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Introduction to Vertebrates: Evolution and Features Explained

Explore the characteristics, evolution, and diversity of vertebrates, including fishes, in this informative guide. Learn about jaw evolution, reproductive strategies, and the different classes of fishes. Discover the transition from aquatic to terrestrial life in lobe-finned fishes.

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Introduction to Vertebrates: Evolution and Features Explained

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  1. 31.3 Vertebrates

  2. Vertebrate Intro • Have all 4 chordate characteristics at some point of development • Embryonic notochord generally replaced by vertebral column • Generally a high level of cephalization (brain and nervous system) with complex sense organs • Closed circulatory system

  3. Vertebrate Intro (cont’d) • Jaw evolution allowed for easier predation • Strong endoskeleton allows for large terrestrial organisms • Complete digestive tract • Generally, sexes are separate (not hermaphrodites) • Sexual reproduction typical

  4. Vertebrate Intro (cont’d) • Evolution of amnion (extraembryonic membrane that encloses a fluid filled sac) • Some lay shelled eggs • Others are placental (e.g. mammals) and development of offspring occurs in female uterus

  5. Fishes • Evolutionary development: (from least to most evolved) • Jawless fishes (superclass Agnatha) • About 63 species • Cylindrical • Up to 1 meter long • Include hagfish and lampreys • Some are parasitic

  6. Fishes (cont’d) • Cartilaginous fishes (class Chondrichthyes) • About 850 species • Include rays, sharks and skates • Have jaws (adapted gill arches – structure that supports gills) • Skeletons made of cartilage (not bone) • Well-developed senses make good predators: • Ability to sense electric currents in water • Have lateral line system that allows them to sense pressure changes in water from movement nearby • Keen sense of smell

  7. Fishes (cont’d) • Bony fishes (class Osteichthyes) • About 20 000 species • Most diverse class of all vertebrates • Types of bony fishes: • Ray-finned fishes • Include fish we commonly eat: trout, cod, salmon • Have a pair of fins with thin bodies • Often have a swim-bladder, which regulates buoyancy • Water passes into mouth and out through gill slits: oxygen is absorbs and carbon dioxide given off • Heart is simple pump with two chambers (one atrium and one ventricle)

  8. Fishes (cont’d) • Lobe-finned fishes • Evolved into amphibians • Had fleshy appendages that were adapted to limbs for terrestrial life • Had a lung used for respiration • E.g. coelacanth, though extinct 20 000 years ago was discovered off the coasts of Eastern Africa

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