Chordate Evolution and Diversity

1. Chordate Evolution and Diversity Brennan Falcy Mr. Cope Biology Period 1 May 21 2011

2. Origin of Chordates • Embryological studies show that the most ancient chordates were related to the ancestor of the echinoderm. • The earliest found chordate is the pikaia, which was first mistaken for a worm, but it’s anatomy proved otherwise. It was a notochord, a tail fin, a tentacle, and a head segment.

3. Diversity of Chordates • All chordates fall into one of six categories; the nonvertebrate chordates, fish, birds, reptiles, fish, and mammals. • 96% of all modern chordates are vertebrate, with fish being the largest group.

4. Cladogram of Chordates The Cladogram of Chordates presents current hypothesis about relationships among chordate groups. It also shows at which points important vertebrate features are found like limbs and jaws.

5. Nonvertebrate Chordates • Only two groups of chordates lack a vertebrate, tunicates and lancelets. • Fossil evidence show that over 550 million years ago, nonvertebrate chordates diverged from the ancestors of vertebrate chordates. • Interestingly, tunicates do not have a notochord in their adult stage, which is a requirement for all chordates. They do however have a notochord in it’s larval form.

6. Jawless Fishes • Fossil evidence dates jawless fishes up to 510 million years ago. These fishes had no jaws or teeth and their skeletons were completely cartilage. • Two of these ancient fishes were the ancestors for two modern classes of fish, hagfish and lamprey. They both lack a vertebrate, but they do have a body part that could be considered a skull, and are therefore called vertebrates.

7. Sharks and Their Relatives • Many of the ancient ancestors evolved an adaptation called jaws. A jaw makes it possible to eat things like plants and animals rather than just filter feeding. • They also adapted other important features, pelvic and pectoral fins. These allow for more control of movement and speed. • Sharks, and all their relatives, are cartilaginous fishes because they have no bone and all cartilage.

8. Bony Fishes • A separate group of fish ancestors adapted skeletons made out of “true bone”, these fish are called bony fishes. Most current bony fish fall under the large ray-finned fish group. • Most ray-finned fishes have paired fins, scales, and gills. They are named ray-finned fish because of their ray like bones in their fins. • Lobe-finned fish are a much smaller group, and have adapted a fleshy fin by a larger bone rather than many smaller bones.

9. Amphibians • Amphibians live their larval life in water, and their adult life on land. They need water to reproduce because their offspring live in water as young. • Amphibians share a common ancestor with the lobe-finned fish, but amphibians later developed limbs where fish didn’t. They also developed a way of obtaining food and breathing on land. • Many of the early amphibians died about 250 million years ago, leaving only the frogs/toads, salamanders and caecilians.

10. Reptiles • A reptile is a vertebrate with scaly skin, developed lungs, strong limbs, and shelled eggs that evolved from amphibians. • The Jurassic and Triassic periods were filled with reptiles (or dinosaurs) that were highly adapted to their surroundings. One group of feathered dinosaurs is said to be a common ancestor of both birds and reptiles. • 66 million years ago, a worldwide extinction occurred, wiping out all life on land and water, bringing and end to the Cretaceous period.

11. Birds • Birds are reptiles that regulate their body temperature. They have strong, lightweight bones, two scaly legs for walking, and two front limbs for flying. • They are the only modern day “dinosaurs” because they are directly related to a group of extinct dinosaurs. • Although they are the only chordates that are related to dinosaurs, they still share a common ancestor with all the other chordates.

12. Mammals • There are some 5000 mammals in the world. Requirements of a mammal are hair, mammary glands in females, endothermy, a four chambered heart, and the need to breath air. • Mammals first appeared 220 million years ago in the Triassic period. During this time, they evolved variously to their environments, resulting in animals as big as whales to as small as mice. • Modern mammals are divided into three groups Monotremes, Marsupials and Placental.