Suuwassea: Beast of the Week

This week we will be looking at an exciting long-necked dinosaur that I actually was lucky enough to help prep bones of during my time at the Academy of Natural Sciences in Philadelphia.  Let's check out Suuwassea emilieae! 

Suuwassea was a plant-eating dinosaur that lived during the late Jurassic period, about 145 million years ago, in what is now Montana, USA.  Its genus name translates from the Native American Crow language to "Ancient Thunder", one of the coolest dinosaur genus names out there.  From snout to tail, Suuwassea would have measured between 45 and 50 feet long.

Suuwassea emilieae reconstruction in watercolors by Christopher DiPiazza

Suuwassea was a member of the sauropod order of dinosaurs.  Sauropods were the iconic group of dinosaurs that are defined by their large bodies, long necks, and small heads.  North America during the late Jurassic was literally shaking with sauropod dinosaurs.  Giants such as Apatosaurus, Brontosaurus, Barosaurus, Diplodocus, Camarasaurus, and Brachiosaurus, all were thriving there.  Suuwassea stands out among them based on where it falls in the sauropod family tree, however.  It belonged to the family within sauropods, called dicraeosauridae.  Dicraeosaurids have mostly been discovered in South America and Africa.  Suuwassea is the only known member from North America.  Dicraeosaurids also tended to be smaller compared to other sauropods with proportionally shorter (relatively speaking) necks.  Despite living among many other sauropod relatives, Suuwassea may have utilized these differences in anatomy to exploit slightly different foods, like lower-growing plants that may have been more cumbersome for something like the much larger Diplodocus or Brachiosaurus to easily get to.

Neck vertebra from Suuwassea on display at the Academy of Natural Sciences in Philladelphia, PA.

Suuwassea possessed vertebra on its neck and back that had longer neural arches than what is typically seen in other groups of sauropods.  This would have given it a slight hump-like appearance in life.  Some of the later dicraeosaurids, like Amargasaurus and Bajadasaurus, would push that feature to extremes, sporting long spine-like structures growing from their vertebra!

That is all for this week!  As always feel free to comment below!

References

Harris, J.D. and Dodson, P. (2004). "A new diplodocoid sauropod dinosaur from the Upper Jurassic Morrison Formation of Montana, USA." Acta Palaeontologica Polonica 49 (2): 197–210.

Sander, P. Martin; Christian, Andreas; Clauss, Marcus; Fechner, Regina; Gee, Carole T.; Griebeler, Eva-Maria; Gunga, Hanns-Christian; Hummel, Jürgen; Mallison, Heinrich (2011-02-01). "Biology of the sauropod dinosaurs: the evolution of gigantism". Biological Reviews of the Cambridge Philosophical Society. 86 (1): 117–155.

Sereno, Paul C.; Wilson, Jeffrey A.; Witmer, Lawrence M.; Whitlock, John A.; Maga, Abdoulaye; Ide, Oumarou; Rowe, Timothy A. (2007-11-21). "Structural Extremes in a Cretaceous Dinosaur". PLOS ONE. 2 (11): e1230.

Prehistoric Dinosaur Mimics

Mimicry is one of the most well-recognized forms of defense in the animal kingdom.  For those who need a refresher, mimicry is defined in biology as the very close resemblance of one organism, or part of an organism, to a different species of organism.  This is usually meant to trick would-be predators.  Common examples are caterpillars with patterns to look like large snakes, or butterflies with spots on their wings that make them look like owls.

A snake!  Actually it's just an upside-down caterpillar.  But frogs, lizards, and songbirds, frequent predators of caterpillars and prey to snakes, might hesitate when attacking this it. Photo: Andreas Kay

How likely do you think mimicry in prehistoric animals was?  Given how vast biodiversity is, I have no doubt that some sort of mimicry took place millions of years ago, but to what extent? And in which species?  Did large non-avian dinosaurs mimic?

Recently on social media I have noticed a slight trend in artists posting images of ceratopsians and hadrosaurs with coloration on their frills and crests meant to mimic the faces of tyrannosaurs.  At first, this might seem like a plausible defense strategy.  Tyrannosaurs, from what we know, were usually the top predators in any community they inhabited during the late Cretaceous.  In fact, it is often said that the only animal that a tyrannosaur would ever need to fear was a larger tyrannosaur!

An adult Lambeosaurus already doesn't have much to fear from any of the other creatures that would be scared off by a tyrannosaur anyway.

But that phrase is exactly why I am highly skeptical of this being a likely mimic strategy.  The sight of a tyrannosaur would no doubt send every other animal in the area running...except for possibly another tyrannosaur.  The problem with this on a ceratopsian or a hadrosaur is the fact that we know tyrannosaurs were the main predators of both of these kinds of dinosaurs.  An adult Chasmosaurus or Lambeosaurus already doesn't have much to fear from any of the other creatures that would be scared off by a tyrannosaur anyway.  Ironically, their only real predator is the only one that wouldn't be scared by it.  In some cases they may even attract the very predator they would hope to repel!

