Tarbosaurus: Beast of the Week

This week we will be checking out a huge tyrannosaurid.  Enter Tarbosaurus bataar!  Tarbosaurus was a large meat-eating dinosaur that lived in what is now Mongolia and China during the late Cretaceous Period, about 70 million years ago.  The largest known individuals infer that they could have been just a little smaller than the largest known Tyrannosaurus, at about 39 feet long from snout to tail.  The genus name translates to "Alarming Lizard".  When alive, Tarbosaurus would have shared its habitat with (and maybe hunted) fellow theropods, Deinocheirus and Therizinosaurus, as well as the hadrosaur, Saurolophus.

Tarbosaurus and young...and lunch life (except lunch...lunch is dead) reconstruction by me.

Tarbosaurus was an extremely large tyrannosaurid, second largest known, right behind Tyrannosaurus.  These two genus are very similar in appearance at first glance, but key differences are present.  In fact, the two may not be as closely related to each other as they each might be to other kinds of tyrannosaurids that are known.  Starting at the head, Tarbosaurus had a laterally slim head.  It's eye sockets were primarily facing sideways, so it wouldn't have had much depth perception.  Thanks to scans of the inside of Tarbosaurus' skull, and looking at the shape of the brain case, scientists can infer that Tarbosaurus would have had a great sense of smell and hearing, but it was lacking in the sight department.  It likely would have hunted relying on its sense of smell mostly, unlike T. rex, which had more forward-facing eyes.  Tarbosaurus' teeth were sharp and curved for crushing and tearing flesh and bone, but weren't as proportionally large.  The actual jaws were less flexible than those of most other tyrannosaurids.  It possessed two extremely short arms with two fingers on each hand.  The arms of Tarbosaurus are proportionally the tiniest out of all tyrannosaurids. (Yes, they were even smaller than T. rex's.)  When examined more closely, it was discovered that the arms of Tarbosaurus commonly endured stress factors, meaning they likely weren't completely useless in life.  Some have suggested they aided in taking down prey but personally I feel they may have had some role when it came to mating.  We may never know!

Tarbosaurus skeletal mount on display at the Cosmacaixa Museum in Barcelona, Spain.

There are a relatively large number of Tarbosaurus specimens on the fossil record.  Among these are small juveniles.  Thanks to these individuals, we know that Tarbosaurus was proportionally leggier when it was little, bulking up as it aged.  The teeth were also more blade-like, and less robust when they were young.  Tarbosaurus probably filled different ecological niches as it aged, preying on smaller, faster prey when it was younger, and moving on to bigger game as it matured.  In fact, thanks to bite marks on bones, we can be fairly certain that an adult Tarbosaurus was eating at least Deinocheirus, the giant, flat-billed, ornithomimid.

Juvenile Tarbosaurus skull

Lastly, we have actually found clues as to what Tarbosaurus' skin was like...well at least parts of it.  A large individual had a small patch of skin (sadly we don't know exactly where because it was messed with by fossil poachers) that shows small, round scales.  These scales are each only about two millimeters wide in diameter.  In addition, a Tarbosaurus footprint was discovered, that showed evidence of being scaly as well.  Because of this evidence, many folks tend to argue that Tarbosaurus and its close relatives wouldn't have had feathers in life.  This is flawed, however, since even modern birds possess similar textures on their own feet.  Plus, other fossilized non-avian dinosaurs have been unearthed with evidence of both scales and feathers on other parts of their bodies than the feet.

That is all for this week!  As always feel free to comment below or on the facebook page!

References

Currie, Philip J.; Badamgarav, Demchig; Koppelhus, Eva B. (2003). "The First Late Cretaceous Footprints from the Locality in the Gobi of Mongolia". Ichnos. 10: 1–12.

Hurum, Jørn H.; Sabath, Karol (2003). "Giant theropod dinosaurs from Asia and North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared" (PDF). Acta Palaeontologica Polonica. 48 (2): 161–190.

Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.

Saveliev, Sergei V.; Alifanov, Vladimir R. (2005). "A new study of the brain of the predatory dinosaur Tarbosaurus bataar (Theropoda, Tyrannosauridae)". Paleontological Journal. 41 (3): 281–289.

Tsuihiji, Takanobu; Watabe, Mahito; Tsogtbaatar, Khishigjav; Tsubamoto, Takehisa; Barsbold, Rinchen; Suzuki, Shigeru; Lee, Andrew H.; Ridgely, Ryan C.; Kawahara, Yasuhiro; Witmer, Lawrence M. (2011-05-01). "Cranial Osteology of a Juvenile Specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia". Journal of Vertebrate Paleontology. 31 (3): 497–517.

Dinosaurs Among Us at the American Museum of Natural History

It's the day after Thanksgiving.  Many people cooked and ate a dinosaur last night.  This is nothing new.  I've been saying it for years.  Yet many people are still blindsided by the fact that birds are, in fact, literal dinosaurs.  (I just graded my tenth grade's vertebrate evolution quizzes...trust me.)  Finally, however, there is something that is available to ANYONE who happens to find themselves in New York City (at least until January) that not only educates, but shows proof of this amazing connection between modern birds around us and the most influential animals we never knew.  Let's go check out the American Museum of Natural History's best (I'm biased.) temporary exhibit, called Dinosaurs Among Us.

I had the privilege of being taken in as an explainer for this exhibit during the spring and summer of this year before I had to move out of New York.  When I first stepped in for the training walkthrough, the amount of sheer information was almost overwhelming, even for a museum.  Essentially this exhibit has a two main messages.  The first is to explain, on a broader sense, by using dinosaurs as the model, how evolution works.  The second is to bring home the fact that birds are dinosaurs, by the use of many awesome physical pieces of evidence, some of which have never been on public display before.

One of the life-sze Microraptor models hanging from the ceiling.  They have been painted glossy black-blue in accordance with the preserved melanosomes in their fossilized feathers.

When you first walk in you are greeted by life-sized life reconstructions of several of the keynote dinosaurs featured in the exhibit.  Most important is probably Citipati, due to the sheer amount of fossil material that has been found, and the fact that the American Museum of Natural History does a lot of field work in Mongolia, where this dinosaur was native to, and therefore has access to a lot of its fossils.  The largest and most dramatic model, however, is definitely Yutyrannus.  To my knowledge, a life-sized life reconstruction of this monster has never been made before this, and it looks great. Many of the life reconstructions actually feature real bird feathers, as well.

My first interaction with the Yutyrannus was a bit rocky.  We're cool now, though.

One key connection between birds and other dinosaurs is the act of nest building.  This exhibit features several spectacular fossils of nests and eggs that were laid by dinosaurs millions of years ago.  The manner in which these eggs were laid actually gives us clues as to just how closely related a species dinosaur mother was to her modern relatives.

Life-size replica of a Gigantoraptor nest on display in Dinosaurs Among Us.  Yes, you're allowed to stand in it.

One very interesting way to tell is whether or not the eggs in a dinosaur's nest were laid in pairs.  Check out this replica of a Gigantoraptor's nest above.  See how the eggs are spaced in twos?  That means that the mother of these eggs had two functioning ovaries, and was producing an egg from each of them.  This is in contrast to nests like...

This, laid by a troodontid, called Byronosaurus.  The eggs aren't arranged in pairs.  This looks more similar to a clutch of eggs laid by a modern bird.  This is because modern birds only have one functional ovary, and therefore only lay one egg at a time, resulting in this arrangement.  (Fun fact: They have two ovaries as an embryo, but lose one as they develop.  This tells us that they evolved from dinosaur ancestors with two.) We used to think this was an adaptation for lightness so they could fly...but here are some non-avian dinosaurs that didn't fly...and went extinct that way.

