NOTES: Chapter 25 Fossils, Phylogeny and Systematics

Origin of Earth 4500 History of Life Boundaries between units in the Geologic Time Scale are marked by dramatic biotic change Eras

Phylogeny: the evolutionary history of a species ● Systematics: the study of biological diversity in an evolutionary context ● The fossil record: the ordered array of fossils, within layers, or strata, of sedimentary rock ● Paleontologists: collect and interpret fossils

● A FOSSIL is the remains or evidence of a living thing -bone of an organism or the print of a shell in a rock -burrow or tunnel left by an ancient worm -most common fossils: bones, shells, pollen grains, seeds.

PETRIFICATION is the process by which plant or animal remains are turned into stone over time. The remains are buried, partially dissolved, and filled in with stone or other mineral deposits. A MOLD is an empty space that has the shape of the organism that was once there. A CAST can be thought of as a filled in mold. Mineral deposits can often form casts. Thin objects, such as leaves and feathers, leave IMPRINTS, or impressions, in soft sediments such as mud. When the sediments harden into rock, the imprints are preserved as fossils. Examples of different kinds of fossils

PRESERVATION OF ENTIRE ORGANISMS: It is quite rare for an entire organism to be preserved because the soft parts decay easily. However, there are a few special situations that allow organisms to be preserved whole. FREEZING: This prevents substances from decaying. On rare occasions, extinct species have been found frozen in ice. AMBER: When the resin (sap) from certain evergreen trees hardens, it forms a hard substance called amber. Flies and other insects are sometimes trapped in the sticky resin that flows from trees. When the resin hardens, the insects are preserved perfectly.

TAR PITS: These are large pools of tar. Animals could get trapped in the sticky tar when they went to drink the water that often covered the pits. Other animals came to feed on these animals and then also became trapped. TRACE FOSSILS: These fossils reveal much about an animal’s appearance without showing any part of the animal. They are marks or evidence of animal activities, such as tracks, burrows, wormholes, etc.

The fossil record ● Sedimentary rock: rock formed from sand and mud that once settled on the bottom of seas, lakes, and marshes Methods for Dating Fossils: ● RELATIVE DATING: used to establish the geologic time scale; sequence of species ● ABSOLUTE DATING: radiometric dating; determine exact age using half-lives of radioactive isotopes

Where would you expect to find older fossils and where are the younger fossils? Why?

Relative Dating: ● What is an INDEX FOSSIL?  fossil used to help determine the relative age of the fossils around it  must be easily recognized and must have existed for a short period BUT over wide geographical area.

Radioactive Dating: ● Calculating the ABSOLUTE age of fossils based on the amount of remaining radioactive isotopes it contains. Isotope = atom of an element that has a number of neutrons different from that of other atoms of the same element

Radioactive Dating: ● Certain naturally occurring elements / isotopes are radioactive, and they decay (break down) at predictable rates ● An isotope (the “parent”) loses particles from its nucleus to form a isotope of the new element (the “daughter”) ● The rate of decay is expressed in a “half-life”

Parent Daughter

Half life= the amount of time it takes for ½ of a radioactive element to decay. To determine the age of a fossil: 1) compare the amount of the “parent” isotope to the amount of the “daughter” element 2) knowing the half-life, do the math to calculate the age!

Parent IsotopeDaughterHalf-Life Uranium-238Lead billion years Uranium-235Lead million years Thorium-232Lead billion years Rubidium-87Strontium billion years Potassium-40Argon billion years Samarium-147Neodymium billion years

Radioactive Dating: Example: Carbon 14 ● Used to date material that was once alive ● C-14 is in all plants and animals (C-12 is too, but it does NOT decay!) ● When an organism dies, the amount of C-14 decreases because it is being converted back to N-14 by radioactive decay

● By measuring the amount of C-14 compared to N-14, the time of death can be calculated ● C-14 has a half life of 5,730 years ● Since the half life is considered short, it can only date organisms that have died within the past 50,000-60,000 years

What is the half-life of Potassium-40? How many half-lives will it take for Potassium-40 to decay to 50 g? How long will it take for Potassium-40 to decay to 50 g?

What is the half-life of Potassium-40? 1.2 billion years How many half-lives will it take for Potassium-40 to decay to 50 g? 2 half-lives How long will it take for Potassium-40 to decay to 50g? 2.6 billion yrs.

How is the decay rate of a radioactive substance expressed? Equation: A = A o x (1/2) n A = amount remaining A o = initial amount n = # of half-lives (**to find n, calculate t/T, where t = time, and T = half-life, in the same time units as t), so you can rewrite the above equation as: A = A o x (1/2) t/T

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t 1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. A) How long is three half-lives? B) How many grams of the isotope will still be present at the end of three half-lives?

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t 1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. A) How long is three half-lives? (3 half-lives) x (10 min. / h.l.) = 30 minutes

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t 1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. B) How many grams of the isotope will still be present at the end of three half-lives? 2.00 g x ½ x ½ x ½ =0.25 g

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t 1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. B) How many grams of the isotope will still be present at the end of three half-lives? A = A o x (1/2) n A = (2.00 g) x (1/2) 3 A = 0.25 g

½ Life Example #2: ● Mn-56 has a half-life of 2.6 hr. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 hr?

