Evidence for Evolution There are many lines of evidence that show that evolution has occurred. They come from both the fossil record and from biology.
Lines of evidence for evolution cited by Darwin • Fossils provide direct evidence for changes in life in rocks of different ages. • Homologous structures - Certain organs or structures are present in a variety of species, but they are modified to function differently. • Modern organisms contain vestigial organs that appear to have little or no use. These structures had a useful function in ancestral species. • Animals that are very different, have/had similar-looking embryos.
Other lines of evidence for evolution come from: • Genetics - DNA molecule • Biochemistry – similar in closely-related organisms, but very different in more distantly related organisms. • Molecular biology - sequences of amino acids in proteins
Evidence for Evolution from Paleontology Many examples of gradual or sequential evolution in the fossil record, including: • Horses • Cephalopods and other molluscs • Foraminifera and other microfossils
Evidence for Evolution from Biology Homologous structures - body parts with similar origin, history and structure, but different functions.
Evidence for Evolution from Biology Vestigial organs suggest a common ancestry. Vestigial organs serve no apparent purpose, but resemble functioning organs in other animals. Vestigial pelvis and femur of a whale in an Eocene fossil
Evidence for Evolution from Biology Similarity of embryos of all vertebrates suggests a common ancestry.
Evidence for Evolution from Biology Biochemistry - Chemicals (such as proteins, antigen reactions of blood, digestive enzymes, and hormone secretions) are more similar in related organisms.
Evidence for Evolution from Biology DNA sequencing – If organisms appear to be similar on the basis of form, embryonic development, or fossil record, we can predict that they would have a greater percentage of DNA sequences in common, compared with less similar organisms. This is proven to be correct in hundreds of analyses.
Ecology and Paleoecology • Ecology = Interrelationship between organisms and their environment. • Paleoecology = Ancient ecology; interaction of ancient organisms with their environment. Depends on comparisons of ancient and living organisms (modern analogs). • Ecosystem = Organisms and their environment - the entire system of physical, chemical, and biological factors influencing organisms.
Ecology and Paleoecology • Habitat = Environment in which an organism lives. • Niche = Way in which the organism lives; its role or lifestyle. • Community = Association of several species of organisms in a particular habitat (living part of ecosystem). • Paleocommunity = An ancient community.
Marine Ecosystem The ocean may be divided into two realms: • Pelagic realm = The water mass lying above the ocean floor. • Benthic realm = The bottom of the sea
Marine Ecosystem Pelagic realm • Neritic zone = The water overlying the continental shelves. • Oceanic zone = The water seaward of the continental shelves.
Marine Ecosystem Benthic realm • Supratidal zone = Above high tide line • Littoral zone (or intertidal zone) = Between high and low tide lines • Sublittoral zone (or subtidal zone) = Low tide line to edge of continental shelf (about 200 m deep) • Bathyal zone - 200 - 4000 m deep • Abyssal zone - 4000 - 6000 m deep • Hadal zone - >6000 m deep; deep sea trenches.
Modes of Life of Marine Animals Plankton - Small plants and animals that float, drift, or swim weakly. • Phytoplankton - Plants and plant-like plankton, such as diatoms and coccolithophores • Zooplankton - Animals and animal-like plankton, such as foraminifera and radiolaria
Modes of Life of Marine Animals Nekton - Swimming animals that live within the water column Benthic organisms or benthos - Bottom dwellers, which may be either: • Infaunal - Living beneath the sediment surface; they burrow and churn and mix the sediment, a process called bioturbation • Epifaunal - Living on top of the sediment surface
Use of Fossils in Reconstructing Ancient Geography Environmental limitations control the distribution of modern plants and animals. • Note locations of fossil species of the same age on a map • Interpret paleoenvironment for each region using rock types, sedimentary structures, and fossils. • Plot the environments to produce a paleogeographic map for that time interval.
Land Bridges, Isolation and Migration Migration and dispersal patterns of land animals can indicate the existence of: • Former land bridge • (Bering Strait) • Mountain barriers • Former ocean • barriers between • continents
Species Diversity and Geography Species diversity is related to geographic location, particularly latitude. • High latitudes have low species diversity • Low latitudes have high species diversity. As a general rule, species diversity increases toward the equator.
Use of Fossils in the Interpretation of Ancient Climatic Conditions Fossils can be used to interpret paleoclimates (ancient climates): • Fossil spore and pollen grains can tell about the types of plants that lived, which is an indication of the paleoclimate. • Plant fossils showing aerial roots, lack of yearly rings, and large wood cell structure indicate tropical climates • Presence of corals indicates tropical climates
Use of Fossils in the Interpretation of Ancient Climatic Conditions • Marine molluscs with spines and thick shells inhabit warm seas • Planktonic foraminifera vary in size and coiling direction with temperature • Shells in warmer waters have higher Mg contents • Oxygen isotope ratios in shells.
Oldest evidence of life Remains of prokaryotic cells (blue-green algae or cyanobacteria) more than 3.5 billion years old. Found in algal mats and stromatolites.
Earliest Metazoan Organisms Metazoans = multicellular organisms • Trace fossils of metazoans about 1 billion years ago • First body fossils of soft-bodied metazoans (worms, jellyfish, and arthropods) about 0.7 billion years ago • Invertebrates with hard parts appeared in late Proterozoic or early Paleozoic.
Early Paleozoic – Cambrian Period • Most animals were deposit and suspension feeders • Trilobites • Brachiopods without hinged shells (inarticulates) • Small cap-shaped molluscs • Soft-bodied worms • Chitin-shelled arthropods • Reef-building archaeocyathids
Trilobites Articulate (hinged) brachiopods Nautiloids Crinoids Rugose (horn) corals Tabulate corals Branching twig-like bryozoans (moss animals) Vertebrates Fishes Amphibians Reptiles Later in the Paleozoic Era
Modern scleractinian corals Bivalves Sea urchins Ammonoids Vertebrates Dinosaurs Primitive mammals Birds Mesozoic Era
Cenozoic Era • Molluscs of many types (but no ammonoids) • Planktonic foraminifera • Sea urchins • Encrusting bryozoans • Barnacles • Vertebrates • Age of mammals • Appearance of humans • Many other vertebrate groups
Extinctions Mass extinctions occurred at the ends of the following periods: • Ordovician • Devonian - roughly 70% of marine invertebrates extinct • Permian - the greatest extinction. More than 90% of marine species disappeared or nearly went extinct • Triassic • Cretaceous - affected dinosaurs, other land animals, and marine organisms; about 25% of all known animal families extinct
Evolutionary History of Plants • Earliest photosynthetic organisms were single-celled organisms in the Precambrian. • Green algae or chlorophytes may be the ancestors of vascular land plants. • Plants invaded the land in the Ordovician, reproducing with spores.
Evolutionary History of Plants – cont’d • First plants with seeds appeared in the Devonian. Gymnosperms (such as conifers). Had pollen. • Carboniferous coal swamps dominated by seedless, spore-bearing scale trees. • Flowering plants appeared in the Cretaceous. Angiosperms. Dominant plants today.