Back to Biology 1402 pageTracing Phylogeny
Chapter 25
Phylogeny and Systematics
Phylogeny - evolutionary history of a species or group of related species
Systematics - the study of biological diversity in an evolutionary context
The Fossil Record
Fossil - preserved remnants or impressions left by organisms that lived in the past
Fossil record - ordered array in which fossils appear in rock strata (layers)
Sedimentary rocks provide richest source of fossils (igneous and metamorphic rocks have been deformed)
Radiometric dating methods used to determine age of fossils - used to construct geological time scale
The Geological Time Scale
Established by geologists - reflects sequence of historical periods on earth
Grouped into four eras (and smaller divisions) which represent a distinct age in history of earth
Boundaries between eras generally characterized by mass extinctions and explosive radiations (appearance of new forms of life)
Fossil record gives relative age of fossils - provides substantial (but incomplete) record of evolutionary history
Eras of Geological Time Scale
Precambrian - from origin of earth until about 570 million years ago - lower forms of life & some vertebrates present at end
Paleozoic - ended 245 million years ago - most modern animal groups appeared at beginning of era
Mesozoic - ended 65 million years ago - radiation of dinosaurs - flowering plants appeared
Cenozoic - present era
Continental Drift
Geological phenomenon - result of "seafloor spreading" - continents tend to "drift" apart
At end of Paleozoic era, all continents joined into supercontinent Pangea
During Mesozoic era, Pangea split into Gondwana and Laurasia - continental land masses separated
Continental drift provides best explanation for biogeographical distribution of organisms - e.g., the diversity of marsupials in Australia
Changes in Biological Diversity
Mass extinctions - caused by variety of factors, primarily environmental change(s) - extinction of dinosaur lineages may have been related to impact of comet (Chicxulub crater in Mexico)
Adaptive radiations - emergence of numerous species from common ancestor - most seem to be correlated with appearance of novel character(s) that provide a new set of living conditions - e.g., the appearance of flowering plants and the evolution of wings in insects
Classification of Biological Organisms
Taxonomy - naming and classifying organisms
Binomial nomenclature - developed by Carolus Linnaeus - each organism has scientific name - a latinized binomial consisting of Genus name followed by species epithet (e.g., Homo sapiens - man)
Species included within hierarchy of higher-level taxonomic categories (taxa)
Hierarchial System of Classification
Developed by Carolus Linnaeus
Major taxonomic categories - Kingdom, Phylum, Class, Order, Family, Genus, Species - each may be subdivided further
More recently, the concept of Domain has been adopted by many taxonomists and systematists
Classification of Man
Domain: Eukarya - the eukaryotes
Kingdom Animalia - the animals
Phylum: Chordata - the chordates
Class: Mammalia - the mammals
Order: Primates - the primate mammals
Family: Hominidae - the hominids
Genus: Homo
Species: sapiens
Scientific name - Homo sapiens
Phylogenetic Systematics
Goal is to classify organisms into groups (taxa) which reflect evolutionary relationships
Requires creation of monophyletic taxa (all members evolved from common ancestor)
Requires comparison of homologous structures - i.e., ones that are similar because of common ancestry
Confusion may result from convergent evolution - evolution of similar structures by unrelated species
Tools of the Systematist
Morphology - primarily homologous structures
Molecular biology - DNA, RNA & protein comparisons - significant recent advances
Analyses
Phenetics - based on statistical analyses - makes no phylogenetic assumptions about characters
Cladistics - emphasis placed on synapomorphies (shared derived characters)