Telling you just how close a particular non-avian dinosaur is related to modern birds is a constant theme throughout this exhibit.  In fact, under each specimen, there is a tiny infograph, modeled after a barometer, with the needle pointing somewhere between the earliest ancestral dinosaur and modern birds.

Dino-Bird-o-meters are all over this exhibit.  In this case, it is telling us that Yutyrannus, a tyrannosauroid, is more closely related to modern birds than it is to many other kinds of dinosaurs.

After eggs and nests the exhibit looks at the actual anatomy of different dinosaurs, especially the bones.  As with single ovaries, hollow bones was another feature we used to think birds evolved specifically for flight.  Since then we have learned that this was also not the case.  Large dinosaurs, like Allosaurus, demonstrated here, and even gigantic sauropods, had hollow bones.  We now think this was a sign of having a more efficient one-way respiratory system that birds retain today.  When a bird breathes air into its lungs, it doesn't simply get exhaled out the same way it went in.  It goes into more chambers throughout the body, including ones connected to hollow cavities in the bones.  Birds today use it to help them fly better, most likely, but prehistoric dinosaurs probably used it for other reasons, like getting oxygen throughout their huge bodies more efficiently.  We have also found similar respiratory systems in modern crocodilians and even some kinds of lizards so...yea definitely not a specific flight adaptation.

This is a broken piece of an Allosaurus leg bone,displayed next to the bone of a modern bird.  The hollow inside has since been fossilized with a different mineral from the actual bone.

Having fused clavicles, or a wishbone, was another feature previously thought to be exclusive to birds...until it started popping up in the fossil record in dinosaurs like Velociraptor.  This exhibit has an awesome articulated Velociraptor specimen on display with the wishbone clearly visible.

Beautifully articulated Velociraptor specimen.  You can see the shallow v-shaped clavicle at the base of the neck.

My favorite specimen in this exhibit would be the Tyrannosaurus wishbone, however.  That's right, T. rex had a wishbone, just like that turkey you ate.  To drive the point home even harder, it is displayed in a case surrounded by the wishbones of various modern birds.

T. rex wishbone.  My favorite piece in the exhibit.

Finally the exhibit goes from internal anatomy, like bones, to external anatomy, like skin and feathers. A myriad of specimens showcasing visible preserved feathers on fossilized bodies is showcased here from the curious quill-like structures of Tianyulong...

Tianyulong cast on display, complete with bristles on the back.

To the extremely feathered, Confuciusornis, in all its plumed glory.

Confuciusornis.  Just one of many feathered specimens on display at Dinosaurs Among Us.

At the end of this exhibit, a common question we receive from guests is "So what defines a bird?" This is a great question.  Yes, birds are dinosuars...but not all dinosaurs were necessarily birds, of course.  It's like saying a Ferrari is a car, but the car I drove to New Jersey to see my family today sure as heck wasn't one!  So what they are really asking is where in the fossil record do we draw the line between birds and non-avian dinosaurs?  What combination of features can we confidently say that all birds must have to be considered a bird?

Archaeopteryx fossil.  For a long time this was the only feathered fossil known to science.  Because of that, Archaeopteryx was referred to as the "first bird" when in reality the line between "bird" and "other dinosaurs" is too blurred determine where one stops and the other begins.

The answer to this is as frustrating as it is beautiful; We don't know!  And to put it bluntly...we shouldn't really care.  Nature has nothing to do with which label we put on which organism.  They evolve to survive and the process just is what it is.  Labeling something a bird based on an anatomical milestone just can't flow with what actually happens.  The amazing side of this seemingly frustrating coin is that this means that the fossil record for non-avian dinosaurs to birds is rich with plenty of specimens to learn from for years to come.  This is in harsh contrast to as little as a few decades ago when all we had to work with as far as feathered, birdlike dinosaurs were concerned, was good old Archaeopteryx, once considered "the first bird" and now just one of many feathered, birdlike dinosaurs.

