Time Line of Animal Evolution 1st Fossil evidence of animals 570 mya = Proterozoic Era Adaptive radiation in early Cambrian Period of the Paleozoic Era Cambrian Explosion due to increased oxygen in atmosphere more energy predators become more mobile
Evolution of Animals Some type of Protist mutated to become multicellular Multicellular organisms start as a single cell (zygote) and grow into organisms with groups of specialized cells performing different functions All animals are multicellular
Proterospongia = Protist & common ancestor to all animals?
Proterospongia: Colonial, Unicellular Protists
Sponge collar cells
Phylum Porifera Sponges 3 types of cells Collar cells Amoebocytes Epidermis cells (protective outer layer of cells) No tissues Cells held together by jelly like substance Skeleton of spicules & spongin protein
Intracelluar digestion Collar cells take in food by endocytosis Food digested in food vacuoles Some food passed to amoebocytes Amoebocytes carry food around sponge body. (circulaton)
Other Porifera Traits Asymmetrical = no symmetry Respiration by diffusion Excretion by diffusion Reproduction = male gametes released into water, filtered out of water by another sponge. Female gametes stay in jelly until fertilized. Zygote grows into a swimming larva. Larva settles to ground & becomes sessile adult
All other Animals have True Tissues