The Fossil Record

The Fossil Record CHAPTER 4

Fossil Preservation Preservation as a fossil usually requires: • Preservable parts. Hard parts (bones, shells, teeth, wood) have a much better chance at being preserved than do soft parts (muscle, skin, internal organs). • Rapid burial by sediment. Burial protects body parts from decay. • No physical, chemical, and biological destruction after burial. Most organismal remains are destroyed by burrowing (bioturbation), dissolution, metamorphism, or erosion.

Forms of Chemical Alteration(aids in preservation) • Carbonization preserves soft tissues of plants or animals as a thin carbon film. • Permineralization -filling of pores (tiny holes) in bone or shell by the deposition of minerals from solution. • Replacement- molecule-by-molecule substitution of a different mineral for the original material.

Imprints of Hard Parts in Sediment • Impressions (molds)- imprints of an organism in the sediment. • External molds are imprints of the outside of a shell • Internal molds are imprints of the inside of the shell • A cast is produced if the mold is later filled or covered by sediment and preserved.

Replacement of ammonite shell by pyrite Mold and cast

Additional Methods of Fossilization • Freezing –mammoths in tundra • Dessication – mummification • Amber – trapped insects • Tar/Asphalt – LaBrea tarpits or peat bogs

Fossils! Amber LaBrea Tar Pits Frozen Mammoth

Trace Fossils • Ichnofossils are the markings in the sediment made by the activities of organisms. • Indicators of movement in the sediment • Tracks, trails burrows • Nests • Coprolites • fossilized feces

Figure 4-11 (p. 111)Traces that reflect animal behavior: (A) crawling traces, (B) resting traces, C) dwelling traces, (D) grazing traces, and (E) feeding traces.

Dinosaur track Worm burrows

The Rank and Order of Life A system of binomial nomenclature is used: • The first of the two names is the Genus and the second name is the species. • The genus and species names are underlined or italicized. The name of the genus is capitalized, but the name of the species is not.

Classification of Organisms The Species • A group of organisms that have structural, functional, and developmental similarities, and that are able to interbreed and produce fertile offspring. • Species are reproductively isolated from one another • Example: • Goats and sheep do not interbreed in nature, so they are separate species • In captivity they can produce fertile offspring!

Taxonomy • Linnaean taxonomic groups • Kingdom • Phylum • Class • Order • Family • Genus • Species

Five kingdoms of organisms • Animalia (animals) • Plantae (plants) • Monera (bacteria and blue-green algae) • Fungi (mushrooms, fungus) • Protista (single-celled organisms)

Proposed revision to current system Organisms are grouped into three superkingdoms or domains: • Bacteria - Kingdom Monera including cyanobacteria (blue-green algae) • Archaea - sometimes called archaebacteria as different from the bacteria as the eukaryotes are from the prokaryotes • Eukarya - animals, plants, fungi, and protists

Cells • All organisms are composed of cells. • There is a fundamental difference between organisms based on the type of cells: • Cells with a nucleus (or nuclei) are eukaryotic cells. Organisms with this type of cell are called eukaryotes. • Cells without a nucleus are prokaryotic cells. Organisms with this type of cell are called prokaryotes. Kingdom Monera (bacteria) only.

Why Study Evolution? • Evolution involves inheritable changes in organisms through time • Fundamental to biology and paleontology • Paleontology is the study of life history and evolution as revealed by fossils • Evolution is a unifying theory that explains a collection of facts • Evolution provides a framework for discussion of life history in later parts of the term

Misconceptions about Evolution • Many people have a poor understanding of the theory of evolution and hold a number of misconceptions, which include: • evolution proceeds strictly by chance • nothing less than fully developed structures are of any use • there are no transitional fossils so-called missing links connecting ancestors and descendants • humans evolved from monkeys so monkeys should no longer exist

