Chapter 18 Mass Extinctions, Opportunities and Adaptive Radiations

Chapter 18 Mass Extinctions, Opportunities and Adaptive Radiations
Figure CO: Dinosaur fossil © Styve Reineck/ShutterStock, Inc.

Extinction

Overview Extinctions are as important in the history of life as are the evolution of new species Explaining extinctions is just as challenging a scientific question as explaining the evolution of new species Extinctions are opportunities for adaptive radiations because extinctions open or re-open niches for new species to invade and occupy To understand extinctions, we need to identify rates, patterns and causes

Extinction Georges Cuvier is credited with establishing the reality of extinction for the scientific community in a lecture to the French Institute in 1796 G.G. Simpson and many other evolutionary biologists have estimated that 99% of all species are already extinct The only drawback to accepting that number is our lack of knowledge of how many species are actually living today, much less how many were alive in the past But not all species have gone extinct; there are some living fossils

Survivors — Lingula A marine organism (brachiopod) occupying vertical burrows in sand and mud has survived morphologically unchanged since the Silurian

Survivors — Horseshoe crabs
The horseshoe crab (Limulus), an inhabitant of marine shores, has lived morphologically unchanged since the Ordovician

Survivors — Cycads and Horsetails

Survivors — My Favorite!
Periplaneta americana: the cockroach

Extinctions We know very little about natural extinctions, especially the precise causes Fossil records demonstrate that extinctions have occurred repeatedly in the past But physical evidence of causative agents are rarely preserved Cause and Effect is hard to establish

Extinctions Habitat Disruption Habitat Modification
Volcanic Eruptions Asteroid Impacts Sea Level Change Habitat Modification Climate Change Mountain-Building Precipitation Change Toxic Materials “Exotic” Species Introductions Continental Drift

Co-Evolution & Niches Any species living in a niche has evolutionary relationships with other species; some casual, some crucial Therefore, the extinction of a species will have repercussions in the niches of all species which have co-evolutionary relationships with the newly extinct species

Rates of Extinction There is much debate about the degree and the importance of different rates of extinction Once again, the incomplete fossil record makes answering the question far more difficult The simple comparison is between a background rate of “uniform” extinctions, and the occasional episodes of “mass” extinctions

Uniform/Background Extinctions
Species Average Survival Time marine invertebrates – 30 million years mammals – 2 to 3 million years one estimate for all fossil species – 4 million years Rate of Species Extinction One estimate for the background extinction rate is for one to seven species to die each year The same source estimated mass extinction rates as being 3 to 4 times the background rate with 75 to 95% of species dying; this is a rate of perhaps 15 to 30 species per year

A major problem in estimating the rate of fossil species extinction is the incomplete fossil record Approximately one quarter of a million fossil species have been identified so far (in ~35,000 genera from ~4,000 families)

Based on current biodiversity (~40 million living species?) and average species extinction rates, there may well have been 5 to 50 billion species present on earth since the origin of life on earth So all our conclusions should be considered very tentative

Extinctions Extinction is the converse of speciation; species arise and species disappear Extinction can be considered at levels of increasing severity and impact: Extinction may be local and limited to demes Extinction may eliminate an entire species Extinction may eliminate most or all of the species in a region, habitat, or ecosystem Extinction may be of much larger scale, eliminating most of the species on a continent or on Earth –these are the mass extinctions At least five mass extinctions have occurred in the history of life on earth Each mass extinction has been followed by the successful adaptive radiations of new organisms

Table T01: Details of the Five Major Mass Extinction Events Since the Cambrian
Source: Raup, D.M. and J.J. Sepkoski, Jr., Science 231 (1986): 833–835.

