MAMMALIAN • E-FREE TRANSLATION.COM • Definition of Mammalian

... claimed. One of man's earliest ancestors was almost certainly a unicellular animal. A little later he very probably passed through a gastraea stage. He traversed fish, amphibian, and reptilian grades. The oviparous monotreme and the marsupial almost certainly represent lower mammalian ancestral stages. But what kind of fish, what species of amphibian, what form of reptiles most closely resembles the old ancestor? How did each of these ancestors look? I do not know. It looks as if our ancestral tree were entirely uncertain and we were left without any foundation ...

— The Whence and the Whither of Man • John Mason Tyler