Chapter 25 – Phylogeny and Systematics

1. Chapter 25 – Phylogeny and Systematics Taxonomy - classifying organisms Phylon = tribe Geny = genesis Systematics – studying biodiversity in an evolutionary context (involves the se of fossil record) Phylogeny=Evolutionary History of a Species/Genus (branch order, branch length)

2. Fossil record—the order of fossils within layers (strata) of sedimentary rock. (helps determine order of events in history, age of rocks, how environments were in history). Hard parts like bones and shells leave fossils - so record is incomplete.

3. FOSSIL GUESSING GAME

4. How are fossils formed? • Sedimentary rocks form from layers of sand and silt that settle to the bottom of seas and swamps. • As deposits pile up, they compress older sediments below them into rock. • The bodies of dead organisms settle along with the sediments, but only a tiny fraction are preserved as fossils.

5. Sedimentary rocks are made from layers of minerals that settle out of water. • Sand forms sandstone. • Mud forms shale. • When pieces of organisms settle along with the inorganic material, they can be preserved as fossils. Petrified Trees – 190 million years old! Dinosaur footprints – 150 million years old! Leaf with intact chlorophyll – 40 million years old!

6. Summary: Most parts of dead organisms decay quickly, but mineral-rich parts can remain as fossils. ex. shells, teeth, bones Fossils that retain organic (soft) material are rare - a cast is made of the soft parts. Many fossils are imprints left by organisms that have since decayed.

7. Paleontologists can determine relative ages of fossils by looking at what’s found in each layer. youngest oldest

8. They can help to correlate the fossil record from multiple locations + serve as guides to the age of rocks they are found in. Index fossils are fossils that are found at different locations.

11. Relative Dating: The geological time scale consists of eras, periods, and epochs. Date a fossil based on where it is found in a rock strata = relative dating. New eras are marked by a distinct change in the types of fossils found.

13. Absolute dating of fossils is usually done by radiometric dating. Fossils contain isotopes of elements accumulated when they were alive.

14. Absolute Dating - Isotopes Two atoms of the same element that differ in the number of neutrons are called isotopes 99% of carbon atoms have 6 neutrons (12C) 1% of carbon atoms have 7 neutrons (13C) Rarest C isotope, has 8 neutrons (14C) - RADIOACTIVE

15. Isotopes – Carbon Dating 14C N 14C

18. Each isotope has a fixed half-life—the number of year it takes for half of the sample to decay.

19. 14C: 12C = 1/4 of ratio in living animal 1/2 life = 5,600 years Clam is 11,200 years old.

20. Isotopes – Carbon Dating 14C

21. Word of Caution: The fossil record is incomplete, but it gives us a good idea of the organisms living during a particular time of the Earth’s history.

22. As the Earth’s mantle moves, the continents drift. Arrowheads show areas of violent tectonic events.

23. The continents came together 250 million years ago -Pangaea. Pangaea started to split about 180 million years ago.

24. Mass extinctions followed by adaptive radiation of survivors. Permian extinctions—90% of marine animals died --around the time Pangaea formed, many volcanic eruptions (global warming) Cretaceous extinctions—dinosaurs --climate cooled, seas receded, volcanic eruptions, perhaps an asteriod or comet collision (iridium layer)

26. Phylogeny = evolutionary history Phylogenetic trees— show probable evolutionary relationships

27. Binomial classification—genus and species (Linneaus System) (Domain) Kingdom Phylum Class Order Family Genus Species Taxonomic unit/ Taxa

28. Cladogram A phylogenetic diagram - cladogram

29. Classification parallels phylogeny.

30. Monophyletic—includes most recent common ancestor and all its descendents Polyphyletic—members come from 2 or more ancestors; does not include the most recent common ancestor Paraphyletic— includes the most recent ancestor, but not all its descendents

31. Homology—likeness from shared ancestry; ex. forelimbs of mammals Analogy—likeness due to convergent evolution; ex. wings of birds and insects In developing phylogenetic trees, we should use only homologies.

32. D a a

33. A cladogram presents the chronological sequence of branching during the evolutionary history of a set of organisms.

34. An outgroup is a species that is kind of related to the species being studied, but not as much as the other species studied are related to each other.

36. Cladistic analysis --classifies organisms according to the order that branches arose along a phylogenetic tree Each branch point is defined by homologies that are unique to the species on that branch.

37. Molecular Biology Comparisons • Amino acid sequence • DNA and RNA sequences • DNA-DNA hybridization—extent of H-bonding between DNA of 2 different species • restriction maps • comparison of restriction fragments • DNA/RNA sequencing Molecular Clocks – UCCP CD

38. Classification based on protein and DNA similarities