What was occurring, in terms of life, 700-540 mya?
-Origin of metazoa
-O2 levels surpass 10%
What kind of life dominated earth for majority of its history?
Oxygen levels have played a major role in the evolution of life on earth. What has it impacted?
Evolutionary process was greatly accelerated
-more energy from oxidative metabolism
-faster growth and reproduction
-more diversity from sexual reproduction
What evolutionary developments have occurred at which oxygen levels?
(Percentages are a percent of present O2 levels)
2.5% - Eukaryotic Cells
4.5% - Origin of sexuality
8.0% - Metazoans
15% - Exoskeletons
35% - First vertebrates
When was the ediacaran period? What occurred during this period?
-first animal fossils (no exoskeleton - soft body animal)
When was the cambrian period? What occurred during this period?
-exoskeleton animals - evolved into hard body animals
Transitioning from the Neoproterozoic Era to the Paleozoic era (edicarian period to the cambrian period), many changes occurred, what were they?
542 mya over a period of 100 my
-soft bodies (imprints) to hard bodies (fossils)
-collagen synthesis allowed hard parts
-O2 below 5% to O2 above 5%
-100's of animal phyla to 34 animal phyla
What global mass extinction events have occurred?
6 big ones
-450-440 mya, 375-360 mya
-End of Permian period, 252 mya, the worst 96% of species killed, set back mammals and ended trilobites
-End of Cretaceous period (K-T boundary) 66 mya, 75% of species, killed dinosaurs
-10,000 ya-present, holocene extinction All 34 animal phyla survived
What were the causes of earlier extinctions?
-Earth icing over
-Plate tectonics causing massive volcanic eruptions
How have Marine animals been affected by mass extinction events?
Largely unaffected except the Permian extinction killed off large numbers of marine species
What animals were killed off by the meteor strike 66 mya?
large animals died, smaller animals were able to shield themselves underground
What is the Holocene extinction?
10,000 ya to Present
-Man killing off animals at higher rate than ever
What is the summary of animal life on earth?
-34 animal phyla
-all evolved from common protist ancestor
-all evolved in Ediacaran/Cambrian (600-500 mya)
-all survived since Cambrian (500 mya)
-no new phyla have evolved since cambrian
-lots of families and many classes went extinct during mass extinction events
What phyla are we studying?
2. Cnidaria and Cnetophora
What is the colonial flagellate hypothesis and what are its steps?
Explanation of the common origin of Metazoa (animals) from protists
1. start with unicellular flagellated protist
2. multiple flagellates make aggregate
3. aggregate form hollow sphere
4. specialized reproductive cells form out of some protists
5. cells begin to fold to make tissues
What are the steps in the common developmental sequence of all animals?
1. Gamete formation
What occurs during gamete formation?
-gametes are produced in
testes - spermatogenesis
in ovaries - oogenesis
What provides nourishment to the sperm during spermatogenesis?
the sertoli cell
What are the parts of the sperm?
When does meiosis ii occur during oogenesis?
after the secondary oocyte has been fertilized
What is ylk for in an egg?
yolk supports embryo through development and different animals have different amounts of yolk
What occurs during Fertilization?
Contact and recognition between egg and sperm
-Polyspermy prevention with fast block and fertilization membrane
-Sperm and egg membranes fuse
-sperm tail disintegrates
What occurs during Cleavage?
Repeated divisions, converting single large cell, zygote, into many smaller cells called blastomeres
What are Isolecithal eggs?
Holoblastic cleavage with equal distribution of yolk because of same size blastomeres
What are the the 2 major holoblastic patterns of cleavage?
Radial Holoblastic Cleavage
Spiral Holoblastic Cleavage
-close together, mosaic/determinate=protostomes
What is the blastula formation during cleavage?
Zygote divided into 100's of cells, which move to form hollow sphere called Blastula.
-The fluid filled cavity inside sphere is called blastocoel.
-The layer of cells of outside of blastula is the blastoderm, 1 layer of germ cells
What is Gastrulation?
Converts spherical blastula into a 2 or 3 layered embryo
How is the second germ layer formed during gastrulation?
One pole of blastula invaginates.
-the new internal cavity is the archenteron
-the opening to the archenteron is the blastopore
What are the two possible outcomes of the blastopore during gastrulation?
-blastopore becomes mouth
-spiral, mosaic cleavage
-blastopore becomes anus
-radial, indeterminate cleavage
What are the two germ layers formed during gastrulation?
-original germ layer of blastula
-2nd germ layer formed after invagination