BIOL10005 Lecture Notes - Lecture 21: Electroreception, Placodermi, The Reptile
LECTURE 21
THE VERTEBRATE STORY
CHAPTER 40 - ECHINODERMS & CHORDATES
VERTEBRATES
•Vertebrates are defined by;
•Vertebrae (backbone) forms around notochord.
•Internal and elaborate skeleton (cartilage or bone).
•Defined head with brain case (skull), and sensory organs.
•There aren’t many vertebrates but they are actually very diverse. The reptile group is very diverse.
•This is an order of evolution from left to right.
CEPHALOCHORDATES
•Cephalochordates lack jaws.
•The earliest vertebrates shared this feature.
•Later vertebrates developed jaws by modifying gill arches.
JAWLESS FISH
•Were once (495-360 million years ago) a very diverse group of
animals
•Early forms had an exoskeleton of bone in the skin and may even
have had electroreception
•Nowadays, only two small groups exist; lampreys and hagfish (both
blood-sucking parasites of fish).
THE EVOLUTION OF JAWS
•Jaws are derived from gill arches of chordates
•The earliest jawed fishes - Late Silurian (420 Mya)
•Some had dermal armour - e.g. Placoderm.
Lecture 21 - Friday 9 September 2016
BIOL10005 - GENETICS & THE EVOLUTION OF LIFE
Document Summary
Vertebrates: vertebrates are defined by, vertebrae (backbone) forms around notochord, internal and elaborate skeleton (cartilage or bone), defined head with brain case (skull), and sensory organs, there aren(cid:282)t many vertebrates but they are actually very diverse. The reptile group is very diverse: this is an order of evolution from left to right. Cephalochordates: cephalochordates lack jaws, the earliest vertebrates shared this feature, later vertebrates developed jaws by modifying gill arches. The evolution of jaws: jaws are derived from gill arches of chordates, the earliest jawed fishes - late silurian (420 mya, some had dermal armour - e. g. placoderm. Lecture 21 - friday 9 september 2016: dermal armour indicates that it(cid:282)s a ferocious predator, but that it(cid:282)s not the only one. Evolves if there are lots of ferocious predators. Ray finned (bony) fishes: ray finned fishes (class actinopterygii) have 25,000 incredibly diverse species.
