Dinosaurs: What Aren't They?

Last week I went over today's living dinosaurs, the birds.  But what about all those other animals that appear to be living dinosaurs?  Isn't it odd how birds are true dinosaurs but animals such as crocodiles and lizards are not?  Well today I would like to explain to you why that is.

Dinosaurs are distinguishable from other reptiles by several characteristics.  The most obvious, however is their posture.  All dinosaurs, alive and extinct, would stand holding their limbs straight below them much like a mammal.  We know this because their leg bones won't fit together any other way. 

Illustration of Diplodocus by artist, Mary Mason Mitchell from the late 1800s, showing what we now consider an incorrect sprawling posture. 

Barosaurus, a dinosaur, standing with an erect posture.

Other reptiles like squamates (snakes and lizards), testudians (turtles and tortoises) and crocodilians stand with their limbs out to the sides of their bodies in a sort of sprawling or semi-sprawling posture. 

Cuban Rock Iguana or Cyclura nubila, a modern lizard.  See how the legs come out to the sides?  Not a dinosaur.

So no, animals like lizards and crocodiles, despite how they superficially resemble what many people believe dinosaurs look like, are not true dinosaurs themselves.  This can also be determined by looking at their evolutionary histories (a bit more complicated to go over in one blog post!). Fun fact though: Crocodillians are more closely related to birds(dinosaurs) than they are to other reptiles like lizards, snakes and testudians.  They still aren't actual dinosaurs though, just very close relatives.

What about all those other prehistoric animals?  Things like the flying pterosaurs, marine plesiosaurs and the sail-finned Dimetrodon. 

Nope.

Nope.

Nope.  This one is actually more closely related to us mammals than to dinosaurs.  Its also way older than the oldest dinosaur by roughly a few million years. 

Its confusing at first, I know.  But if you look at the defining characteristics of a true dinosaur, none of these guys meet all of them.  And again, the whole different evolutionary history thing is important too.  The point I want to bring across here is just because an animal is a big scaly prehistoric creature, doesn't mean it is automatically a dinosaur.  There were lots of interesting prehistoric animals running around in the earth's past just like there are today.  Dinosaurs didn't account for everything!

Works Cited

Holtz, Thomas R., and Luis V. Rey. Dinosaurs: The Most Complete, Up-to-date Encyclopedia for Dinosaur Lovers of All Ages. New York: Random House, 2007. Print.

Kenneth D. Angielczyk, Dimetrodon Is Not a Dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and their Evolution Evolution: Education and Outreach, Volume 2, Number 2, 257-271

Birds are Dinosaurs: Simple Fact!

Hello everyone.  As I was browsing through my previous posts I noticed that I make reference to modern birds being dinosaurs on a few occasions.  I decided to dedicate this post to explaining exactly why modern science proves this since many people who read this may still be skeptical about the whole "birds are dinosaurs" thing.  I understand it's a difficult concept for most of us to wrap our brains around without any explanation.  After all, we have been taught for years and years (depending on how old said person is) that "dinosaurs are all extinct blah blah blah..."  It's tough when dinosaurs have always been the poster child for extinction and then all of the sudden some are still alive...in the form of birds no less.  Birds.  Like penguins...and budgies...and chicken.

...chicken?  I guess these tasty things are more accurate than we thought!

Dinosaurs and birds don't look anything alike!  How can they possibly be the same kind of animal?

Sure many dinosaurs were absolutely HUGE and most birds tend to be tiny and light with feathers.  So...

This seventy-foot long Brontosaurus...

...is related to this tiny Hummingbird???

Valid question.  Its true the sauropod is big and the hummingbird is tiny.  Also the two animals seem to lead very different lifestyles one being a lumbering land animal and the other a flitting flier.  But nature works in interesting ways.  Many times two animals may not appear to be related at all but if you check out their DNA or even just their fundamental physical characteristics that may not be obvious at first glance it can be discovered that they are, in fact, closely related.  I could just as easily make the same argument that...

...this huge Blue Whale has nothing in common with...

...this tiny, flying bat.

Yet everyone can agree that these two animals are still both mammals and therefore closely related despite how one is very large and lives in the ocean while the other is very small and flies.  Whats the difference?  The difference is that one of these ideas has been drilled into our heads since elementary school and the other hasn't!

But birds are the only animals that have feathers!  That should make them unique enough not to be grouped with dinosaurs.

This is just false.  Over the years paleontologists have been discovering many dinosaur fossils that have feathers or show direct evidence of feathers that are most definitely not birds.

Velociraptor, for example, is a dinosaur that lived during the Cretaceous, a time when true birds had already evolved.  Interestingly enough, Velociraptor had these little bumps on its wings that match exactly to bumps found on modern bird wings where the feathers attach to the body.  These structures are called quill knobs. 
 

Velociraptor arm bone with quill knobs.

