Animal Origins

1. Animal Origins Bringing it all together History of Life Basic Animal Body Plan Animal Groups: Understanding evolutionary relationships among phyla of animals The Cambrian Explosion Other body plan features Symmetry Segmentation Tissue Types

2. Bringing it all together • Evolutionary History of Life • Basic Animal Body Plan—germ layers and gastrulation • Animal Groups: Taxonomy and Systematics

3. History of life: Rememberanimals appear about 500 MYA (sheet 176 out of 200) • Animals show up about

4. 3 layer embryo (remember/redo board drawing) Gastrulation (remember…tube within a tube…most important event of our lives) Basic Animal Body Plan:

5. Remember…canimalcules—finding common shared characteristics Taxonomy of major animal groups (phyla) reflecting their evolutionary history, is based on shared common characteristics related to basic body plan formation during development…{next slide} Taxonomy and Systematics

7. Understanding evolutionary relationships among animal phyla • Goal is to see which major groups are closely related • Adults are so different that it is difficult to find shared common characteristics • Embryos do share many characteristics and can be easily compared

8. Animals with no mesoderm • Least complex groups • Embryo has only ectoderm and endoderm • Called “diploblastic” • Usually have radial symmetry • Include Cnidaria (corals, sea anemones, jellyfish) and Ctenophora

10. Three-layer embryos—have mesoderm • Called “triploblastic” • Formation of coelom (body cavity) • Acoelomate (no body cavity) • Pseudocoelomate (body cavity between endoderm & mesoderm) • Coelomate (body cavity surrounded by mesoderm)

12. Two ways for coelom to form in embryo Schizocoely in Protostomes– mesodermal cells fill the blastocoel, forming a solid band of tissue around the gut, then a space opens inside the mesodermal band. Enterocoely – portions of the gut lining form pockets that pinch off and form a ring of mesoderm.

14. Protostomes (mouth first) versus Deuterostomes (anus first)

15. What’s in the fossil record?The Cambrian Explosion http://palaeo.gly.bris.ac.uk/Palaeofiles/Cambrian/Index.html

16. Symmetry • Radial symmetryapplies when more than two planes passing through the longitudinal axis can divide the organism into mirror image halves. • Jellyfish • Biradial symmetry– two planes will divide the organism. • Comb jellies

17. Radiata • The Cnidarians (jellyfish, corals & sea anemones) and Ctenophores (comb jellies), the radial or biradial animals, comprise the Radiata. • No front/back • Weak swimmers • Can interact with environment in all directions.

18. Symmetry • Bilateral symmetryis found in organisms where one plane can pass through the organism dividing it into right and left halves. • Better for directional movement. • Monophyletic group called Bilateria.

19. Cephalization • Bilateral symmetry is associated with cephalization, differentiation of a head. • Nervous tissue, sense organs, and often the mouth are located in the head. • Advantages for organisms moving head first – directional movement. • Elongation along anteroposterior axis.

20. Tissue Structure and Function • A tissue is a group of similar cells specialized for performing a common function. • Different types of tissues have different structures that are suited to their functions. • Tissues are classified into four main categories: • Epithelial • Connective • Muscle • Nervous

21. Epithelial Tissue • Epithelial tissue covers the outside of the body and lines organs and cavities within the body.

22. Connective Tissue • Connective tissue functions mainly to bind and support other tissues. • Contains sparsely packed cells scattered throughout an extracellular matrix.

23. Muscle Tissue • Muscle tissueis composed of long cells called muscle fibers capable of contracting in response to nerve signals. • Smooth • Skeletal • Cardiac

24. Nervous Tissue • Nervous tissue senses stimuli and transmits signals throughout the animal. • A neuron (nerve cell) receive signals at the dendrites and send them out via the axons.