Gaps in the Fossil Record

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Transcript Gaps in the Fossil Record

Gaps in the Fossil Record
Fossilization is rare
The fossil record is biased toward organism's displaying hard parts.
Time/location biases:
The mechanism of fossilization tend to occur nonrandomly about the
Fossilization in one area (or time) may be more likely than in other
areas or at different times.
Fossilization thus is biased towards individuals who live in
environments in which fossilization is more likely (e.g., not in tropical
rain forests).
Tar Pits
• Tar pits form when crude oil
seeps to the surface through
fissures in the Earth's crust; the
light fraction of the oil
evaporates, leaving behind the
heavy tar, or asphalt, in sticky
La Brea Tar Pits of Los Angeles
• In today's ecosystems herbivores are much more abundant than
carnivores. It is therefore curious that at La Brea about 90% of the
mammal fossils found represent carnivores. Most of the bird fossils
are also predators or scavengers, including vultures, condors, eagles,
and giant, extinct, storklike birds known as teratorns.
• Why is this the case?
• Herbivores chased into tar pit – get stuck. Carnivores
then get stuck – wailing brings more carnivores
Vestigial Structures
• Vestigial organs - body structures
which have lost their function and
some of their structure.
• Evolutionists believe they were
useful in ancestral species but are
slowly being phased out in modern
• It is evolutionally correct to get rid
of unneeded baggage.
Common Vestigial Organs and
The wings on flightless birds
Hind Leg Bones in Whales and Snakes
Erector Pili and Body Hair
The Human Tailbone
The Blind Fish Astyanax
The Sexual Organs of Dandelions
Fake Sex in Virgin Whiptail
Lizards (Vestigial Behavior)
Male Breast Tissue and Nipples
The Human Appendix
Evolution of the Whale
• A mammal that
must breathe air
• Front fins have
arm bones
• There are rear
legs imbedded in
the rear fat
• Swim differently
from all fish
Comparative Anatomy
• Comparing Skeletal
Structures –
Human scapula
Gorilla scapula
• 1. Homologous structures - similarity in structure
due to common descent, irrespective of the diverse
uses to which they may be put. E.g. vertebrate
– a. Adaptive radiation - the progressive modification of
a structure to serve many different purposes. It is
attained by mutual fitting of structure, function and
environment. Readily apparent in the forelimbs of
mammals which have been modified by changes of
proportions, fusion of parts, or loss of parts., e.g.
swimming, digging, running, flying
• Analogous structures - similarity in structure
based on adaptation for the same function, not
common descent. E.g. wings have developed
independently in insects, reptiles, birds, and bats.
– a. Analogous structures are the result of morphological
convergence - structures "fitted" for a particular
purpose tend to be similar, regardless of origin. E.g.
body shape and flippers in dolphins, penguins and fish
Embryonic Comparison
The embryonic development of all
vertebrates shows remarkable
similarities as you can see from
these drawings.
The branchial grooves are matched
on the inside by a series of paired
gill pouches. In fishes, the pouches
and grooves eventually meet and
form the gill slits, which allow
water to pass from the pharynx over
the gills and out the body.
In the other vertebrates shown here,
the grooves and pouches disappear.
In humans, the chief trace of their
existenceis the eustacian tube and
the auditory canal.
Phylogenic Tree
Charles Darwin
• At 21 he earned a degree in
• He then served as a naturalist
on the HMS Beagle which
traveled around the world for
5 years.
• During this voyage, he made
the observations which later
became his theory of
• Published On the Origin of
Species by Means of Natural
The Galapagos Islands
• An island group near the western coast of Equador in
South America.
• The animals and plants on the islands were similar
but not identical to those on the South American
• Darwin’s Finches – the birds differed from each other
primarily in the shape of their beaks.
The Questions
• Why are the birds on
the islands similar but
not identical to the
birds on the mainland?
• Why do the finches
from different islands
differ from one
• How did the birds
get to the islands?
• What is it about each
island that made the
birds develop
different beaks?
Selective Breeding
6 lbs.
• Selective Breeding – the process by which
humans select particular desirable traits and
breed only the individuals with those trait.
(ie. Tomatoes, flowers, corn, horses, etc.)
• Dogs – What special traits have been bred
into these dogs
Dog Breeding
Golden Retriever
Old English Sheepdog
Alaskan Malamute
Doberman Pinscher
• Darwin concluded that wild animals and
plants could change just as selective
breeding had changed human controlled
species, but that process would take longer
since the variations would be due to chance.
Survival of the Fittest
According to Malthus humans have the potential to
reproduce beyond the capacity of their food
Starvation, disease, and war affect the size of human
The same thing affects animals – starvation, disease
and predators affect he size of populations
• Only the most fit survive to reproduce –
thus contributing more of their genes to the
gene pool.
• Environmental factors are an enormous
stimulus to evolution.
The process by which organisms with the traits which
make it easier to survive survive and reproduce and
thus have greater influence on the gene pool .
• 4 steps
1) Overproduction –the species produces more offspring than will
reach maturity
2) Genetic Variation – some traits increase the chances that an
organism will survive
3) Struggle to Survive- not enough food, predators, environmental
4) Successful Reproduction- the ones with better survival traits
live to reproduce
How does genetic variation
• Sexual reproduction
• Mutation – changes in genes
Insecticide Resistance
Drug Resistant Bacteria
• Antibiotic use
New Species Formation
• Speciation – the process by which two populations
of a particular species become so different they
can no longer interbreed (thus making them
different species).
• 1) Separation – geographic isolation
• 2) Adaptation – environmental conditions change
and each population adapts independent of the
• 3) Division- the organisms become so different
they can no longer interbreed
The Finches of the Galapagos