Monday, May 4, 2020

Stellasaurus: Beast of the Week

This week we'll be checking out a newly described ceratopsian dinosaur.  Say hello to Stellasaurus anchellae!  Stellasaurus lived in what is now Montana, USA, during the late Cretaceous period, about 75.2 million years ago.  From beak to tail it measured about 20 feet long and would have eaten plants when alive.  The genus name, Stellasaurus, translates to "Star Lizard" due to its flamboyant horn ornamentation and in honor of the late rockstar, David Bowie, and his song, "Starman".

My life reconstruction of Stellasaurus done in watercolors.  Ziggy Stardust-style facial markings and body stripes may have been an adaptation to communicate with members of its own species.  (Nature has produced weirder things.)

Stellasaurus is characterized by having a massive nose horn that curved backwards, towards the tail end of the animal, much like the horn of a modern rhinoceros.  Stellasaurus' nose horn was also slightly laterally compressed, like a blade, rather than having a more rounded cross-section, which is unusual for ceratopsians.  Finally, this dinosaur sported two long, upwards-facing horns on either side of its frill.  The evolutionary purpose of these horns was likely for some sort of intraspecies communication, likely display and/or combat with rivals.  Because there is just so much variation in headgear amongst ceratopsian species, it is unlikely they were purely for defense against predators.  Stellasaurus was a member of the centrosaurine group of ceratopsians, which are characterized by their deeper snouts and proportionally smaller neck frills.

Right and left views of Stellasaurus' massive rhinoseros-like nose horn. (image from Wilson's 2020 paper linked below)

There are a lot of ceratopsian taxa on the fossil record.  New members of this wildly successful group of dinosaurs are being published every year.  That being said, Stellsasaurus is a particularly important find because it appears to help show an actual evolutionary line in action.  We know evolution is an ongoing process of older forms of organisms changing over time into newer forms in response to environmental changes.  That being said, it isn't common to be able to say with certainty one taxa was a direct ancestor or descendent of another in the fossil record.  However, looking at the frill horns of Stellasaurus, and then comparing them to the frill horns of other ceratopsians that lived in the same place as it from different times, paleontologists were able to see a likely linear transition between at least five different kinds of ceratopsians!

Left and right sides of Stellasaurus' frill and frill horns.  Note how it has two growing from each side.  (Image from Wilson's 2020 paper linked below.)
A close relative of Stellasaurus, Styracosaurus, which lived slightly earlier than Stellasaurus, had similar frill horns, but they were more numerous, with three on each side instead of Stellasaurus' two.  Einiosaurus, which lived a bit after Stellasarus, only had one of these frill horns on each side.  The even younger Achelousaurus, also had two horns on its frill, but they angled slightly outwards.  Finally, the youngest piece to the puzzle, Pachyrhinosaurus, also had these horns, but they were even more dramatically curved outwards.  The only thing that may not seem to match up is the difference in nose ornamentation between Stellasaurus' backwards curving horn, and Einiosaurus' extremely forward-facing horn, but keep in mind there were millions of generations of dinosaurs between these individuals, and therefore many more transitional forms that existed there.  Maybe we'll find yet another ceratopsian to fit into this line to make it even more detailed!

Stellasaurus provides a crucial puzzle piece in showing a possible direct transitional line among several different taxa of centrosaurine ceratopsians.

That is all for this week.  As always please leave your thoughts below!

References

Wilson, John P.; Ryan, Michael J.; Evans, David C. (2020). "A new, transitional centrosaurine ceratopsid from the Upper Cretaceous Two Medicine Formation of Montana and the evolution of the 'Styracosaurus-line' dinosaurs"Royal Society Open Publishing7 (4).

Thursday, April 23, 2020

Bird Feeders: Sharing Our Earth with Wildlife

This Earth Day I want to focus on birds.  Birds are by far the most successful vertebrates on land today.  They outnumber all other vertebrates, including us, mammals, in terms of species diversity, as well as in sheer numbers.  With this in mind, paired with the fact that birds are dinosaurs, you could say the "age of dinosaurs" people often think ended millions of years ago, is still going stronger than ever.  A great way to see a wider variety of live dinosaurs without even leaving your home is by setting up a bird feeder.  Feeders come in a variety of sizes and types and can be set up even on windows of small apartments if need be.  I put together a list of thoughts to remember that I hope will help you get the most out of your bird feeder.

