Guildayichthyidae

Guildayichthyidae is a prehistoric family of marine fish from the Mississippian Bear Gulch Limestone of Montana.^[1][2] It is the only family in the order Guildayichthyiformes. Guildayichthyids possess an uncommon mixture of primitive and modern characteristics in their skull bones.^[3]

Guildayichthyidae Temporal range: Late Mississippian PreꞒ Ꞓ O S D C P T J K Pg N ↓
Fossil of Discoserra pectinodon
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	†Guildayichthyiformes Lund, 2000
Family:	†Guildayichthyidae Lund, 2000
Genera
See text

Their taxonomy has long been debated, with studies placing them within the Neopterygii, while others placed them within the Cladistia. A 2025 study found them to most likely be the sister group to the extinct Bobasatraniiformes, with the two forming an early-diverging clade within the crown group Actinopterygii.^[4]

Taxonomy

This family consists of the following genera and species:^[1]

• Genus Guildayichthys Lund, 2000
  • Species Guildayichthys carnegiei Lund, 2000
• Genus Discoserra Lund, 2000
  • Species Discoserra pectinodon Lund, 2000