Let’s Put Some Skin on That (how much we know, and don’t know, about the soft stuff)

Now here’s where things get a little muddy.  Bones are easy.  They’re hard, relatively common, and all bones that look about the same are going to have similar functions.  Back-boned critters all kinda have the same basic pattern.  Same with muscle.  The only squishy thing with muscle is determining how much is where, then you can figure out the basic shape on top of the bones.

 

But what about skin?  We’re pretty good at figuring out how a dinosaur works on the inside, but what did they look like on the outside?

Here is where a little mud or volcanic ash comes in handy.

When an animal is buried in soft, fine-grained sediment, then the critter’s skin, scales, fur, or feathers leave an impression.  Just like stamping into soft clay.  With more refined techniques in recovering fossils in the field (or prepping them at the museum), paleontologists are finding more “skin stamps” than ever before.

 

Corythosaurus casuarius skeleton, by Barnum Brown, 1916.

A hadrosaur mummy.  Keep in mind that the animal was most likely dead and already decomposing when it was buried.  We can’t know for sure if it had more fat under the skin than showed here or not.  Notice how thick and muscular the tail base is. 🙂

Photo not mine.  If you know who needs credit, please let me know. 🙂

Corythosaurus skin.

Bell, 2012

More hadrosaur skin impressions.  The impressions that look like a honeycomb are actually impressions of what’s underneath the bumps.  Reminds me of bubble wrap. 😛

040813-nws-skin003.JPG
Photo courtesy of Black Hills Institute of Geological Research

Triceratops skin impression.  No one knows if those larger osteoderms would look just as they do here, or if larger quills or spikes where attached.  Speaking of quills…

File:Psittacosaurus mongoliensis.jpg
wikipedia commons

A beautiful fossil of Psittacosaurus (distant, small cousin of Triceratops) at the Senckenberg Museum of Frankfurt.  We can’t be sure about color, but you can see the pattern of darker and lighter scales.  Notice how much muscle this critter has, and those quills!  A one-of-a-kind find.  Remember my post a couple weeks back about how hard it is for an animal to be fossilized?  How much more amazing that we have something like this?

Here’s a closer look at those quills…

high resolution images of Psittacosaurus tail quills, from the paper studying the specimen

The general consensus is that these quills are a feather-like integument. Here’s what we don’t know…

  • If all species of Psittacosaurus had them (there’s 18, all very different from each other), and if they did, how much & where.
  • If any other ceratopsians had them.  Psittacosaurus was part of a line that died out, so it’s rather unlikely that Triceratops & co. had them.

 

Now that we’re on the subject of feathers…just look at this exquisite fossil of archaeopteryx. 🙂 It never gets old…takes my breath away every time I see it.

Photo not mine.  If you know who needs credit, please let me know. 🙂

Archaeopteryx used to be famous for being the “first bird”, now we know that just about every smallish dinosaur (and even some big ones) where wearing similar outfits.  Yes, most carnivorous dinosaurs are known to have feathers, it’s just a question of what kind, and how much. 🙂

12386.ngsversion.1422035753869.adapt.470.1
Photo courtesy of Institute of Fossil Paleontology and Paleoanthropology, Beijing

I know that looks like fur, but those are fluffy feathers all over this little sinosauropteryx.  Notice the bands of light and dark color on its tail.

Here are some more birdy feathers on a larger dinosaur.

This is Zhenyu- Zhenya- Zen- Oh forget it.  Let’s just say she’s a cousin of those infamous raptors from Jurassic Park.  She’s about five feet long, so closer to the real turkey-sized Velociraptor.  Fully feathered.  Just look at those glorious wings!

Photo courtesy of Stephen Brusatte

Here’s a close up of those feathers.  Notice the full wing in photo D below.  You can clearly see primary, secondary, and covert feathers, just like what you’d see on a modern bird wing.

But wait, it gets better. 😀

Not quite as pretty, but look at figures A, B, and C below.  The bumps that those arrows are pointing to are called quill knobs, and figure D shows us what that means. 😀

Keep in mind that this fossil came from a critter called Dakotaraptor.  This guy was every bit as big as the ones in Jurassic Park.  And it has wings.

Image from paper studying Dakotaraptor.

A prettier reconstruction of Dakotaraptor’s wing.

Photo courtesy to Robert DePalma.

These and other fossils from even larger dinosaurs such as yutyrannus (T-rex’s Chinese cousin) that also preserve feathers, can give us clues for exactly how diverse and widespread feathers are in the dinosaur family tree.

 

The flying reptiles called pterosaurs, for example.

Picture not mine, if you know who needs credit, please let me know.

With fossils like these we can learn about the structure of the wing, and that these animals also had a fur-like coat of feathery fuzz covering their bodies.  No scaly or naked skin here.

 

So there is a lot we do know, but still so much left in the dark.  With bones, muscles, and a few hints of soft tissue, next time we’ll be heading off into uncharted waters.