A Tufted Titmouse (left) and female Downy Woodpecker (right) sharing a meal at our feeder.  

Tip 1: Feeding wildlife is dangerous.

First off, I want to make it clear that most of the time it is an absolutely terrible idea to feed wildlife.  Normally when this happens, wild animals learn to associate humans with food, and therefore will start seeking humans out instead of foraging for food, themselves, like they naturally would be.  This is how you get what are referred to as "problem animals", like deer, bears, or even alligators, that lose all fear of humans and start living way to close to people for comfort.  Sadly these animals are often humanely killed by local authorities because they start posing a threat to people.  In addition to this, well-meaning people often feed wildlife inappropriate foods that don't meet the animal's nutritional needs, and in some cases actively hurt the animals.  Feeding bread to ducks, for instance, is actually detrimental to the ducks since they can't digest it and it can lead to developmental problems.

Snow White was super inappropriate when it came to interacting with wildlife.  Don't be like Snow White. 

Tip 2: Wildlife Still Needs Our Help.  It just needs to be given the right way.

Hold on...I started by saying I was going to tell you how to set up a bird feeder...but then said feeding wildlife is bad?  Which is it!?  Let me explain.  Bird feeders are a little different from blatantly throwing food at animals outside since in the case of bird feeders, the wildlife never associates the food with humans.  As far as the birds know you and the food you put out are completely unrelated.  This fact, paired with the assumption that the quality of food you're providing the birds is appropriate and adds to, not replaces, their wild diet (which we will cover below), results in a totally safe scenario for all parties, with some added food available for the birds, and entertainment for you!  I'm a firm supporter of the idea that wildlife should stay wild.  However, I also completely support the idea of humans actively helping protect and preserve wildlife when it's needed and if it's done appropriately.  Wild bird numbers have been consistently dropping at an alarming rate and it's absolutely in response to human activity, predominantly pollution, habitat destruction, and climate change.  So putting a bird feeder out is a small way to maybe help some wild birds get some extra energy and nourishment in their already stressful daily lives living in the wild.

Tip 3: The variety of animals present is entirely dependent on the habitat available.

In order for wildlife to be present there must be a habitat.  It sounds like a no-brainer, but it's important to keep in mind. The kinds of birds that will come to your feeder will depend on the kind of habitat you are currently near.  That being said keep in mind that urban areas with lots of human development are absolutely habitats for wildlife, too.  I have seen lots of really interesting species that make their homes in highly populated cities.  If you do live on a property where you have a yard and the ability to control the kinds of plants and landscaping that's present, you can change the habitat and possibly attract more species over time.

Habitats are less restricted by space than you think.  This is important especially if you live in a small home with no yard, or in an apartment.  This doesn't mean you can't still provide at least a small change to make your home a little better for wildlife.  Many flowers and other native plants do just fine in potted plants that can exist on windowsills.  Bird feeders that attach directly to windows via suction cups are easy to find and purchase.  My point is no matter what kind of home you live in, attracting more wildlife is always possible.

Eastern Bluebirds only nest in meadows and fields, so if you don't have a space like that nearby, you are unlikely to see them very often.  I took this photo miles away from my house because I don't have the right habitat near my property for this species.

Tip 4: Insect protein is essential for nutritious bird feeders.

The more variety in food is in your feeder, the more variety in wildlife you'll attract.  Lots of people simply buy a bag of seeds to fill their feeders.  If you really want to attract more species of birds, as well as provide them with more useful nutrients, make sure your bird feeders have insects in them!  Keep in mind that in the wild, many songbirds eat a lot of insects.  In fact, songbirds, even the ones that are often associated with eating seeds and fruit, are one of the strongest forces that control insect populations in the world, alongside bats and amphibians.  Luckily any garden store, or other place that already sells wild bird seed, will have bags of dried mealworms that you can mix into your feeder.  Some bird feed companies also make bags that include both seeds and insects together.

