1. Animal Evolution and Diversity
Chapter 26
Animal Evolution and Diversity

2. Invertebrate Evolution and Diversity
Section 1
Invertebrate Evolution and Diversity

3. Origins of the Invertebrates
It is not known when the first multicellular animals evolved from single-celled eukaryotes.
Animals probably evolved from ancestors they shared with choanoflagellates. Fossil evidence indicates that animals began evolving long before the CAMBRIAN EXPLOSION, which occurred between 530 and 515 million years ago.

4. Origin of the Invertebrates
Fossils from Ediacara Hills in AUSTRALIA date from roughly 565 to 544 million years ago. Their body plans are different from those of anything alive today.
Some seem to be related to invertebrates such as JELLYFISHES and WORMS.

5. Origins of the Invertebrates
Cambrian fossils (dating back about 542 million years ago) show how animals evolved complex body plans over a span of million years.
Many had body SYMMETRY, a front and back end, specialized cells, and APPENDAGES, structures such as legs or antennae protruding from the body. Some had hard body parts that became fossilized.

6. Origins of the Invertebrates
By the end of the Cambrian, the basic body plans of the modern phyla were established.
Today, invertebrates are the most ABUNDANT animals on Earth.

7. Cladogram of Invertebrates
The cladogram of invertebrates presents current hypotheses about evolutionary relationships among major groups of modern invertebrates.

9. Cladogram of Invertebrates
The major invertebrate phyla are the SPONGES, cnidarians, ARTHROPODS, nematodes (ROUNDWORMS), flatworms, annelids, MOLLUSKS, and echinoderms.

10. Cladogram of Invertebrates
Sponges have PORES in their bodies.
Cnidarians are RADIALLY symmetrical animals with stinging tentacles.
Arthropods have SEGMENTED bodies, a hard external skeleton, jointed appendages, and cephalization.

11. Cladogram of Invertebrates
NEMATODES, or round worms, are nonsegmented worms with PSEUDOCOELOMS.
Their digestive tracts have TWO openings.
Platyhelminthes, or FLATWORMS are the simplest animals to have THREE germ layers, BILATERAL symmetry, and cephalization.

12. Cladogram of Invertebrates
Annelids are WORMS with segmented bodies and a true COELOM.
LARVAE are the immature stages of development in some animals, such as MOLLUSKS.

13. Cladogram of Invertebrates
Many mollusks have a FREE-SWIMMING larval stage called a TROCHOPHORE. The trochophore is also characteristic of many annelids, indicating that annelids and mollusks are closely RELATED.

14. Cladogram of Invertebrates
MOLLUSKS are soft-bodied animals that usually have a SHELL.
They also have a true COELOM and complex organ system.
Echinoderms have SPINY skin and exhibit RADIAL symmetry.

15. Chordate Evolution and Diversity
Section 2
Chordate Evolution and Diversity

16. Origins of the Chordates
Embryological studies suggest that the most ancient chordates were related to the ancestors of the ECHINODERMS.
Fossils of the earliest chordates (CAMBRIAN Period) show MUSCLES arranges in a series, traces of FINS, sets of feathery GILLS, a head with paired sense organs, and a SKULL and SKELETAL structures likely made of CARTILAGE, a strong connective tissue that is softer and more flexible than bone.

17. Origins of the Chordates
Modern chordates are very diverse, consisting of SIX groups: the nonvertebrate chordates and the five groups of the vertebrates— FISHES, AMPHIBIANS, REPTILES, BIRDS, and MAMMALS.

18. Cladogram of Chordates
The cladogram of chordates presents current hypotheses about relationships among chordate groups.

20. Cladogram of Chordates
NONVERTEBRATE chordates: the tunicates and the lancelets lack BACKBONES.
JAWLESS fishes: Lampreys and hagfishes lack vertebrae and have NOTOCHORDS as adults.

21. Cladogram of Chordates
SHARKS and their relatives: They have jaws and skeletons made of CARTILAGE.
BONY fishes: These animals have skeletons made of TRUE BONE.
Most modern bony fishes are RAY-FINNED fishes.

22. Cladogram of Chordates
One group of ancient LOBE-FINNED fishes evolved into the ancestors of TETRAPODS, which are FOUR-limbed vertebrates.
AMPHIBIANS: Amphibians live in water as LARVAE but on land as ADULTS.
They breathe with LUNGS as adults, but most require water for REPRODUCTION.

23. Cladogram of Chordates
REPTILES: Reptiles have dry, scaly skin, well-developed LUNGS, strong LIMBS, and SHELLED eggs that do not develop in water.
BIRDS: Birds can regulate their INTERNAL body TEMPERATURE.
They have an outer covering of FEATHERS, strong yet lightweight BONES, two legs covered with SCALES that are used for walking or perching, and front limbs modified into WINGS.

24. Cladogram of Chordates
DINOSAURS and birds are now considered to be in one clade, which is part of the larger REPTILES clade.
Modern birds are, therefore, REPTILES. The traditional class of Reptilia, which is not a clade, includes living reptiles and dinosaurs but not birds.

25. Cladogram of Chordates
MAMMALS: Mammals produce MILK from mammary glands, have HAIR, breathe air, have FOUR-chambered hearts, and regulate their internal BODY TEMPERATURE.