Category Archives: Theropod Dinosaur Evolution

Siats Meekerorum

New megapredator of the Cretaceous announced by Lindsay Zanno in the Daily Planet theater.  Super awesome, check it out!  Collaboration with our friends and colleagues at The Field Museum of Natural History in Chicago.  Lindsay’s coauthor is Peter Makovicky.

The big announcement in the Daily Planet Theater at the NC Museum of Natural Sciences
Discovered in Utah, Mussentuchit Member of the Cedar Mountain Formation.  Arrrrrgh.
Discovered in Utah, Mussentuchit Member of the Cedar Mountain Formation. Arrrrrgh.

Did Plants Make Feathered Dinosaurs Dumb?

Short answer, no.

Want to know more… by all means read on.

Today, colleagues from the University of Bristol, National University of Mongolia, Ohio University and I took aim at the doctor/patient confidentiality pact by publishing some very personal information on a research subject of ours.  Fortunately, I don’t think this particular patient is going to get their feathers ruffled about it.  Turns out, paleontologists are smarter than we often get credit for.  In fact, we’ve got this whole messy doctor/patient thing figured out… just work on patients that are already dead… in this case, for over 90 million years.

copyright Mark Anderson
copyright Mark Anderson

One fortuitous day, we got the chance to do just that.  The only good skull of a rare and whacky group of theropod dinosaurs known as Therizinosauria made the trek from Mongolia to the UK on holiday.  While there, UK paleontologists realized that the skull of the therizinosaur Erlikosaurus was REALLY, REALLY, REALLY, overdue for its check-up.  So they took Erlikosaurus’s head to a CT scanning facility for its 90 million year annual physical.

The fossilized skull of Erlikosaurus andrewsi from the Cretaceous of Mongolia
The fossilized skull of Erlikosaurus andrewsi from the Cretaceous of Mongolia

Why Erlikosaurus?  Well, for starters, therizinosaurs are downright weird animals, which makes them really interesting to weird people (erg.. uh.. cough.. I mean “scientists”). Although they are theropods and therefore cousins of bloodthirsty predators like Velociraptor, therizinosaurs were clearly not taking a bite out of anyone.  Sometimes it is hard to envision an advanced therizinosaur like Erlikosaurus as doing anything at all, other than finding a nice soft spot in the Cretaceous landscape to pop a squat and eat all day long.  A quick run down of the therizinosaur anatomy makes this blaringly evident.  These guys had tiny heads, tightly packed minuscule teeth, long necks, stocky legs with fat feet, hand claws up to four feet long, and giant bloated bellies. They also reached enormous body sizes up to 13,000 lbs. When I was in grad school I used to get this point across by comparing therizinosaurs to a cross between a gorilla, an ostrich, and Edward Scissorhands.  If you ask me, the analogy is still apropros.

Luis Rey's vision of what an advanced therizinosaur looked like in the flesh.
Luis Rey’s vision of what an advanced therizinosaur looked like in the flesh.
How to build a therizinosaur 101.
How to build a therizinosaur 101.

The question is… did the loss of predatory behavior coincide with a loss of smarts and a loss of sensory capabilities in therizinosaurs?  No one knew. By CT scanning the skull, we were able to reconstruct soft tissue of the brain and inner ear of Erlikosaurus and tackle this intriguing question.  The result?  Despite its rather slow appearance, Erlikosaurus was not a dumb as a box of rocks.  Although, these kind of estimates are admittedly crude, it seems as if Erlikosaurus was just a bit shy on the intelligence scale when compared to early birds, but likely a bit ahead of the great hunter T. rex.  Pair this with the fact that Erlikosaurus had above average hearing capabilities for an animal its size and a higher than predicted sense of smell, and suddenly therizinosaurs don’t seems as dimwitted as…. well, as they look.

Scans did reveal that one Erlikosaurus sense could’ve benefited from some improvement–its vision, which probably wasn’t the best.  Whatever these guys were eating, they were likely munching in the pure light of day.

Reconstructed soft tissues in the head of Erlikosaurus: brain (blue), cranial nerves (yellow), and inner ear (pink).
Reconstructed soft tissues in the head of Erlikosaurus: brain (blue), cranial nerves (yellow), and inner ear (pink).

The implications are interesting. Despite leaning toward vegetarianism, therizinosaurs seem to have kept the keen sensory toolkit they inherited from their predatory ancestors.  All of which means that the brainpower and good senses of therizinosaurs had more to do with their place on the family tree as close cousins to birds than their dietary preference.  Its also good to know that, should you ever encounter Erlikosaurus as a result of, say a time machine fluke, it could hear your terrified whimpers but would be kind enough not to eat you.  (Just don’t sneak up on it at night or you could lose an eye).