Downy Woodpeckers, like all woodpeckers, eat insects year round.  A suet block, like the one this male is feeding from, is essentially a powerbar for birds, loaded with protein from both ground nuts and insects.  

Tip 5: You don't need to hate on squirrels so much.

I see people often complaining that they get too many squirrels eating out of their bird feeders. I've even witnessed many people state they actively avoid setting up bird feeders because they're so turned off by the squirrels.  Where I live we have Eastern Gray Squirrels.  They're extremely common, but they're still native, and therefore a part of the natural environment.  They help plant trees by burying seeds and nuts (and forgetting to retrieve them) as well as provide a valuable food source for many charismatic predators, like hawks and owls.  In addition, even though it may seem like squirrels are hogging all the bird seed, I assure you the birds are still getting meals out of the feeder.  That being said if you still want to reduce the frequency of squirrel feeding and increase that of birds, many bird feeders have mechanisms that (somewhat) deter squirrels built into them, like perches that collapse under the weight of a squirrel, but not a bird.  You can also buy bird seed that has hot peppers in it which squirrels don't like, but birds do.  That's right.  birds have different taste receptors from mammals, including the inability to register capsaicin, the chemical that makes you feel like your mouth is on fire when you eat spicy food.  (When I was a zookeeper the cockatoos LOVED to snack on chili peppers.)

The neighborhood we live in has a high concentration of melanistic Eastern Gray Squirrels.  Melanism is when an animal is born with more melanin, the pigment that makes skin and hair darker.  


Tip 6: Clean your bird feeder between fillings.

When your bird feeder is empty, scrub it thoroughly with soap and water and let it air dry for a day before you fill it up again.  Old food residue will start to harbor bacteria and fungus that will make birds sick when they use the feeder.  Not letting the feeder dry all the way before filling will also grow fungus that can be harmful to birds.  Same goes for hummingbird feeders.

This is a male and female Eastern Golfinch that visits our feeder almost every day.  This photo was taken in early March, and you can see the male wasn't quite shedding away all of his brown winter feathers for his bright yellow mating season feathers.  The female, although more drab than the male, also turns more yellow in the warmer months. 


Tip 7: Don't be surprised if your bird feeder becomes a bird feeder... feeder.

By this I mean that if you have songbirds visiting your feeder enough, their predators will start to hang around too for obvious reasons.  Since putting up my feeder this past winter, I see the local Coopers Hawk and a young Red-Shouldered Hawk showing up more often.  As with the squirrels, some people don't like birds of prey at their feeders because they feel bad for the pretty songbirds that are at the feeder.  In my opinion it is important to keep in mind that regardless how cute these little birds are, they are still an active piece in the local ecosystem, and being food for a predator is an inevitable and necessary fate for some of them.  After all, the predators need to eat too.

Predators of songbirds, like the Barred Owl I photographed in October, are a necessary part of any ecosystem.  Owls especially also heavily control rodent populations.

Tip 8: KEEP YOUR CATS INDOORS!!!

There is literally no positive aspect of having an outdoor cat.  None.  Not for the cat, and certainly not for any wild animals that now have to share space with the cat.  A recent scientific study came out that proves just how many birds and other native animals domestic cats really kill and the numbers are horrifying.  It's estimated that domestic cats are responsible for the deaths of BILLIONS of wild birds per year.  Billions.  With a B.  That's more bird deaths than by window collisions!  Some might argue that an outdoor cat is simply part of the environment and doing its part as a predator.  This opinion is extremely wrong for a few reasons.  First of all, domestic cats are originally native to Northern Africa, from where they spread to there rest of the globe with humans as pets, and therefore have no business in most ecosystems where they're killing birds.  So this is why outdoor cats are such a problem, but the birds of prey that also kill small birds I previously mentioned, are not.  Second, even if you were to try to reason that cats are taking the place of other predators that previously lived in these areas before humans developed over them, like bobcats, you'd still be wrong.  This is because one bobcat can have a territory that stretches for several miles which they will defend from other bobcats violently.  Plus, although Bobcats do eat birds naturally, they don't kill them nearly as frequently as one domestic cat does.  Domestic cats also aren't nearly as territorial so many individuals can be roaming the same small space, and since they're often being fed by their humans anyway, they're killing birds out of instinct/play, not to survive.  Another important point is that being outdoors unsupervised is extremely dangerous for the cat, as well.  Typical lifespans of cats that are allowed to roam outdoors are significantly shorter than those of cats that stay indoors.  They're exposed to parasites, fleas, all sorts of diseases, and of course are at risk of being killed by cars and even wild predators, like coyotes and even large birds of prey.  If you're a cat owner like me, you can keep your cat perfectly happy indoors with toys and plenty of attention in the form of play sessions with you, the owner.  You can also totally get your cat used to a leash for outdoor adventures that is safe for both the cat and the local wildlife.

