- Paleozoic Era ( Cambrian, Ordovician, Silurian, Devonian,
Carboniferous, Permian periods)
- Mesozoic Era (Triassic, Jurassic, Cretaceous)
- Cenozoic Era (Paleogene, Neogene)
CAMBRIAN AND ORDOVICIAN PERIODS
Ediacaran Period – Precedes the Cambrian period. The animal fossil record from this period is
sparse, possibly because animals had yet to evolve hard shells, which make for easier
fossilization. The Ediacaran biota include the oldest definite multicellular organisms with tissues,
and the most common types resemble segmented worms, fronds, disks, or immobile bags.
Cambrian Period –
• The Cambrian is the first geological period of the Paleozoic Era, lasting from 542 to
488.3 Mya. It is succeeded by the Ordovician. The Cambrian marked a steep change in
the diversity and composition of Earth's biosphere. The incumbent Ediacaran biota
suffered a mass extinction at the base of the period, which corresponds to an increase in
the abundance and complexity of burrowing behaviour. This behaviour had a profound
and irreversible effect on the substrate which transformed the seabed ecosystems. Before
Cambrian, the sea floor was covered by microbial mats. By the end of the period,
burrowing animals had destroyed the mats through bioturbation, and gradually turned the
seabeds into what they are today. As a consequence, many of those organisms who were
dependent on the mats went extinct, while the other ses adapted to the changed
environment who now offered new ecological niches.
• There are also suggestions that some Cambrian organisms ventured onto land, producing
the trace fossils Protichnites and Climactichnites.
• In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating
organisms were rare, with the majority living on or close to the sea floor;and
mineralizing animals were rarer than in future periods, in part due to the unfavourable
ocean chemistry. 
Cambrian burrowers – Aset of organisms that either pushed through the sand/dirt in the
ground or ingested it and released it from the back end in order to move forward (Ex.marine
worms, priapulids, and anychophora
Cambrian swimmers – the first free-swimming animals appear. swim by means of lateral lobes
similar to today’s cattle fish.
Cambrian Explosion – the sudden appearance of tons of new animals during the Cambrian
eon as seen from Cambrian rocks. Although life may have existed before this, the only records we have are the ones in fossils and fossilization only started occurring at this time. At the time,
there was no competition or limitation in resources therefore many species survived.
The Ordovician Period started at a major extinction event called the Cambrian–Ordovician
For most of the Late Ordovician, life continued to flourish, but at and near the end of the period
there were mass-extinction events that seriously affected planktonic forms like conodonts,
graptolites, and some groups of trilobites. Brachiopods, bryozoans and echinoderms were also
heavily affected, and the endocerid cephalopods died out completely, except for possible rare
The Ordovician–Silurian Extinction Events may have been caused by an ice age that occurred
at the end of the Ordovician period as the end of the Late Ordovician was one of the coldest
times in the last 600 million years of earth history.
End Ordovician Extinction - Basic mechanism: climate changes from very warm to very cold
and back to very warm. Changes in ocean circulation were the results of the climate changes.
Both benthic (ocean bottom) and pelagic fauna were faced with conditions they were unable to
cope with.More than 100 invertebrate families becam extinct in the End–Ordovician extinction
event, and a total of almost half the genera. The brachiopods and bryozoans were decimated,
along with many of the trilobite, conodont and graptolite families.
Slushball earth hypothesis - contends that Earth was not completely frozen over during
periods of extreme glaciation in Precambrian times. Rather, in addition to massive ice sheets
covering the continents, parts of the planet (especially ocean areas near the Equator) could
have been draped only by a thin, watery layer of ice amid areas of open sea. Under this
scenario, photosynthetic organisms in low-ice or ice-free regions could continue to capture
sunlight efficiently and survive long periods of extreme cold.
Snowball earth - hypothesis posits that the Earth's surface became entirely or nearly entirely
frozen at least once, some time earlier than 650 Ma (million years ago). Proponents of the
hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial
origin at tropical paleolatitudes, and other otherwise enigmatic features in the geological record.
Burgess Shales Fossils – A shale is a sedimentary rock that has layers that are easily split.
These were found in abundance at the Yoho National Park in British Columbia, that had
preserved soft-bodied organisms from the Cambrian period in great details.
Doushantuo fossils – microfossils that look like embryos of multicellular organisms.
Doushantuo fossils are all aquatic, microscopic, and preserved to a great degree of detail. The
latter two characteristics mean that the structure of the organisms that made them can be studied at the cellular level, and considerable insight has been gained into the embryonic and
larval stages of many early creatures. One contentious claim is that many of the fossils show
signs of bilateral symmetry, a common feature in many modern-day animals which is usually
assumed to have evolved later, during the Cambrian Explosion.