The Five Major Mass Extinction Events
Why are Mass Extinction Events defined by the relatively abrupt disappearance of at least 75% of marine animal species? Because over the 500 million years of metazoan existence, the most complete fossil records are for marine animals Geologists tend to divide that time into Eras and Periods by mass extinctions, which are followed by adaptive radiations of new forms; or simply by major adaptive radiations of new forms (index fossils)

Mass Extinction Events
Note that this chart tracks all animal families, not just marine animals, and at the family level, not the species level

The Ordovician Extinction Event
#1 The Ordovician Extinction Event The second-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct and the second largest overall in the overall loss of life Between about 450 Ma to 440 Ma, two bursts of extinction occurred, separated by one million years This was the second biggest extinction of marine life, ranking only below the Permian extinction

At the time, all known metazoan life was confined to the seas and oceans More than 60% of marine invertebrates died; brachiopods, bivalves, echinoderms, bryozoans and corals were particularly affected The immediate cause of extinction appears to have been the tectonic movement of Gondwana into the south polar region

Gondwana drifting south led to global cooling, glaciation and falling sea levels The falling sea levels disrupted or eliminated expansive shallow marine habitats along the continental shelves The event was preceded by a fall in atmospheric CO2, a global cooling, and the newly forming Appalachian Mountains may have been the CO2 sink

Middle Ordovician

The Devonian Extinction Event
#2 The Devonian Extinction Event The third-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct The timing is less well understood Conflicting hypotheses propose from as few as two to as many as seven related bursts of extinction centered on 365 Ma to 440 Ma, over as little as one half to as many as 25 million years The extinction seems to have primarily affected marine life

By the late Devonian, there were massive reefs built by stromatolites and corals in the oceans, while the land had been colonized by plants and insects Vascular plants were becoming tall and changing the soils as well as the co-evolving biota Euramerica and Gondwana were beginning to converge into what would become Pangea Hard-hit groups include brachiopods, trilobites, and reef-building organisms; the latter almost completely disappeared, with coral reefs only returning upon the evolution of modern corals during the Mesozoic Surprisingly, jawed vertebrates seem to have been unaffected by the loss of reefs, while agnathans were in decline long before the end of the Devonian

The causes of the Devonian extinctions are unclear The extinction of ~20% of all animal families and 70-80% of all animal species Leading theories include changes in sea level and ocean anoxia, possibly triggered by global cooling (glaciation on Gondwana) or oceanic volcanism The widespread oceanic anoxia prohibited organic decay and allowed the preservation of sedimented organic matter as petroleum and coal The impact of a comet or another extraterrestrial body has also been suggested, but the evidence is weak

Late Devonian / Early Carboniferous
continents drifting together to form pangaea

The Permian Extinction Event
#3 The Permian Extinction Event The Earth's most severe mass extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct It is the only known mass extinction of insects Some 57% of all families and 83% of all genera were killed Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after other extinction events

There were from one to three distinct pulses of extinctions that occurred about million years ago There are several proposed mechanisms for the extinctions The earlier phase was likely due to gradual environmental change, while the latter phase may has been due to a catastrophic event

Suggested mechanisms for the latter catastrophic extinction pulse include: large or multiple bolide (meteor/comet) impact events increased volcanism and sudden release of methane clathrate from the sea floor gradual changes include sea-level change, anoxia, increasing aridity, and a shift in ocean circulation patterns driven by climate change Excess dissolved CO2 acidified the oceans, contributing to the decline of shelled organisms

Most fossil insect groups found after the Permian–Triassic boundary differ significantly from those that lived prior to the P–Tr extinction Over two-thirds of terrestrial labyrinthodont amphibians, sauropsid ("reptile") and therapsid ("mammal-like reptile") families became extinct Large herbivores suffered the heaviest losses

Late Permian

The Triassic Extinction Event
#4 The Triassic Extinction Event The first of the final two more modest of the five major extinction events The extinction occurred around 208 million years ago and happened rapidly in less than 10,000 years just before Pangaea started to break apart This extinction struck marine life and terrestrial life profoundly At least half of the species now known to have been living at that time went extinct In the oceans, a whole class (conodonts) and 20% of all marine families disappeared Conodonts were early eel-like chordates

On land, all large crurotarsans (non-dinosaurian archosaurs) other than the crocodilians, some remaining therapsids, and many of the last large amphibians were wiped out This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period Statistical analysis of Triassic marine losses suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions

Several explanations for this event have been suggested, but all have unanswered challenges: Gradual climate change or sea-level fluctuations during the late Triassic; however, this does not explain the suddenness of the extinctions in the marine realm Asteroid impact, but no impact crater has been dated to coincide with the Triassic–Jurassic boundary; the largest late Triassic impact crater occurred about 12 million years before the extinction event Massive volcanic eruptions (known from the central Atlantic magmatic province -- an event that triggered the opening of the Atlantic Ocean) that the would release CO2 or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter)

Late Triassic / Early Jurassic

The Late Cretaceous Extinction Event
#5 The Late Cretaceous Extinction Event The second of two more modest extinction events, the fifth and final of the five major extinction events There is agreement that it was a relatively rapid extinction event dated to 65.5 million years Widely known as the K–T extinction event, it is associated with a geological signature known as the K–T boundary, usually a thin band of iridium-rich sedimentation found in various parts of the world

The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era Essentially all non-avian dinosaurs, mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates became extinct Stem mammalian clades passed through the boundary with few extinctions and began their remarkably successful adaptive radiations across the globe

Scientists theorize that the K–T extinctions were caused by one or more catastrophic events, such as massive asteroid impacts Like the Chicxulub impact, a 10km diameter meteorite, leaving a crater ~200 Km in diameter or increased volcanic activity Impact caused acid rain, ash that blocked out the sun for months, severe global cooling (nuclear winter). Increase in atmospheric CO2, resulting in global warming, the final blow to dinosaurs & many other Cretaceous species.

Several bolide impacts may have contributed to massive volcanic activity, such as the Deccan traps of west-central India, one of the largest volcanic features on Earth, have been dated to the approximate time of the extinction event Deccan traps

These geological events may have reduced sunlight and decreased photosynthesis, leading to a massive disruption in Earth's ecology Other researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate

What Happened to the Dinosaurs?
Sediments were deposited by enormous tsunamis (tidal waves) along the coastline 70% of known fossil species, including non-avian dinosaurs, were wiped out

What Happened to the Dinosaurs?

Before the end of the Cretaceous, flight evolved independently three times: insects, flying reptiles, birds (avian dinosaurs) By the end of the Cretaceous 65 Mya, most dinosaurs along with other large marine reptiles and various invertebrates died out No land vertebrate larger than a large dog survived the KT boundary event The angiosperm radiation was well underway during the Cretaceous, but the shift from gymnosperm- to angiosperm-dominated forests may have been triggered by the Late Cretaceous Extinction

Late Cretaceous

Note in the left chart that global temperatures have fluctuated dramatically over the time of life on earth but those dramatic changes do not always correlate with mass extinction events

Plants are relatively immune to mass extinction, with the impact of all the major mass extinctions "negligible" at the family level Even the reduction observed in species diversity (of 50%) may be mostly due to differential preservation of plant fossils However, a massive rearrangement of ecosystems does occur, with climax communities and dominant plants, plant abundances and distributions changing profoundly after mass extinctions

Figure 01: Percentage of marine animal extinctions
Mass Extinctions It is important to remember that mass extinctions are just temporary increases in extinction rates that are significantly more severe than the average background extinctions rates (illustrated in green) which also fluctuate through time Percentage of Species Wiped Out Ordovician-Silurian - 85% Late Devonian - 82% Permian-Triassic - 96% End Triassic - 76% Cretaceous-Tertiary - 76% background rate Figure 01: Percentage of marine animal extinctions Adapted from Fox, W. T., Paleobiology 13 (1987):

Mass Extinction Probable Causes
To the degree that mass extinctions are real, rather than artifacts of a poor fossil record, the causes are probably complex and multifactorial

Abiotic Causes for Mass Extinctions
Plate Tectonics Intermingling of Biotas / Introduced species effects Trophic Stability Changes in Sea Level and ocean chemistry Volcanic Activity changing atmospheric gases and dust levels Ice Ages with glaciations, falling sea levels, increased tropical aridity Planetary Collisions Cosmic Forces & Periodic Galactic Cycles

Trophic Stability When a landmass (a) is broken in two (b), this adds area along the perimeter where they split; this adds to the intertidal area which is a species and nutrient rich habitat When two landmasses (b) are brought together (a), this results in loss of available intertidal area

Trophic Stability The larger the land mass, the less climatic buffering from the oceans, which are heat sinks Therefore, during the time of Pangaea’s stability, there may have been more extremes of hot and cold, and wet and dry, in the supercontinent’s interior

Changes in Sea Level Movement of the Earth’s crustal plates results in their slow collision with each other Usually one plate over rides another, as shown here Note how the ocean basin between them changes in size and depth, thereby changing sea level against the side of the continents

Volcanic Activity Locally, lava flows sterilize and reform the surface, start fires, and their explosive blasts may also create damage within the surrounding habitat

Volcanic Activity Large volumes of volcanic dust enter the atmosphere and become a possible cause for the cooling of the earth by blocking out the sun’s rays and reducing photosynthesis

Ice Ages Formation of glaciers causes:
Vulcanism or other forces may contribute to the cooling of the earth and the formation of glaciers that covers a part of the earth’s surface for periods of time Formation of glaciers causes: Ocean levels drop (due to water trapped in glaciers as ice) Decrease in O2 levels Increase in salt (mineral) content of oceans Changes in natural environments

Ice Ages and Extinctions
Ice ages (blue) are indicated along this geologic time line for comparison to five mass extinction episodes (red) There is no tight correlation between ice ages and mass extinctions

Extraterrestrial Impacts
Extraterrestrial impacts are known to have battered the moon and Earth repeatedly since 4 Bya More than 100 large craters are known on Earth: Ten meteors, each one km in diameter, are estimated to have each produced 20-km–wide craters at a frequency of one every 400,000 years A 50-km–wide crater is produced every 12.5 My A 150-km–wide crater is produced every 100 My Extraterrestrial impacts frequently cause extinctions, but other than the K-T Cretaceous event, are probably not the single major cause of mass extinctions

Extraterrestrial Impacts

Cosmic Forces & Periodic Galactic Cycles
Supernova (explosion of a star) Influence on earth radiation levels and destroys ozone layer May have influenced extinctions (no scientific proof as yet) Changes in the properties of the Milky Way as the Solar System orbits around the galaxy’s center

Major Indirect Causes for Mass Extinctions
Continental-Flood Basalt Lava (3 of 5) 2. Abrupt Falls in Sea Levels (1 of 5) Asteroid/Bolide Impacts (4 of 5) Changes in CO2, H2S, and other green house gases and changes in O2 levels may also play a role Ordo- sea level falls; KT, Dev, PT, T - Asteroid; KT, T, PT - Flood Basalt Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

The Impact of the Late Cretaceous Extinction
The loss of the non-avian dinosaurs left many open niches and within 15 My, the mammals had radiated widely, occupying some of those niches, and finding others which had never existed before because there were also large changes in the plant communities

The Cenozoic The Last 65 My
Figure 02A: Continental landmasses: Early Eocene Here you can see how plate tectonics gradually rearranged the continental plates Continental drift and Climate change increased the diversity of habitats Especially reduced were the scope of tropical forests where dinosaurs had lived Angiosperms radiated widely adapting to these changes Figure 02B: Early Oligocene Figure 02C: Late Miocene Adapted from Janis, C.M., Ann. Rev. Ecol. Syst., 24 (1993):

The Radiations of Mammals
Traits, such as small size, that were of benefit during the Cretaceous extinction might not have been the traits that were most advantageous before extinction, when large dinosaurs dominated Changing climates and habitats created new opportunities Mammalian endothermy also permitted expansion into colder latitudes, altitudes, and into active nocturnal lifestyles

The Impact of Extinctions
There has been much speculation about the impact of the loss of the dinosaurs. Had dinosaurs not gone extinct, would the mammals have remained a minor component of the earth’s fauna ― small nocturnal insectivores? Would dinosaur lineages continued their advances in intelligence and social behavior?

The Butterfly Effect?

South America: Island Continent
One of the more interesting stories of the Cenozoic mammalian radiations is that of South American where placentals and marsupials evolved in isolation for about 30 My Birds also radiated widely in South America at this time, producing some of the top carnivores Figure B02A: Xenarthrans the largest was ~3 meters tall Figure B02B: Ungulates Adapted from Steel, R., and A.P. Harvey. The Encyclopaedia of Prehistoric Life. Mitchell-Beazley, 1979.

South America: Island Continent
Many of the South American marsupials and placentals became extinct as invading North American placental mammals diversified rapidly and took their place; a few S American species managed to expand to the north Here extinction resulted from competition for the same habitats & niches Figure B01A-D: Continental drift

Intermingling of Biotas — North and South America
Separate faunas and floras evolved on these continents when they were separate during the Cenozoic About 2 to 3 million years ago, the Isthmus of Panama formed, providing a land bridge between the continents that became a route of migration and exchange between the continents Among the placental mammals, many arising in North America dispersed south, and many originating in South America dispersed north This led to many extinctions, more in the South than in the North

Co-Evolution — Niches — Extinction
osage orange

Avocados and Osage Oranges only make sense in the light of megafauna That is because American gomphotheres (related to elephants) and ground sloths ate and dispersed those large-seeded fruits While those megafauna went extinct around 10,000 years ago, many large-seeded plants in the Americas are still around today If those plants once relied on those large creatures to disperse their seeds, why have they not gone they way of the dispersers?

Approximately 100 species of these New World large-seeded plants are thought to have once been dispersed by megafauna Scientists conclude that many large-seeded plant species, that once relied on bygone American elephants and gomphotheres, now rely on present-day small and medium-sized mammals such as primates, tapirs, along with domestic pigs and cows, for seed dispersal As those medium-sized mammal species become threatened, the large-seeded plants face possible extinction again

Australia: Island Continent
Equally interesting adaptive radiations of plants, invertebrates, and vertebrates occurred in Australia, New Zealand, and New Guinea

Gliding Locomotion Gliding has evolved more often than actual flying!
marsupial honeyglider Gliding has evolved more often than actual flying! Figure 03: Flying fish Courtesy of Shannon Rankin, NMFS, SWFSC/NOAA placental flying squirrel

Invading the Air: Flying Reptiles
Known adaptations for sustained powered flight have appeared only three times in the evolution of terrestrial vertebrates: in pterosaurs, birds and bats. Pterosaurs and Pterodactyls Figure 05: Pteranodon © Paul B. Moore/ShutterStock, Inc. Figure 04A: Pterodactyloids Figure 04B: Rhamphorhynchoids

Avian Dinosaurs: Birds
Based on cladistic classification, all birds nest within the dinosaur lineage Figure 08: Phylogenetic relationships between birds and sauropod and ornithischian dinosaurs Figure 06A & B: Archaeopteryx Reproduced from Heilmann, G. The Origin of Birds. Appleton, 1927 (Reprinted Dover Publication, 1972)

The Origin of Feathers Feathers evolved from reptilian scales for insulation and display Three major hypotheses for their origin: Feathers were an adaptation for insulating the (presumed) warm-blooded and ground-dwelling reptilian ancestors of birds Ancestral birds were tree-dwelling reptiles that used their developing wings to glide from branch to branch Ancestral birds were ground-dwelling runners whose feathers formed planing surfaces increasing their speed

The Origin of Feathers Figure 07A: Compsognathus Figure 09: 4-winged Microraptor The evidence favors origin from ground-dwelling ancestors However, the next stage may have been to move upward in the environment and then glide down Figure 07B: Archaeopteryx Figure 07C: Gallus C adapted from Dingus, L. and Rowe, T. The Mistaken Extinction: Dinosaur Evolution and the Origin of Birds. W. H. Freemanm, 1998. A and B adapted from Carroll, Robert. Patterns and Processes of Vertebrate Evolution. Cambridge University Press, 1997.

The Origin of Flight

Evolutionary Reversal: Flightlessness
The extinction of the dinosaurs opened up a large number of vacant terrestrial niche spaces The Ratites filled some of those niches Figure 10: Large flightless birds Adapted from Feduccia, A. The Age of Birds. Harvard University Press, 1980.

The Final Vertebrate Fliers – The Bats
Megachiroptera Microchiroptera The two sub-orders of bats are Megachiroptera (“megabats”) and Microchiroptera (“microbats”) Megabats most commonly eat fruit; have no echolocation, larger eyes than the microbats, and a longer snout The microbats possess echolocation (except for Rousettes and relatives), eat insects, blood, small mammals, and fish, lack the claw at the second forelimb, have poor eyesight, and possess a broader snout than the megabats The oldest known bat fossil (53 Mya), Onychonycteris finneyi , discovered in Wyoming, has wings like a modern bat but lacks adaptations for echolocation

The First Fliers – The Insects
Arthropods exploit almost every conceivable ecological habitat Insects evolved from crustaceans and the first fossil dates to the Devonian, ~400 Mya Insects underwent what may be the most explosive radiation of any animals since the Cambrian, diversifying into 900,000 extant species and perhaps as many as eight million undescribed species

The Insects The enormous diversification of insects has been attributed to the modular organization of the insect body in which antennae can evolve independently of wings, mouthparts independently of legs, and so forth — a process known as mosaic evolution Homeotic mutations, so common in insects, explain the comparative ease with which individual segments can be altered in a body plan that consists of serially repetitive elements

Arthropod Phylogeny Insects Some of the largest prehistoric flying insects were dragonflies whose wingspan could be as much as 0.75 meters

The Evolution of Insect Flight
The Paranotal hypothesis suggests that the insect's wings developed from paranotal lobes, a preadaptation found in insect fossils that is believed to have assisted stabilization while hopping or falling (not well supported by evidence)

The Epicoxal hypothesis suggests that the wings developed from movable abdominal/ tracheal gills found in many aquatic insects; these tracheal gills started as extensions of the respiratory system and over time were modified into locomotive purposes, eventually developed into wings; the tracheal gills are equipped with little winglets that perpetually vibrate and have their own tiny straight muscles

The Endite-Exite hypothesis suggests that the wings developed from the adaptation of endites and exites, appendages on the respective inner and outer aspects of the primitive arthropod limb; the innervation, articulation and musculature required for the evolution of wings are already present in podomeres (perhaps the strongest evidence)

The Paranota plus Leg Gene Recruitment hypothesis suggests that the wings developed from mostly immobile winglike projections from the back of the thorax. Then, once these projections were in place, already-existing genes for limb development were expressed on the back as well as in the legs, resulting in the formation of the joints and musculature needed to make functioning wing There have been some other hypotheses

Insect Flight – Direct Two living orders with direct flight muscles (mayflies and odonates - dragonflies and damselflies) and a variety of extinct insects that cannot fold their wings over their abdomen form a paraphyletic grade, the "Paleoptera“ The wing muscles of Paleopterans insert directly at the wing bases, which are hinged so that a small movement of the wing base downward, lifts the wing itself upward like rowing through the air In mayflies, the hind wings are reduced, sometimes absent, and play little role in their flight, which is not particularly agile In odonates, the fore and hind wings are similar in shape and size, and operated independently, and as aerial predators evolved more advanced flight ability Paleopteran insects Basic motion of the insect wing in insect with an direct flight mechanism. Scheme of dorsoventral cut through a thorax segment with wings a wings b joints c dorsoventral muscles d longitudinal muscles

Insect Flight - Indirect
Other than two orders with direct flight muscles (mayflies and odonates - "Paleoptera“), all other living winged insects fly using a different mechanism, involving indirect flight muscles This mechanism evolved once, and is a synapomorphy for the infraclass Neoptera It corresponds with the appearance of a wing-folding mechanism, which allows Neopteran insects to fold the wings back over the abdomen when at rest This ability has been lost secondarily in some groups, such as all butterflies The wing muscles of Paleopterans insert directly at the wing bases, which are hinged so that a small movement of the wing base downward, lifts the wing itself upward Neopteran insects Basic motion of the insect wing in insect with an indirect flight mechanism. Scheme of dorsoventral cut through a thorax segment with wings a wings b joints c dorsoventral muscles d longitudinal muscles

Insect Social Organization
Social Insects are one of Wilson’s pinnacles of Social Behavior Division of labor different morphological types (castes) diffusible hormones (pheromones) special foods, chemical signals Kin or Group selection? Figure 12A: Swarm of caterpillars © Joy Stein/ShutterStock, Inc.

Increased Complexity? Measuring complexity
Has complexity increased during organismal evolution? Not a “Great Chain of Being” Measuring complexity genome gene (copy) number increase in the size of organisms number of genes that encode proteins number of parts or units in an organism Measuring complexity number of cell types possessed by an organism; increased compartmentalization, specialization, or subdivision number of gene, gene networks or cell-to-cell interactions number of interactions between the parts of an organism

Increased Complexity? Increased genome? Yes.
Increased gene (copy) number? Yes, but highly variable.

Increased Complexity? Increased number of genes that encode proteins? Yes, but highly variable. Increased number of parts or units in an organism? Yes, in the transition from Prokaryotic to Eukaryotic cells; Yes, in the development of Metazoans, but with little change in 500 My; Much less in multicellular plants, and very little in Fungi. Many exceptions, especially among parasites and pathogens; many of their organelles or organs become simplified or disappear altogether (reversals). Increased number of interactions between the parts of an organism? Yes, probably, but very difficult to measure.

Figure 13: Time of origin of various animals
Increased Complexity? Increase in Numbers of Types of Cells? Yes Increased specialization, compartmentalization, or subdivision? Yes, but not for the last 500 My. Increased number of gene, gene networks or cell-to-cell interactions? Yes, but with many exceptions, especially the streamlined genomes of Eubacteria. Figure 13: Time of origin of various animals Adapted from Valentine, J. W., A. G. Collins, and C. P. Meyer, Paleobiology 20 (1994):

Modularity as a Form of Complexity
Developmental modules allow for adaptation of subunits in structures under somewhat separate levels of regulatory gene control Figure B04: Dentary bone of the rodent lower jaw Figure B03: Dentary bone of the rodent lower jaw In the honeypossum, we have an example of a reduction in complexity due to a homeotic gene change Courtesy of Brian Hall Figure B05: Western Australian honey possum Figure B06: Bone of the mammalian lower jaw Reproduced from Parker, W. K., Stud. Mus. Zool. Univ. Coll. Dundee (1890):

Increase in Organismal Size?
Increase in organismal size in a lineage is not routinely used as a criterion of complexity because no sustained size increase occurs within many lineages In many lineages, dwarf and giant forms evolve in response to specific ecological situations Dwarf and Giant forms: Especially on islands At high altitudes and latitudes Since dwarf and giant forms are neither more nor less successful than their average sized related taxa, and often live contemporaneously, size is a poor criterion for demonstrating trends in increasing complexity

Increase in Organismal Size?

Is There a Potential Sixth Major Extinction?
Increased extinctions began around 1700 AD Sixth Extinction by Richard Leakey and Roger Lewin (1995) Are we creating a mass extinction to rival the other major events in the geologic past? Species are becoming extinct at a rate of: ~ 4,000 – 30,000 species/year ~100/day ~1 species every 15 minutes

Is There a Potential Sixth Major Mass Extinction?
Why are species becoming extinct so rapidly? Human population growth Human impact on the environment Deforestation and Desertification Fragmentation and Destruction of Natural Habitats Contamination of Habitats mining wastes salts from irrigation and aquifer depletions Global Warming / Climate Change

Global Warming Increasing global temperatures
Rising ocean levels as polar ice caps and glaciers melt Changing seasonal weather patterns More frequent occurrence of weather extremes (e.g., stronger storm systems, increase in droughts & floods) Global migration of pathogens and disease vectors (HIV, malaria, bilharzia, cholera, etc.) typhoon Haiyan Philippines 2013

Human-Caused Holocene (Anthropocene) Mass Extinction
#6 Human-Caused Holocene (Anthropocene) Mass Extinction Human-caused extinctions of the last 10,000 years: Excessive Predation (food, fur, collecting, exotic pets, pest eradication, Chinese medicine, etc.) Destruction of keystone species Introduction of Exotic Species Competitors, Predators Diseases Exotic Pet Trade Air and Water pollution Soil and Ocean Pollution Golden Toad of Costa Rica described 1866, extinct 1989

Extinction — Commensalism
The flightless dodo lived on the island of Mauritus off the coast of Africa It was first described to science ~1600 The last Dodo bird was killed in 1662 It fed on plants and seeds, including the seeds of the Calvaria/Tambalcoque tree

Extinction — Co-Extinction
The Calvaria/Tambalcoque tree’s seeds had evolved thick coats to survive the passage through the grinding gizzard of the dodo With the extinction of the dodo, these seeds no longer made such an abrading trip through the digestive tract, the coat remained thick, and the young tree embryo could not so easily germinate

There Goes the Neighborhood
Humans arrive and megafaunas and many other species go extinct Australia 40,000 years ago Pacific Islands 30,000 years ago Americas 15,000 years ago Madagascar 2000 years ago New Zealand 1500 years ago Indian Ocean Islands 1500 years ago

Recent Extinctions Auroch (1627) & Dodo (1662)
Stellar’s Sea Cow (1768) Mascarene Island Giant Tortoise (1795) South African Cape Lion (1858) Quagga (1883) Passenger Pigeon (1914) Tasmanian Wolf (1936) Bali Tiger (1937) / Javan Tiger (1976) Kaua’i ‘O’o (1987) Golden Toad (1989) Baiji White Dolphin (2006) Chinese Paddlefish (2007) Christmas Island Pipistrelle (2009) Vietnamese Rhinoceros (2010) Pinta Island Tortoise (2012)

Where Will You Be in 2050? By 2050, it is estimated that the earth's human population will be ~9.1 billion (range 7.4 – 10.6) [7.0 billion in 2011] nearly 11 billion people by 2100 > 60% of those people will live in Africa, Southern Asia and Eastern Asia 50% of all species on the planet will be either endangered or extinct

By ? 50% of all species on the planet will be either endangered or extinct Habitat destruction Global Warming 25% mammalian species 15% bird species In The Future of Life (2002), E.O. Wilson of Harvard calculated that, if the current rate of human disruption of the biosphere continues, one-half of Earth's higher lifeforms will be extinct by 2100 Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Our Future Earth – 250 Million Years Ahead
Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (

A Simple Cladogram of the Tree of Life
In 2100, I expect all these higher taxa to be alive, but the destruction of individual species will be enormous and inevitable in the mean time In 250 million years, I expect most of these higher taxa to be alive, but I’m less confident for Homo sapiens

Chapter 17 End Victim of its own fecundity and adaptability

Radiations of the Metazoans in the Phanerozoic

What Happened at the Big Five Mass Extinctions?

"The picture's pretty bleak, gentlemen the world's climates are changing, the mammals are taking over, and we all have a brain about the size of a walnut."

A map of the world in 2007, with colours to highlight the population density of each country or territory. Numbers on the legend are in people per km2, and all countries smaller than 20,000 km2 are represented by a dot.

Chapter 18 Mass Extinctions, Opportunities and Adaptive Radiations

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Chapter 18 Mass Extinctions, Opportunities and Adaptive Radiations

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Presentation on theme: "Chapter 18 Mass Extinctions, Opportunities and Adaptive Radiations"— Presentation transcript:

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About project

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