Evolution: Historical Background • Evolution, the idea that today’s organisms have descended with modification from ancestors that lived during the past • Usually attributed solely to Charles Darwin, • Seriously considered long before he was born (by some ancient Greeks and by philosophers and theologians during the Middle Ages) • Nevertheless, the prevailing belief in the 1700s was that Genesis explained the origin of life

Evolution: Historical Background • During the 18th century, naturalists were discovering evidence that could not be reconciled with literal reading of Scripture • In this changing intellectual atmosphere, scientists gradually accepted a number of ideas: • the principle of uniformitarianism, • Earth’s great age, • that many types of plants and animals had become extinct, • and that change from one species to another occurred • What was lacking, though, was a theoretical framework to explain evolution

Lamarck • Jean-Baptiste de Lamarck • (1744-1829) is best remembered for his theory of inheritance of acquired characteristics, • According to this theory, • new traits arise in organisms because of their needs/wants • Somehow are passed on to their descendants • Lamarck’s theory was widely accepted • With more evidence, proved to be invalid…

Lamarck’s Theory • Lamark’s theory was totally refuted • Decades later • Discovered that genes are the units of heredity • Cannot be altered by any effort by an organism

Lamarck’s Theory of Inheritance • Ancestral short-necked giraffes stretched their necks to reach leaves high on trees • Their offspring were born with longer necks

Darwin • In 1859, Charles Robert Darwin (1809-1882) • published On the Origin of Species • In it he detailed his ideas on evolution • formulated 20 years earlier • and proposed a mechanism for evolution

Natural Selection • Plant and animal breeders • practice artificial selection by selecting those traits they deem desirable • and then breed plants and animals with those traits • thereby bringing about a great amount of change • Observing artificial selection • gave Darwin the idea that a process of selection among variant types • in nature could also bring about change

Darwin and Wallace • Darwin and Alfred Russel Wallace (1823-1913) • A natural process was selecting only a few individuals for survival • Darwin’s and Wallace’s idea • called natural selection • was presented simultaneously in 1859

Natural Selection—Main Points • Organisms in all populations • posses heritable variations such as • size, speed, agility, visual acuity, • digestive enzymes, color, and so forth • Some variations are more favorable than others • some have a competitive edge • in acquiring resources and/or avoiding predators • Not all young survive to reproductive maturity • Those with favorable variations are more likely to survive and pass on their favorable variations

Naturally Selected Giraffes According to the Darwin-Wallace theory: • giraffe’s long neck evolved because ancestors with longer necks had an advantage and reproduced more often

“Survival of the Fittest” • Natural selection is commonly referred to as “survival of the fittest” • This is misleading because • natural selection is not simply a matter of survival but involves differential rates of survival and reproduction

Which is favored in Natural Selection? • One misconception about natural selection: • Only biggest, strongest, fastest animals survive • These characteristics might provide an advantage but…. • Natural selection may favor: • the smallest if resources are limited • the most easily concealed • those that adapt most readily to a new food source • those having the ability to detoxify some substance • those that are able to withstand extreme heat • Etc.

Limits of Natural Selection • Natural selection works on existing variation in a population • It could not account for the origin of variations • Critics reasoned that should a variant trait arise, it would blend with other traits and would be lost • The answer to these criticisms • existed even then in the work of Gregor Mendel, but remained obscure until 1900

Mendel and the Birth of Genetics • During the 1860s, Gregor Mendel: • Performed a series of controlled experiments • True-breeding strains of garden peas • Strains that when self-fertilized always display the same trait, such as flower color • Traits are controlled by a pair of factors, now called genes • Genes occur in alternate forms: alleles • One may dominate • One allele from each parent (pair)

Importance of Mendel’s Work • The factors (genes) controlling traits • do not blend during inheritance • Traits not expressed in each generation • may not be lost • Therefore, some variation in populations • results from alternate expressions of genes • Variation can be maintained

Genes and Chromosomes • Complex, double-stranded helical molecules • of deoxyribonucleic acid (DNA) • called chromosomes • are found in cells of all organisms • except bacteria, • which have ribonucleic acid (RNA) • Specific segments of DNA • are the basic units of heredity (genes) • The number of chromosomes • varies from one species to another • Example: fruit flies 8; humans 46; horses 64