Ediacaran fossils - consisted of enigmatic tubular and frond-shaped, mostly sessile organisms
which lived during the Ediacaran Period. Trace fossils of these organisms have been found
worldwide, and represent the earliest known complex multicellular organisms. They appear
immediately prior to the Cambrian.
algal mat is a layer of usually filamentous algae on marine or fresh water soft bottoms. It may
be considered one of many types of microbial mats. Algae and cyanobacteria are ubiquitous,
often forming within the water column and settling to the bottom. In shallow environments, they
are often dessiccated and revived with the next introduction of water and sunlight. Stromatolites
can form in this way (see Shark Bay for a modern example). Any puddle of water can start the
process - sunlight initiates the process and photosynthesis soon creates a green layer within the
puddle. The puddle can dry up and leave a thin layer of 'algal' mat and even leave mudcracks
behind. Cyclicity involves the repeated process of wetting (rain), algal production, and redrying
of the new deposit. This results in layer upon layer of algal mats and intervening thin layers of
Reef - a rock, sandbar, or other feature lying beneath the surface of the water. Many reefs
result from abiotic processes—deposition of sand, wave erosion planning down rock outcrops,
and other natural processes—but the best-known reefs are the coral reefs of tropical waters
developed through biotic processes dominated by corals and calcareous algae. Created by
Predators – organism that is hunting
Carnivore - An animal that primarily eats other animals.
Herbivore - An animal that obtains energy and nutrients primarily by eating plants.
Omnivore - An animal that feeds at several trophic levels, consuming plants, animals, and other
sources of organic matter.
Hermaphrodite - The mechanism in which both mature egg-producing and mature sperm-
producing tissue are present in the same individual.
Homeotic genes control the development of the embryo for where the head, middle, and back
Hox genes - a type of homeotic genes that control where each parts of the body grow out of
(legs out of back end, eyes on the head)
The genome decides what gets made (For example the fruitfly will have the genome for fruitfly
legs not human legs) Homeotic mutants - A mutant in which one body part, organ or tissue, is transformed into
another part normally associated with another segment.
Transcription factors – in eukaryotes these fold the genetic information together so that the
right thing is expressed. At anterior end there will be a high concentration of the gene that
expresses the end as anterior, at the posterior same will happen. Down the length of the embryo
cells receive a different amount of gene concentration. When you sequence transcription
factors you find them in other animals. All transcription factors are in all the animals (universal)
just expressed in different amounts. Transcription factors sequences in animals, you will see a
pattern. A set of transcription factors work on the genome of all animals to create the organized
pattern we see today.
Animals and fungi share a common ancestor, and homeotic genes are found in both as well as
Amoebocyte - is a mobile cell (moving like an amoeba) in the body of invertebrates such as
echinoderms, mollusks or sponges. They move by pseudopodia. Similarly to some of the white
blood cells of vertebrates, in many species amebocytes are found in the blood or body fluid and
play a role in the defense of the organism against pathogens. Depending on the species, it may
also digest and distribute food, dispose of wastes, form skeletal fibers, fight infections, and
change into other cell types. Also known as explosive cells.
Archeocyte – see amoebocytes
Ectoparasites - A parasite that lives on the exterior of its host organism. Ex. lice
Endoparasite - A parasite that lives in the internal organs of its host organism. Ex.tapeworm
Embryonic tissue has 3 layers:
1. Endoderm – the innermost layer. eventually develops into the lining of the gut (digestive
system) and, in some animals, respiratory organs.
2. Mesoderm - forms the muscles of the body wall and most other structures between the
gut and the external covering.
3. Ectoderm - The outer-most layer. forms the external covering and nervous system
Some animals have a diploblastic body plan that includes only two embryonic layers,
endoderm and ectoderm, but most are triploblastic, having all three germ layers.
Mesoderm formation - The formation of a mesoderm led to the development of a coelom.
