animal origins

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

Bringing it all together

• Evolutionary History of Life

• Basic Animal Body Plan—germ layers and gastrulation

• Animal Groups: Taxonomy and Systematics

History of life:

Rememberanimals appear about 500 MYA (sheet 176 out of 200)

• Animals show up about

EVENT         

TIME BEFORE PRESENT(BYA--billions of years ago(MYA--millions of years ago)

SHEET NUMBER ONTHE TYPICAL ROLL

Formation and Solidification of Earth 4.6-4.0 BYA 1

Oldest Rocks Known 3.8 BYA 10

Earliest evidence of life--carbon forms in rock

3.8 BYA 10

Earliest fossil prokaryotic cells 3.5 BYA 25

Oxygen levels rise steeply due to increase in photosynthetic activity

2.5 BYA 75

Complex eukaryotic cells appear in fossil record

1.5 BYA 125

First multicellular organisms in fossil record

600 MYA 170

Burgess Shale--exposion of multicellular diversity--most multicellular animal groups represented in primitive form

515 MYA 176

First land vertebrates 350 MYA 183

Archaeopteryx--precursor to birds (and other dinosaurs)

150 MYA 192

End Cretaceous Extinction--goodbye dinos, hello mammalian, bird, flowering plant diversity

65 MYA 196

Lucy--Australopithecus 4 MYA 1 (last 1/4 of sheet)

Homo erectus, fire 1 MYA 1 (last 1/20 of sheet)

Start of agriculture, settlements 10,000-20,000 years ago 1 (last fibers)

Basic Animal Body Plan:• 3 layer embryo

(remember/redo board drawing)

• Gastrulation (remember…tube within a tube…most important event of our lives)

Taxonomy and Systematics• 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}

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

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

• Called “triploblastic”• Formation of coelom

(body cavity)– Acoelomate (no body

cavity)– Pseudocoelomate

(body cavity between endoderm & mesoderm)

– Coelomate (body cavity surrounded by mesoderm)

Three-layer embryos—have mesoderm

Two ways for coelom to form in embryoSchizocoely 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.

Protostomes (mouth first) versus Deuterostomes (anus first)

What’s in the fossil record?The Cambrian Explosion

http://palaeo.gly.bris.ac.uk/Palaeofiles/Cambrian/Index.html

Symmetry

• Radial symmetry applies 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

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.

Symmetry

• Bilateral symmetry is 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.

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.

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

Epithelial Tissue• Epithelial tissue

covers the outside of the body and lines organs and cavities within the body.

Connective Tissue

• Connective tissue functions mainly to bind and support other tissues.– Contains sparsely packed cells

scattered throughout an extracellular matrix.

Muscle Tissue

• Muscle tissue is composed of long cells called muscle fibers capable of contracting in response to nerve signals.– Smooth– Skeletal– Cardiac

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.