Fossils & Evolution Chapter 41 Ch. 4—Key concepts Systematics is the study of the kinds (diversity) of organisms and of the evolutionary relationships among them. A goal of systematics is to classify organisms “naturally,” so that the various groups are evolutionarily meaningful. Cladistics is a scientifically testable method for inferring evolutionary relationships on the basis of shared, derived characters.

Fossils & Evolution Chapter 42 Ch. 4—Key terms Taxonomy / systematics Cladistics / cladogram Principle of Parsimony Cladistic classification –Monophyletic grouping –Paraphyletic grouping –Polyphyletic grouping

Fossils & Evolution Chapter 43 Classification Classification is necessary because there are more species than any person can keep track of… Purpose of classification is communication –“Birds” is a convenient and readily understood category for all feathered vertebrates

Fossils & Evolution Chapter 44 Taxonomic categories Taxonomy = the science of classification Linnean taxonomic hierarchy (nested structure of groups within groups): Kingdom Phylum Class Order Family Genus species

Fossils & Evolution Chapter 45 Classification and Evolution Biologic classification should reflect evolutionary relationships –Species with a common ancestor should be grouped into a single genus –Closely related genera should be grouped into a single family

Fossils & Evolution Chapter 46 Systematics If classification is to reflect phylogeny, how do we assess genealogic relationships among species? Systematic approaches –Evolutionary taxonomy –Cladistics

Fossils & Evolution Chapter 47 Evolutionary taxonomy “Intuitive” taxonomy based on the views of “authorities” Genealogic relationships inferred on the basis of –Morphology –Stratigraphy –Biogeography Pitfall: often not scientifically testable

Fossils & Evolution Chapter 48 Cladistics Cladistics is a method of inferring genealogy and classifying organisms on the basis of shared, derived traits In a group of related species, two species are judged to be most closely related if they share a “derived” trait that is not shared by other species in the group

Fossils & Evolution Chapter 49 Cladistics All living things are related (like cousins) Any two taxa share a common ancestor ASSUMPTIONS me my cousins grandpagrandma my sister my parents

Fossils & Evolution Chapter 410 Cladistics Branch tips are taxa being investigated Node represents latest common ancestor (possessing features shared by taxa at branch tips)

Fossils & Evolution Chapter 411 Cladistics When more than two taxa are being considered, there are multiple possible branching arrangements Two taxa are considered to be closely related if they share derived traits that are not present in the third taxon

Fossils & Evolution Chapter 412 Trees, trees, trees……. number of taxa being investigated number of possible trees ,752 39, ,032 12,818, ,137,824

Fossils & Evolution Chapter 413 Cladistics procedure: e.g., coelomates 0 = absent 1 = present

Fossils & Evolution Chapter 414 Test two hypotheses coelom turtle fish human brachiopod coral turtle fish human brachiopod coral coelom notochord tetrapod mammary glands mammary glands tetrapod Tree length = 5 steps Tree length = 4 steps

Fossils & Evolution Chapter 415 Cladistics procedure (cont.) Given multiple hypotheses, the favored one is the one that requires the fewest steps –Simplest explanation is most parsimonious

Fossils & Evolution Chapter 416 Cladistics and classification “Clade” = an ancestor and all of its descendants –A clade is a monophyletic group Clades should form the basis for a classification that reflects genealogic relationships A B C D rectangles surround monophyletic groups

Fossils & Evolution Chapter 417 Cladistics and classification A B C DA B C D E F Paraphyletic group—doesn’t contain all descendants of a given ancestor Polyphyletic group—contains descendants from more than one immediate ancestor

Fossils & Evolution Chapter 418 mammals turtles Lizards & snakes crocs dinosaurs birds Class Mammalia Class Reptilia Class Aves Cladistic analysis of amniotes

Fossils & Evolution Chapter 419 mammals turtles Lizards & snakes crocs dinosaurs birds Amniota Reptilia Sauria Archosauria Dinosauria

Fossils & Evolution Chapter 420 Old World Monkeys gibbons Orangutan Gorilla Chimpanzee human Family Pongidae Family Hominidae Cladistic analysis of Old World apes

Fossils & Evolution Chapter 421 Old World Monkeys gibbons Orangutan Gorilla Chimpanzee human Superfamily Hominoidea Family Hominidae Unnamed clade Tribe Homininae

Fossils & Evolution Chapter 422 Cladistics Now the most widely used method for classification and phylogeny reconstruction But, beware of “derived” traits that have originated independently in multiple lineages –e.g., eyes in arthropods, mollusks and vertebrates Biogeographic and stratigraphic information cannot be ignored

Fossils & Evolution Chapter 423 Molecular systematics Classification and phylogeny reconstruction on the basis of genetic and other biochemical information (rapid advances beginning in 1980’s) Example: –Identify sequence of base pairs in the same gene segment among taxa being analyzed

Fossils & Evolution Chapter 424 Structure of DNA Double helix Strands bonded by base pairs A = adenine T = thymine G = guanine C = cytocene

Fossils & Evolution Chapter 425 Data Matrix

Fossils & Evolution Chapter 426 Cladistic analysis of base pair sequences