Viviparity

Aristotle adopted the popular division, in the formation of which men had been guided by a happy instinct, and in so doing he has been followed by all zoologists until almost in our own day the Amphibia have been separated from the reptiles and made to form a fifth class.

First, however, he divided his Sanguineous group into two subdivisions, the Vivipara and the Ovipara.

Of these, the Vivipara, including the biped man, the quadrupedous beasts, and the apodus cetacea, were manifestly superior to the Ovipara, for their more perfect organs of respiration and the more mature condition of their young at birth testified indisputably to their greater heat.

The Ovipara include the birds, the reptiles, and the fishes.

Of these, the fishes were clearly at the bottom.

Mm-hmm.

And this paper is l- by, um, Leandro Gaitano and colleagues, who are at various institutions across Argentina, and it is called The Early Origin of Viviparity in the Mammalian Lineage.

Mm-hmm.

So spoiler alert, this might be questioning the paradigm that, uh, viviparity evolved once in theory in mammals.