Another, larger dinosaur, called Yutyrannus was discovered with feathers as well.  This is the largest dinosaur known to show actual feathers at about thirty feet long.  It was a close relative of Tyrannosaurus rex. 

Yutyrannus bones clearly showing feathers.

Don't misinterpret me here.  I am saying that birds are a kind of dinosaur.  Not all dinosaurs were necessarily birds though.  Just like a dog is a mammal yet not all mammals are necessarily dogs. 

Well what if feathers evolved multiple times and it's just a coincidence that both birds and dinosaurs had them?  Its not like birds have anything else in common with dinosaurs!

Well, hypothetical nonbeliever, birds actually have a LOT of features that are common only to them and other dinosaurs.  The most obvious of these is something that you can see any bird doing at any time; walking or standing on two legs.  Birds are obligate bipeds.  This means that they walk on two legs and two legs only.   Birds and certain dinosaurs are the only known animals in history to be obligate bipeds.  Yes, many animals, including us humans, walk on two legs BUT we can also drop down to all fours if we wanted to.

Nonobligate biped. 

Birds and some dinosaurs, on the other hand, have front limbs that physically can't be used for movement on the ground. 

This tyrannosaurid, Lythronax, couldn't use its front limbs for walking even if it tried.

All these examples so far just show evidence from extinct dinosaurs.  Do modern birds have any features that are like dinosaurs?

Of course!  Its common knowledge that all birds have feathers.  But did you know that all birds also have scales like a reptile...or a dinosaur?  Check out the foot of any bird.

Bald Eagle...with scales.

Check out this one!  It even has the exact same shape as some (other) dinosaur feet! 

Rhea...with scales as well as a very distinct three forward facing toe design identical to...

...the foot of this Tyrannosaurus rex!

We looked at feet now lets check out the hand claws on some birds.

Wait a minute!  Birds don't have hand claws!  They have wings!

Actually, some have both.  Take a look at this modern bird called a Hoatzin.  

 

   Aaaaaaand zoom in on the wing...

Dino Claws!

So there you have it!  I realized that just saying "birds are dinosaurs" isn't really enough so this is my blog post with my arsenal of science to back the statement up.  There is also a lot of other evidence out there but I would be writing a novel of a post if I tried to include it all (hips...leg joints...the list goes on)  If you still have questions about this, or any other dinosaur topic for that matter, you are always more than welcome to post or message us on our facebook page where I can answer you. 


Works Cited

American Museum of Natural History. "Velociraptor had feathers." ScienceDaily 2007-09-20. Accessed 2012-07-20.

Hutchinson, J.R. (2006). "The evolution of locomotion in archosaurs". Comptes Rendus Palevol 5 (3–4): 519–530

Xu, X.; Wang, K.; Zhang, K.; Ma, Q.; Xing, L.; Sullivan, C.; Hu, D.; Cheng, S. et al. (2012). "A gigantic feathered dinosaur from the Lower Cretaceous of China"  Nature 484: 92–95.

Prehistoric Animal of the Week: Allosaurus

This week we're in the Morrison Formation of the Late Jurassic again to take a look at the lion of the Jurassic. Let's give a Jersey Boys welcome by pumping our fists for Allosaurus.

Allosaurus fragilis
Allosaurus, truly a "Different Lizard", was named by Marsh during the Bone Wars in the 1877. Allosaurus had a length of around 28 feet (8.5 meters) in length though larger specimens have been measured in at almost up to 39 feet (12 meters) in length. Allosaurus inhabited the western United States during the Late Jurassic from 155 to 150 million years ago. Allosaurus finds can be found in the Morrison formation commonly and also the Cleveland-Lloyd Dinosaur Quarry. Related finds can be found in Europe, indicating a possible related species from Portugal known as A. europaeus.

Allosaurus fragilis life restoration: Christopher DiPiazza

From the remains of Allosaurus, we can tell that Allosaurs may have hunted in packs, taking down larger prey like Barosaurus, Diplodocus, and even Apatosaurus. Other prey included early ornithopods, like Camptosaurus, and stegosaurids, such as Stegosaurus. Competition from other predators would have come in the form of Ceratosaurus. It's been suggested that Saurophaganax is a species of Allosaurus known as A. maximus, but the matter itself is heavily disputed. Many species have given for Allosaurus and therefore it makes the taxonomic history of this animal of heavy interest. There's even been suggestions of an Allosaurus from Australia as well. One thing is certain, Allosaurus is a very popular theropod.

Allosaurus skeletal mount at the American Museum of Natural History in New York.

References

Paul, G.S. "Princeton Field Guide to Dinosaurs". Princeton University Press. p. 94-96.

Join us next week as we venture off and take another look at a new animal. That does it for this week everybody, stay here at JBHD as we aim to educate you all about the prehistoric!