Mystery Fossil

Mystery Fossil
A COMPARATIVE ANATOMY PUZZLE

Amelia holding 2 bright green pieces of a 3D printed fossil with jagged shapes

Hi! My name is Amelia Zietlow. I’m a vertebrate paleontologist. I study fossils of ancient vertebrates and bones from vertebrates living today.

The bright green thing I’m holding here is a plastic 3D copy of a mysterious fossilized bone. Scientists dug up the real fossil in North Dakota. (It was broken in half, which sometimes happens.)

table with many fossil bones arranged on it and one highlighted and labeled mystery fossil

Putting a fossil skeleton together is like doing a puzzle!
Even though scientists found all these fossilized bones together, the skeleton of this animal might be incomplete.

Help me figure out what kind of bone this fossil is and what animal it came from!

We're going to use COMPARATIVE ANATOMY, which means we'll compare this fossil with bones of other animals to look for similarities and differences.

oblong fossil with jagged protrusions along the length on one side

Here is our REAL mystery fossil. Do you think it is part of a vertebrate skull, spine, or limb?

spine

skull

limb

What do all vertebrate skeletons have in common? FIND OUT!

It's a Puzzle!

I’ve made drawings of all the bones in our mystery animal’s skull. Let’s put them together like a puzzle. Then we will be a step closer to identifying our mystery animal.

What do you think the common name for maxilla is?

lower jaw bone

brain case

upper jaw bone

Every vertebrate has a unique upper jaw bone. But animals in the same VERTEBRATE GROUP have bones that are more similar.

long skull with specific bones colorized in different colors and the maxilla labeled

Here are examples of skulls from THREE VERTEBRATE GROUPS. Look at the upper jawbones. Which group do you think our mystery skull belongs to?

animal skull with one extra long tooth on top and bottom and smaller chunkier teeth

mammal

animal skull with needle teeth in varying lengths

ray-finned fish

reptile

You got it!

ANSWER: reptile

GREAT JOB! You figured out that our jawbone belongs to a reptile!

Here’s why: Our mystery bone has big teeth, unlike most fishes. (Quit thinking about sharks!) And the teeth in our jawbone are too simple to belong to a mammal. They lack cusps, or complex shapes.

mammal skull varied shape cusped teeth, fish skull with small teeth, and reptile skull with pointer to large simple teeth showing checkmark

Let's narrow it down even more! Which reptile group does our mystery animal belong to?

Here are skulls from MAJOR REPTILE GROUPS. Compare our mystery skull to the other reptile skulls. Look at the upper jaw bone and how the rest of the skull bones are arranged. Which group do you think our mystery animal belongs to?

lizard

dinosaur

crocodilian

You got it!

ANSWER: lizard

That was a hard one! Good job checking out those details. Our mystery skull belongs to a lizard.

Here's why: Our jawbone has uniform teeth but no extra holes. Dinosaur jawbones have extra holes.

skulls of a lizard, dinosaur, and crocodile pointing out features are and are not similar to mystery bone in skull with green checkmark next to lizard

Almost there! What KIND OF LIZARD is our mystery animal?

We have a few other clues to use to finally solve this puzzle:

This lizard lived 80 million years ago. (Other fossils in the rock told me how old the rock is.)

This fossil was found in a type of rock called shale. That tells me the animal was on the ocean floor when it fossilized.

Which one of these was a lizard that lived in the ocean 80 million years ago?

Ambulocetus
(an ancestor of whales)

Styxosaurus
(a plesiosaur)

mosasaur under water attacking another creature

Jormungandr
(a mosasaur)

You got it!

ANSWER: Jormungandr (a mosasaur)

Our mystery fossil belongs to a mosasaur!

Mosasaurs were lizards that lived in the ocean, like our fossil. They ate fish and other animals, including other mosasaurs (like in this illustration). Mosasaurs lived from about 100 million to 66 million years ago, so our fossil’s age fits too.

artist rendering of Jorgmungandr eating another mosasaur with pterosaurs flying overhead

While Ambulocetus had a long, toothy jaw like our fossil, they were mammals. They are ancestors of today's whales. Ambulocetus lived 48-50 million years ago and may have been covered with hair.

Plesiosaurs lived in the ocean from about 215 million years ago to about 66 million years ago. While that's the right timeframe for our mystery animal, plesiosaur skull bones fused differently than lizards' did.

Let me show you more about Jormungandr, our mystery mosasaur!

SHOW TRANSCRIPT

[MUSIC]

[Close-up of hands opening drawer containing mosasaur fossils]

AMELIA ZIETLOW (Paleontologist): Mosasaurs are a really cool group to work on. They're big giant lizards with big, scary teeth.

