountain Zoo, using part of its termite mound as a lookout area.  It'll stand on its hind legs, but runs around on all fours. 

A Jefferson's ground sloth (Megalonyx jeffersoni) exaggerates the size of the fish it caught last summer at the Rocky Mountain Dinosaur Resource Center (RMDRC) in Woodland Park, Colorado.  Just like the gerenuk, the ground sloths would have reared up on their hind legs to consume vegetation off of a higher level.

A Glossotherium skeleton on display at the American Museum of Natural History in New York, walking quadrupedally.

The duck-billed hadrosaur dinosaurs and the iguanodonts are good examples of facultative bipeds.  They would have been capable of moving around on both two or four legs, depending on whether they were grazing lazily (quadrupedal) or moving more quickly (bipedal).

An Anatotitan skeleton on display at the American Museum of Natural History in New York.  You can see this skeleton is moving around on all fours....

....but the animal could also walk bipedally.

Stegosaurus was initially thought to be bipedal, and although most modern reconstructions show the armored dinosaur as a quadruped, fossil trackways at the Morrison Natural History Museum (MNHM) in Colorado demonstrate quite clearly that the baby Stegosaurus, tiny little six pound hatchlings, were entirely capable of moving around on their back legs!

Baby Stegosaurus model on display at the Morrison Natural History Museum, right next to the very first baby Stegosaurus track ever discovered by museum director Matthew Mossbrucker in 2007.

For stegosaur and hadrosaur dinosaurs, most of their weight was centered over their hips, and the same is true of some of the long-necked dinosaurs, such as Apatosaurus and Brontosaurus.  Fossil trackways of baby Apatosaurus at the MNHM show that the babies could run around on their hind legs, to keep up with their parents, and probably keep out of their way as well!  The little baby Apatosaurus tracks at the MNHM show the animal scooting along on its back legs, sort of like the modern basilisk lizard from South America.

Two trackways made by infant apatosaur dinosaurs, on display at the Morrison Natural History Museum.  The lower trackway has tracks from both the front and back feet, while the upper trackway has only hind foot tracks, and are spaced two to three times further apart than the ones in the lower trackway.  This shows that these baby dinosaurs would have been capable of running around on their hind legs!

Very few mammals are facultative bipeds, or even bipeds at all, with exceptions such as pangolins, jerboas, and kangaroo rats, as well as the regular old kangaroos.  Apparently, even cockroaches in the genus Periplaneta can run on their hind legs as well, if they get going fast enough!

A Parma wallaby at the Cheyenne Mountain Zoo, moving around on its hind limbs.

Here, you can see the same Parma wallaby, moving on all four legs.

A mounted skeleton of the Pleistocene kangaroo Simosthenurus at the American Museum of Natural History in New York.  As you can see, even though it looks like its twerking, it is on its hind legs, grabbing some vegetation.

Although Indominus was never shown really running on all four legs, and most of the time seemed like a biped, there were a few times where the beast would drop down to all four legs.  At those times, Indominus looked a bit like some of the earliest dinosaurs might have, as well as their close cousins.  Poposaurus and Postosuchus are both dinosaur cousins for whom the possibility of facultative bipedalism, or just regular bipedalism, has been suggested in the past.  Even if those specific critters weren't facultative bipeds, there were definitely cousins of theirs that were.


Works Cited:

Alexander, R. (n.d.). Bipedal animals, and their differences from humans. J Anatomy Journal of Anatomy, 321-330.

Weinbaum, J. (2013). Postcranial skeleton of Postosuchus kirkpatricki (Archosauria: Paracrocodylomorpha), from the Upper Triassic of the United States. Geological Society, London, Special Publications, 525-553.

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:

No I Did Not Mean Triceratops, I Meant Ceratops

Recently, the folks over at the Best Western Denver Southwest purchased yet another fossil cast for their amazing hotel!*  This time, the cast is of a skull nicknamed "Judith," a specimen that is referred by some paleontologists to the dinosaur genus Ceratops.  And, no, I didn't mean to say Triceratops.  Don't feel bad if you haven't heard of Ceratops montanus: as a matter of fact, I hadn't really heard of it either until several weeks ago, when Greg Tally informed me that the Morrison Natural History Museum would soon be receiving a very large box in the mail!  Judith is still in the Cretaceous Room here at the MNHM, where she will stay for at least a few more weeks.  I really didn't know much at all about this dinosaur, and was eager to learn more.  Unfortunately, there's not much out there, as Ceratops is based on just a few bones that were discovered in the late 1800s.  Despite the lack of material, Ceratops does have a pretty fascinating history, and is an incredibly important dinosaur; not because of what has been discovered about the fossils themselves, so much as what these fossils resulted in.