There's two reasons why a tyrannosaur might be outright drawn into the image of its own species.  The first is like many vertebrates, tyrannosaurs needed to find a mate in order to reproduce.  So it is likely that at least during certain parts of the year, a tyrannosaur would mistake a mimicking Lambeosaurus as a potential partner only to discover that it's a meal upon closer inspection.

It is likely that at least during certain parts of the year, a tyrannosaur would mistake a mimicking Lambeosaurus as a potential partner only to discover that it's a meal upon closer inspection.

The second reason is that we have substantial fossil evidence that at least some tyrannosaurs engaged in intraspecies combat, specifically in the form of biting each other on the face, thanks to healed teeth marks in some skulls.  Plus, territorialism is very common across many kinds of large meat-eaters in general so this makes sense.  So a tyrannosaur might see a ceratopsian with its likeness on its frill, mistake it for a rival, and charge in for a challenge only to discover that it is once again a meal upon closer inspection.

A tyrannosaur might see a ceratopsian with its likeness on its frill, mistake it for a rival, and charge in for a challenge only to discover that it is once again a meal upon closer inspection.

Lastly, and perhaps this is best reason why visual mimicry wouldn't work for repelling tyrannosaurs, is the fact that we have very strong evidence that tyrannosaurs had excellent senses of smell.  So even though these plant-eating dinosaurs would look like a fearsome predator, a tyrannosaur would be able to identify them as what they truly were before they even saw them assuming the wind was blowing in the right direction.

That being said, I highly doubt mimicry in large plant-eating dinosaurs of large meat-eating dinosaurs (their direct predators) was very likely in real life.  And to be fair, most of the artists I witnessed producing these pieces admit that it was just for fun, which is fine.  However, it still got me thinking a lot about mimicry in general and I decided it was an interesting enough subject to cover for this post.

So I wonder if there was a more likely form of mimicry in prehistoric dinosaurs.  To explore this further we need to look at mimicry today and how it works.  In general, if an animal exhibits mimicry to ward off predators, it will typically mimic the likeness of an animal at least two levels above them on the food chain.  This way, they are mimicking a predator that will almost definitely scare away their direct predators, but at the same time the higher predator they are mimicking usually won't view them as a regular food source, as well.

A butterfly mimicking an owl is specifically doing so to scare away smaller birds, which themselves are regularly preyed on by real owls.

For example, butterflies that mimic the face of an owl with yellow spots on their wings are specifically trying to scare away their main predator, smaller birds, which themselves are regularly preyed on by real owls.  At the same time, real owls very rarely, if ever, eat butterflies.  So the butterfly isn't really taking a risk looking like an owl.

In general, if an animal exhibits mimicry to ward off predators, it will typically mimic the likeness of an. animal at least two levels above them on the food chain.

So back to the idea of mimicking a tyrannosaur.  I came up with a fun little idea of a much smaller plant-eater that may not find itself in direct contact with tyrannosaurs as often due to it living in more dense underbrush, but does have to worry about being preyed on by smaller predators, like dromeosaurs. So what if they had some sort of mimicry of a large, toothy monster on their bodies?  I'm not saying it's a true hypotheses of mine, but it's less unlikely than the imagery on a larger plant-eater.

Smaller plant-eating dinosaurs may not have been regularly be preyed on by adult tyrannosaurs.  So looking like one may have helped it survive attacks by more direct predators, like dromeosaurs.  

Another form of less specific mimicry is coloration to form generalized eyespot patterns that don't particularly mimic any specific species.  This is actually already commonly depicted by paleoartists, especially when it comes to ceratopsian frills.  Bold, circular patterns to give the illusion of eyes is common in a lot of animals alive today.

Are these Butterfly fish looking at you?  Which end is the head and which is the tail? Photo credit: Chris Huss

The first way this can help an animal is to draw attention from the place where the real eyes are, the head.  This can throw a predator off when attacking, and might save the animal's life.  Being directly chomped on the head is usually a death sentence.  But being bitten elsewhere might be a better chance of survival.

The second way general eyespots can help an animal is to suggest to a predator that it is being watched when in fact, it very well may not be.  A ceratopsian with eyespots could be completely oblivious as it munches away on plants while a tyrannosaur is taking a few extra seconds deciding if it's even worth it to try and ambush.  In nature, a few seconds can be more than enough time for the prey animal to realize it is being stalked and give it a start in running away or defending itself.

A dinosaur sporting eyespots could be completely oblivious while a tyrannosaur is taking a few extra seconds deciding if it's even worth it to try and ambush.

Mimicry is a widely successful form of defense that can be observed across many kinds of organisms alive today.  It was very likely also utilized in prehistoric species, but to what extent and in which species is still mostly a mystery.  What do you think?  Do any other kinds of prehistoric animals seem likely candidates for mimicry?


