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

• http://www.mbayaq.org/efc/video_library/video_library.aspx

• Then click on “Anemone Feeding”

• Jellyfish Swimming• http://www.youtube.com/watch?v=760lUxyle6I

Bilateral Symmetry

• Central nervous system in head

• Active movers• Frilled lizard video• http://video.nationalgeographic.com/video/pl

ayer/animals/reptiles-animals/lizards/lizard_frilled_ontherun.html?fs=animals.nationalgeographic.com

• Crocodile gallop video• http://www.flmnh.ufl.edu/natsci/herpetology/

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

http://worms.zoology.wisc.edu/urchins/rad_spir.html

Schizocoelous Enterocoelous

Sister Taxon

Model of Early Animal Evolution

Evolution of Animals

• Earliest animal fossils

• Fossilized embryos from China

• 575 mya

Ediacaran Fauna

• 565-550 mya• Australia• Soft-bodied

animal fossils• What type of

symmetry?

Ediacaran Fauna

• Animal fossil• Many body segments• Head• What type of

symmetry?

Cambrian Explosion

• 535-525 mya• Animal diversity ↑↑• 50% extant animal

phyla in fossil record

Burgess Shale Fossils

Cambrian Explosion

• First animals with hard mineralized skeletons

• 1st 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. 2008. Biology, 8th ed. Pearson Benjamin Cummings.

Slides 19 and 28 are from Campbell, et al. 2005. Biology, 7 th ed.