Mossy rocks The Cambrian gets started At the beginning of the Cambrian Period, about 542 million years ago, there were sea creatures like hydras, jellyfish, sponges and seaweed living in [...]
A moss-covered rock During the Cambrian period, about 540 million years ago, some early plants evolved from earlier algae that could live on land, outside of the water. These plants [...]
A fish skeleton Before there were bones One-celled animals don't have any support system that holds them in a certain shape. Plants do have a support system, but it's the [...]
An annelid, or segmented worm When did annelids evolve? Roundworms probably evolved into segmented worms, or annelids, about 545 million years ago. What's a roundworm? More about the Proterozoic All our [...]
The yellow string is one of the arm nerves of a cat By around two billion years ago, some eukaryote cells were able to sense changes in their surroundings and [...]
Evolution of mollusks: Slugs are a kind of mollusk. When did the first mollusks appear? Mollusks are animals like mussels, clams, snails and slugs. Their name means "soft", because mollusks don't have [...]
Fish Stomach The first multi-cellular animals like hydras had no stomachs, or you could say they were all stomach, because they were shaped like a bag. Roundworms, a little later, [...]
Chordates include this giraffe from Kenya What is a chordate? Any animal that has a spinal cord is a chordate. This group covers most of the creatures you see at [...]
History of fish: it looks like a severed tentacle but it's a lamprey. When did fish evolve? About 510 million years ago, in the Cambrian period, some of the worms [...]
