Phylogenetic species concept (PSC) The concept of a species as an irreducible group whose members are descended from a common ancestor and who all possess a combination of certain defining, or derived, traits (see apomorphy). ... "phylogenetic species concept." A Dictionary of Biology. .
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The biological species concept has its limitations (although it works well for many organisms and has been very influential in the growth ofevolutionary theory). ... In thisexample, Ensatina salamander lineages A and B are separate species.Each has a common ancestor that individuals of other species do not.
I hope that this helps you out
I believe its is because the fossils of these animals looked like living species and they had a connection to the modern. A fossil is any preserved evidence of life from a past geological age, such as the impressions and remains of organisms embedded in stratified rocks. Fossils are created when organisms die, are in cased in dirt and rock, and are slowly replaced by minerals over time.