Chapter 5

Macroevolution: Processes of Vertebrate and Mammalian Evolution

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.

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• Cladistics

Ancestral and Derived Characters

• Ancestral characters • Derived characters

Evolutionary Trees

• Development of Passenger Vehicles– The first divergence

is between cars and trucks (I).

– A later divergence occurs between luxury cars and sports cars (II).

Evolutionary Trees

• Development of Passenger Vehicles – SUVs diverge from trucks,

but like sports cars, they have a decorative racing stripe.

– This is a homoplasy and does not make SUVs sports cars.

– Classifications based on a characteristic that can appear independently in different groups can lead to an incorrect conclusion.

Evolutionary Relationships of Birds and Dinosaurs

• (a) Traditional view, showing no close relationship. (b) Revised view, showing common ancestry of birds and dinosaurs.

Cladogram

• Shows relationships of birds, dinosaurs, and other terrestrial vertebrates. There’s no time scale, and both living and fossil forms are shown along the same dimension. Ancestor- descendant relationships aren’t indicated.

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

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

Use only defined derived charactersNo 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.

Definition of Species• Recognition species concept

– The key aspect is the ability of individuals to identify members of their own species for purposes of mating.

• Ecological species concept – The concept that a species is a group of

organisms exploiting a single niche. • Phylogenetic species concept

– Splitting many populations into separate species based on an identifiable parental pattern of ancestry.

Allopatric Speciation

• Living in different areas.• Important in the divergence of closely

related species from each other which leads to reproductive isolation.

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 vs. Interspecific

Recognition of Fossil Species

– Splitters vs. Lumpers

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.

Geological Time Scale

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

• (a) Positions of the continents during the Mesozoic. Pangea is breaking up into a northern landmass (Laurasia) and a southern landmass (Gondwanaland). (b) Positions of the continents at the beginning of the Cenozoic.

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.

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.

Reptilian and Mammalian teeth

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

Major Events in Early Vertebrate Evolution

Endothermic

• Able to maintain internal body temperature by producing energy through metabolic processes within cells; characteristic of mammals, birds, and perhaps some dinosaurs.

Major Mammalian Groups

• Monotremes• Marsupials• Placental

Adaptive Radiation

Convergent Evolution

Gradualism versus Punctuated Equilibrium