agnathans, gnathostomes and the crainiates.

• What is the focus of the study material?

  Vertebrate evolution
• What are the two major categories of animals?

  Invertebrates and vertebrates
• How many extant species of vertebrates are there?

  Approximately 66,178 species
• Which group of vertebrates is the most abundant?

  Fish with over 32,000 species
• What are the main subphyla of Chordata?

  • Urochordata
  • Cephalochordata
  • Craniates
• What are the characteristics of chordates?

  Dorsal hollow nerve cord, notochord
• What is paedomorphosis in vertebrates?

  Larva becomes sexually mature without adult form
• What are the three classes of Urochordata?

  Sea squirts, salps, larvaceans
• What is the significance of the neural crest in craniates?

  Forms peripheral nervous system and myelin sheath
• What is the origin of craniates based on fossil evidence?

  Fossils found in China, 530 MYA
• What characteristics define Myxini?

  Hagfishes with a cartilage skull and no jaws
• How long can Myxini grow?

  Up to 60 cm in length
• What is the function of slime produced by Myxini?

  Repels scavengers and coats gills
• What do vertebrates possess that distinguishes them from other craniates?

  A vertebral column
• What is the function of the vertebral column?

  Supports body and protects nerve cord
• What are the common characteristics of phylum Vertebrata?

  • Vertebral column
  • Skull (cranium)
  • Well-developed circulatory system
  • Internal organs in coelom
  • Three-part brain
  • Duplication of Hox gene complex
• What does Petromyzontida represent?

  Oldest living lineage of vertebrates
• What is the feeding mechanism of adult lampreys?

  Parasitic, feeding on fish blood
• What is the skeleton composition of Petromyzontida?

  Cartilage with no collagen
• What are conodonts known for?

  Being jawless and having cone teeth
• When did later vertebrates emerge?

  During Ordovician, Silurian, and Devonian periods
• What initiated mineralisation in vertebrates?

  • Transition in feeding mechanisms
  • Early vertebrates likely suspension feeders
  • Increased body size for larger particles
• What are the earliest known mineralised vertebrate structures?

  Conodont dental elements
• What is the significance of mineralisation in vertebrates?

  Facilitated scavenging and predation