| Guildayichthys Temporal range: Late Serpukhovian, | |
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| Fossil of Guildayichthys at the Royal Ontario Museum | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | †Guildayichthyiformes |
| Family: | †Guildayichthyidae |
| Genus: | †Guildayichthys Lund, 2000 |
| Species: | †G. carnegiei |
| Binomial name | |
| †Guildayichthys carnegiei Lund, 2000 | |
Guildayichthys is an extinct genus of marine fish that belonged to the order Guildayichthyiformes that lived in Montana during the Mississippian. It is a monospecific genus with the only species in this genus being Guildayichthys carnegiei. It has a highly compressed, discoidal body. It also has short teeth.
It was named after John Guilday who was a curator at the Fossil Mammals of Carnegie Museum in Pittsburgh, Pennsylvania. It was named after Guilday for his "unique appreciation of the beauty of life".
