DIVERSIFICATION AND EXTINCTION Macroevolution large scale evolutionary change

DIVERSIFICATION AND EXTINCTION

Macroevolution ¤ large scale evolutionary change significant enough to warrant the classification of groups or lineages into distinct genera or higher level taxa But where did we start? ¤ Primary Abiogenesis – First living things arose from non-living material ¤ H. Urey and S. Miller, 1952, abiogenesis experiment

Diversification and Extinction Life on Earth has existed for more than 3. 5 billion years. 8 3. 5 billion years ago, all organisms were unicellular 8 Multicellular organisms like fungi, plants, and animals are thought to have appeared around 550 million years ago 8 Dinosaurs dominated the planet from 250 mya to around 65 mya 8 The Cambrian Explosion occurred around 542 mya, and lasted for about 40 my. 8 This explosion of diversity actually ended with a mass extinction 8 70% of life on earth disappeared after which animals, representing all present day major phyla, began to appear 8

Mass Extinctions and Diversification 8 The Cambrian explosion began the Paleozoic era 8 The Paleozoic era ends with a series of cataclysmic events that caused the extinction of 90% of marine mammals 8 After a mass extinction there is always an era of mass diversification (WHY? ? ? ) 8 After the extinction of the dinosaurs (likely caused by the impact of a meteor 65 mya) mammals evolved 8 Before extinctions: lots of well adapted species that do not really need to evolve anymore 8 After extinctions: many niches now available = opportunity for rapid evolution= strong disruptive forces = mass diversification

History of Life on Earth

Appearance of Life on Earth

The Rate of Evolution Theory of Gradualism (Darwinism) 8 Dramatic evolutionary changes in species 8 This changes are caused by the accumulation of many small, on-going changes and processes 8 But… we are missing transitional forms (read more on this) in the fossil record. . . WHY? ? ? Theory of Punctuated Equilibrium 81972 – N. Eldredge and S. J. Gould 8 Sometimes speciation occurs rapidly in evolutionary time and then new species will remain unchanged for a long period of time.

Punctuated Equilibrium 8 Speciation occurs “rapidly” in small isolated populations so intermediate fossils are rare 8 After the initial burst of evolution, species do not change significantly over long periods of time 8 Both theories are needed to explain what is found in the fossil record

Punctuated Equilibrium 8 These phylogenetic trees show the difference between the two theories

Phylogeny is the study of evolutionary relatedness between and among species

Phylogeny and Cladistics 8 We use a cladogram (mathematical phylogenetic tree) to represent theoretical sequences of events that determine relatedness 8 We build these trees through the use of Cladistics – a way to determine evolutionary relationships based on the presence or absence of recently evolved traits.

Cladistics 8 Cladistics uses synapomorphies shared traits that have evolved only once and have been inherited by two or more species e. g. , fins are paired appendages (2) tetrapods have 2 pairs (4) 4 evolved from 2 8 Cladograms are then used to predict hypotheses concerning evolutionary events 8 NOTE: ancestral features cannot be use to determine relationships

Cladistics 8 Cladograms are then used to predict hypothesis concerning evolutionary events 8 See page 351 – Lets draw this together. 8 Practice #1

Your Task Pp. 351 - Practice #1 Pp. 2 -9