Greg Tally peers through one of the fenestrae (literally means "window" in Latin) in the skull of Judith, the Ceratops montanus skull for the hotel that is temporarily on display at the Morrison Museum.  Photo Credit: Greg and Meredith Tally

When it comes to giving an animal or a group of animals a scientific classification, there are a lot of hoops you have to jump through, and a bunch of rules you have to follow.  Sometimes, groups of animals are named after the best known and understood animal in that group.  For example, Stegosaurus is the genus of dinosaur that defined the group of animals called the stegosaurs, and Tyrannosaurus is the genus of dinosaur that defined the group of animals called the tyrannosaurs.  Sometimes, it isn't quite as simple.  Think about it this way: Las Vegas is easily the most famous city in Nevada, and I'm sure I'm not the only one who spent a significant portion of their childhood thinking that Las Vegas was the capital of Nevada.  However, it is Carson City that holds the official title of capital.  Even though Las Vegas receives much more attention than Carson City, the state of Nevada isn't simply going to change where its capital is, and to the best of my knowledge, a change like that never really happens.

Although that comparison was a bit of a stretch and had about as many holes as the skull of Chasmosaurus, I think you get my point.  The same thing goes for scientific names.  Although Triceratops is the best known individual of the dinosaurian group called the ceratopsians, this group is still called the ceratopsians, as opposed to being called the triceratopsians.  That's because it was Ceratops, and not Triceratops, that was described by scientists first.

Ceratops montanus, temporarily on display at the Morrison Natural History Museum.  Photo Credit: Greg and Meredith Tally

The year was 1888, and paleontology in western North America was still going strong.  We've talked about the Bone Wars between paleontologists Othniel Charles Marsh and Edward Drinker Cope before, and we are going to revisit Marsh in this post.  To maximize the number of fossils he could describe, Marsh called upon the talents of a large number of fossil collectors, including the always brilliant Arthur Lakes in Morrison, Colorado.  Another of these collectors was a man named John Bell Hatcher.  Although Hatcher should also be remembered for a large number of his contributions to paleontology, for our purposes here we remember Hatcher as the man who discovered Ceratops.  On a trip to a known dinosaur fossil site near the Judith River in Montana, Hatcher discovered a number of fossils.  One of these fossil discoveries was composed only of a pair of horn cores.

Doesn't sound like much, does it?  Well, truth be told, it wasn't, though it was enough for Marsh to realize that he had something new.  If you click HERE, you can view the two page paper that Marsh published in 1888 that briefly described this new discovery as an animal called "Ceratops montanus."  There are several things of interest that we should take away from this paper, some of which are:

