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Biology 3466B Study Guide - Final Guide: Phanerozoic, Cambrian Explosion, Multicellular Organism

Course Code
BIOL 3466B
Yolanda Morbey
Study Guide

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Macroevolutionary Patterns Ch. 2 & 18 pg. 689-717 / 46-48 / 61-65
How Organic Remains Fossilize
Fossils are traces left by organisms of the past… There are
4 general categories of formation:
1. Compression:
Organic material buried in sediment before
decomposition leaving an impression in material
below, from weight of the sediment.
2. Cast & Model:
Remains decay after being buried in sediment.
Molds unfilled spaces
Cast filled with new material and hardened into
These fossils preserve info about external and
internal surfaces
3. Permineralized:
Structures buried in sediment and dissolved
materials precipitate into the cell.
These fossils preserve internal structure detail
4. Unaltered Remains:
Preserved in environments that discourage loss
from weathering.
These fossils represent a small fraction of the
fossil record, found in peat bogs, permafrost… etc
The fossilization process requires:
1. Durability
2. Burial Water saturated sediments
3. Lack of oxygen
Strengths and Weaknesses of Fossil Record:
Fossilization results in 3 types of sampling bias:
1. Geographic Propensity of fossils to come from
lowland and marine habitats
2. Taxonomic Marine organisms dominate fossil
record but make up 10% of extant species
3. Temporal Earth’s crust is being recycled, so old
rocks are rarer than new. States that the ability to
sample life forms should decline with time.
Life Through Time:
Geological time scale is a hierarchy divided into eons,
eras, periods, epochs and stages.
Radioisotopes and accurate dating techniques allowed
absolute time intervals to be assigned.
Phanerozoic era beings with the Cambrian Explosion and
ends in the present.
3 Component Eras:
1. Paleozoic (Ancient Life):
Begins with radiation of animals, ends with mass
extinction at the end of the Permian.
2. Mesozoic (Middle Life):
“Age of Reptiles” beginning at the end of the
Permian extinction and ends at the KT boundary
with the extinction of the dinosaurs
3. Cenozoic (Recent Life):
“Age of Mammals” consisting of Tertiary Period
(5 epochs) and Quaternary Period (2 epochs)
Almost all animal phyla currently recognized appeared in
fossils ~40 MYA during the Cambrian Period.
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Macroevolutionary Patterns Ch. 2 & 18 pg. 689-717 / 46-48 / 61-65
Ediacaran Fauna
First evidence of animals in fossils from these fauna were
places around the end of the Proterozoic era (early life)
Most are impression/compression fossil types without
shells or hard parts
Generally small in size and simple morphologically.
Have asymmetrical or radial symmetry.
Fossilized embryos support hypothesis that bilaterians
evolved pre-Cambrian, coming from the Doushantou
In Doushantou rocks, phosphate minerals replaces the
soft tissue leaving fine anatomical details.
Some Ediacaran specimen qualifying as fossils are actually
“Trace Fossils” … remnants of burrows, fecal pellets,
animal tracks or other traces.
Burgess Shale Fauna:
Variety of large, complex and bilaterally symmetric forms.
Most species rich lineages of present day animals found.
Primarily compression/impression fossils with great detail
but little overlap with Ediacaran Fauna.
Many fossils referred to as Problematica because they
represent unique phyla that under further study were
close relatives of living phyla.
Number of phyla existant during the Cambrian is now
recognized as an observed diversity today.
Burgess Shale Fauna consist of major morphological
innovations including large body size, segmented parts,
limbs, antennae, shells, external skeletons, etc.
Earliest members of all major animal lineages were found
in this fossil record at the same time in geographically
distant areas.
Phylogeny and Morphology
Lineages found at the base of the tree (Fig 18.12, 699)
predominate in the Ediacaran Fauna.
More heavily derived groups were found in the Burgess
Shale Fauna.
Diploblasts / Triploblasts:
Cnidaria/Ctenophora are Diploblasts, 2 embryonic tissue
types. Remaining animals are Triploblasts.
Tissue types in Diploblasts:
1. Ectoderm, Produce adult skin and nervous system
2. Endoderm, Produce gut and associated organs
Triploblasts have a unique “Mesoderm” which develop
into gonads, heart, muscle, connective tissues and blood.
The origin of diplo/triploblastsa re important because
they made it possible for muscle-lined, fluid-filled cavities
to evolve.
Animals evolved 2 basic methods for producing a
multicellular body with 3 embryonic tissue types.
Bilaterians consist of proto/deuterosomes that differ in
how they undergo gastrulation; a mass movement of
cells that rearranges the embryonic cells after cleavage,
defining the three embryonic tissue types.
Protosomes gastrulation forms the mouth first,
Deuterosomes forms the anal region first.
Lophotrochzoans / Ecdysozoans:
Protosomes consist of 2 major groups.
Ecdysozoans are molting animals whereas
lophotrochzoans have a lophophore, a feeding structure
They’re both evolutionary innovations that appeared in
the Cambrian Explosion represented by the Burgess Shale
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