Lesson 8: Evolution Flashcards
Learning objective for lesson 8: Students will understand the basic theory of evolution and understand how to interpret a phylogenetic tree
The theory of evolution was
first conceived by the British naturalist
Charles Darwin. Darwin’s theory explains how new
species come into existence, how organisms
become adapted to their environments, and
why specific groups of organisms share specific
traits.
Heritable means
s that
the trait is part of an organism’s genetic code
and, therefore, either will be, or (depending on
the type of reproduction) has a chance to be,
copied to the organism’s offspring
One source for new
heritable traits is random genetic mutation. In
order for selection to occur on any given trait,
there must be
variation in that trait in a
population
natural environments have limited
resources, and __ for these resources
permits only some organisms to successfully
reproduce before they die.
competition
The theory of evolution combines these four
basic principles of life together:
the differential
success of certain variations of a heritable trait,
because of competition for limited resources,
leads to the change over time (evolution) of
that trait in a population.
While new
traits may be introduced by random mutations,
the determination of which traits are
successfully passed on to later generations is
not random. Instead, it is based on a specific
criterion:
how well each trait improves an
organism’s reproductive success.
The competitive selective process by
which detrimental traits are competitively
discarded and advantageous traits are retained
is called
natural selection
Organisms are grouped together based on their
most recent
shared common ancestors
hadrosaurs, pachycephalosaurs, ceratopsians, ankylosaurs,
and stegosaurs are grouped together, and we call this group the
Ornithischia.
These
ornithischians and the saurischians share a
more recent ancestor with each other than they
do with all other amniotes, and we call this
group
Dinosauria.
all dinosaurs
are classified together in a group because all
dinosaurs evolved from a single species of
amniote tetrapod
A character is
any heritable
trait that can be described and labeled
shared derived character is
a character that is
present in two or more groups and their
common ancestor, but is not present in any
more distantly related groups
A shared derived
character is also called a
synapomorphy.
f ornithischians have a
special bone in the lower jaw that forms a beak,
called the
predentary, and no other dinosaurs
have this special beak bone. Thus, the character
of the predentary was passed on to all
ornithischians from their ancient shared
ancestor and is a synapomorphy
Ouranosaurus is an
iguanodont with a beak and
grinding teeth, hoofed toes, and long processes
on the vertebrae of the back that form a sail.
Spinosaurus has the __ hip
saurischian hip
arrangement where the pubis points forwards
Ouranosaurus has the __hip
ornithischian hip
arrangement where the pubis points
backwards.
Spinosaurus and Ouranosaurus both
have a sail, but we do not consider the sail to be
__, or __,
between Spinosaurus and Ouranosaurus.
synapomorphy, or shared derived character
Spinosaurus has many of the synapomorphies
of __ and __.
saurischians and theropods
Ouranosaurus has many of the synapomorphies
of __ and __.
ornithischians and ornithopods
Therefore,
the most likely evolutionary scenario is that the
sail in Spinosaurus evolved __of the
sail in Ouranosaurus
independently
The evolution of similar traits in
two different lineages is termed
convergent
evolution.
The idea that “all
other things being equal, the simplest answer is
usually the right one” is called
parsimony. Parsimony is also referred to as Occam’s razor. It is simpler to assume that the one character in common between Ouranosaurus and Spinosaurus (the sail) is the result of convergent evolution, than it would be to
assume that the huge number of similarities
between Ouranosaurus and iguanodonts are all
the result of convergence.