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Adaptation
Fish Evolution: 500 Million Years
The 500-million-year evolutionary story of fish - from jawless ostracoderms through cartilaginous and bony radiations to the 35,000+ species alive today.
System: Skeletal Level: Intermediate Discipline: Ichthyology
📖 Overview
Fish are the oldest and most diverse vertebrate group. Their fossil record begins in the Cambrian with jawless conodonts and ostracoderms, expands through Devonian placoderms and early sharks, and eventually radiates into the two lineages that dominate today - cartilaginous fish (sharks and rays) and bony fish. All terrestrial vertebrates - amphibians, reptiles, birds, mammals - descend from a lobe-finned bony fish ancestor.
⚙️ Mechanism
Diversification via adaptive radiation, whole-genome duplication events (two at vertebrate origin, one in ray-finned fish), and repeated colonisation of new environments.
🔑 Key Concepts
Adaptive radiation, whole-genome duplication, tetrapod origin, mass extinctions and recoveries.
✨ Fun Fact
Every land vertebrate - every mammal, bird, reptile, amphibian - is technically a modified lobe-finned fish. In cladistic terms, humans ARE fish.