The Alamo Impact and the Fossil Evidence
The Devonian was a time of high global sea level and generally very warm temperatures. The high seas formed shallow, warm, well lit marine environments perfect for harboring diverse marine communities. In particular, sponges called stromatoporoids formed impressive reefs along continental margins. In the location of present-day southern Nevada was a transitional area from the warm shelf environment into deeper marine settings.
Along this onshore-offshore gradient lived a variety of animals including corals, sponges, brachiopods, gastropods, and even fish. When this area was impacted during the Alamo event there was an instantaneous killing of anything within the target area. The rocks that make up the Alamo Breccia contain many fossils of animals that made the rocks deposited before the impact event. The rocks above the Alamo Breccia (deposited after the impact) contain rocks that have a very similar fossil makeup to those deposited before the impact. From this we can conclude that the animals living in the surrounding area were able to re-populate the decimated target rocks immediately