Comparing Fossils to Each Other

HANDOUT F

The following fossils are ordered by the approximate age of the fossils found of that type of organism, from oldest to youngest. What patterns do you see?

Eusthenopteron: Below is an image of an Eusthenopteron fossil and a proposed image of a Eusthenopteron based on the fossils found. Eusthenopteron fossils are about 385 million years old. Although these organisms looked like normal fish, they had some unique features: • They had internal nose bones and gills, unlike other fish that only use gills to breathe. • They had tiny but distinct arm and leg bones that were more like human arm and leg bones, unlike other fish that just have fin bones. • They had bone marrow inside the bones, which is the first time this is found in the fossil record.

Panderichthys: Below is an image of an Panderichthys fossil and a proposed image of a Panderichthys based on the fossils found. Panderichthys fossils are about 383 million years old. Panderichthys had some unique features: • They had a flattened head and internal nose bones at the top of the face instead of the front of the face, but still had gills. • They had eyes that are closer together and at the top of the head. • They lacked fish fins on the top and bottom of the body. • They had tiny arm and leg bones in fins that were more like human arm and leg bones rather than like fish bones.

Tiktaalik: Below is an image of an Tiktaalik fossil and a proposed image of a Tiktaalik based on the fossils found. Tiktaalik fossils are about 375 million years old. Tiktaalik had some unique features: • They had a flattened head and body. • They had internal nose bones at the top of the face instead of the front of the face, but still had gills. • They had eyes that were closer together and at the top of the head. • They lacked fish fins on the top and bottom of the body. • They had tiny arm and leg bones in fins that were more like human arm and leg bones rather than like fish bones. • The front arm bones that stacked in a way that is only found in organisms that support their weight with their arms or legs. • They had a functional neck, more like a crocodile than fish.

Acanthostega: Below are images of Acanthostega fossils and a proposed image of a Acanthostega based on the fossils found. Acanthostega fossils are about 365 million years old. Acanthostega had some unique features: • They had a flattened head and body. • They had internal nose bones at the top of the face instead of the front of the face, but still had gills. • They had eyes that were closer together and at the top of the head. • They lacked fish fins on the top and bottom of the body. • They had tiny arm and leg bones in fins that were more like human arm and leg bones rather than like fish bones. • The front and back arm bones that stacked in a way that is only found in organisms that support their weight with their arms and legs. • They had distinct fingers on each hand. • They had a functional neck, more like a crocodile than fish. • They had lungs, unlike other fish.

Ichthyostega: Below is an image of an Ichthyostega fossil and a proposed image of a Ichthyostega based on the fossils found. Ichthyostega fossils are about 360 million years old. Ichthyostega had some unique features: • They were the first animal fossils found that looked like amphibians, like frogs. • They had a more stable skeleton with distinct ribs. • They had lungs and gills. • The front and back arm bones that stacked and somewhat hinged in a way that is only found in organisms that support their weight with their arms and legs. • They had distinct fingers on each hand.