Presentation on theme: "1 Lecture 3: Origins of Animals Developmental, molecular and paleontological perspectives."— Presentation transcript:
1 Lecture 3: Origins of Animals Developmental, molecular and paleontological perspectives
2 What is an animal? Multicellular adults, heterotrophic, eukaryotes. Most feed by ingestion of food into a gut Cells lack cell walls, adhere by means of specialised junctions, secrete extra-cellular matrices using collagen. Most animals possess specialised cells for: a) signal transmission - nerves b) contraction for movement - muscles
3 Animal Life History Typically a small flagellated sperm fertilises a larger egg to form a diploid zygote. Zygote undergoes cleavage. Formation of a blastula Blastula undergoes gastrulation during which embryonic tissue layers form Many animals have distinct larval stage
4 Figure 32.1 Early embryonic development (Layer 1)
5 Figure 32.1 Early embryonic development (Layer 2)
6 Figure 32.1 Early embryonic development (Layer 3)
9 Figure 32.3 One hypothesis for the origin of animals from a flagellated protist
10 Figure 32.4 A traditional view of animal diversity based on body-plan grades
11 First major split Parazoans (no true tissues) versus eumetazoa (all other animals)
12 Second major split Radial versus bilateral symmetry Cnidaria (jellyfish and anemones) and Ctenophora (comb jellies) versus rest of animals Bilateral symmetry associated with cephalisation (development of a head) Some bilateral animals have acquired radial symmetry (e.g., some echinoderms)
28 Cambrian Explosion Nearly all major animal phyla appear in Cambrian rocks (545 to 525 million years ago) Many weird and wonderful creatures appear suddenly in the fossil record Question: Is the fossil record giving us a faithful picture of what happened.
29 First appearance of animals in the fossil record
30 < Spriggina Annelid Worm? Arthropod? Cyclomedusa > Benthic Polyp 1-5 mm in diameter Nemiana > Sea anemonea? Algal?
31 < Dickinsonia Annelid Worm? Cnidarian? Charnia > Sea pen- up to 1m in length
32 British Colombia, Canada Discovered in 1909 by Charles Walcott Deep water deposit Around 515 million years (10 million years after Cambrian explosion) Burgess Shale and the Cambrian Explosion