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.

The Mace Brown Museum of Natural History

On our trip last summer to South Carolina visiting our friends the Beckleys, we got to visit the Mace Brown Museum of Natural History at the College of Charleston which, as small museums go, I was definitely impressed with.  They had quite the collection laid out in a very pleasing fashion, the lighting was great, and I definitely recommend stopping by for a visit.  They had a very nice assortment of fossils that were either local critters, or animals that had been found nearby and likely would have also been found in the area.  I started making this post way back then, and I never got a chance to finish it, so I just wanted to share a few pictures of some of the interesting animals that they had on display.

For me, last summer was the "Summer of the Giant Ground Sloths."  Up until that time, I had only seen a few ground sloth skeletons on display, including the skeleton at The Living Desert in Palm Desert, California and a mounted skeleton of a Harlan's ground sloth (Paramylodon harlani) behind the scenes at the Denver Museum of Nature and Science.  But last summer, I got to see mounted specimens at the Mace Brown Museum, the Rocky Mountain Dinosaur Resource Center, and the American Museum of Natural History.  The sloth skeleton above is the mid-sized ground sloth Glossotherium, from approximately 1.8 MYA during the Pleistocene Epoch in Florida.  The arm below is from the enormous Eremotherium, one of the earliest South American animals that migrated into North America during the Great American Interchange, approximately 2.2 MYA.  This specimen is thought to be approximately 1.6 MY old, from Florida.  That little sign placard next to the arm was probably about 2x3 inches.  These sloths were simply enormous.

I also got my first good look at a bizarre group of bizarre, dermal-armored animals known as pampatheres.  Below, we have the giant armadillo-like pampathere Holmesina septentrionalis from the Pleistocene Epoch, between around 2 - 1.5 MYA, also from Florida.  According to the signs, Holmesina is one of the largest pampatheres, and was given its current name by the famous paleontologist George Gaylord Simpson, which can be read by clicking HERE.  Originally, Holmesina was described as a species of Glyptodon by Joseph Leidy, who later thought that the animal was actually a type of giant armadillo, but Simpson was able to set the record straight in 1930.  This animal is in the same order as the armadillos and the glyptodonts, and like the other two groups, is completely covered in dermal armor.  The second picture shows a close up of that dermal armor on the front legs.

This picture displays the skulls of two rodents.  The one on the left belongs to Castor canadensis, the North American beaver.  The one on the right, however, that is freaking huge, is also from a beaver, just a gigantic extinct beaver.  Meet Castoroides ohioensis, a beaver the size of a black bear!  From what I have been able to find, it is unknown whether Castoroides built dams like its modern counterpart.  What is known is that it was one gigantic enormous beaver.

I also got to see my first fossil penguin (cast or otherwise) not still surrounded by matrix.  This is a cast of the skull of the penguin Palaeospheniscus, a genus of fossil penguin that was abundant during the Miocene of South America.  Their fossils have been discovered in Peru and Argentina, both places where penguins of the genus Spheniscus, such as the Magellanic and Humboldt penguins, are found today.

Works Cited: