Materpiscis

Materpiscis (Latin for "mother fish") is a genus of pyctodontid placoderm from the late Devonian period, about 380 million years ago. A fossil of this armored placoderm shows an embryo and umbilical cord inside its body. So "Materpiscis" is the oldest known vertebrate to show viviparity (giving birth to live young). Viviparity of one kind or another is quite common in certain kinds of fish, for example sharks.
The holotype was found in the Kimberley area of northern Western Australia. Fossils from the Gogo Formation are preserved in limestone nodules, so dilute acetic acid is used to dissolve the surrounding limestone and reveal the fossil. These fossils are often preserved in three dimensions with minimal distortion.
The species was named "Materpiscis attenboroughi" in honour of David Attenborough who first drew attention to the significance of the Gogo fish sites in his 1979 series "Life on Earth".