Chapter 5: Macroevolution and the tree of life
Phylogeny = pattern of evolution that is often represented as a branching tree diagram. The tree of
life is a single great evolutionary tree that links all species living and extinct back to a single
hypothetical species 3500 million years ago in the Precambrian.
Natural selection:
1. Nearly all species produce far more young than can survive to adulthood
2. The young that survive tend to be those best adapted to survive (larger at birth, faster
growing, nosier in the nest, faster to escape predation, less disease etc.)
3. Characters are inherited from parent to offspring, so the characters that ensure survival will
tend to be passed on (size, aggressiveness, speed, freedom from disease, etc)
4. These survival characters will increase generation by generation
Biological species concept: a species consists of all individuals that naturally breed together and that
produce viable offspring. Gene pool = the overall array of genetic material in all the individuals with
the population. Gene flow = the occasional wandering of individuals from one area to another which
interbreed with members of neighbouring populations.
Speciation = the process of splitting of a population to form two species. Populations could be split
and gene flow prevented by a barrier, such as a new strip of water. The separated populations would
then diverge because: each population would start a different gene pool and selection pressures
would be different on either side of the barrier. This can cause a divergence in genotype (genetics)
and phenotype (appearance).
Shape of a phylogeny
1. Phyletic gradualism model: sloping branching, most evolution takes place within
species lineages and speciation events no special additional amount of evolution
2. Punctuated equilibrium model: almost no evolution takes place within species
lineage and evolution is concentrated in speciation events that coincide with major
sideway shifts.
Features that are needed to construct evolution:
1. Abundant specimens
2. Fossils with living representatives
3. Information on geographic variation, so rapid specification events could be distinguished
from migration in and out of the area
4. Good stratigraphic control: no gaps and good dating
Species selection = a model of evolution could imply a different kind of process that occurred at the
same time as natural selection, so the species level characters differ from the individual level.
Cladistics are used to reconstruct life’s hierarchy. Clades are groups that had a single origin and
include all the descendants of that common ancestor.
- Paraphyletic groups: single common ancestor but do not include descendants
- Polyphyletic: random assemblages that arose from more than one ancestor.
- Apomorphies: derived characters that arrised once only in evolution
- Synamorhpies: apomorphies shared by two or more species
Comparing molecules can also be used to reconstruct the tree of life. Time estimation comes from
the concept of the molecular clock. It is used in amino acids and nucleic acids (DNA and RNA). This
can not be used for ancient animals.
, Chapter 16: Fishes and basal tetrapods
Vertebrates : have a backbone with individual vertebrae. Phylum Chordata. The skeleton is made
from bone and cartilage (flexible, gristly tissue). The skeleton can grow with the animals, which lets
them become very large. Two key defining characters are the head and neural crest tissues.
The first vertebrates had no jaws (ostracoderms) and age from the Early Cambrian. In the Late
Cambrian and Ordovician, the commonest vertebrates were the conodonts (protoconodonts,
paraconodonts and euconodonts (complex)) Conodonts lived from the Cambrian to Triassic. Fishes
became common and diverse from the Late Silurian to Devonian.
The basal vertebrates (including conodonts) lacked jaws, they slurped their food. Jaws arose because
the strengthening bars of cartilage or bone between the gill slits. Jaws appeared in Devonian.
In the Devonian, bony fishes also appeared
1. Actinopterygians: with ray-like fish (ancestors of carp to salmon, seahorse and tuna). After
the Devonian, actinopterygians have radiated 3 times.
2. Sarcopterygians: lobe fines that had thick, muscular, limb0like fins. (rare today)
During the Carboniferous, numerous shar-like fishes arose and they were an important marine
predator. A second shark radiation took place in the Triassic and Jurassic. There are now 42 families.
Tetrapods (viervoeters): early bony fishes had both lungs and gills, so the problem for the first
tetrapods was finding support on land. They arose from fishes during the Devonian and moved on
land 390 Ma. They diversified during the Carboniferous and Permian.
Amphibians live in or close to water, they are adapted to the land but still rely on the water for
breeding and water balance. Reptiles made a clear break from the water by producing a cledoic egg
which did not have to be laid in water.
Synapsids (Late Carboniferous and early Permian) were small sized insectivorous and carnivores with
powerful skulls and sharp, fleshpiercing teeth. They are also named pelycosaurs and were ancestors
of the dinosaurs. They radiated in the Therapsida. The transition from synapsid to mammal is marked
by an shift of the jaw joint in the middle ear. Dinosaurs and mammals arose together. The synapsids
gave rise to mammals and the diapsids gave rise to dinosaurs.