Couldn’t say the same about T. rex.

The paper “The Endocranial Anatomy of Therizinosauria and its Implications for Sensory and Cognitive Function” by S. Lautenschlager, E. Rayfield, P. Altangerel, L. Zanno, and L. Witmer, is freely available to the public via the journal PLoS ONE

Did Plants Make Feathered Dinos Fat?

This post-Thanksgiving week, as you try to erase the memory of Uncle Henry indulging in his third slice of pumpkin pie, you may be delighted at the prospect of a distraction.  In that case, try this one on for size.  If your holiday meal included the traditional turkey, than you’ve just fed your family on the roasted carcass of a small dinosaur.  Yes, that’s what I said, a small dinosaur.  Feel better?  Yeah… I didn’t think so.

Turkeys, like all birds, are members of a fascinating group of dinosaurs called theropods.  Paleontologists love theropods, in part, because they were the Harry Houdini of the Cretaceous Period, managing a great escape when all other dinosaurs bit the big one 65 million years ago.  This small factoid means that rather than always having to marvel at extinct animals, paleontologists can also study a small group of living dinosaurs in the flesh (how cool is that?!).  And while living birds are cool, theropod dinosaurs on the whole were even cooler back in their heyday.  Think: if birds are Maxwell Smart, than Cretaceous theropods are James Bond.  This is because Cretaceous theropods also included animals like T. rex and Velociraptor, meaning that birds could have hosted some wicked and weird relatives at their holiday meals. (Can you imagine if cousin Utahraptor dropped by for Christmas dinner?)

Kids, come eat your dino, I mean turkey, wait no, dinosaur… never mind.

Thankfully, a lot of Cretaceous theropods were more into veggies than flesh, including some very odd-looking and unusually large critters whose evolutionary history is just beginning to unfold.  And while the benefit to your waistline that comes from choosing more vegetables over meat this holiday is clear, the same cannot necessarily be said for these veggie-loving theropod dinosaurs.

Scientists have long considered larger body size to be advantageous to vegetarian animals.  Larger guts can fit larger digestive tracts allowing animals to get more energy from food with a lot of fiber and few calories.  For that reason, scientists tend to think that bigger is better when it comes to plant eating animals.  Interestingly enough, as you get closest to birds on the theropod family tree, the biggest species are also the ones we think ate plants not prey.  Could this mean that feathered theropods fit the same pattern?  A colleague of mine and I were dying to find out.

We began by estimating body mass for 47 species of feathered theropods representing three major groups that abandoned a strictly meat-eating diet–ornithomimosaurs (“bird-mimics”), oviraptorosaurs (“egg-thieves”), and the bizarre therizinosaurs (“scythe-lizards”).  Our results showed that all three groups had members of gigantic proportions (up to 100 times more massive than an average person).  The largest oviraptorosaur weighed over 7,000 pounds, and the biggest ornithomimosaurs and therizinosaurs topped out at over 13,000 pounds! rivaling the size of the great T-rex. 

The biggest members of three feathered dinosaur groups Oviraptorosauria, Ornithomimosauria, and Therizinosauria topped out at an whopping 7,000-13,000 lbs, rivaling the mass of the largest predators of the day.

Nonetheless, just because some feathered dinosaurs got big, doesn’t mean that large size was an evolutionary advantage.  To test whether these feathered dinosaurs were being driven to large body size by natural selection, we fitted a variety of evolutionary models to the data, looking to see which model best described the pattern.  Turns out that plant eating theropods experimented with larger and smaller body sizes as they evolved and there was no clear drive to get big, no simple, overwhelming advantage to reach gigantic proportions.  However, we did find one interesting pattern… different species from the same time and place tended to be about the same relative size.

Although we were a bit disappointed not to find a trend toward large body size, in a way this latter discovery was much more interesting.  It suggests that changing environments during the evolution of these animals played a bigger role in body size evolution.  Different climates, range sizes, resource abundance all exerted a stronger influence on the evolution of size than the simple relationship between eating plants and being big.

The largest ornithomimosaur, Deinocheirus (shown here with paleontologist Altangerel Perle) is known from the latest Cretaceous. This same time and place preserves the most massive therizinosaurs.  Image © Louie Psihoyos/Corbis

Of course, there are two other possibilities… first, these theropods might have been eating a high proportion of caloric plant material like fruits, nuts, and seeds instead of low fiber foods to begin with or, (and this one is always the elephant in the room for paleontologists), bias in the fossil record is messing with our data.

As in all good science, this research raised more questions for us than it answered.  Back to the drawing board.


You can read more about this research in the November 28th online edition of the journal Proceedings of the Royal Society B.  Thanks to my colleague Peter Makovicky of the Field Museum for his contribution to this blog post.