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Introduction
Biology 351
Comparative Anatomy
Dr. Tony Serino
Misericordia Univ.
Comparative Anatomy
• The study of morphology between species to
understand evolutionary trends.
• Evolutionary Morphology
• Uses both living and extinct species
• Can be combined with Comparative
Physiology
Darwin’s Theory
(1859)
Darwin’s Observations
• All species over produce
• Most populations are
normally stable
• Natural resources are limited
Darwin’s Observations
Individuals of a
population vary
from one another
Much of this variation
is inheritable
Darwin’s Inferences
• Over reproduction leads to a struggle
(competition) for resources and survival
with only a fraction surviving to reproduce
successfully
• Those who are better fitted (adapted) to
their environment more often succeed to
survive and reproduce
• This results in the population changing to
increase the frequency of those alleles
which increase the survival rate.
Evolution- Descent with modification by
means of natural selection to better adapt to
their environment
• Differential success in the survival and
reproduction of individuals in a population
changes the frequency of alleles in the gene
pool such that the population adapts to its
environment (increases its fitness)
Descent with Modification
Evidence of Evolution
• Biogeography –
study of the
geographic
distribution of
populations
Evidence of Evolution
• Comparative Anatomy & Physiology –
study of common characteristics,
processes, and/or behaviors
•Homologous
Structures
•Vestigial
organs
Evidence of Evolution
• Fossil Record
Fossils
Evidence of Evolution
• Comparative Embryology –study of animal
development
Evidence of Evolution
• Molecular Biology study of important
molecules in living
cells; degree of
conservation of
molecular structure
indicates relatedness
between species
Microevolution
• Generational changes in allele
frequency in a population over
time.
• May lead to formation of new
species
Darwin in 1874
Mechanisms for Microevolution
• Genetic drift –random changes in small gene pool
survival based on random chance (seeds happen to
fall on fertile ground)
Genetic Drift: Founder Effect
• Small random number of individuals move to a new location
• Chance alone dictates what alleles moved to start new
population
• Ex. Galapagos finches – a storm blew a completely random
number of birds from the main land to the islands.
Genetic Drift: Bottleneck Effect
• Large environmental change that randomly kills off
most of the population
Other Mechanisms for
Microevolution
• Gene flow –change in gene pool
frequencies due to migration of
individuals between populations
• Mutation –change in gene structure
changes allele frequency (only mechanism
that can create new alleles)
• Non-random mating –changes allele
frequency due to choices in mating; ex.
Inbreeding, assortative mating, sexual
selection
• Natural Selection –change in allele that
adapts the population better to its
environment
Types of Natural Selection
Speciation –generation of new species
• Two types:
– Anagenesis –one species
evolves into another
– Cladogenesis –one species
evolves into several new
species (like, in adaptive
radiations); forms a lineage
or clade
Cladogenesis
• Requires reproductive
isolation to occur
– Behavior, Temporal, Mechanical,
Gametic, etc.
Main modes for reprod. isolation:
• Allopatry –geographical
isolation leading to
reproductive isolation
• Sympatry –reproductive
isolation arising within the
parent’s population habitat
Grand Canyon Ground Squirrels
The formation of the Grand Canyon 10,000 ya
led to allopatric isolation of the rims squirrel
populations eventually forming new species
Macroevolution –refers to large scale
patterns, trends and rates of change in groups
of species over time
• Two theories on rate of evolution:
Gradualism and Punctuated Equilibrium
• Related concepts:
– Pre-adaptation –pre-existing structures used to
fulfill new role (biological role vs. function)
• Ex: feathers (as insulator and later flight),
• Some fish fins  tetrapod limbs for walking
Heterochrony –evolutionary changes in
the timing or rate of developmental growth
Tree dwelling salamanders have
shorter more webbed feet; growth
of the foot ends sooner.
Heterochrony
–change in timing of developmental development; may result in:
Allometric Growth –differential
growth of body regions results in the adults
shape
Heterochrony
–change in timing of sexual development; may result in:
Paedomorphosis (Neoteny)
Retention of juvenile characteristics in the adult
Plate
tectonics
Continental Drift
Adaptive Radiations
Geological
Time Scale
Geologic
Timeline of
Earth
*mya –
millions of
years ago
Era
Period
Time (mya)*
Quaternary
Cenozoic
(Age of
Mammals)
Important Events
Historical time; Ice age, Humans appear
1.8
Tertiary
Mammals, Teleosts, Birds, Insects and angiosperms undergo
major radiation
65
Cretaceous
144
Mesozoic
(Age of
Dinosaurs)
Jurassic
Cretaceous extinction (includes dinosaurs), angiosperms
appear
Dinosaur and gymnosperms dominate
206
Triassic
Major radiation of dinosaurs and gymnosperms; extinction
near end of period of many early dinosaur groups
245
Permian
Permian Mass Extinction (half of all life forms become
extinct); radiation of reptiles
290
Paleozoic
(Age of Fish)
Carboniferous
(Pennsylvanian
and Mississipian
periods)
(Age of
Amphibians)
Devonian
(Age of Teleosts)
Amphibians and vascular plants dominate, first reptiles and
seed plants appear
363
Radiation of bony fish, first amphibians and insects appear;
extinction of many jawless fish
409
Silurian
Diversity of jawless fish and early vascular plants; first
jawed fish appear
439
Ordovician
510
Marine alga abundant, colonization of land by arthropods
and plants
543
Radiation of most modern animal phyla (Cambrian
Explosion)
Cambrian
Precambrian
Formation of Earth and its biosphere, Life begins
(Archaebacteria) about 3800 mya; Oxygen begins to
dominate atmosphere about 2700 mya; 600 mya soft-bodied
invertebrates and algae thrive (Pre-cambrium Explosion)
4600
Types of Macroevolution:
Convergent Evolution
Types of Macroevolution:
Co-evolution
-ants and acacia tree
-lions, prey, and scavengers
Types of Macroevolution:
Divergent Evolution
Phylogeny –course of evolution
• Dendrograms –branching “tree” diagrams depicting
possible phylogeny usually by assorting organism by their
similarities or common features
• Systematics –study of biological diversity in an
evolutionary context; links groups together is some logical
pattern
– Traditional systematics –places organisms in same
taxon (group) if they share homologous structures
– Phylogenetic systematics (cladistics) –places organisms
in the same clade (lineage) (all the organisms in that
lineage plus their common ancestor)
Example of Lungfish –traditional may put with other organisms with lung;
Cladistics would group only with fish
Hierarchal
Classification
-usually only group organisms
together by morphological structures
Binomial system for naming species
Cladistics –uses multiple characters to
group organisms
-may include morphology, fossils, molecular data, etc.
Cladograms allow us to explore relationships easily, but
can lead to redundant terminology
Cladistic Relationships
Monophyletic taxons include an ancestor and all of its descendants
Paraphyletic taxons include a common ancestor but only some (not all)
of its descendents (an artificial grouping)
Polyphyletic taxons place animals together for non-homologous
similarities (an artificial grouping)
Other Important Anatomical Concepts
Similarity Comparisons
• Homology –structures in
two different species are
homologous if they can be
traced back to a feature in a
common ancestor
• Analogy –structures which
share a common function
• Homoplasy –structures
with similar appearance
Note: primitive vs. derived
Symmetry
Body Planes
Anatomical Directions
Segmentation (metamerism)