Animation Description
Images of seven animals, shark, tuna, frog, human, hare, caiman, and parrot, are connected by a branching evolutionary tree beneath them. An arrow shows that time progresses in the upwards direction on the tree. A horizontal line on the root of the tree is marked A. Then the branch leading to the shark splits off to the left. On the other branch (which leads to the remaining animals), trait B evolved. Then the branch leading to the tuna splits off to the left. On the other branch (which leads to the remaining animals), trait C evolved. Then the branch leading to the frog splits off to the left. On the other branch (which leads to the remaining animals), trait D evolved. Then a branch splits off to the left that itself splits into two, leading to the human and hare. At the base of this branch, trait F evolved. The last branch, which extends up and to the right splits into the caiman and parrot branches. At the base of this branch, trait E evolved. When line A is clicked, the line is relabeled "vertebrae," indicating that vertebrae evolved in the common ancestor of all the animals on the tree. Also, a red line appears across the top of the all the branches on the tree indicating that each lineage has inherited this trait. A text description of vertebrae appears along with an image of a human spinal column. When line B is clicked, the line is relabeled "bony skeleton," indicating that a bony skeleton evolved in the common ancestor of all the animals on the tree, except for the shark. Also, a red line appears across the top of the all the branches except the shark indicating that each of these lineages has inherited this trait. A text description of a bony skeleton appears along with a photo of a skeleton belonging to a four-legged animal such as a cat or dog. When line C is clicked, the line is relabeled "four limbs," indicating that this trait evolved in the common ancestor of frogs, humans, hares, caiman, and parrots. Also, a red line appears across the top of those lineages indicating that each has inherited this trait. A text description of four limbs appears along with a photo of a dog. When line D is clicked, the line is relabeled "amniotic egg," indicating that this trait evolved in the common ancestor of humans, hares, caiman, and parrots. Also, a red line appears across the top of those lineages indicating that each has inherited this trait. A text description of the amniotic egg appears along with a diagram of an egg in an embryo being nourished via organs within the egg. When line E is clicked, the line is relabeled "two skull openings," indicating that this trait evolved in the common ancestor of caiman and parrots. Also, a red line appears across the top of those lineages indicating that each has inherited this trait. A text description of the two skull openings appears along with a diagram of a skull with two skull openings (in addition to the nostrils and eyes) behind the eye area. When line F is clicked, the line is relabeled "hair," indicating that this trait evolved in the common ancestor of humans and hares. Also, a red line appears across the top of those lineages indicating that each has inherited this trait. A text description of hair appears along with a photo of a hairy chimpanzee.
Animation Text
Panel 1
Each of the letters on the cladogram represents the appearance of a certain inherited feature. Click on each of the letters to learn more. Begin with the feature that evolved first (A), then proceed in alphabetical order.
Panel 2
A: vertebrae
The skeletal units of the spinal column, or backbone, that protect the spinal cord and support the body.
Panel 3
B: bony skeleton
Although "bone" tissue evolved earlier, a true bony skeleton does not appear until the ancestors of bony fishes and consists of hardened bone, not cartilage.
Panel 4
C: four limbs
Possessing four limbs for terrestrial locomotion, unless secondarily lost or modified for other types of locomotion, as in the flippers of whales or wings of bats. Animals with four limbs are called tetrapods.
Panel 5
D: amniotic egg
An egg with a fluid-filled amniotic sac that cushions and protects the developing embryo.
Panel 6
E: two skull openings
Two additional openings (besides the eyes and nostrils) on the side of the skull behind the eyes. Animals with such openings are called "diapsids."
Panel 7
F: hair
Fine filaments growing from the skin, consisting of special epidermal cells, and providing insulation.
Panel 8
The inheritance of these features provides evidence of ancestry and relatedness.