INTRODUCTION TO ANIMAL DIVERSITY Chapter 32 Our Kingdom We are Animals
Animals Are • Species-rich • Morphologically diverse lineage of multicellular organisms on the tree of life • Distinguished by two traits • they eat • they move • The largest and most abundant predators, herbivores, and detritivores
Animals Are • Multicellular, heterotrophic eukaryotes • Heterotrophs • ingest food • find food by tunneling, swimming, filtering, crawling, creeping, slithering, walking, running, or flying. • Dominant consumers in both aquatic and terrestrial habitats • Animal cells lack cell walls • Distinguished by two tissues • Nervous tissue and muscle tissue • Most animals reproduce sexually with the diploid stage usually dominating the life cycle
Methods in the Study of Animals • Analyzing Comparative Morphology • The Evolution of Tissues • Symmetry and Cephalization • Evolution of a Body Cavity • The Protostome and Deuterostome Patterns of Development • The Tube-within-a-Tube Design • A Phylogeny of Animals Based on Morphology • Using the Fossil Record • Evaluating Molecular Phylogenies
Themes in the Diversification of Animals • Suspension (Filter) Feeding • Deposit Feeding • Herbivory • Predation • Parasitism • FeedingMovement • Types of Limbs: Unjointed and Jointed • Are All Animal Appendages Homologous? • Reproduction and Life Cycles
Key Lineages of Animals • Choanoflagellates (Collar Flagellates) • Porifera (Sponges) • Cnidaria (Jellyfish, Corals, Anemones, Hydroids, Sea Fans) • Ctenophora (Comb Jellies) • Acoelomorpha
Monophyletic and Very Diverse The animals are a monophyletic group Animals are very diverse 34 major animal phyla are recognized
Analyzing Comparative Morphology Most morphological diversity in animals is based on differences in mouths and limbs
Basic Architecture Four features define an animal's body plan the number of tissue types in embryos the type of body symmetry the presence or absence of a fluid-filled cavity the way in which the earliest events of embryo development proceed
The Evolution of Tissues All animals other than sponges have tissues tightly integrated structural and functional units of cells. Diploblasts embryos have two types of tissues or germ layers Ectoderm Endoderm Triploblasts embryos have three types of tissues Ectoderm Endoderm Mesoderm germ layers develop into distinct adult tissues
Symmetry and Cephalization A basic feature of a multicellular body is the presence or absence of a plane of symmetry radialsymmetry at least two planes of symmetry. bilateral symmetry a single plane of symmetry face their environment in one direction.
Cephalization Bilateral symmetry allowed Evolution of a head, or anterior region, where structures for feeding, sensing the environment, and processing information are concentrated
Evolution of a Body Cavity Animals may or may not have an internal, fluid-filled body cavity coelom forms from within the mesoderm lined with cells from the mesoderm
Advantages of a Coelom Creates a medium for circulation Makes space for internal organs A hydrostatic skeleton fluid-filled chamber allows movement even without fins or limbs.
The Protostome and Deuterostome Patterns of Development • Coelomates are bilaterally symmetric • except echinoderms • three embryonic tissue layers • Bilatera • protostomes • arthropods, mollusks, and segmented worms • deuterostomes • vertebrates and echinoderms
Differences in Early Development Three events in early development differ in protostomes and deuterostomes Cleavage Gastrulation coelom formation
Cleavage Rapid series of mitotic divisions Spiral cleavage mitotic spindles of dividing cells orient at an angle to the main axis of the cells resulting in a helical arrangement Radial cleavage mitotic spindles of dividing cells orient parallel or perpendicular to the main axis of the cells resulting in a pattern of cells stacked directly on top of each other
The Tube-within-a-Tube Design The basic animal body plan is a tube-within-a-tube design in which the outer tube forms the body wall and the inner tube forms the gut
Ancestor? • The animal kingdom all developed from a common ancestor ( monophyletic) probable during the Precambrian era. • Probably a colonial choanoflagelate that lived about700 million years ago. Modern choanoflagellates are tiny, have a stalk and live in ponds and lakes) • A hypothesis of animal origin from flagellated protists says that the colony of cells in the protist evolved into a sphere and then differenciated and especialized creating two layers of cells.
Single cell Stalk The common ancestor of living animals • May have lived 1.2 billion–800 million years ago • May have resembled modern choanoflagellates, protists that are the closest living relatives of animals Figure 32.3
Digestive cavity Somatic cells Hollow sphere of unspecialized cells (shown in cross section) Reproductive cells Colonial protist, an aggregate of identical cells Beginning of cell specialization Infolding Gastrula-like “protoanimal” closest living relatives of animals • a colonial, flagellated protist Figure 32.4
A Phylogeny of Animals Based on Morphology The phylogenetic tree indicates that a group of protists called the choanoflagellates are the closest living relatives of animals and that the Porifera (sponges) are the most ancient animal phylum.
Radially symmetric phyla are placed on the tree next because their tubelike body plans are relatively simple. Among the bilaterally symmetric phyla, the acoelomates and pseudocoelomates appeared first, followed by the coelomates.
Two major events occurred after the coelomates split into the protostomes and deuterostomes radial symmetry evolved segmentation evolved independently in both lineages of coelomates.
Using the Fossil Record Most major groups of animals appear in the fossil record starting about 580 million years ago The fossil record is generally consistent with the morphological phylogeny.
(b) (a) Neoproterozoic Era (1 Billion–524 Million Years Ago) • Early members of the animal fossil record are known as the Ediacaran fauna( first fossils of animals about 575 mya). Simple radial forms and segmented bodies with legs. Figure 32.5a, b
Paleozoic Era (542–251 Million Years Ago) • The Cambrian explosion marks the earliest fossil appearance of many major groups of living animals • Is described by several current hypotheses such as predator- prey relationships, oxygen increase and evolution of the hox genes Figure 32.6
Mesozoic Era (251–65.5 Million Years Ago) • During the Mesozoic era • Dinosaurs were the dominant terrestrial vertebrates • Coral reefs emerged, becoming important marine ecological niches for other organisms • The first mammals appeared (tiny, nocturnal insect eaters
Cenozoic Era (65.5 Million Years Ago to the Present) • The beginning of this era • Followed mass extinctions of both terrestrial and marine animals • Modern mammal orders and insects diversified during the Cenozoic • Also flowering plants appeared