exam 4 ch 18.2 Flashcards
Metazoans (animals) evolve
Tonian & Cryogenian1.0Ga – 635Ma:
Complexity of multicellular life expands; Eumetazoans to chordates.
Ediacaran 635-538.8Ma:
The evolution and radiation of nitrogen-fixing photosynthetic cyanobacteria and resulting changes to the nitrogen cycle in the open oceans led to photosynthesis expanding dramatically also increasing Oxygen levels
850-540Ma NeoProterozoic Oxygenation event (Second Great Oxidation Event):
Weakened planetary greenhouse effect resulting in much of the planet covered by ice
720 to 635Ma Cryogenian (Snowball Earth):
Metazoans have multicellular bodies that form a blastula
during development
800-760Ma Animals (Metazoans) evolve:
Animal embryo at the early stage of development when it is a hollow ball of cells
Blastula:
First fossils of primitive sponges (Porifera)
760Ma Evidence of Metazoans (animals) evolving into sponges:
share gene-chromosome combinations, while chromosomes of sponges and other
animals are arranged in a different manner
Comb jellies (ctenophores) and non-animals
were the first lineage to branch off from the animal tree.
Comb jellies (ctenophores)
Comb jellies (ctenophores) have a high diversity of
synapse
700Ma Phylogeny suggests Animals evolved into ctenophores (comb jellies):
Sponges & Comb jellies (ctenophores) have two germ layers?
the endoderm and ectoderm and undergo gastrulation.
Sponges are predicted to have lost their?
nervous-like cells
Cells on the outside of an embryo migrate inward, reorganizing it into a multilayered structure
Gastrulation:
The ozone layer forms, complexity of multicellular
life expands.
Ediacaran 635Ma – 538.8Ma:
Oxygen reaches high enough levels to form a thin ozone layer capable of protecting life from
harmful wavelengths of UV radiation
600 Ma ozone layer forms:
First likely fossil indicating Fungi colonized the land during the Ediacaran
635Ma Fungi:
Fossils for possible oldest evidence of amoebae in terrestrial habitats
during the Neoproterozoic, coexisting with terrestrial Fungi.
20-635Ma Land colonized:
Land plants (embryophytes) are considered to have
evolved from a branch of green algal ancestors that developed carotenoids, chlorophyll a and b, and ability to store carbohydrates like starch during this time
25 Ma Green algal (streptophytes) ancestor of land plants:
Metazoans evolve a third germ layer
34–604 Ma Eumetazoans evolve:
Organisms that undergo gastrulation and have embryonic tissues organized into 3 germ layers; a mesoderm,
ectoderm, and endoderm.
Eumetazoans:
Outer cell layer.
Ectoderm:
Inner cell layer.
Endoderm:
Middle cell layer – formed from cells migrating inward from other 2 layers
Mesoderm:
Bilaterians evolve from early Eumetazoans to have bilateral symmetry during embryonic development
fossils of Bilaterians:
An extinct group of organisms that dominated the Earth During the Ediacara
Ediacaran biota (Flora & Fauna):
Evolutionary radiation of prehistoric Ediacaran biota as well as an increase
in animal diversity
Avalon explosion, ~575Ma
A rapid increase in the diversity of species in a clade
Evolutionary radiation:
Process where floral and faunal groups are replaced over time
Biotic replacement:
Organisms with mouth and anus openings in
which the anus forms before the mouth during embryonic development
Fossils for Bilaterians evolving into Deuterostomes:
Mouth forms first
Split from Protostomes:
Cells that work together to perform rudimentary spinal cord and vertebrae-like
functions
Notochord:
ossils of bilaterians evolving into chordates: Organisms with a notochord.
