BIOL 1521 Lecture Notes - Lecture 8: Synapsid, Ostracoderm, Agnatha
Animal Evolution: Vertebrates
Vertebrate Evolution
• All about the origins of fish
• Tetrapods are descended from lobe-finned fish with lungs that adapted to walking on land
• Over half of all described vertebrate species are fish
Myllokunmingia
• Earliest vertebrate
• Agnathan
• 530 mya
Haikouicthys
• First notochord
• Endoskeleton (but not mineralized)
• Agnathan
• Gill pouches
Early vertebrates in the Ordovician
• Innovations in nervous system and skeleton
• Early vertebrates included conodonts and ostracoderms
Jaws evolved from modified gill arches
Major phylogenetic milestones of the Devonian
• "Age of fishes"
• New division of plantae emerge
• Tetrapods colonize land
What challenges do fish have to overcome on their way to terrestrial life?
• Respiration (organs)
• Structural support
• Movement
Amniotes: Reptiles, Birds, Mammals
• Amniotic egg protects embryo
• Adaptations to the skin reduce water loss (but limit gas exchange)
o Scales, feathers, hair, cuticle
• Rib cage ventilation replaced throat-based ventilation
Important Terms
• Amniote groupings are based on openings in the temporal region of the skull
o Anapsid: early amniotes and turtles
o Synapsid: mammalian ancestors
o Diapsid: archosaurs and lepidosaurs, birds, most modern reptiles
Overcoming zygote desiccation
• Amniotic egg involves 4 extra embryonic membranes
• Most amniotes also rely on an outer shell to reduce desiccation
o Chorion: gas exchange
o Allantois: waste storage
o Yolk sac: nutrients
o Amnion: fluid-filled chamber
The origin of birds
• Descended from small theropods, a group of carnivorous dinosaurs
• Feathered therapods evolved into birds
find more resources at oneclass.com
find more resources at oneclass.com
