ch32

Chapter 32

INTRODUCTION TO ANIMAL DIVERSITY

Biologists have identified about 1.3 million living species of animals, and estimates of the total number of animal species run far higher, from 10 to 20 million to as many as 100 to 200 million.

CHARACTERISTICS OF THE ANIMAL ANIMAL KINGDOM The following characteristics describe most animals 1. Heterotrophs that Heterotrophs  that inhabit the sea, fresh water and land. !ost animals ta"e their food by ingestion. ingestion . 2. #iploid m!ti"e!!!#r e$#r%otes. e$#r%otes . Cells are speciali$ed and organi$ed into tissues, organs, etc. Their cells lac" cell wall of any "ind. Tissues are held together by structural proteins, the most common being "o!!#gen. "o!!#gen . 3. !ost repro&"e se'#!!%, se'#!!% , with large non%motile eggs and small flagellated sperms. &. The diploid diploid $ygote $ygote produced produced by fertili$ation fertili$ation divides by mitotic mitotic divisions, divisions, resulting resulting in a ball of cells that usually hollows out to become a (!#st!#. (!#st!# . 'ponges are an e(ception. • • •

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)ygote * eight%cell stage * blastula * gastrula * embryo develops... )!#st!# is )!#st!#  is a hollow ball of cells with a blastocoel or cavity in its center. G#str!#tion is G#str!#tion  is a rearrangement of the (!#sto"oe! cells, (!#sto"oe!  cells, where on end folds inward, and cells fill the blastocoel forming a three%layered structure e"to&erm, e"to&erm , meso&erm and meso&erm  and en&o&erm. en&o&erm . 'ome animals develop directly through transient stages into adults+ other animals include a !#r*#! st#ge that st#ge  that undergoes met#morphosis, met#morphosis , a resurgence of development that transforms the !#r*# into !#r*# into an adult.

. !ost are are capable capable of locomo locomotion tion at at some stage stage of of their lives. lives. -. !ost can respond adaptively adaptively to e(ternal e(ternal stimuli stimuli and have well%develop well%developed ed sense organs and nervous system. !ost phyla have muscular and nervous tissues.  bout 3 3 phyla the the ma/ority of of which are are invertebrates. invertebrates. The animal "ingdom is probably monophyletic and probably evolved from colonial flagellate protists related to the choanoflagellates at least 00 million years ago. hylogenetic trees are sets of hypotheses that are refined to accommodate new data. !eta$oans 1. 2. 3. &.

!ult !ultic icel ellu lula lar  r  !otil !otility ity at at some some stag stage e of the their ir life life ete etero rotr trop ophi hic c #iplob #iploblas lastic tic or or triplob triplobla lasti stic c

HISTORY OF THE ANIMAL KINGDOM

The animal "ingdom includes the e(tant and e(tinct species. 'ome biologists estimate that up 4 of animal species are e(tinct. 'ome calculations based on molecular cloc"s suggest that the ancestors of animals diverged from the ancestors of plants about 1. 5 1.6 billion years ago. Neoprotero+oi" Er# ,- (i!!ion to ./0 mi!!ion %e#rs #go1 This era is also "nown as the recambrian. The earliest accepted fossil animals are about  million years ago. These fossils are "nown collectively as the E&i#"#r#n 2#n#. 2#n# . •

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7irst described from the 8diacara ills of southern ustralia, but have since been found all over the world. 'everal body plans have been observed animals with both radial and bilateral symmetry, feather%li"e and worm or tube%li"e forms, etc. !ost of the animals in the 8diacaran fauna appear to be cnidarians and possibly mollus"s.

3#!eo+oi" Er# ,./0 to 0.- mi!!ion %e#rs #go1  t the beginning beginning of of the Cambrian, Cambrian, about about & m.y.a. m.y.a. there was was an e(plosive e(plosive radiation radiation of multicellular animals. This event is called the C#m(ri#n e'p!osion. e'p!osion . •

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9apid evolutionary changes occurred in the late rotero$oic and ended in the 8arly Cambrian.   change from mostly simple simple organisms organisms to comple( comple( organisms organisms comparable comparable to present present day animals. This happened in &0 million years, &2 % 2 m.y.a.

:t was a period of great evolutionary innovation. lmost all meta$oa phyla appeared at this time. H%potheses #(ot the "#ses o2 the C#m(ri#n e'p!osion These three hypotheses are not mutually e(clusive. 8cological causes •

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redators feed on the most abundantly prey species thus reducing their numbers and letting others use the resources. Cropping of a dominant species opens many niches, which become occupy by species previously e(cluded. :ncrease in prey species leads to an increase in predators.

;eologic causes • •

vendian>ediacara.html http>>palaeo.gly.bris.ac.u">alaeofiles>Cambrian>controversies>timetable>timetable.html http>>www.teaching%biomed.man.ac.u">bs1>bs1&->biodiversity>orirelho.htm The Cambrian period was followed by the