Aeronian
In the geologic timescale, the Aeronian is an age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon that began 440.5 ± 1.0 Ma and ended 438.6 ± 1.0 Ma. The Aeronian Age succeeds the Rhuddanian Age and precedes the Telychian Age, all in the same epoch.
During the Aeronian the Sedgwickii Event occurred in which graptolite diversity was greatly reduced. This event has been attested in locations such as today's Canada, Libya as well as in La Chilca Formation in Argentina.
It was also from this time that the first gnathostomates appeared, represented by the genera Qianodus and Fanjingshania.