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: Remember animals 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 ON THE TYPICAL ROLL Formation and Solidification of Earth BYA1 Oldest Rocks Known3.8 BYA10 Earliest evidence of life--carbon forms in rock 3.8 BYA10 Earliest fossil prokaryotic cells3.5 BYA25 Oxygen levels rise steeply due to increase in photosynthetic activity 2.5 BYA75 Complex eukaryotic cells appear in fossil record 1.5 BYA125 First multicellular organisms in fossil record 600 MYA170 Burgess Shale--exposion of multicellular diversity--most multicellular animal groups represented in primitive form 515 MYA176 First land vertebrates350 MYA183 Archaeopteryx--precursor to birds (and other dinosaurs) 150 MYA192 End Cretaceous Extinction--goodbye dinos, hello mammalian, bird, flowering plant diversity 65 MYA196 Lucy--Australopithecus4 MYA1 (last 1/4 of sheet) Homo erectus, fire1 MYA1 (last 1/20 of sheet) Start of agriculture, settlements10,000-20,000 years ago1 (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 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.

Protostomes (mouth first) versus Deuterostomes (anus first)

What’s in the fossil record? The Cambrian Explosion

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.