½ Life Example #2: ● Mn-56 has a half-life of 2.6 hr. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 hr? A = ? n = t / T = 10.4 hr / 2.6 hr A 0 = 1.0 mg n = 4 half-lives A = (1.0 mg) x (1/2) 4 = mg

½ Life Example #3: ● Strontium-90 has a half-life of 29 years. What is the mass of strontium-90 in a 5.0 g sample of the isotope at the end of 87 years?

½ Life Example #3: ● Strontium-90 has a half-life of 29 years. What is the mass of strontium-90 in a 5.0 g sample of the isotope at the end of 87 years? A = ?n = t / T = 87 yrs / 29 yrs A 0 = 5.0 gn = 3 half-lives A = (5.0 g) x (1/2) 3 A = g

BIOGEOGRAPHY: the study of the past and present distribution of species ● Formation of Pangaea m.y.a. (Permian extinction) ● Break-up of Pangaea – 180 m.y.a. (led to extreme cases of geographic isolation!)  EX: Australian marsupials!

Apparent continental drift results from PLATE TECTONICS

Permian mass extinction Extinction of >90% of species Macroevolution & Phylogeny Cretaceous mass extinction Asteroid impacts may have caused mass extinction events

Mass extinctions: ● Permian (250 m.y.a.): 90% of marine animals; Pangaea merges ● Cretaceous (65 m.y.a.): death of dinosaurs, 50% of marine species; low angle comet

Macroevolution & Phylogeny K-T impact event

5 Kingdom classification system in use through the late 1900s

5 Kingdom classification system in use through the late 1900s gave way to Woese’s 3 Domains

5 Kingdom classification system in use through the late 1900s gave way to Woese’s 3 Domains and multiple Kingdoms

“Did King Philip Come Over From Great Spain?”

Linnaeus convinced us to use a hierarchical classification system Darwin provided us with the mechanism by which evolution results in descent with modification ● Taxonomy – naming & classifying organisms ● Systematics – naming & classifying organisms according to their evolutionary relationships ● Phylogenetics – reconstructing the evolutionary relationships among organisms Systematic Phylogenetics

Macroevolution & Phylogeny – hypothesized genealogy traced back to the last common ancestor (i.e., the most recent) through hierarchical, dichotomous branching ● Phylogenetic tree ● Cladistics – the principles that guide the production of phylogenetic trees, a.k.a., cladograms

Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram ● Node – branch point, speciation event

Macroevolution & Phylogeny ● Lineage or clade – an entire branch Phylogenetic tree, phylogeny, or cladogram

Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram ● Lineage or clade – an entire branch

Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram ● Lineage or clade – an entire branch

Macroevolution & Phylogeny A CLADE is a monophyletic group, i.e., an ancestral species and all of its descendents Phylogenetic tree, phylogeny, or cladogram

Macroevolution & Phylogeny A CLADE is a monophyletic group, i.e., an ancestral species and all of its descendents Phylogenetic tree, phylogeny, or cladogram

Macroevolution & Phylogeny A clade is a monophyletic group, i.e., an ancestral species and all of its descendents Phylogenetic tree, phylogeny, or cladogram

Macroevolution & Phylogeny Taxonomic groups often reflect true clades…

Constructing a Cladogram ● Sorting homology vs. analogy... ● Homology: likenesses attributed to common ancestry ● Analogy: likenesses attributed to similar ecological roles and natural selection ● Convergent evolution: species from different evolutionary branches that resemble one another due to similar ecological roles

Cladistic Analysis HOMOLOGIES: Similar characters (e.g., morphological, behavioral, molecular, etc. traits or features) suggest relatedness… Wasps [Hymenoptera]

Cladistic Analysis But, not all similarity derives from common ancestry! CONVERGENT EVOLUTION: can produce superficially similar traits that lack homology with one another

Cladistic Analysis Homologous characters share common ancestry **Lack of similarity among taxa results from DIVERGENCE

Cladistic Analysis Analogous characters do not share common ancestry **Similarity among taxa results from CONVERGENCE

Cladistic Analysis As a general rule, the more homologous characters shared by two species, the more closely they are related Sequences of DNA & RNA (nucleotides) and proteins (amino acids) are used as characters; as a general rule, the more recently two species shared a common ancestor, the more similar their sequences

Cladistic Analysis Each nucleotide can be treated as a character Character changes (mutations) from the ancestral to the derived state include: Substitutions Insertions Deletions …AGCTCTAGG… …AGCTATAGG… …AGCTCTAGG… …AGCTGATCTAGG… …AGCTCTAGG… Mutations

Cladistic Analysis All similar characters Analogies Homologies Shared Primitive Characters (ancestral) Shared Derived Characters (unique to a clade) **The sequence of branching in a cladogram then represents the sequence in which evolutionary novelties (shared derived characters) evolved

Cladistic Analysis Ingroup vs. Outgroup An outgroup helps identify shared ancestral and shared DERIVED CHARACTERS (unique to a clade)