Basically, they were alive at one time but they have all died off. (gone extinct)
mammals,birds ,insects,primates , and sea creatures
in prehistoric times, ichthyosaurs lived in Nevada.
sharks
dinosaurs
sharks
Jellyfish
Humans.
In mesozoic era there are creatures are living, examples. DINOSAURS, Mammoth and others.
bear dog
It is produced from creatures that lived on Earth in the past.
once living things are living things that once lived but dead now
Fossils usually indicate that the terrain was once underwater, either under an ancient sea where sea creatures became fossilized, or marshland where land and amphibians once lived and died.