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Vertebrate Evolution

Vertebrate Evolution. Vertebrate Evolution Steps. Vertebral column Jaws, paired appendages (fins), bony skeletons Lungs Legs Amniotic Egg. Hagfishes. Agnathans : hagfishes and lampreys eel-like in shape

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Vertebrate Evolution

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  1. Vertebrate Evolution

  2. Vertebrate Evolution Steps • Vertebral column • Jaws, paired appendages (fins), bony skeletons • Lungs • Legs • Amniotic Egg

  3. Hagfishes • Agnathans: hagfishes and lampreys • eel-like in shape • an ancient vertebrate lineage that predates the origin of paired fins, teeth, and bones hardened by mineralization (ossification). • Hagfishes are the most primitive living “vertebrates” • cartilage skeleton • lack vertebrae: have a strong flexible rod of cartilage which extends the length of the body

  4. 1. Vertebrate Column • Lampreys: notochord persists as the main axial skeleton, but pairs of cartilaginous projections extend dorsally, partially enclosing the nerve cord with what might be a vestige of an early stage vertebral column.

  5. 2. Jaws, paired appendages, and bones! • The gnathostomes, have true jaws and also two sets of paired appendages. • In “fishes” these paired appendages function in swimming. • In tetrapods, the appendages are modified as legs to support movements on land.

  6. More on jaws and fins… • Jaws and paired fins were major evolutionary breakthroughs. • Expression of some of the Hox genes may determine whether sets of paired appendages develop in the embryo • Jaws, with the help of teeth, enable the animal to grip food items firmly and slice them up – eat new types of food. • Paired fins, along with the tail, enable fishes to maneuver accurately while swimming. • With these adaptations, many fish species were active predators, allowing for the diversification of both lifestyles and nutrient sources.

  7. Where did the jaws come from? • Vertebrate jaws evolved by modification of the skeletal rods that have previously supported the anterior pharyngeal slits. • The remaining gill slits remained as the site of respiration.

  8. Bones! • Nearly all bony fishes have an ossified endoskeleton with a hard matrix of calcium phosphate. • Bony fishes are the most numerous group of vertebrates, both in individuals and in species (about 30,000 species).

  9. 3. Lungs… • During the Devonian period, a diversity of plants and arthropods already lived on land • trees and other large vegetation were transforming terrestrial ecosystems • terrestrial habitats created new living conditions and food for fishes living near the water’s edge • A diversity of fishes resembling modern lobe-fins and lungfishes evolved.

  10. What’s a lungfish?! • Three genera of live today • Live in stagnant ponds and swamps. • Can gulp air into lungs to provide oxygen, but also have gills • When ponds shrink during the dry season, some lungfishes can burrow into the mud and aestivate. • Probably the ancestor of amphibians

  11. 4. Legs…transition to land • The fossil record chronicles the transition to land over a 50-million-year period from 400 to 350 million years ago. • fossils of Acanthostega not only have the bony support of gills but also the same basic skeletal elements as the walking legs of amphibians, reptiles, and mammals.

  12. Tetrapods continued… • Tetrapod: A vertebrate possessing two pairs of limbs, such as amphibians, reptiles, birds and mammals. • Legs were used underwater first… • In shallow water, leg-like appendages were probably better equipment crawling through the dense vegetation • Amphibians used these leg-like appendages to walk on land • benefited from abundant food and relatively little competition

  13. Tetrapod Evolution

  14. 5. Amniotic Egg • The amniote clade consists of the mammals, the birds, and the vertebrates commonly called reptiles, including turtles, lizards, snakes, and crocodiles. • The evolution of amniotes from an amphibian ancestor involved many adaptations for terrestrial living including • the amniotic egg • waterproof skin • increasing use of the rib cage to ventilate the lungs

  15. The incredible egg! • Among tetrapods, most amphibians lay eggs in water or an otherwise moist environment. • The other terrestrial tetrapods are amniotes, producing shelled, water-retaining eggs which allow these organisms to complete their life cycles entirely on land. • While most modern mammals do not lay eggs, they retain many of other key features of the amniotic mode of reproduction.

  16. Homework: Vertebrate Diversity Notes • Directions: Use pages 686-706 to take notes on the key characteristics and unique evolutionary adaptations of each of these groups: • Chondrichthyes • Osteichthyes • Amphibia • Modern Reptiles • Birds • Mammals (Monotremes, marsupials, and eutherian mammals)

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