References

Bona, Sebastiano De, et al. “Predator Mimicry, Not Conspicuousness, Explains the Efficacy of Butterfly Eyespots.” Proceedings of the Royal Society B: Biological Sciences, vol. 282, no. 1806, 2015, p. 20150202.

Peterson, J. E.; Henderson, M. D.; Sherer, R. P.; Vittore, C. P. (2009). "Face Biting On A Juvenile Tyrannosaurid And Behavioral Implications". PALAIOS. 24 (11): 780–784. Bibcode:2009Palai..24..780P. doi:10.2110/palo.2009.p09-056r. Archived from the original on August 11, 2013.

Tanke, Darren H.; Currie, Philip J. (1998). "Head-biting behavior in theropod dinosaurs: paleopathological evidence (PDF). Gaia. 15: 167–184. Archived from the original (PDF) on 2008-02-27. [not printed until 2000]

Witmer, L. M.; Ridgely, R. C. (2009). "New Insights Into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior". The Anatomical Record. 292(9): 1266–1296.

Globidens: Beast of the Week

This week we will look at a prehistoric sea monster with teeth unlike any other.  Check out Globidens!

Globidens was a mosasaur, a kind of meat-eating marine lizard, that was about twenty feet long from snout to tail.  Fossils of different species within the genus have been found in the United States, Morocco, Angola, and Indonesia which flourished throughout the late cretaceous period from 85 to 66 million years ago.  The genus name, Globidens, translates to "Globe Teeth" because of its unusual sphere-shaped teeth.

Globidens phosphaticus cracking the shell of an ammonite.  Watercolor life reconstruction by Christopher DiPiazza.

Globidens is most known for its teeth, which were unlike those of any other mosasaur, most of which had cone-shaped teeth, like Tylosaurus, or blade-like teeth, like Platecarpus.  Globidens, on the other hand, had teeth that weren't sharp at all, but had wide bulbous crowns.  The skull looks like this beast had a mouth full of big, round mushrooms growing out of its jaws!  These blunt, teeth were ideal for crushing hard objects, leading paleontologists to hypothesize that it specialized in hunting prey with shells, like mollusks, crustaceans, and possibly even turtles.  In addition to the teeth, Globidens had a robust lower jaw, which would have been controlled by enormous muscles in life, giving it an extremely powerful bite.  Paleontologists suspect it may have had one of the strongest bite forces of any mosasaur, despite not being the largest-bodied member of the family.  After the discovery of it's teeth, a Globidens skeleton with shell fragments of large prehistoric bivalves in the stomach cavity proved the already strong hypothesis of its preferred food.

Skull of Globidens phosphaticus, which lived in what is now Angola, on display at the Smithsonian National Museum of Natural History in Washington D.C.

Other than the jaws, Globidens had other notable features.  Its snout was relatively short for a mosasaur.  A shorter snout, allows for a higher concentration of pressure when biting down, so this was likely another adaptation that supported its strong biting pressure.  The eye sockets were large and housed wide scleral rings (a disc-shaped bone that supports the eyeball in life) which supports the idea that this creature had good vision, and likely could see well in low light, like the seafloor where much of its prey would have dwelled.  Lastly, Globidens' bones were dense which this is another adaptation of an animal that wants to be able to dive deeper underwater.  In addition to wanting to dive into deeper waters to find its preferred food, Globidens would also be avoiding other species of mosasaurs that it shared its habitat with that were even larger than it, like Tylosaurus, which was more of a surface predator.

Amazingly, Globidens wasn't the last lizard to evolve strange round teeth for crushing shells.  A kind of lizard alive today, called a Caiman Lizard (genus Dracaena) native to central and South America, has teeth almost exactly like those of Globidens, just on a smaller scale, which it uses to crush the shells of snails.  Even more interesting is the Caiman Lizard is from a totally different family of lizards from mosasaurs, so the shell-crushing teeth evolved convergently.  Evolution is amazing!

The modern day Caiman Lizard independently evolved similar feeding adaptations to that of Globidens because it also eats hard-shelled prey. (photo credit: Reptiles Magazine)

That is all for this beast!  Can you think of any other animals (alive or extinct) that have similar crushing adaptations?  As always feel free to comment below!

References

LeBlanc, Aaron; Mohr, Sydney; Caldwell, Michael (2019). "Insights into the anatomy and functional morphology of durophagous mosasaurines (Squamata: Mosasauridae) from a new species of Globidens from Morocco". Zoological Journal of the Linnean Society.

Martin, J. E. and Fox, J. E. 2007. Stomach contents of Globidens, a shell-crushing mosasaur (Squamata), from the Late Cretaceous Pierre Shale Group, Big Bend area of the Missouri River, central South Dakota. Geological Society of America Special Papers, 427:167-176.

Massare, J. A. 1987. Tooth Morphology and Prey Preference of Mesozoic Marine Reptiles. Journal of Vertebrate Paleontology, 7(2):121-137.

Russel, Dale (1975). "A new species of Globidens from South Dakota, and a review of globidentine mosasaurs". Fieldiana Geology. 33 (13): 235–256.