| Early Devonian | |
| Color: | Early Devonian |
| Time Start: | 419.2 |
| Time Start Uncertainty: | 3.2 |
| Time End: | 393.3 |
| Time End Uncertainty: | 0.4 |
| Caption Map: | Map of Earth as it appeared 400 million years ago during the early Devonian, Emsian stage |
| Image Outcrop: | Rhynie chert.jpg |
| Caption Outcrop: | Sample from the Lower Devonian Rhynie chert |
| Timeline: | Devonian |
| Chrono Name: | Early Devonian |
| Strat Name: | Lower Devonian |
| Name Formality: | Formal |
| Celestial Body: | earth |
| Usage: | Global (ICS) |
| Timescales Used: | ICS Time Scale |
| Chrono Unit: | Epoch |
| Strat Unit: | Series |
| Timespan Formality: | Formal |
| Lower Boundary Def: | FAD of the graptolite Monograptus uniformis |
| Lower Gssp Location: | Klonk, Czech Republic |
| Lower Gssp Accept Date: | 1972[1] |
| Upper Boundary Def: | FAD of the conodont Polygnathus costatus partitus |
| Upper Gssp Location: | Wetteldorf Richtschnitt section, Wetteldorf, Eifel, Germany |
| Upper Gssp Accept Date: | 1985[2] |
The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage, which was followed by the Pragian from and then by the Emsian, which lasted until the Middle Devonian began, .[3] During this time, the first ammonoids appeared, descending from bactritoid nautiloids. Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the order Agoniatitida, which in later epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida. This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic Era.