 

Quick Question: These fossils are all amazing, but there is still so much we don’t know.  Take a quick look at the lion and tiger above, and then look at the skulls below.  Can you tell which one is which?  Leave your answer in the comments, I’d love to hear from you! 🙂

 

Fleshing out the Bones Series:

Here’s the Easy Part (figuring out muscle and other fun anatomy)

They say the dead tell no tales…Obviously whoever coined that phrase never studied the bones of prehistoric animals, because the fossils of dead critters sure say a lot.  Dry bones all kinda look the same, but take a closer look and you can see the clues left behind.

 

Last Monday, we went through a basic rundown on how paleontologists can figure out how to put the bones together.  How they take the bits and pieces they find in the field and build up the skeletons you see in museums.  Now before we move on to the soft stuff I just want to make one thing clear.

Unless it’s something totally new, most dinosaurs don’t have as much guesswork as I implied in my post.

Take Allosaurus, for example.  Tons of bones, from many different animals, gives us a good overall picture of the species and its growth cycle.  So for many dinosaurs, the difference from one skeleton to another is pretty small for the average enthusiast like myself.  And honestly, the skeletons of lions and tigers are almost identical.  We wouldn’t have a clue how obviously different they are without everything on top of the bones.

But I’m getting ahead of myself now.  We’ll come back to the lion and tiger example next Monday. 🙂

So what can bones tell us about an animal?

  • A skull can tell us about how the animal sensed the world around it.  The size and shape of its brain, how good its sense of smell, if it had binocular vision like we do…all that good stuff.
  • Teeth and special adaptations in the skull can give us clues to diet and wacky feeding habits.  Take a quick look at woodpecker skulls and you’ll see what I mean. 🙂
  • The shape of the joints, and points of muscle attachment, can show us how the animal might’ve moved.  It also gives us a basic silhouette to work with.
  • Bumps on the forearm, called “quill knobs”, show where large feathers where attached.  As well as other marks of soft tissue like where crests might attach.

 

These are just a few things bones can tell us, and how can we know this?

Take a close look the next time you eat a chicken drumstick or turkey leg.  The bone is not perfectly smooth, and it has a very specific shape.  There are ridges, bumps, little divets on one side…these are all marks where the muscles and tendons attached.

The chicken drumstick is actually a great example, because the bones of birds and crocodilians can be a sort of Rosetta Stone for translating dino bones.  Birds and crocs are the closest living relatives of dinosaurs, and birds are now classified as a group within dinosauria.

Long story short, the bones of living relatives like birds and crocs are a good starting point for figuring out dinosaur anatomy.  Not perfect, since crocs aren’t dinos, and modern birds fit into a specific niche inside the huge and diverse group of animals we call dinosaurs.  But crocs and birds can help fill in a few places that we would otherwise be clueless about.

  • How much muscle?  Crocs and birds have a different structure to their muscles than mammals.
  • So we know the shape and size of the critter’s brain, but what does that mean?  Crocs and birds today can give us clues.
  • Other soft bits like organs, and how dinos metabolisms worked…looking at birds and crocs can help figure out mysteries in the bones, like how dinosaurs got so big.

But now we’re heading into squishier territory than even muscles.  Bones are pretty solid (for the most part).  Muscles and soft tissue directly attached to the bone is just a matter of translating the markings correctly…but next Monday we’ll dip our toes into the mud and find out how much we know, or don’t know, about the soft outsides.

 

skull-1170772_640

Quick Question: Take a moment to notice all the little bumps, ridges, and dimples in this skull.  Notice that triangular dip at the back of the lower jaw, and the high ridges that make that triangle shape.  Powerful muscles to close the jaw attach here and go through that “loop”, where they attach to the back of the neck and head. This is one powerful critter!  Can you guess what it is?  

Hint: those teeth will tell you it’s not a dinosaur or reptile. 😉 I’d love to hear your answer in the comments! 🙂

Fleshing out the Bones Series:

The World’s Toughest Jigsaw Puzzle

A six-year-old walks down the hall, eyes wide as he stares open mouthed at the skeletons towering high above him.  Dagger teeth, gleaming claws, curving necks and long, sweeping tails…It’s almost surreal how the bones are suspended in the air, as if the skin around them was just invisible.

Of course, now I know about the armature of steel.  How each bone has it’s own pocket to nestle in.  If one bone needs cleaning or repairs, then there’s no need to take down the whole skeleton.  But how do we know what the skeletons looked like?

In the last post, we talked about how unlikely it is to find a complete skeleton, or even a mostly complete skeleton.  If you haven’t read it yet, then check it out, because it’s pretty amazing what happens between dead dinosaur and museum. 🙂

But kid’s books and movies always show the whole dinosaur under some random hill.  It’s gotten downright ridiculous, so that Bob the Builder and his team can dig into a hill, find a complete skeleton of a brontosaurus “standing” in the dirt, and then simply leave it there to be the entrance to their dinosaur themed amusement park.

Convenient.

articulated brachiosaur color copy.png
Every paleontologist’s dream.  Please excuse the ugly sloppiness.  I was practicing speed. 🙂

Truth is, building the complete skeleton is only the first part of figuring out just what these critters looked like.

