Article · Wikipedia archive · Last revised Jun 6, 2026

Guildayichthyidae

Guildayichthyidae is an extinct family of marine fish from the Mississippian Bear Gulch Limestone of Montana. It is the only family in the order Guildayichthyiformes. Guildayichthyids possess an uncommon mixture of primitive and modern characteristics in their skull bones.

Last revised
Jun 6, 2026
Read time
≈ 1 min
Length
213 w
Citations
5
Source
Guildayichthyidae
Temporal range:
Fossil of Discoserra pectinodon
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Guildayichthyiformes
Lund, 2000
Family: Guildayichthyidae
Lund, 2000
Genera

See text

Guildayichthyidae is an extinct family of marine fish from the Mississippian Bear Gulch Limestone of Montana.12 It is the only family in the order Guildayichthyiformes. Guildayichthyids possess an uncommon mixture of primitive and modern characteristics in their skull bones.3

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

References

References

  1. Lund, Richard (2000). "The new Actinopterygian order Guildayichthyiformes from the Lower Carboniferous of Montana (USA)" (PDF). Geodiversitas. 22 (2): 171–206.
  2. Albert, James S.; Johnson, Derek M. (23 November 2011). "Diversity and Evolution of Body Size in Fishes". Evolutionary Biology. 39 (3): 324–340. doi:10.1007/s11692-011-9149-0. S2CID 255346377.
  3. "Exquisitely-Preserved Guildayichthys Mississippian Bear Gulch Fish". FossilMall.
  4. Stack, Jack. "An ontological morphological phylogenetic framework for living and extinct ray-finned fishes (Actinopterygii)". The Anatomical Record. n/a (n/a). doi:10.1002/ar.70090. ISSN 1932-8494.