If you have an interest in paleontology, birds, or nature in general PLEASE visit this exhibit if you have not already.  The American Museum of Natural History has been a prominent part of my life since I was born.  I've seen lots of fantastic temporary exhibits come and go.  That being said, this exhibit blew me away.  I purposely didn't write about and include photos of everything in there.  In fact, I only showed you a smaller portion of what this exhibit has to offer to further encourage you to go out and see it in person for yourself.   

Gorgonops: Beast of the Week

This week we will be checking out a prehistoric beast with an even beastlier name!  Let's look at Gorgonops!  Gorgonops was a creature that lived in what is now Southern Africa during the late Permian era, between 260 and 254 million years ago.  It was a synapsid, which means it belonged to the same group as mammals, yet it also shared characteristics with animals we consider reptiles. Because of this, Gorgonops and its close relatives are also informally referred to as "mammal-like reptiles".  The much more famous, Dimetrodon, is an earlier example of a synapsid that is also a "mammal-like reptile"s.  The largest Gorgonops measured about six feet long from snout to tail and would have eaten meat when alive.  Within the genus, there are a few species of Gorgonops recognized by science.  Gorgonops torvus was the first to be discovered and is probably the most well-understood because multiple specimens of it have been found.  Gorgonops whaitsi was larger than G. torvus and had a more robust snout.

Gorgonops whaitsi life reconstruction by Christopher DiPiazza.

Gorgonops' genus name translates to "gorgon face" in reference to the gorgon, a monster from Greek mythology that resembled a woman with snakes for hair.  According to the legend, looking directly at a gorgon's face would turn a person to stone.  (Medusa was the most famous gorgon.)  In contrast to this, Gorgonops possessed extremely long, sharp teeth in the front of it's mouth, which gave its skull a particularly menacing look.  Because of this, it was named in honor of the mythical creature.  It is unlikely that looking at an actual Gorgonops would turn anyone to stone, however, and snakes wouldn't evolve for tens of millions of years after Gorgonops' time.

Kinda like that...but not.

The first Gorgonops was discovered and named during the 1800s by a man named Richard Owen. (Somewhat Unrelated Fun Fact: Mr. Owen also coined the term "dinosaur")  Since then, several other kinds of related animals from the same family have been unearthed.  Since Gorgonops was the first, the name of this family is known as gorgonopsidae.

Gorgonops whaitsi skull from the American Museum of Natural History

Gorgonops is most well-known for its teeth, which, like I said earlier, were proportionally long, sharp, and curved.  They were similar in appearance to the canines on some carnivorous mammals, and because of their sheer length they are often compared to saber-tooth cats, despite the fact that gorgonopsids and cats aren't actually directly related beyond both being synapsids.  In addition to the two, downward-facing saber teeth, Gorgonops also possessed shorter teeth for nipping in the front of its face and shorter, broader teeth just behind the sabers, probably for cutting.  It is likely that Gorgonops delivered a killing bite to prey with the long teeth, puncturing vital areas, like the neck.  Then it would use other teeth to actually strip the meat off the carcass.  It is also very possible the long teeth had a role to play within the species, possibly for display.  This possibility would hinge on whether or not the teeth of gorgonpsids were visible or covered in some kind of soft tissue in life.

That is all for this week!  As always, feel free to comment below or on the facebook page!

References

Gebauer, E.V.I. (2007). Phylogeny and evolution of the Gorgonopsia with a special reference to the skull and skeleton of GPIT/RE/7113 ('Aelurognathus?' parringtoni) (PDF) (Ph.D. thesis). Tübingen: Eberhard-Karls Universität Tübingen. pp. 1–316.

Jacobs, L. L., Winkler, D. A., Newman, K. D., Gomani, E. M. & Deino, A., 2005, Therapsids from the Permian Chiweta Beds and the age of the Karoo Supergroup in Malawi. Palaeontologia Electronica. Vol. 8, #1, pp. 28A: 21-23