Fossil record & taxonomy Evidence & classification of life on earth

The fossil record Paleontologists – SCIENTISTS THAT STUDY FOSSILS. MORE THAN 99% OF ALL SPECIES THAT EVER LIVED ON EARTH HAVE BECOME EXTINCT. FOSSILS CAN BE COMPLETE AS A PERFECTLY PRESERVED ANIMAL OR TINY FRAGMENTS OF BONE OR LEAF. DO ALL ORGANISMS LEAVE BEHIND FOSSILS? MOST FOSSILS FORM IN SEDIMENTARY ROCK – WHICH FORMS WHEN EXPOSURE TO RAIN, HEAT, WIND AND COLD BREAKS DOWN EXISTING ROCK INTO SMALL PARTICLES OF SAND, SILT & CLAY. LAYERS FORM AND BUILD UP ON TOP OF THE REMAINS. THE WEIGHT OF LAYERS OF SEDIMENT GRADUALLY COMPRESSES THE LOWER LAYERS AND WITH CHEMICAL ACTIVITY, TURNS THEM INTO ROCK. Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils. Index fossils are used to compare relative ages of fossils. Radioactive dating allows scientists to use radioactive isotopes to determine the age of fossils – some fossils have radioactive rock around them. The half-life of the radioactive substance allows researchers to determine fossil ages.

Earth’s early history Geologic time scale is used by paleontologists to represent evolutionary time. It was developed by studying rock layers and index fossils across the globe. After Precambrian time, the basic divisions of the geologic time scale are eras and periods. Precambrian time (vendian period) 650 – 544 million years ago Paleozoic 544 – 245 million years ago Mesozoic 245 – 65 million years ago Cenozoic 65 million years ago – present Origin of life – Miller and urey simulated conditions of early earth by filling a flask with hydrogen, methane, ammonia & water to represent atmosphere making certain microorganisms are not contaminating the flask. Then, they passed a spark through the mixture to simulate lightning. Several amino acids began to accumulate. Origin of eukaryotic cells ??? Sexual reproduction & multicellularity – allows for increased genetic variability and a faster rate of evolution. Sexual reproduction – IE, gene recombination, evolves first and then multicellular organisms began to develop.

Patterns of evolution Large-scale evolutionary patterns are referred to as macroevolution. There are 6 patterns of macroevolution that we will consider: Extinction Adaptive radiation Convergent evolution Coevolution Punctuated equilibrium Changes in developmental genes Extinction occurs because of resource competition and environmental change. As a result, natural selection causes some species to adapt and survive and others to become extinct. Evolutionary biologists believe that the mass extinction of the dinosaurs ending the cretaceous period cleared the way for the evolution of modern mammals and birds. What happened to the dinosaurs? When mass extinction occurs, many different species disappear and leave habitats open to provide ecological opportunities for the surviving organisms.

Patterns of evolution Adaptive radiation – fossil studies have shown that a single species or a small group of species has evolved through natural selection into diverse forms that live in different ways. Example: Dinosaurs were the products of adaptive radiation among ancient reptiles. When they ruled, animals remained small and scarce. Why?

Patterns of evolution Convergent evolution – the process by which unrelated organisms evolve to resemble each other. Example: A shark is a fish, a penguin is a bird and a dolphin is a mammal – however, they all share similar physical characteristics such as flipper/fins & a streamlined body. This is because they’ve all adapted to aquatic habitats. Why do you think these adaptations increase these organisms’ fitness?

Patterns of inheritance Coevolution – an evolutionary change in one organism may be followed by a corresponding change in another organism and when two species evolve in response to changes in each other over time. Example: many flowering plants can reproduce only if the shape, color, and odor of their flowers attract a specific type of pollinator. Darwin predicts the existence of a, then, undiscovered moth based on the location of nectar in an orchid. Example: poisonous plant compounds vs herbivorous insects

Patterns of evolution Punctuated equilibrium – long & stable periods of very little evolutionary change interrupted by brief periods of more rapid change.

Finding order in diversity Taxonomy Finding order in diversity EACH LEVEL IS CALLED A TAXON 

Finding order in diversity Biologists use a classification system to name organisms and group them in a logical manner. The discipline of naming organisms is called taxonomy. Latin & greek are commonly used to name organisms. Carolus Linnaeus developed the two-word naming system binomial nomenclature. First part of scientific name is the genus. Second part of scientific name is the species. Example: the grizzly bear is the URSUS ARCTOS AND THE POLAR BEAR IS THE URSUS MARITIMUS. - THESE ANIMALS ARE IN THE SAME genus BUT ARE NOT THE SAME SPECIES. ORGANISMS DETERMINE WHO BELONG TO THEIR SPECIES BY CHOOSING WITH WHOM THEY WILL MATE. IE, ONLY ORGANISMS IN THE SAME SPECIES WILL REPRODUCE AND PRODUCE VIABLE OFFSPRING. SPECIES ARE GROUPED INTO LARGER TAXA SUCH AS GENUS AND FAMILY ACCORDING TO VISIBLE SIMILARITIES AND DIFFERENCES. Phylogeny is evolutionary relationships among organisms. Biologists group organisms into categories that represent lines of evolutionary descent (phylogeny) – not just physical similarities. All members of a genus share a recent common ancestor. Organisms that look similar may not share a common ancestor - convergent evolution!!

A Cladogram shows evolutionary relationships among a group of organisms. 

Modern evolutionary classification The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships. The more similar the Dna sequences of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms.

Kingdoms & domains As evidence about microorganisms continues to accumulate, biologists recognize that monerans (bacteria) are composed of two distinct groups – eubacteria & archaebacteria. 6-kingdom system of classification includes: Eubacteria Archaebacteria Protista Fungi Plantae Animalia 3-domain system of classification includes: Bacteria Archaea Eukarya BACTERIA – unicellular, prokaryotic, thick cell walls around cell membrane made of peptidoglycan & corresponds to eubacteria. Archaea – unicellular, prokaryotic, extreme environments, anaerobic, cell walls lack peptidoglycan but have isoprene chains.