The fact that transitional species have been found at all is remarkable, and it offers further support of gradual, evolutionary change.
persists into the Pliocene (Wadi Natrun, Egypt; Garaet Ichkeul; Ain Brimba) but apparently disappears before the end of this period, and is absent from north Africa until the middle Pleistocene (Ain Mefta).
However, two hypotheses regarding speciation also exist.
Moving to rocks that are about 550 million years old, fossils of simple, multicellular animals can be found.
At 500 million years ago, ancient fish without jawbones surface; and at 400 million years ago, fish with jaws are found.
Fossils are traces of organisms that lived in the past.
When fossils are found, they are analyzed to determine the age of the fossil.