Organs formed inside a coelom can freely move, grow, and develop independently of the body
wall while fluid cushions and protects them from shocks.The mesoderm forms: skeletal muscle,
the skeleton, the dermis of skin, connective tissue, the urogenital system, the heart, blood (lymph
cells), the kidney, and the spleen. Coelom – a fluid filled cavity that cushions and protects the internal organs and allows them to
move independently. The coelom also helps with Surface Area to Volume ratio in an animal
because large internal organs can be compressed into the coelom which provides nutrients for
them, instead of relying on a greater surface area of an organism to diffuse the nutrients to the
Acoelomate - animals (a = without; koiloma = cavity), such as
flatworms (phylum Platyhelminthes), do not have a body cavity
that separates the gut from the muscles of the body wall.
instead, a mass of cells, derived largely from mesoderm, packs
the region between the gut and the body wall
Pseudocoelomate animals (pseudo = false), including the
roundworms (phylum Nematoda) and wheel animals (phylum
Rotifera), have a pseudocoelom, a fluid-filled space between
the gut and the muscles of the body wall that has no
mesodermal lining around the endoderm. The muscles of the
body wall, derived from mesoderm, form the outer lining of the
pseudocoelom, and its inner lining is the gut, which has no
muscles. Internal organs lie within the pseudocoelom and are
bathed by its fluid.
Coelomate animals have a coelom, a fluid-filled body cavity
completely lined by mesoderm. In vertebrates, this lining takes
the form of the peritoneum, a thin tissue derived from
mesoderm. The inner and outer layers of the peritoneum
connect, forming mesenteries, membranes that surround the
internal organs and suspend them within the coelom.
Coelomates/Pseudocelomates = “tube within a tube”
Assymetric body plan – irregular body shape.
Radial symmetry - body parts are arranged regularly around a central axis, like the spokes on
a wheel. Thus, any cut down the long axis of a radially symmetrical animal divides it into
matching halves. Example. Cnidaria (hydras, jellyfishes, and sea anemones) and Ctenophora
Bilateral symmetry - they have left and right sides that are mirror images of each other on
either side of the body's midline. Bilaterally symmetrical animals also have front (anterior) and
back (posterior) ends, as well as upper (dorsal) and lower (ventral) surfaces
Hydrostatic skeleton - A structure consisting of muscles and fluid that, by themselves, provide
support for the animal or part of the animal; no rigid support, such as a bone, is involved. Cephalization – the development of an anterior head where sensory organs and nerve tissue
Schizocoelom – annelids, molluscs,
Entercoelom – sea urchins and starfish
All Bilateral Animals are divided into
Deuterostomes or Protostomes:
Developmen Protostom Deuterostom
t Trait es es
Cleavage Spiral Radial
Cell Determinant Indeterminant
Mesoderm Near Outpocketing
Fate of Mouth Anus
Coelom Schizocoely Entercoely
Deuterostomes - A division of the Bilateria
in which blastopore forms the anus during
development and the mouth appears later (includes Echinodermata and Chordata). At first glance, deuterostome animals—such as
echinoderms, chordates, and hemichordates, let alone Xenoturbella—are not obviously similar,
reflecting modifications of their bodies that mask underlying developmental and genetic
Protostomes - A division of the Bilateria in which the blastopore forms the mouth during
development of the embryo and the anus appears later.
Blastopore - As development proceeds, an opening on the surface of the embryo eventually
connects the developing gut, called the archenteron, to the outside environment. The opening at
one end of the archenteron in the gastrula that gives rise to the mouth in protostomes and the
anus in deuterostomes.
Gastrula - The developmental stage resulting when the cells of the blastula migrate and divide
once cleavage is complete.
Blastula - The hollow ball of cells that is the result of cleavage divisions in an early embryo.
Cleavage - a series of cell divisions an egg undergoes shortly after fertilization
Spiral cleavage - The first two cell divisions divide a zygote as you might slice an apple, cutting
it into four wedges from top to bottom. In some animals, subsequent cell divisions occur at
oblique angles to the vertical axis of the embryo, ultimately producing a mass in which each cell
at the top of the embryo lies in the groove between the pair of cells below it
Radial cleavage - the third cell division is perpendicular to the vertical axis of the embryo,
cutting each of the four cells near its midsection. The fourth cell division is vertical, producing a
mass of cells that are stacked directly above and below one another
Deposit Feeders - organism that lives on its food source, eating its way through the food
source. Ex. Gastropods who eat organic material and sediments.
Detrivores, also known as detritophages or detritus feeders or detritus eaters or saprophages,
are heterotrophs that obtain nutrients by consuming detritus (decomposing organic matter). By 
doing so, they contribute to decomposition and the nutrient cycles.
Filter feeders - (a sub-group of suspension feeders) are animals that feed by straining
suspended matter and food particles from water, typically by passing the water over a
specialized filtering structure. Some animals that use this method of feeding are clams, krill,
sponges, some fish and sharks, and baleen whales. Filter feeders can play an important role in
Mass feeders – organisms that use any parts of their body to cut and kill their prey. Ex.
Humans tigers falcons sharks
Suspension feeders – filter-feeders SPONGES
Of the phylum Porifera (characterized by cell groups that are independent of each oth