It’s like the world’s toughest jigsaw puzzle, with a few minor complications…

  • No box with the picture to get a clue on what you’re building
  • No idea how many pieces there are supposed to be, just that there should be at least oh, 2,000 or so…right?  Just how many bones does your average dino have anyway?
  • After a summer spent combing the hills, maybe this is what you end up with…

fossil bits color.png

So what do you do?

Luckily, bones can tell you a lot, especially teeth.  An expert can tell you these are sauropod bones.  Even better, an expert can tell you these belong in the family brachiosauridae .

 

Now here comes the fun part…putting the puzzle together.

You look at all the other fossils in the family.  Maybe there are more of the same “genus”, brachiosaurus.  Maybe these bones are enough to tell which species of brachiosaurus you’re looking at, and you can look at those for reference.  And so on and so forth until you and your colleagues have determined what a complete skeleton of your brachiosaur might look like.

Of course, the whole process is a long, drawn out, very complicated business.  This is just my humble rundown. 🙂

Long story short- except in very few cases where paleontologists discover an articulated skeleton, like the lovely dilophosaurus here- then most skeletal reconstructions have at least a few missing parts, which are then filled in by educated guesses based on closely related animals.

wikipedia commons.

Now that you have all the pieces, how do they fit together?

Knowing where all the pieces go relies on reference to other skeletons, research, and a great deal of know-how on the bones themselves.

Bones can tell us a lot, because the soft and squishy bits that hold them together leave scars.  Knowing how to interpret these scars is where dry bones get interesting, because this is the beginning of figuring out how the animal looked in life.

Next post we’ll talk about muscles, tendons, and all the soft stuff under the skin that we don’t usually see in the museum.

Quick Question: Did you like to see fossil exhibits as a kid?  What impressed you the most about them?  I’d love to hear your answer in the comments! 🙂

 

Fleshing out the Bones Series:

The Miracle of Fossilization

Life is full of everyday miracles.  The sort of things that are so unlikely to happen, it’s amazing they happen at all.

 

Take fossils for example.  Let’s start with something big- a sauropod, or long-necked dinosaur.  Should be easy to fossilize right?

Unfortunately we need a dead one for our fossil, so let’s skip the sad story.

Let’s just say an old brachiosaurus (Let’s call him old Mr. B) came to the riverbank for one last drink of water…Now we have a very large feast for scavengers all up and down the riverbank.  They won’t have to worry about hunting for months!  Well, maybe weeks, depending on how many critters are joining the buffet.

Mr. B is not going to stay in one piece.  A leg over here…head gone…a chunk of tail in the belly of another…By the time the scavengers are done picking the bones clean, bits and pieces are going to be scattered and broken all over the riverbank.

That pile of bones bleaches in the sun for a few more months.  The bones dry out and turn brittle.  Insects and small, nocturnal mammals with ever-growing teeth gnaw on them.

The skies turn dark, storm clouds gather, and a week of constant rain raises the river.  More rain from the north rushes in, and in a few short hours, flood waters pour in strong enough to uproot trees and toss huge rocks as easily as pebbles.

The rush of water and debris lifts the heavy bones and carries them downriver.  A few ribs catch on the roots of a thick, strong tree, but the other bones are torn free and get carried on.  A leg bone settles in a small undercurrent and sinks into a deeper spot in the river.  The rest of the bones get carried on…

On and on, the skeleton is fragmented by the force of the water.

Silt- dirt and debris carried by the current- covers the bones.

Over time, enough layers of silt build up and are flattened by the layers above them.  Water, pressure, and time cement the layers of silt into sedimentary rock like sandstone and mudstone.

Water seeps down through the rock.  Bone is porous, and so water can seep through it.  The water leaves mineral deposits behind, like the hard water deposits that build up in the dishwasher.

Like a sponge drenched in salt water and left to dry in the sun, the bones slowly harden like solid rock.

But that’s not all.  It’s not enough to be fossilized.  The rock needs to stay intact.

The earth is constantly moving.  Rocks that hold fossils can be pushed down and melted in Earth’s liquid mantle.  Or pushed up into mountains, only to be erased by wind and rain.

As if that wasn’t enough, we have to find these fossils.  Exposed fossil bone erodes quickly in the face of wind, rain, and sun.  Scientists usually have good ideas where to find fossils based on previous discoveries, but many times it’s the kid playing by the bluff who finds them.  Or the hiker who sees that spot in the rock that doesn’t look like the rest…

Even when the fossil is found, it can be lost, destroyed, or stolen.

archaeopteryx fossil

My point here is, it’s amazing we have any fossils at all!  More amazing still, the exquisite beauty of fossils like the Lagerstatten of Germany and places like it.  Just look at the archaeopteryx at the top of the paragraph here (those feathers are so perfect, they look better than my chickens’ feathers!).

I am truly humbled to think about the beauty of the world around us, of humanity, of life.  That it’s possible to see remnants of creatures gone for millions of years.  That we can even dream of what they might have looked like.

I look at a fossil like this, and I see a miracle.  And then I look at the world today, see the people in my life…or even just take a moment to watch my hands and the way they move as I type these words…the complexity behind the mechanics of their movement.

An everyday miracle. 🙂

Fleshing Out the Bones Series: