Broad Patterns of Evolution

Broad Patterns of Evolution 0 23

Overview: Lost Worlds Past organisms were very different from those now alive The fossil record shows evidence of macroevolution, broad changes above the species level; for example The emergence of terrestrial vertebrates The impact of mass extinctions The origin of flight in birds

Figure 23.1

Figure 23.UN01 Cryolophosaurus skull

Concept 23.1: The fossil record documents life’s history The fossil record reveals changes in the history of life on Earth Video: Grand Canyon

Figure 23.2 1 m 100 mya Rhomaleosaurus victor 175 200 0.5 m Dimetrodon 270 Tiktaalik 300 4.5 cm 375 Coccosteus cuspidatus 400 1 cm Hallucigenia 500 2.5 cm 510 Dickinsonia costata 560 Stromatolites 600 1,500 Tappania 3,500

Figure 23.2a Stromatolite cross section

Figure 23.2b Stromatolites

Figure 23.2c Tappania

Figure 23.2d 2.5 cm Dickinsonia costata

Figure 23.2e 1 cm Hallucigenia

Figure 23.2f 4.5 cm Coccosteus cuspidatus

Figure 23.2g Tiktaalik

Figure 23.2h 0.5 m Dimetrodon

Figure 23.2i 1 m Rhomaleosaurus victor

The Fossil Record Sedimentary rocks are deposited into layers called strata and are the richest source of fossils The fossil record indicates that there have been great changes in the kinds of organisms on Earth at different points in time

Few individuals have fossilized, and even fewer have been discovered The fossil record is biased in favor of species that Existed for a long time Were abundant and widespread Had hard parts

How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils The absolute ages of fossils can be determined by radiometric dating A “parent” isotope decays to a “daughter” isotope at a constant rate Each isotope has a known half-life, the time required for half the parent isotope to decay

Figure 23.3 1 16 Accumulating “daughter” isotope ½ Fraction of parent isotope remaining Remaining “parent” isotope ¼ ⅛ 1 2 4 3 Time (half-lives)

Radiocarbon dating can be used to date fossils up to 75,000 years old For older fossils, some isotopes can be used to date volcanic rock layers above and below the fossil

The geologic record is a standard time scale dividing Earth’s history into the Hadean, Archaean, Proterozoic, and Phanerozoic eons The Phanerozoic encompasses most of the time that animals have existed on Earth The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic Major boundaries between geological divisions correspond to extinction events in the fossil record The Geologic Record Animation: The Geologic Record

Table 23.1

Table 23.1a

Table 23.1b

The oldest known fossils are stromatolites, rocks formed by the accumulation of sedimentary layers on bacterial mats Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants for more than 1.5 billion years

Early prokaryotes released oxygen into the atmosphere through the process of photosynthesis The increase in atmospheric oxygen that began 2.4 billion years ago led to the extinction of many organisms The eukaryotes flourished in the oxygen-rich atmosphere and gave rise to multicellular organisms

The Origin of New Groups of Organisms Mammals belong to the group of animals called tetrapods The evolution of unique mammalian features can be traced through gradual changes over time

Figure 23.4 Reptiles (including dinosaurs and birds) Key to skull bones Articular Dentary OTHER TETRA- PODS Quadrate Squamosal †Dimetrodon Early cynodont (260 mya) Synapsids †Very late (non-mammalian)cynodonts Temporal fenestra (partial view) Therapsids Cynodonts Mammals Hinge Synapsid (300 mya) Later cynodont (220 mya) Temporal fenestra Hinge Original hinge New hinge Therapsid (280 mya) Very late cynodont (195 mya) Temporal fenestra Hinge Hinge

Figure 23.4a Reptiles (including dinosaurs and birds) OTHER TETRAPODS †Dimetrodon Synapsids †Very late (non-mammalian)cynodonts Therapsids Cynodonts Mammals

Synapsids (300 mya) had single-pointed teeth, large temporal fenestra, and a jaw hinge between the articular and quadrate bones

Therapsids (280 mya) had large dentary bones, long faces, and specialized teeth, including large canines

Figure 23.4b Synapsid (300 mya) Key to skull bones Articular Quadrate Dentary Temporal fenestra Squamosal Hinge Therapsid (280 mya) Temporal fenestra Hinge

Early cynodonts (260 mya) had large dentary bones in the lower jaw, large temporal fenestra in front of the jaw hinge, and teeth with several cusps

Later cynodonts (220 mya) had teeth with complex cusp patterns and an additional jaw hinge between the dentary and squamosal bones

Very late cynodonts (195 mya) lost the original articular-quadrate jaw hinge The articular and quadrate bones formed inner ear bones that functioned in transmitting sound In mammals, these bones became the hammer (malleus) and anvil (incus) bones of the ear

Figure 23.4c Early cynodont (260 mya) Key to skull bones Articular Temporal fenestra (partial view) Quadrate Dentary Squamosal Hinge Later cynodont (220 mya) Original hinge New hinge Very late cynodont (195 mya) Hinge

The history of life on Earth has seen the rise and fall of many groups of organisms The rise and fall of groups depend on speciation and extinction rates within the group Concept 23.2: The rise and fall of groups of organisms reflect differences in speciation and extinction rates

Figure 23.5 † † † Lineage A † † Common ancestor of lineages A and B Lineage B † 0 4 3 2 1 Millions of years ago

Plate Tectonics At three points in time, the landmasses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago According to the theory of plate tectonics, Earth’s crust is composed of plates floating on Earth’s mantle

Figure 23.6 Crust Mantle Outer core Inner core

Tectonic plates move slowly through the process of continental drift Oceanic and continental plates can separate, slide past each other, or collide Interactions between plates cause the formation of mountains and islands and earthquakes Video: Lava Flow Video: Volcanic Eruption

Figure 23.7 North American Plate Eurasian Plate Juan de Fuca Plate Philippine Plate Caribbean Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Scotia Plate Antarctic Plate

Consequences of Continental Drift Formation of the supercontinent Pangaea about 250 million years ago had many effects A deepening of ocean basins A reduction in shallow water habitat A colder and drier climate inland

Figure 23.8 Present Collision of India with Eurasia 45 mya Cenozoic Eurasia North America Present-day continents Africa 65.5 mya India South America Madagascar Australia Antarctica Laurasia Laurasia and Gondwana landmasses 135 mya Gondwana Mesozoic The supercontinent Pangaea Pangaea 251 mya Paleozoic

Figure 23.8a Laurasia Laurasia and Gondwana landmasses 135 mya Gondwana Mesozoic The supercontinent Pangaea Pangaea 251 mya Paleozoic

Figure 23.8b Present Collision of India with Eurasia 45 mya Cenozoic North America Eurasia Present-day continents Africa 65.5 mya India South America Australia Madagascar Antarctica

Continental drift can cause a continent’s climate to change as it moves north or south Separation of landmasses can lead to allopatric speciation For example, frog species in the subfamilies Mantellinae and Rhacophorinae began to diverge when Madagascar separated from India

Figure 23.9 1 2 2 1 Mantellinae (Madagascar only): 100 species Rhacophorinae (India/southeast Asia): 310 species 60 20 40 0 80 Millions of years ago (mya) India Madagascar 88 mya 56 mya

The distribution of fossils and living groups reflects the historic movement of continents For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached

Mass Extinctions The fossil record shows that most species that have ever lived are now extinct Extinction can be caused by changes to a species’ environment At times, the rate of extinction has increased dramatically and caused a mass extinction Mass extinction is the result of disruptive global environmental changes

Broad Patterns of Evolution