1. Marsh originally suspected that this new creature was "nearly allied to Stegosaurus of the Jurassic, but differs especially in having had a pair of large horns on the upper part of the head."  Marsh got the location of the horns right, but the close relation to Stegosaurus.....not so much.  Given the enormously tiny sampling of bones he had to work with though, it's not a surprise that Marsh compared this new animal to something that he already knew a good deal about.  Keep in mind that this is the very first scientific description of a ceratopsian dinosaur, so Marsh just had to go off of what had already been discovered.  Which was nothing.
2. Marsh notes that the "position and direction" of the horns could be likened to the enormous Meiolania, an extinct turtle from Australia, as well as the lizards in the genus Phrynosomax, the horned lizards.  He also notes that amongst the dinosaurs, the "only known example of a similar structure....is the single median horn-core on the nasals of Ceratosaurus," a mid-sized theropod dinosaur from the Late Jurassic Morrison Formation.   
3. In 1887, the year before this paper was published, geologist Whitman Cross sent Marsh a pair of horn cores about two feet in length and six inches across at their widest point.  Discovered right smack dab in the middle of where Denver, Colorado is today, Cross relayed to Marsh that they had been discovered in beds of Cretaceous rock.  Marsh, however, decided that these horns must have belonged to some sort of enormous bison, and gave the horns the name "Bison alticornis."  Perhaps Marsh was still suffering from the misconception that the 1887 discovery was, indeed, an enormous extinct bison, as these 1887 Denver horn cores are not mentioned in the brief Ceratops paper.  It is mentioned, however, that if the horns were discovered "detached," their "resemblance in form and position of the posterior horn-cores to those of some of the ungulate mammals is very striking," and the horns would "naturally be referred to that group."  I have no evidence to support my hypothesis, but I wonder whether this comparison to the mammalian ungulates is insurance on the part of Marsh, as perhaps at this point he had recognized the true nature of the 1887 horn cores.  This is pure conjecture on my part, and is mostly irrelevant anyways, as in 1889 Marsh recognized the dinosaurian nature of the Denver cores, and referred them to the genus Ceratops.  Today, these horn cores are regarded as belonging to Triceratops.
4. Marsh mentions that several limb bones, vertebrae, and teeth were also found in the Ceratops horizon, as well as several bits of dermal armor, and states that he believes they also belonged to Ceratops.  Whether this is true or not I do not know, but what I do know to be false is Marsh's next sentence, in which he states that the bones "indicate a close affinity with Stegosaurus, which was probably the Jurassic ancestor of Ceratops."  The specimen is housed in the Smithsonian today, under the catalogue number USNM 2411.  A search through the online records of the Smithosonian shows that 2411 consists only of a partial skull, which seems to be consistent with what I've read in other sources.  I'm not sure whether these other skeletal elements mentioned above have found a definitive dinosaurian home, or whether their true owner is uncertain.  
5. The final paragraph is, in my opinion, inarguably the most important.  The paragraph reads as follows: "The remains at present referred to this genus, while resembling Stegosaurus in various important characters, appear to represent a distinct and highly specialized family, that may be called the Ceratopsidae."  In this paragraph, Marsh has created the group of dinosaurs that, more colloquially, we refer to as the ceratopsians.  Or, more colloquially than that, "those dinosaurs that look like Triceratops with those horns."

Ceratops was discovered in what scientists now call the Judith River Formation.  Several other ceratopsians have been discovered in this formation, and due to the small amount and fragmentary nature of the material that was originally described as Ceratops, most paleontologists consider the dinosaur to be a nomen dubium.  Nomen dubium pretty much means that the material is too fragmentary for it to be diagnostic, and can't really be used in the future to determine whether new specimens are the same as the original or not.  Whether or not the newly discovered Judith specimen currently on display at the Morrison Museum is, indeed, Ceratops is still up in the air, as the paper has not been published yet.  Almost all of my Ceratops knowledge is out on the table for all to see, so I am not going to speculate or attempt to draw conclusions about something that I don't really know enough about to have an informed opinion on.  Guess we will just have to wait and see!  In the meantime, come on by the Morrison Natural History Museum and the Best Western Denver Southwest to see Judith, and much more!

*If you've been living underground amongst worms and fossils for the last few months, you might not have heard of the hotel, so you can check out some incredible pictures of the best Best Western by clicking HERE and HERE.

Works Cited:

The Dino Hotel Nears Completion! Part 2

As I mentioned IN THE LAST POST, the Best Western Denver Southwest is nearing its completion!  Soon, it will be the most powerful natural history hotel/museum in the entire galaxy!  In this post, we are going to see more of what makes this dinosaur hotel so freaking awesome!  Let's check out some of the skulls and bones that are going to go in the hotel!  First off, an awesome skull of an Acrocanthosaurus!

A bunch of other awesome bones for the hotel were delivered a few months ago to the Morrison Natural History Museum since the lobby at the hotel wasn't finished yet!  Any guesses as to what is inside of the crate?

I hate to say it, but your guesses were probably wrong.  Here is what was inside, with Pyg modeling for scale!  First off, a pair of Brachiosaurus femora!

A Pachycephalosaurus skull!

One day when the Pachycephalosaurus skull was at the museum, Dr. Bob came in one day with a few other pachycephalosaur skulls belonging to Stygimoloch and Dracorex, and had us paint them!  

You can see that all three skulls are approximately the same size: there's NO way that they are all the same animal, as some paleontologists believe!

Another great picture of the Pachycephalosaurus skull!

Here's another dinosaur skull, this one is Edmontosaurus!

And the third and final awesome skull, a Camarasaurus!

The hotel has many other cool specimens, such as this Allosaurus skull, which was in the lobby!

Not only are there some FANTASTIC skulls, the hotel has some casts of fossil skeletons, as well!  Here is the plan for Wadsworth the Stegosaurus, hanging above the front desk!