One of our cats, Beaker, wasn't a fan of the leash at first, but now she loves her (wildlife-safe) outdoor adventures.

Tip 9: Citizen Science is fun.

Citizen science is when amateurs or non-professionals participate and contribute to scientific research.  This can take lots of forms, like volunteering at your local nature center to help gather data on local wildlife populations.  However, some citizen science can be done without even leaving your house, like something as simple as counting the number of birds that visit your feeder.  Free apps like ebird and iNaturalist allow you to document bird numbers and species as you see them, and scientists can use that data for their research.  Not able to identify every bird that you see?  No problem!  Both these apps have features that actually help you identify mystery animals in real time, so you're learning to identify local wildlife you share your home with, too.  It's also fun to rack up as many bird species as possible and compare to other folks doing the same thing in their homes!

Northern Cardinals, like this female who visited our feeder yesterday, use their powerful beaks to crack open shells of nuts.
I hope this list of tips helped inspire you to start your own bird feeder.  If you already have a feeder I'd love to know what kind of visitors you're getting.  I personally have spotted a total of 28 species at my feeder since setting up this past winter.  Share your species count or the coolest bird you've seen on your property in the comments below!

Sunday, April 19, 2020

Pterodaustro: Beast of the Week

This week we will be taking a look at a bizarre pterosaur.  Let's check out Pterodaustro gulnazui!

Pterodaustro was a pterosaur that lived in what is now Argentina, during the Cretaceous, about 105 million years ago.  Adults had a wingspan between eight and nine feet long and they would have likely eaten meat in the form of very small animals (more on that in a bit).  The genus name translates to "Wing from the South" and the species name honors paleontologist, Roman Gulnazu.

Pterodaustro life reconstruction I produced in watercolors.  Because this creature was likely a filter feeder it is often restored with pink coloration, like a modern flamingo, but many other animals that filter feed, like ducks, do not become this color and there is no reason to think Pterodaustro was more likely pink than not.  

Pterodaustro is a well-studied pterosaur.  It is known from multiple complete skeletons, including adults, juveniles, and even eggs with embryos still inside.   Thanks to this array of specimens paleontologists know a lot about this strange creature's life appearance and growth pattern.  

 By far the most striking feature about Pterodaustro is its face, particularly its mouth.  This pterosaur sported a long, thin beaklike mouth that gently curved upwards.  Growing up from the lower jaws were over a thousand bristle-like structures.  These structures, although hair-like, were actually highly specialized teeth.  It is thought that Pterodaustro used these modified teeth for filter feeding tiny creatures out of the water, much like a modern flamingo, or some whales with  do with their baleen.  Pterodaustro also had very small, teeth on the upper jaws, possibly for processing its food after trapping it in the mouth with its unusual lower teeth.  A few Pterodaustro skeletons were found to have tiny rocks in their stomach cavities.  Many reptiles, including dinosaurs, lizards, and even modern birds, are known to have swallowed tiny rocks, called gastroliths, which help aid in crushing up food inside the stomach or crop once eaten.  Pterodaustro is the first example of a pterosaur that also did this.  Because of these rocks, it is implied that the food Pterodauestro was eating wasn't soft, so it was probably specifically filtering tiny crustaceans that sported exoskeletons that needed to be crushed and broken after capture.

Pterodaustro skeletal cast on display at the Museo Argentina de Ciencias Naturales in Burinos Aires, Argentina.

