SciShow
Bones Began as Mineral Batteries
Today, bones hold us up. But for ancient jawless fishes, bones may have been a way to store energy for long journeys. Plus, new research indicated that hippos and cetaceans may have evolved their aquatic traits separately.
Visual Learning Systems
What Is a Fish?: Different Types of Fishes
This lively video investigates the wide, colorful assortment of fish found on the planet. Concepts and terminology: saltwater, freshwater, cold-blooded, fins, backbone, eggs, scales, and gills.