HANDOUT F Comparing Fossils to Each Other 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. © Teachers’ Curriculum Institute Fossils and the History of Life 10 HANDOUT F 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. © Teachers’ Curriculum Institute Fossils and the History of Life 11 HANDOUT F 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. © Teachers’ Curriculum Institute Fossils and the History of Life 12 HANDOUT F 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. © Teachers’ Curriculum Institute Fossils and the History of Life 13.