Pterodaustro had a long, thin neck and a relatively long torso for a pterosaur.  It's legs hind legs were proportionally short so it may not have been a very fast walker.  In order to get into the air to fly, takeoff also would have been relatively difficult because of its short legs would have hindered it from launching very far from the ground.

The Pterodustro eggs on the fossil record are similar to other known pterosaur eggs in that they would have had somewhat soft shells, more similar to those of modern turtles than birds.  The babies would have only been a few inches long when first hatched and would have grown very quickly for their first two years of life until they became sexually mature.  They would have continued to grow at a slower pace for four to five more years.

That is all for this week!  As always please leave a comment below!

References

Chinsamy, A., Codorniú, L., and Chiappe, L. M. (2008). "Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui"Biology Letters4 (3): 282–285.

Codorniú, L., Chiappe, L.M., Arcucci, A., and Ortiz-Suarez, A. (2009). "First occurrence of gastroliths in Pterosauria (Early Cretaceous, Argentina)". XXIV Jornadas Argentinas de Paleontología de Vertebrados

John D. Currey (1999). "The design of mineralised hard tissues for their mechanical functions". Journal of Experimental Biology202 (23): 3285–3294.
Witton, Mark P. (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press.

Sunday, February 23, 2020

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 Society86 (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 ONE2 (11): e1230.


Wednesday, February 12, 2020

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)Gaia15: 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 Record292(9): 1266–1296.

Sunday, February 9, 2020

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 Geology33 (13): 235–256.

Friday, January 31, 2020

Prehistoric Beast at the Smithsonian National Museum of Natural History: Deep Time

Even though I was born and raised in Northern New Jersey, I have always had a close relationship with Maryland and Washington D.C. because a large part of my family lives there.  That being said I have been to the Smithsonian National Museum of Natural History several times over the years.  I wrote about it here back in 2016 and then again more recently for its seasonal exhibit, The Last American Dinosaurs.  This past June, however, the main fossil hall was opened to the public again after being renovated and I was finally able to visit it for myself.  Let's check it out!

The David H. Koch Hall of Fossils takes place in an open hallway on the main floor of the museum.  Large dinosaurs are of course a focal point, but the overall exhibit is meant to explore the concept of deep time, and all the different life forms that have existed and what they can teach us, not just the most popular ones.  A popular question is "How does paleontology benefit humanity?" Personally, I find this question a bit egocentric and closeminded.  Nature shouldn't be directly paying us in order to be valued.  Despite this truth, studying deep time does in fact provide us with valuable information to better ourselves.  This exhibit does a good job addressing this question by forcing us to look at prehistoric animals in new ways, their direct relationships with life today, and of course, the concept of extinction.  Understanding extinctions from the past can tell us information about current extinctions (of which there are unfortunately many occurring) and how we can best prevent them. The earth has changed climate patterns many times throughout history and resulted in many observable extinctions in the fossil record, but never as rapid as the one caused by humans now.  Looking back and seeing the consequences of catastrophic events in the past can give us insight on how to best combat the crisis that is currently happening.

Diplodocus (left) and Camarasaurus (right) re the two largest dinosaurs on display.

The first fossil you see when approaching the exhibit is the first ever discovered specimen of the beloved spike-tailed dinosaur, Stegosaurus.  This is a wonderfully complete specimen, showcasing all the plates, the tail spikes, and even the bony throat armor, which many people don't realize this iconic dinosaur had.  Because this specimen was partially disarticulated, however, it posed as a sort of puzzle for paleontologists as to exactly how the plates were arranged and how the animal stood and carried itself in life for a long time.  The specimen is right there in the hallway at eye level behind a wall of glass so visitors can get very close to it and see all the details and textures on the bones.

Stegosaurus holotype on display.

The other side of the hall is the museum's active paleontology lab.  You can watch employees and volunteers behind glass prepping fossils for study or display.  This is a really great feature for educational purposes.  So many kids go into museums with dreams of working with real fossils one day.  This gives them a chance to see up close what that really entails.  It also is a chance for people of all ages to see that fossils aren't simply yanked out of the ground, perfectly complete and ready to display.  Fossils are often encased in excess rock on all sides from being taken out of the field and require sometimes years of careful work to remove all that rock until the fossil is ready to be studied. Sometimes we can't even identify what creature a fossil is from until much or all of the prep work is done!

