Pen Formation
# Pen Formation

The Pen Formation is a Campanian-age geologic unit in the western United States.

## Vertebrate fauna

Sharks are well known from the Pen Formation.

* Lonchidion selachos
* Squalicorax kaupi
* Cretorectolobus olsoni
* Ischyrhiza mira
* Scapanorhynchus texanus
* S. raphiodon
* Cretolamna appendiculata

Other fishes include Xiphactinus, the ray Ptychotrygon, and gar. The nodosaurid ankylosaurs Acantholipan and CPC 273 have also been found in the Pen Formation.

## Footnotes

* 1 2 3 4 5 6 7 8 9 10 11 "Big Bend National Park," Hunt, Santucci, and Kenworthy (2006); page 65.
* ↑ Héctor E. Rivera-Sylva; Eberhard Frey; Wolfgang Stinnesbeck; Gerardo Carbot-Chanona; Iván E. Sanchez-Uribe; José Rubén Guzmán-Gutiérrez (2018). "Paleodiversity of Late Cretaceous Ankylosauria from Mexico and their phylogenetic significance". Swiss Journal of Palaeontology. in press. doi:10.1007/s13358-018-0153-1.
