Chapter 5

Chapter 5Macroevolution: 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 traitsConstruct classifications to show evolutionary relationshipsFocus on homologies

Approaches to Classification Evolutionary Systematics Cladistics

Differences Might use any homologous characterAttempts to make ancestor-descendant links Attempts to place fossils in a chronological framework

Use only explicitly defined derived charactersNo attempt is made to make conclusions regarding ancestor-descendant relationshipsAll 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

ERA PERIODBegan m.y.a. EPOCH

Began m.y.a.

CENOZOIC

Tertiary 1.8 HolocenePleistocene

0.011.8

Quaternary 65

PlioceneMiocene

OligoceneEocene

Paleocene

523345565

Geological Time Scale

ERA PERIOD (Began m.y.a.)

MESOZOIC Cretaceous 136Jurassic 190Triassic 225

PALEOZOIC

PermianCarboniferous

DevonianSilurian

OrdovicianCambrian

280345395430500570

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 ita) 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.