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Lecture 14

BIO153 Lecture 14.pdf

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Christoph Richter

2009 BIO153: Lecture 14 The Origth of Animals Mar 11 , 2009 Topics: ▯ fossil record ▯ evolution of complexity ▯ evolution of the coelom Animalia = derived from anima (soul) Animals are diverse in form and function – they move! ▯ all are motile at some stage: crawl, walk, run, swim, burrow, sail, glide, fly… (may be sessile or planktonic as adults) ▯ show great anatomical complexity ▯ show tremendous diversity of body plans While there is great diversity of body plans, there are also many constraints on the “engineering” of animals. Challenges faced by multicellular animals: Advantages of being multicellular: ▯ tissue differentiation ▯ division of labour, more complex functions ▯ larger body size possible Challenges of being multicellular: Surface area - volume ratio ▯ small animals: gases, nutrients, wastes move by diffusion ▯ larger animals need organ systems to pump gases, nutrients, wastes in/out Habitat challenges: ▯ marine animals are isotonic; freshwater animals must eliminate water (leaks in osmotically) ▯ terrestrial animals: lack of buoyancy; protection of gametes and zygote Locomotion challenges: ▯ sessile / slow animals tend to have radial symmetry 1 ▯ fast animals need to be bilaterally symmetrical; cephalization is part of this trend Common attributes of all animals: ▯ multicellular ▯ no cell walls ▯ heterotrophs ▯ motile ▯ embryo goes through blastula stage (blastula = hollow ball of cells) Animals are monophyletic members of the Opisthokont lineage (along with fungi) The origin of animals: … sometime in the Precambrian… ▯ starting ~725 mya: supercontinent Rodinia starts to break up into smaller land masses ▯ this leads to an increase in favourable habitats (more continental shelf edges and shallow seas) ▯ new niches ▯ a prolonged period of glaciation causes oceanic upwelling ▯ increasing primary production by cyanobacteria and photosynthetic protists (increased levels of O 2 ▯ warm, mild climate permits large bodies & synthesis of biomineralized skeletons 2 This culminated in the Cambrian “explosion” ~ 570 – 515 mya: appearance of almost all metazoan phyla - including chordates -- incredible diversification in a relatively short time! Key events (key assemblages of fossils): 1. Doushantuo fossils: ▯ discovered in 1998 in Guizhou Province, China ▯ microscopic ▯ clusters of cells ▯ embryos ▯ cell division without increase in volume ▯ evidence of co
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