Chondrichthyes

460mya Chondrichthyes

This group of cartilaginous fish include Rays, Sharks, Skates, Chimaeras.  The species in this class have a flexible skeleton made of cartilage instead of bone.

Cartilage is the flexible substance found that gives human noses and ears their shape! Only their teeth, and sometimes their vertebrae, have calcium in them! That why when you find fossils of sharks you find teeth and vertebrae but no other bones.  

Chimaeras have large heads and long bodies that taper to a whiplike tail. The skin is smooth and rubbery and has no scales. Sharks and skates and rays have gills that open to the outside, have no swim bladder, and have a sandpaper-like skin covering rather than scales. Sharks range in size from tiny to huge. Skates and rays are flat from top to bottom and have massive pectoral fins and long, sometimes whiplike tails.

Species in this class have paired fins, hard scales, a two-chambered heart, and a pair of nostrils. Most species have 5-7 gill slits on each side of their body. Some species produce egg cases, others give birth to live young.

These top predators of the ocean have been overfished for their fins which are considered a delicacy in Chinese soup dishes.  Ninety percent of their populations have been decimated to the extent that it has disrupted the food chains in some areas.  Many species are under threat of extinction if efforts to create protected marine parks are not successful.

Ancestor's Trail
  1. Ancestor's Trail Hike
  2. Why Is Life On Earth Carbon-Based?
  3. Metazoans
  4. 900MYA we had a common ancestry with Choanoflagellates (non-animal eucaryotes)
  5. 800mya we had a common ancestry with Sponges
  6. 780mya we had a common ancestry with Placozoans
  7. 730mya Ctenophores
  8. 680mya Cnidarians
  9. 630mya Flatworms
  10. 590mya Protosomes
  11. 570mya Ambulacrarians
  12. 565mya Tunicates
  13. 560mya Cephalocordates
  14. 530mya Agnatha
  15. 460mya Chondrichthyes
  16. 440-450mya FIRST GREAT EXTINCTION
  17. 440mya Actinopterygii
  18. 417mya Dipnoi
  19. 360-375mya SECOND GREAT EXTINCTION
  20. 340mya Amphibians
  21. 310mya Sauropsids (lizard-faced non-mammalian chordates)
  22. 251mya THIRD GREAT EXTINCTION
  23. 205mya FOURTH GREAT EXTINCTION
  24. 180mya Monotremes
  25. 140mya Marsupials
  26. 105mya Afrotheres
  27. 95mya Xenarthrans
  28. 85mya Laurasiatheres
  29. 75mya Glires (Rodents and Lagomorphs)
  30. 70mya Non-primate Eurachonta (Cologus and Tree shrews)
  31. 65mya FIFTH GREAT EXTINCTION
  32. 63mya Prosimians
  33. 58mya Tarsiers
  34. 40mya Platyrrhini
  35. 25mya Catarrhini
  36. 18mya Lesser Apes
  37. 14mya Orangutans
  38. 7mya Gorillas
  39. 6mya Chimpanzees and Bonobos
  40. Human Evolution on the Ancestor's Trail
  41. 7 BILLION HUMANS