One thing I always appreciated about the Smithsonian was that it makes a point to give you a sense of what it might have been like to actually step into the prehistoric environments from all sides by surrounding you with all kinds of elements, not just the biggest, most charismatic animals.  This newest version of the fossil hall was no exception.  There are many displays that show you what the smaller animals, invertebrates, and plants would have looked like from the same community.

The Smithsonian has lots of exhibits starring smaller fossil organisms that would have coexisted the more charismatic giants everyone already knows and loves.

Another great feature of this exhibit is the presence of several free-standing miniature dioramas of various reconstructed environments across time.  These are complete with scale models of land formations, bodies of water, plants, and of course the animals that are featured in the environments.  The fact that they can be viewed from all sides lets more visitors enjoy them at once, and also makes small details more visible.

Miniature diorama showcasing early Permian life.  Note how guests can view from both sides.

Of course the big skeletons of dinosaurs draw the most attention regardless of all the other wonderful features included in this exhibit.  That being said, many of the most iconic species are posed showcasing behaviors that are less common in art and other popular media, forcing visitors to think of their favorite prehistoric beasts in ways they never have before.

A perfect example of this is the Smithsonian's Allosaurus.  Allosaurus is widely known as a predatory dinosaur, often depicted attacking/killing/threatening/eating other dinosaurs.  It's hard not to with teeth and claws like that!  This Allosaurus, however, is posed in a resting position, tenderly guarding a nest of eggs.  Dinosaur eggs and families are no stranger to museum exhibits, but it's hardly ever the top predators who are shown tending to them.  This mount forces us to remember that ALL dinosaurs, even the most fearsome hunters, started tiny and helpless.

Parent Allosaurus.

Another unusual mount that is much more dynamic is their Stegosaurus in the process of knocking the meat-eater, Ceratosaurus, to the ground with its tail.  Just like the case with the nesting Allosaurus, this is a scenario that likely could have happened but is not often portrayed.  People naturally expect the predator to win the fight, even though they likely didn't more than half the time.  Being a predator is dangerous because it forces an animal to confront and kill other animals or starve trying.  Other animals don't want to be eaten so they do everything in their power to escape, or in the case of the Stegosaurus, fight back with formidable defensive weapons.  It is because of this that predators of most species typically have higher mortality rates.

Stegosaurus in the process of knocking over Ceratosaurus.  Notice all the bony throat armor included on this mount.

For those out there who just can't survive without seeing some good old fashioned predatory carnage, look no further than the Smithsonian's mount of the world's favorite carnivore, Tyrannosaurus rex.  T. rex is posed standing over a defeated Triceratops', separating the poor horned dinosaur's head from the rest of its lifeless body.  This scene was inspired by relatively recent studies regarding unhealed Tyrannosaurus bite marks on the frills of Triceratops skulls, suggesting that the meat-eaters would pull the heads off their ceratopsian victims in order to get to the neck meat when feeding.  The same Triceratops skeleton was previously displayed in a walking position in the previous American Dinosaurs exhibit as well as the main fossil hall before renovations.

Tyrannosaurus with Triceratops.

Nestled in the heart of all these massive dinosaurs is a beautiful section on the relationship between modern birds and other dinosaurs.  It points out the fact that birds ARE dinosaurs, as well as going into how they achieved flight.  There is a gorgeous mechanical model of a bird suspended from above guests that provides a moving visual demonstration of the mechanics of dinosaur flight compared to that of pterosaurs and other flying animals.

Say it with me.  BIRDS. ARE. DINOSAURS.

There is of course so much more to see in this hall I just can't fit into one post.  Of course the best way to enjoy this exhibit is seeing it in person.  If you're ever in the DC area, make the Smithsonian your first priority!

References

Kaplan, Matt. “How to Eat a Triceratops.” Nature, 2012, doi:10.1038/nature.2012.11650.