Evolution of Animals (Metazoa) BIOL 1407

Animal Body Plan Tissues –Absent = Parazoa –Present = Eumetazoa

Radial Symmetry Encounter environment equally from all sides Sessile, sedentary or planktonic Sea Anemone Feeding Video eo_library.aspxhttp:// eo_library.aspx Then click on “Anemone Feeding” Jellyfish Swimming

Bilateral Symmetry Central nervous system in head Active movers Frilled lizard video ayer/animals/reptiles- animals/lizards/lizard_frilled_ontherun.html?f s=animals.nationalgeographic.comhttp://video.nationalgeographic.com/video/pl ayer/animals/reptiles- animals/lizards/lizard_frilled_ontherun.html?f s=animals.nationalgeographic.com Crocodile gallop video brittoncrocs/images/cj-gallop2.mpghttp:// brittoncrocs/images/cj-gallop2.mpg

Number of Germ Layers Diploblastic: has two germ layers –Endoderm –Ectoderm Triploblastic: has three germ layers –Endoderm –Mesoderm –Ectoderm

Question?

Body Cavities What is a body cavity? –Fluid-filled cavity separates digestive tract from body wall

Body Cavities Advantages: –Fluid cushions organs –Acts as hydrostatic skeleton –Allows internal organs to move independently of body wall –Allows internal organs space for folding

Development Protostome –Fate of blastopore –Type of cleavage: spiral and determinate –Coelom formation Deuterostome –Fate of blastopore –Type of cleavage: radial and indeterminate –Coelom formation

Animation of Spiral and Radial Cleavage

Schizocoelous Enterocoelous

Sister Taxon

Model of Early Animal Evolution

Evolution of Animals Earliest animal fossils Fossilized embryos from China 575 mya

Ediacaran Fauna mya Australia Soft-bodied animal fossils What type of symmetry?

Ediacaran Fauna Animal fossil Many body segments Head What type of symmetry?

Cambrian Explosion mya Animal diversity ↑↑ 50% extant animal phyla in fossil record

Burgess Shale Fossils

Cambrian Explosion First animals with hard mineralized skeletons 1 st arthropods, chordates & echinoderms

Hypotheses for Cambrian Explosion (1) Predator-prey coevolution (2) Rise in atmospheric oxygen levels  ↑ metabolic rate and body size (3) Evolution of Hox genes  developmental flexibility

Traditional Phylogenetic Tree Was based on body plans –Tissues absent or present –Type of symmetry –Types of body cavities –Protostomes versus deuterostomes

Modern Phylogenetic Tree Based on molecular data

Modern Phylogenetic Tree Reinforces some of traditional tree –Parazoa vs. Eumetazoa –Radial vs. Bilateral –Deuterostomes are a clade

Modern Phylogenetic Tree Radical affects on other parts –Body cavity characteristics are analogous –Two main lineages for most invertebrates Lophotrochozoa Ecdysozoa

Lophotrochozoa Clade named for presence of either a: –Lophophore (horse-shoe shaped ciliated feeding apparatus) –Trochophore larva

Lophotrochozoa

Ecdysozoa Clade was named for presence of Ecdysis = molting Produce an exoskeleton Must be shed as animal grows

The End Unless otherwise specified, all images in this presentation came from: Campbell, et al Biology, 8 th ed. Pearson Benjamin Cummings. Slides 19 and 28 are from Campbell, et al Biology, 7 th ed.