First, here is Good Sir Wadsworth before being brought inside!

Wadsworth being hung up!

And finally, the lobby, complete in all of its glory!  Notice the Brachiosaurus femora off to the left, and the Edmontosaurus skull in the cabinet around the middle of the picture!

Here are some more great pictures from the lobby!  Here are the curiosity cabinets under construction:

And the final product, with the Allosaurus skull above the fireplace!

If you travel to the dining hall, right off the lobby, you can enjoy lots of fun food, just as an enormous Tylosaurus (now named Sophie) would have done 70 million years ago!  First, some pictures of Sophie!

The flipper of the specimen!

As we mentioned before, this Tylosaurus wasn't hungry when it died!  In the stomach of this beatsie are the remains of a small creature called Dolichorhynchops!  To learn more about both Tylosaurus and Dolichorhynchops, click the link HERE!

Some days, you can also check out a fun-filled and exciting fossil table, crammed full of awesome goodies!  Here are several shots of that!

They also have an awesome donation box for the Morrison Museum!  This mosasaur skull, belonging to another Western Interior Seaway critter called Clidastes, will sit inside of it!

Indeed, this hotel is full of prehistoric from top to bottom!  Actually, literally to the top, as the hotel will have a Pteranodon weathervane!  Here are the plans, and the actual weathervane itself!

Want to hear more about the hotel, but just won't be in the area anytime soon?  Not a problem!  Like their Facebook page by clicking HERE!  Not only do they share lots of awesome pictures and fun facts, they also create lots of fun Dino Memes!  Here is one of my favorites (partly because they included a link to our Xiphactinus: The Inception Fossil post when they uploaded the picture to Facebook!), but partly because it's an awesome meme!

And here is the first in a series of "Fun Fact" memes that I am working on with the Tally's!

Hope to see you all at the hotel!

Other Things at the Quarry: Dinosaur Road Trip With Grace Part 5

PREVIOUSLY, ON BATTLESTAR GALACTICA:

-Grace Albers and I are taking a trip down to Dinosaur National Monument in Utah and Colorado.
-We checked out some cool petroglyphs and then camped the night.
-We arrived at the quarry and checked out all of the awesome bones on the quarry face.
-And now....

In the last post, we looked at a bunch of pictures that we took from the second floor viewing platform of the quarry face.  In this post, we have traveled below the viewing platform to the first floor to check out some of the awesome fossils that they had below!  Below is a diagram of the quarry wall that shows where the original discovery of the site was made!

Here we have the skull of a species of Allosaurus called Allosaurus jimmadseni!  I believe that this species has not been officially described, but to be honest, the genus Allosaurus is a bit of a mess, so I'm not really sure what exactly is going on!

The arm of Allosaurus.

The foot bones that were discovered of Allosaurus jimmadseni inside a reconstructed footprint!

The skull of Allosaurus jimmadseni in situ (which means that it still is in the rock).

The skull of Allosaurus!

The reconstructed skeleton of Allosaurus!

This nearly complete juvenile skeleton of Camarasaurus is apparently the most complete sauropod skeleton ever found!

One of the signs at the quarry said that a new species of sauropod, called Abydosaurus, has been discovered in the monument in a different geologic formation called the Cedar Mountain Formation!

Here is the skull of Apatosaurus louisae.

A Camarasaurus tooth on the left and several Diplodocus teeth on the right!

Skin impressions of another sauropod dinosaur called Barosaurus!

One of the tail spikes of Stegosaurus!

One of the plates of Stegosaurus!

Some of the baby Stegosaurus bones discovered in the quarry!

The skull of the small ornithopod Dryosaurus!

Unidentified lizard legs and feet.

A small crocodilian called Hoplosuchus.

A fossil conifer cone.

A fossil conifer branch with shoots!

The fossilized remains of an extinct salamander called Iridotriton!

The fossilized remains of the extinct frog Rhadinosteus!

A fossilized shell belonging to a juvenile Glyptops, a type of turtle!

A lungfish tooth plate from a fish called Ceratodus!

The shell of another extinct turtle called Dinochelys.

A fossil clam.

The fossilized belly scales of the extinct crocodilian Goniopholis.

The fossilized jaw bone of the same extinct crocodile, Goniopholis!

Next time: a few more petroglyphs and the Harper's Corner Drive!