Reproduction and Cell Division Reproduction in organisms may be: • sexual • asexual • alternation of sexual and asexual generations • Asexual reproduction can occur through: • binary fission (cells that split in two) - only among single-celled organisms • budding in which the parent " sprouts" an appendage that may separate to grow into an isolated individual, or remain attached to the parent (as in colonial organisms). Budding occurs in some unicellular and some multicellular organisms. • spores shed by the parent (as in a seedless plant) that germinate and produce male and female sex cells (leading to alternation of sexual and asexual gererations).

Evolution evolving • During the 1930s and 1940s, • paleontologists, population biologists, • geneticists, and others developed ideas that • merged to form a modern synthesis • or neo-Darwinian view of evolution • They incorporated • chromosome theory of inheritance • into evolutionary thinking • They saw changes in genes (mutations) • as one source of variation

Evolution • They completely rejected Lamarck’s idea of inheritance of acquired characteristics • They reaffirmed the importance of natural selection

Where does Variation Arise? • Evolution by natural selection works on variation in populations most of which is accounted for by the reshuffling of alleles from generation to generation during sexual reproduction • The potential for variation is enormous • Thousands of genes with several alleles, and with offspring receiving 1/2 of their genes from each parent • New variations arise by mutations • change in the chromosomes or genes

Mutations • Mutations result in a change of the hereditary information • Mutations that take place in sex cells • Inheritable • Chromosomal mutations • affecting a large segment of a chromosome • Point mutations • individual changes in particular genes • Mutations are random with respect to fitness • they may be beneficial, neutral, or harmful

Mutations • If a species is well adapted to its environment, • most mutations would not be particularly useful • and perhaps would be harmful • But what was a harmful mutation • can become a useful one if the environment changes

What Causes Mutations? • Some mutations are induced by mutagens • agents that bring about higher mutations rates such as • some chemicals • ultraviolet radiation • X-rays • extreme temperature changes • Some mutations are spontaneous • occurring without any known mutagen

Evolutionary Terminology • Population - a group of interbreeding organisms. • Gene pool - the sum of all of the genetic components in a population. • Speciation - the origin of new species.

Speciation • The phenomenon of a new species arising from an ancestral species • Involves change in the genetic makeup of a population • May bring about changes in form and structure • During allopatric speciation, • species arise when a small part of a population • becomes isolated from its parent population • This involves the creation of geographic barriers

Allopatric Speciation • Geographic barriers may form across parts • of a central population’s range, • thereby isolating small populations that speciate

Allopatric Speciation • A few individuals: • May reach a remote area and no longer exchange genes with the parent population • This out-migration can lead to the formation of a peripheral isolate that gives rise to a new species while the parent population persists without change

Adaptive radiation • The branching of a population to produce many species through many separate speciation events. • The descendant species are each adapted to particular environment and living strategies.

Honey Creeper • Bill/beak diversity--adaptive radiation

Gradual or Rapid Evolution? We ponder whether evolution occurs in jumps or in a gradual progression: • Phyletic gradualism - gradual progressive change by means of an almost infinite number of small, subtle steps (traditional idea) • Punctuated equilibrium - sudden changes "punctuating" (or interrupting) long periods of little change, termed stasis (Gould and Eldridge, 1977). Most change occurs over a short period of time (new idea)

Phylogeny • Phylogeny = the sequence of organisms placed in evolutionary order. • Diagrams called phylogenetic trees are used to display ancestor-descendant relationships. • Branches on the tree are called clades.

Phylogeny • Stratophenetic- • Traditional view, where evolutionary tree shows succession of life through time, dependant on fossil record • Cladistic- • Organisms are analyzed based on characteristics they share to determine ancestor-descendant relationships • Build cladogram showing closeness of organisms

The Fossil Record