jawed vertebrates and the origins of tetrapods.

• What are gnathostomes?

  Vertebrates that have jaws
• How do gnathostomes compare to Agnatha?

  Gnathostomes far outnumber Agnatha
• What are the living groups of gnathostomes?

  • Sharks and relatives
  • Ray-finned fish
  • Lobe-finned fish
  • Amphibians
  • Reptiles and birds
  • Mammals
• What does the term "gnathostome" mean?

  It means "jaw-mouth"
• What are the advantages of jaws in gnathostomes?

  They allow gripping, slicing, and active predation
• How do jaws improve digestion in gnathostomes?

  They allow manipulation of food for better digestion
• What is the role of jaws in herbivory among gnathostomes?

  Jaws help in grasping and processing plant material
• What is a derived characteristic of gnathostomes?

  Duplication of Hox genes into four clusters
• What does the enlarged forebrain in gnathostomes indicate?

  It indicates improved olfaction and vision
• What is the lateral line system in aquatic gnathostomes?

  A system sensitive to vibrations in water
• How did jaws evolve according to the hypothesis presented?

  From modification of skeletal rods supporting gill slits
• When did gnathostomes first emerge?

  Mid-Ordovician period, ~470 MYA
• What features made early gnathostomes successful?

  Paired fins and efficient swimming
• What are placoderms?

  Earliest fossil gnathostomes
• What is a notable example of a placoderm?

  Dunkleosteus, an armored fish
• What happened to placoderms during the Carboniferous period?

  They became extinct early in the period
• What are acanthodians?

  Early gnathostomes that radiated in the Devonian
• What is the significance of the hyoid attachment in acanthodians?

  It aids in mouth opening mechanism
• What does Chondrichthyes refer to?

  Sharks, rays, and their relatives
• What is the skeleton composition of Chondrichthyes?

  Cartilage often impregnated with calcium
• Why is the cartilaginous skeleton of Chondrichthyes considered secondarily derived?

  It is not the primitive condition for vertebrates
• What adaptations do sharks have for buoyancy?

  Oil in the liver and continual swimming
• How do sharks perform gas exchange while resting?

  By using jaw and pharynx muscles to pump water
• What is the digestive adaptation found in sharks?

  A spiral valve in the intestine
• What is the reproductive strategy of oviparous sharks?

  Eggs hatch outside the body
• What is a unique feature of rays compared to sharks?

  Most rays are bottom-dwellers
• What is the primary threat to chondrichthyes?

  Overfishing
• What does Osteichthyes refer to?

  Bony fish and tetrapods
• What is a defining characteristic of Osteichthyes?

  Ossified endoskeleton with calcium phosphate
• What is the function of the operculum in Osteichthyes?

  It protects the gill chamber
• How do Osteichthyes control buoyancy?

  Using a swim bladder
• What did Charles Darwin propose about tetrapod lungs?

  They evolved from swim bladders
• What is the lateral line system in Osteichthyes?

  A row of tiny pits sensitive to vibrations
• What are Actinopterygii?

  Ray-finned fish
• How many species are in Actinopterygii?

  Approximately 32,000 species
• What are the key features of Sarcopterygii?

  Rod-shaped bones surrounded by muscle
• How many extant lineages are there in Sarcopterygii?

  Three extant lineages
• What are the three extant lineages of Sarcopterygii?

  Coelacanths, lungfish, and tetrapods
• What is significant about coelacanths?

  Thought extinct, rediscovered in 1938
• How do lungfish adapt to dry seasons?

  They burrow in mud and aestivate