Fossil Record Knowledge Check
a.
Summarize the process by which an organism’s remains become fossilized. What are
some factors that can influence fossil discoveries and our knowledge of the fossil
record? What are some limitations of the fossil record?
Fossilization happens in the soft tissues of an organism decay within layers of sediment. The
hard parts, usually bones, teeth, shells, and exoskeletons, are left behind in that sediment pocket
and then are eventually re-mineralized when water seeps into these cavities and leaves minerals
behind. Fossilization happens in sediment because it protects the organism's remains from
scavenging animals, erosion, weather disturbances, and decay that would occur on the surface.
b.
Describe two macroevolutionary processes. Explain how we can or cannot see them in
the fossil record.
Adaptive Radiation is when extinction frees up an ecological niche, and other organisms will
take those unclaimed resources. This group of organisms diversifies rapidly from their ancestral
species into a multitude of new species. This happens when there's a change in the environment
that causes there to be new resources or an abundance of preexisting resources. A great example
of this is the Darwinian finches on the Galapagos islands adapting to their individual
environments within these respective island ecosystems.
Evolutionary changes can temporarily speed up as natural selection is influenced by how fast an
environment changes and how fast genetic changes appear and spread. "Punctuated Equilibrium"
describes this process of rapid evolution in between periods of slow evolutionary changes.
Because the fossil record is incomplete, it is hard to track and predict these changes accurately,
but there has been proof of this occurring in fossils of sea organisms called bryozoan. One
species of bryozoan appeared about 140 million years ago and remained unchanged for about 40
million years. Suddenly, there was a rapid level of diversification in the fossil record, followed
by another period of stability and no substantial changes in the species.
c.
Compare and contrast two of the different species definitions, be sure to include issues
with identifying species using these two definitions.
Anagenesis is a gradual transition from one species to another by slowly accumulating genetic
changes over time. The gene pool of the ancestral population is eventually replaced by their
interbreeding descendants and is overwritten and made extinct. An example of this is the
peppered moth from a few modules ago, and its color changes as an environmental response.
Cladogenesis is when a parent species splits into two or more distinct species. It can occur after
extinction events, new ecological niches, dramatic environmental changes, etc. An aspect of
Natural Selection. An example of this is seen in the salamanders found within California that
have evolutionary changes due to being separated geographically.