[Pan of another mosasaur fossil, with close-ups]

AMELIA ZIETLOW: They actually have an extra row of teeth on the roof of their mouth as well that would have helped them to hang on to fish and other slippery animals that they would have preyed on.

[Head shot of Amelia Zietlow; she is a white woman with long strawberry-blonde hair and glasses. She is wearing a black tank-top and has a mosasaur skull pendant around her neck.]

AMELIA ZIETLOW: A lot of mosasaurs have teeth that are conical or cone-shaped.

[Amelia holds up a cone-shaped tooth that is about one-and-a half inches long; she shows its serrated edge]

AMELIA ZIETLOW: Some of them, the edges are serrated like a steak knife. And then others have these round bubble-shaped teeth . . .

[Amelia picks up another, rounder tooth that has a small point and no edges]

AMELIA ZIETLOW: that they would use to smash open hard-shelled prey like ammonites and clams.

[Amelia seated in a room with cabinets and a full bookshelf]

AMELIA ZIETLOW: They're also very exciting scientifically because there's a lot we still don't know about them.

[Amelia scans a wall-size mosasaur fossil that is embedded in matrix. She is using a hand-held scanner that emits bright flashes of light.]

AMELIA ZIETLOW: In paleontology, when we find a new specimen, we need to describe it.

[close-up of Amelia measuring part of a mosasaur maxilla with calipers; the skull has large teeth overhanging its mandible.]

[Amelia seated in a room with cabinets and a full bookshelf]

AMELIA ZIETLOW: Jormungandr is a mosasaur from North Dakota that I was invited to help describe by paleontologists in North Dakota. It is . . .

[Pan of many fossilized bones of a mosasaur skull spread out on a white background]

AMELIA ZIETLOW: most of us skull and the first couple of neck vertebrae of a mosasaur that lived about 80 million years ago.

[Amelia stands before a 3-D printer, holding a bright green 3-D print of part of a mosasaur maxilla]

AMELIA ZIETLOW: We can see a lot of anatomical details, like here. You've got little holes where the teeth are replacing. Because this one was found in North Dakota, it's still in the collections at the museum in North Dakota.

[3-D printer making another bright green copy of the mosasaur maxilla]

AMELIA ZIETLOW: So it's helpful that these copies exist so that researchers who are unable to travel that far necessarily can still get data from the animal.

[Amelia seated in a room with cabinets and a full bookshelf]

AMELIA ZIETLOW: Mosasaurs came from ancestors that lived on the land, but they ultimately lived in the water.

[Artist rendering of a mosasaur underwater, biting into the neck of a smaller mosasaur. The mosasaur has a long narrow body, a pointed snout, rounded flippers, and a diamond pattern on its skin.]

AMELIA ZIETLOW: A mosasaur is basically a big lizard. Mosasaurs look very similar to,

[A Komodo dragon, a seven-foot-long lizard, walks through a rainforest. It has heavily armored skin and its belly hangs about six inches off the forest floor.]

AMELIA ZIETLOW: for example, today's Komodo dragons and other monitor lizards, and that makes them good for study because . . .

[Amelia seated in a room with cabinets and a full bookshelf]

AMELIA ZIETLOW: we have this close living relative that we can directly compare them to.

[Amelia stands before a gray 3-D print of a nearly complete mosasaur skull that is a long as her arm. She picks up the two-piece, bright green 3-D print of the mosasaur maxilla, then sets it back down next to the gray 3-D print of a nearly complete mosasaur skull]

AMELIA ZIETLOW: So this is the 3-D print of the right maxilla next to a 3-D print of the whole skull of Jormungandr. And so we can see here where this part actually fits. It fits in the front part of the face on the right side. Two bones form the upper jaw, the maxilla and the premaxilla, which is the snout at the tip here.

[Amelia points to other parts of the gray 3-D printed skull]

AMELIA ZIETLOW: Moving back, these are the nostrils, and you can actually see on the maxilla, on our print, where the nostril would be based on this little divot here.

[Amelia points to a groove in the top edge of the green 3-D printed maxilla. Next, Amelia points to other parts of the printed skull.]

AMELIA ZIETLOW: So right here the eye would have gone in this hole right here. The jaw muscles would have attached up here and gone down through here, down onto the lower jaw. And that's what would help pull the lower jaw up. This back here is actually where the ear is. So their eardrum would have gone right in here.

[Amelia points toward an oval-shaped bone at the very back of the skull.]

AMELIA ZIETLOW: This bone is called the quadrate because it is so involved in different parts of mosasaur anatomy and biology. So it's both the ear and the bone that connects the skull to the lower jaw. It's very diagnostic, which means it's very helpful for identifying different kinds of mosasaurs because it has lots of lumps and bumps that are affected by the different soft tissues around it. So we can usually identify what kind of mosasaur we have based on this one bone alone.

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PaleontOLogy > Mystery Fossil

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