Phylogeny = pattern of evolution that is often represented as a branching tree diagram. The tree of
life is a single great evolutionary tree that links all species living and extinct back to a single
hypothetical species 3500 million years ago in the Precambrian.
Natural selection:
1. Nearly all species produce far more young than can survive to adulthood
2. The young that survive tend to be those best adapted to survive (larger at birth, faster
growing, nosier in the nest, faster to escape predation, less disease etc.)
3. Characters are inherited from parent to offspring, so the characters that ensure survival will
tend to be passed on (size, aggressiveness, speed, freedom from disease, etc)
4. These survival characters will increase generation by generation
Biological species concept: a species consists of all individuals that naturally breed together and that
produce viable offspring. Gene pool = the overall array of genetic material in all the individuals with
the population. Gene flow = the occasional wandering of individuals from one area to another which
interbreed with members of neighbouring populations.
Speciation = the process of splitting of a population to form two species. Populations could be split
and gene flow prevented by a barrier, such as a new strip of water. The separated populations would
then diverge because: each population would start a different gene pool and selection pressures
would be different on either side of the barrier. This can cause a divergence in genotype (genetics)
and phenotype (appearance).
Shape of a phylogeny
1. Phyletic gradualism model: sloping branching, most evolution takes place within
species lineages and speciation events no special additional amount of evolution
2. Punctuated equilibrium model: almost no evolution takes place within species
lineage and evolution is concentrated in speciation events that coincide with major
sideway shifts.
Features that are needed to construct evolution:
1. Abundant specimens
2. Fossils with living representatives
3. Information on geographic variation, so rapid specification events could be distinguished
from migration in and out of the area
4. Good stratigraphic control: no gaps and good dating
Species selection = a model of evolution could imply a different kind of process that occurred at the
same time as natural selection, so the species level characters differ from the individual level.
Cladistics are used to reconstruct life’s hierarchy. Clades are groups that had a single origin and
include all the descendants of that common ancestor.
- Paraphyletic groups: single common ancestor but do not include descendants
- Polyphyletic: random assemblages that arose from more than one ancestor.
- Apomorphies: derived characters that arrised once only in evolution
- Synamorhpies: apomorphies shared by two or more species
Comparing molecules can also be used to reconstruct the tree of life. Time estimation comes from
the concept of the molecular clock. It is used in amino acids and nucleic acids (DNA and RNA). This
can not be used for ancient animals.
, Chapter 16: Fishes and basal tetrapods
Vertebrates : have a backbone with individual vertebrae. Phylum Chordata. The skeleton is made
from bone and cartilage (flexible, gristly tissue). The skeleton can grow with the animals, which lets
them become very large. Two key defining characters are the head and neural crest tissues.
The first vertebrates had no jaws (ostracoderms) and age from the Early Cambrian. In the Late
Cambrian and Ordovician, the commonest vertebrates were the conodonts (protoconodonts,
paraconodonts and euconodonts (complex)) Conodonts lived from the Cambrian to Triassic. Fishes
became common and diverse from the Late Silurian to Devonian.
The basal vertebrates (including conodonts) lacked jaws, they slurped their food. Jaws arose because
the strengthening bars of cartilage or bone between the gill slits. Jaws appeared in Devonian.
In the Devonian, bony fishes also appeared
1. Actinopterygians: with ray-like fish (ancestors of carp to salmon, seahorse and tuna). After
the Devonian, actinopterygians have radiated 3 times.
2. Sarcopterygians: lobe fines that had thick, muscular, limb0like fins. (rare today)
During the Carboniferous, numerous shar-like fishes arose and they were an important marine
predator. A second shark radiation took place in the Triassic and Jurassic. There are now 42 families.
Tetrapods (viervoeters): early bony fishes had both lungs and gills, so the problem for the first
tetrapods was finding support on land. They arose from fishes during the Devonian and moved on
land 390 Ma. They diversified during the Carboniferous and Permian.
Amphibians live in or close to water, they are adapted to the land but still rely on the water for
breeding and water balance. Reptiles made a clear break from the water by producing a cledoic egg
which did not have to be laid in water.
Synapsids (Late Carboniferous and early Permian) were small sized insectivorous and carnivores with
powerful skulls and sharp, fleshpiercing teeth. They are also named pelycosaurs and were ancestors
of the dinosaurs. They radiated in the Therapsida. The transition from synapsid to mammal is marked
by an shift of the jaw joint in the middle ear. Dinosaurs and mammals arose together. The synapsids
gave rise to mammals and the diapsids gave rise to dinosaurs.
