A single fossil is known, coming from the Messel Pit in southwestern Germany.

Pengornis is known from a single fossil, described by Zhou et al. in 2008.

A single fossil from the Baja California peninsula indicates the family once inhabited warmer waters.

A single fossil of hagfish shows that there has been little evolutionary change in the last 300 million years.

Two species were described, each from a single fossil find.

A single fossil (consisting of a single lower leg bone, or tibia) was found in Germany.

The single fossil is an incomplete semi-articulated skeleton the size of a sparrow.

The single known fossil is a partial upper leg bone, specifically the lower section of the right tibiotarsus.

It was described in 2010 on the basis of a single fossil from Oklahoma.

It is known from a single, hand-sized fossil from the middle Triassic period of Spain.