| Thaynes Formation | |
| Type: | Formation |
| Age: | Triassic |
| Prilithology: | Limestone |
| Region: | Montana, Idaho, Wyoming |
| Country: | United States |
| Underlies: | Ankareh Formation |
| Overlies: | Woodside Formation |
The Thaynes Formation is a geologic formation in Montana and Idaho, United States. It was recently elevated to group status, as the Thaynes Group.[1]
It preserves fossils dating back to the Triassic period, such as Ammonoidea, Actinopterygii, Actinistia, Conodonta, Gastropoda, Nautiloidea, Ichthyosauria, and others. A diverse fauna known as the Paris biota[2] has been described from the Thaynes Formation.