Oncorhynchus mykiss
Category: Fish
# Evolutionary Timeline of Rainbow Trout Rainbow Trout (*Oncorhynchus mykiss*) belong to the salmonid family, with roots tracing back to ancient fish lineages. Their evolution involved adaptations to diverse aquatic environments, influenced by geological changes, climate shifts, and predation pressures. Key milestones include: - **Cambrian Period (~500 MYA)**: Emergence of early chordates, ancestors to all vertebrates including fish. - **Devonian Period (~400 MYA)**: Rise of ray-finned fishes (Actinopterygii), providing foundational skeletal and fin structures for mobility. - **Cretaceous Period (~100 MYA)**: Divergence of teleost fishes, enhancing sensory and reproductive adaptations. - **Eocene Epoch (~50 MYA)**: Origin of salmonids from early teleosts, driven by cooling climates and freshwater habitat expansions. - **Pleistocene Epoch (~2 MYA - Present)**: Speciation of Rainbow Trout in North Pacific regions, shaped by glaciation cycles promoting anadromous (migratory) lifestyles and genetic diversity. Environmental pressures like ice ages and tectonic shifts isolated populations, leading to specialized traits such as streamlined bodies for migration and keen senses for survival.