Dating early hominids

They may have spent very brief periods out of water and would have used their legs to paw their way through the mud.

From amphibians came the first reptiles: Hylonomus is the earliest known reptile.

Acorn worms have a gill-like structure used for breathing, a structure similar to that of primitive fish.

The animal is sometimes called a conodont, and sometimes a conodontophore (conodont-bearer) to avoid confusion.Acorn worms are considered more highly specialised and advanced than other similarly shaped worm-like creatures.They have a circulatory system with a heart that also functions as a kidney.It is thought that the earliest multicellular animal was a sponge-like creature.Sponges are among the simplest of animals, with partially differentiated tissues.