A snake skeleton with a long spine and rows of ribs curves in an S-shape against a dark background

Steve Huskey, Ph.D.

Super Skeletons!

Skeletons have an important job. Read on for the scoop on skeletons!

By Andrew Klein

From the October/November 2026 Issue

Learning Objective: Students will compare and contrast four different skeleton types.

Lexile: 840L; 610L

Key Focus Area: Evolution and Natural Selection,

Standards

What You Need to Know About the Human Skeleton

Watch a video about the human skeleton.

Support System: An Internal Skeleton Made of Bone

Pascal Goetgheluck/Science Source

Bones don’t bend easily. To bend, flexible snakes have hundreds of spinal bones, which act like a set of tiny hinges.

Almost all vertebrates—animals with a backbone—have the same type of skeleton. Amphibians, birds, mammals, reptiles, and most fish have skeletons made of bone inside their bodies. This bony structure is called an endoskeleton.

“Without a skeleton, your body would collapse on the floor like a blob,” explains Steve Huskey. He’s a scientist who studies animal skeletons. Bones give the body structure and protection. The skull shields the brain. The rib cage guards the heart and lungs. When muscles flex, they pull on bones to create movement at flexible connections called joints.

The number and arrangement of bones vary widely across the animal kingdom. The python holds the world record for most bones in an animal. At more than 30 feet (9 meters) long, this giant tropical snake can have up to 1,800 bones! Adult humans, by comparison, have 206.

Most vertebrates have the same type of skeleton. Vertebrates are animals with backbones.

Birds, mammals, and most fish have skeletons made of bone inside their bodies. This type of skeleton is called an endoskeleton.

“Without a skeleton, your body would collapse on the floor like a blob,” explains Steve Huskey. He’s a scientist who studies animal skeletons.

Bones support and protect the body. The skull shields the brain. The rib cage protects the heart and lungs. When muscles flex, they pull on bones to move the body. Muscles help bodies bend at flexible places called joints.

Different animals have different numbers of bones. The python has more bones than any other animal. At more than 30 feet long, this giant snake can have up to 1,800 bones! Adult humans, by comparison, have 206 bones.

Built-In Armor: An External Skeleton Made of a Hard Outer Material

What do ants, crabs, and spiders have in common? They all have skeletons on the outside of their bodies. These exoskeletons (see Vocab Lab) didn’t appear by accident. Animals with better protection survived longer and reproduced more, passing on these features.

Huskey calls the exoskeleton a superpower suit for the animal kingdom—it protects, senses the environment, and helps animals move. Muscles attach to the inner surface of the exoskeleton. These muscles pull on parts of the skeleton to move structures like legs and claws.

Most invertebrates—animals without a backbone—have this type of skeleton to protect their soft bodies. Exoskeletons are the most common type of skeleton on Earth today.

What do ants, crabs, and spiders have in common? They all have skeletons on the outside of their bodies. These exoskeletons (see Vocab Lab) developed over many generations. Animals with better protection survived longer. They also had more offspring. Their offspring inherited these features.

Huskey says the exoskeleton is like a superpower suit for animals. It protects animals. It also helps them sense the world and move. Muscles attach to the inside of the exoskeleton. These muscles pull on parts of the skeleton to move structures like legs and claws.

Most invertebrates have this type of skeleton. Invertebrates are animals without a backbone. It protects their soft bodies. More animals have exoskeletons than any other type of skeleton.

Made for Swimming: An Internal Skeleton Made of Cartilage

Press your fingers against the tip of your nose. Feel that firm yet bendy tissue? That is cartilage. Sharks, rays, and skates have skeletons made of this rubbery, lightweight material. “When you pick up a stingray’s skeleton, you barely even feel like you’re holding it,” says Huskey.

Recent studies suggest sharks and rays once had bony skeletons like most fish. Over millions of years, they evolved—or changed—to have lighter skeletons made of cartilage. This feature allows these fast, agile hunters to use less energy as they slice through the water. This advantage would be passed on to their offspring.

Press your fingers against the tip of your nose. Feel that firm but bendy material? That is cartilage. Sharks, rays, and skates have skeletons made of cartilage. It’s flexible and very light. “When you pick up a stingray’s skeleton, you barely even feel like you’re holding it,” says Huskey.

Scientists think that the ancestors of sharks and rays once had bony skeletons. Over millions of years, they changed. Now, they have lighter skeletons made of cartilage. Lighter skeletons help these animals hunt using less energy. Cartilage also helps them move through the water. Their offspring would also have this helpful trait.

Bendy Body: A Skeleton Made of Liquid

An earthworm wriggling over the ground has no bones. But it does have a skeleton—just not one you can see. Animals such as worms, jellyfish, and octopus have hydrostatic skeletons. They use liquid instead of bones for support. They flex to move fluid around their body as they stretch, wiggle, or swim.

“If all the liquid came out, an earthworm would deflate into a flat tube,” says Huskey. On land, animals with hydrostatic skeletons stay small. Their bodies can only hold so much liquid, so there’s not enough internal support for a large body size.

Animals that live in water don’t have this issue. That’s why creatures like jellyfish can grow to be enormous—the water provides the support. Some jellies grow to the size of a small car!

An earthworm wriggling over the ground has no bones. But it does have a skeleton. It’s just not one you can see. Worms, jellyfish, and octopuses have hydrostatic skeletons. They use liquid instead of bones to support their bodies. They move liquid through their body as they stretch, wiggle, or swim.

What would happen if all the liquid came out? “An earthworm would deflate into a flat tube,” says Huskey. On land, animals with hydrostatic skeletons stay small. Their bodies can only hold so much liquid. It is not enough to support a big body on land.

Animals that live in water don’t have this issue. The water around them gives them extra support. That’s why jellyfish can grow to be huge. Some jellyfish grow to the size of a small car!