Chapter 5 Macroevolution: Processes of Vertebrate and Mammalian Evolution

Chapter Outline  The Human Place in the Organic World  Principles of Classification  Definition of Species  Vertebrate Evolutionary History: A Brief Summary

Chapter Outline  Mammalian Evolution  The Emergence of Major Mammalian Groups  Processes of Macroevolution

Classification  Classification is used to order organisms into categories to show evolutionary relationships.  Example - human classification  Kingdom: Animalia  Subkingdom: Metazoan  Phyla: Chordata  Subphyla: Vertebrata  Class: Mammalia

Classification: Definitions  Metazoa  Multicellular animals.  Chordata  The phylum of the animal kingdom that includes vertebrates.  Vertebrates  Animals with segmented bony spinal columns; includes fishes, amphibians, reptiles, birds, and mammals.

Principles of Classification  The field that specializes in establishing the rules of classification is called taxonomy.  Organisms are classified first on the basis of physical similarities.  Basic physical similarities must reflect evolutionary descent in order for them to be useful.

Principles of Classification  Homologies  Similarities based on descent from a common ancestor.  Analogies  Similarities based on common function, with no assumed common evolutionary descent.  Homoplasy  The separate evolutionary development of similar characteristics in different groups of organisms.

Homologies

Two Approaches to Classification  Evolutionary systematics  A traditional approach in which presumed ancestors and descendants are traced in time by analysis of homologous characters.  Cladistics  Attempts to make rigorous evolutionary interpretations based solely on analysis of certain types of homologous characters.

Ancestral and Modified Characters  Ancestral characters  Refers to characters inherited by a group of organisms from a remote ancestor and thus not diagnostic of groups (lineages) that diverged after the character first appeared.  Derived characters  Refers to characters that are modified from the ancestral condition and thus are diagnostic of particular evolutionary lineages.

Approaches to Classification Evolutionary Systematics Cladistics Goal Construction of a phylogenetic tree Construction of a cladogram Similarities  Compare specific traits  Construct classifications to show evolutionary relationships  Focus on homologies

Approaches to Classification Evolutionary Systematics Cladistics DifferencesMight use any homologous character Attempts to make ancestor-descendant links Attempts to place fossils in a chronological framework Use only explicitly defined derived characters No attempt is made to make conclusions regarding ancestor-descendant relationships All members of an evolutionary group are interpreted in one dimension

Definition of Species  Biological species concept  Depiction of species as groups of individuals capable of interbreeding, but reproductively isolated from other such groups.  Speciation  Process by which a new species evolves from a prior species.  Speciation is the most basic process in macroevolution.

Speciation Model

Recognition of Fossil Species  The minimum biological category we would like to define in fossil primate samples is the species.  Variations  Intraspecific - Variation is accounted for by individual, age, and sex differences seen within every biological species  Interspecific - Variation represents differences between reproductively isolated groups.

Recognition of Fossil Species  Defining where species boundaries begin and end is often difficult.  “Splitters” are researchers who claim speciation occurred frequently during hominid evolution.  “Lumpers” assume speciation was less common and see much variation as being intraspecific.

Recognition of Fossil Genera  A genus is a group of species composed of members more closely related to each other than to species from any other genus.  Species that are members of the same genus share the same broad adaptive zone.  Members of the same genus should all share derived characters not seen in members of other genera.

Geological Time Scale ERAPERIOD Began m.y.a.EPOCH Began m.y.a. CENOZOIC Tertiary1.8 Holocene Pleistocene Quaternary65 Pliocene Miocene Oligocene Eocene Paleocene

Geological Time Scale ERAPERIOD(Began m.y.a.) MESOZOIC Cretaceous136 Jurassic190 Triassic225 PALEOZOIC Permian Carboniferous Devonian Silurian Ordovician Cambrian

Geological Eras  Paleozoic  The first vertebrates appeared 500 m.m.y.a.  Mesozoic  Reptiles were dominant land vertebrates.  Placental mammals appeared 70 m.Y.A.  Cenozoic  Divided into two periods: Tertiary and Quaternary and 7 epochs: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene and Holocene.

Continental Drift  The movement of continents on sliding plates of the earth’s surface.  As a result, the positions of large landmasses have shifted drastically during the earth’s history.

Continental drift  The positions of the continents during the Mesozoic (c. 125 m.y.a.).  Pangea is breaking up into a northern landmass (Laurasia) and a southern landmass (Gondwanaland).

Continental drift  The positions of the continents at the beginning of the Cenozoic (c. 65 m.y.a.).

Ecological Niches  The positions of species within their physical and biological environments, together making up the ecosystem.  A species’ ecological niche is defined by such components as diet, terrain, vegetation, type of predators, relationships with other species, and activity patterns, and each niche is unique to a given species.

Epochs  Categories of the geological time scale.  In the Cenozoic, epochs include  Paleocene  Eocene  Oligocene  Miocene  Pliocene  Pleistocene  Holocene

Mammalian Evolution  The Cenozoic era is known as the Age of Mammals.  After dinosaurs became extinct, mammals underwent adaptive radiation, resulting in rapid expansion and diversification.  The neocortex, which controls higher brain functions, comprised the majority of brain volume, resulting in greater ability to learn.

Lateral View of the Brain

Reptilian and Mammalian teeth  Mammals are heterodont, they have different kinds of teeth; incisors, canines, premolars, and molars.

Adaptive Radiation  A process that takes place when a life form rapidly takes advantage of the many newly available ecological niches.  A species, or group of species, will diverge into as many variations as two factors allow: 1. Its adaptive potential. 2. The adaptive opportunities of the available niches.

Major Mammalian Groups  Monotremes  Primitive, egg laying mammals  Marsupials  Infants complete development in an eternal pouch  Placental  Longer gestation allows the central nervous system to develop more completely

Quick Quiz

1. The scientific discipline that delineates the rules of classification is a) paleontology. b) stratigraphy. c) homology. d) taxonomy.

Answer: d  The scientific discipline that delineates the rules of classification is taxonomy.

2. An advantage of heterodont dentition is that it a) allows the animal to defend itself more efficiently. b) allows for processing a wide variety of foods. c) opens up new ways of interacting with potential mates. d) allows the animal to grab prey that it could not catch otherwise.

Answer: b  An advantage of heterodont dentition is that it allows for processing a wide variety of foods.

3. The group of mammals that reproduce by laying eggs and who generally have more primitive traits than the other mammals are the a) monotremes. b) metatherians. c) marsupials. d) placentals.

Answer: a  The group of mammals that reproduce by laying eggs and who generally have more primitive traits than the other mammals are the monotremes.

4. The divergence of reptiles into many different forms describes a) analogies. b) sexual selection. c) adaptive radiation. d) homologies.

Answer: c  The divergence of reptiles into many different forms describes adaptive radiation.