Extinction: past, present, future

1. Extinction: past, present, future Gwen Raitt BCB 705: Biodiversity

2. What is Extinction? • Extinction is the process through which a species or higher taxonomic category ceases to exist. • Extinction may also be defined as the disappearance of any evolutionary lineage (from populations to species to higher taxonomic categories) because of death or the genetic modification of every individual. • Where a lineage has changed such that a new (daughter) species is recognised, the extinction of the original (parent) species may also be called pseudoextinction. • The new and original species are known as chronospecies. • Extinction may be regarded as the result of failing to adapt to environmental changes. • Extinction is a natural process.

3. The Fossil Record – Key to the Past The Occurrence of Fossil-Bearing Rocks • Fossils are usually found in sedimentary rocks. • Sedimentary deposits are most likely in low-lying areas. • Each site may have fossils representing a limited fraction of geological time because: • Sediment deposition was not continuous, • Sedimentary rocks erode. • The further back in time, the fewer the sedimentary depo-sits that are available because of: • Erosion, • Metamorphosis.

4. The Fossil Record – Key to the Past An Incomplete Record • The fossil record is known to be incomplete. • Some time periods are poorly represented by sedimentary rock formations. • Lazarus taxa • Many large extinct species are poorly represented. • The rate of description of new fossil species is steady. • Fossil formation depends on the durability of the specimen, burial and lack of oxygen. Most organisms do not form fossils because: • They do not have hard skeletal parts, • They get eaten, • They occur where decay is rapid or deposition does not occur, • They did not live/die during a period of sedimentation.

5. The Fossil Record – Key to the Past Problems with Interpretation and Classification • Determining fossil’s age is difficult because: • Radiometric methods cannot be used directly on the fossil, • Fossils deposited over a brief time interval are often mixed before the sediment becomes rock, • Identifying fossils may be difficult because the nature of the fossil may hide the diagnostic traits. • For palaeontology, a species is a morphologically identifiable form. • Some living species cannot be morphologically separated by skeletal features so a single fossil “species” may consist of more than one biological species. • For some groups, living species can be differentiated by skeletal features so fossil species are probably also skeletally unique. • Species representation in the fossil record is poor so palaeontologists tend to consider genera and higher taxa.

6. The Geologic Time Scale

7. Background Extinction and Extinction Events • Extinction is natural (Freeman & Herron 1998). The normal extinction rate is known as background extinction or the background extinction rate (Futuyma 1998). • Background extinction rates are constant within clades but vary greatly between clades (Freeman & Herron 1998). • Extinction events were used to demarcate the geological time periods (Leakey & Levin 1995). • gg • Raup & Sepkoski (1984) suggest that mass extinction events occur periodically at about 26 million year intervals.

8. Some Quantified Effects of Mass Extinctions Table 6.1: The Effects on Skeletonized Marine Invertebrates of the ‘Big Five’ Mass Extinctions (modifieda from p713, Futuyma 1998) a Modifications come from Anderson (1999), Lévêque & Mounolou (2001), Broswimmer (2002), Futuyma (2005) and Wikipedia Contributors (2006c). b Time periods are given for the older mass extinctions because the literature gives variable dates. c The species percentages are estimated from statistical analyses of the numbers of species per genus.

9. Causes of Mass Extinctions • Extinction events were used to demarcate the geological time periods (Leakey & Levin 1995). • Click on the text box and right click on the mouse and a menu should appear and you select the Copy • The move to the slide you wish to paste to and right click on the mouse and a menu should appear and you select the Paste • Raup & Sepkoski (1984) suggest that mass extinction events occur periodically at about 26 million year intervals.

10. End Ordovician Mass Extinction • The earliest of the five mass extinctions. • Happened about 439 million years ago. • Impacts on life forms: • Plants, insects and tetrapods had not yet developed so they were not affected. • Marine organisms affected: brachiopods, cephalopods, echinoderms, graptolites, solitary corals and trilobites. • Suggested causes include: • Climate change, • A drop in sea level, • Asteroid or comet impacts, • A gamma ray burst.

11. Late Devonian Mass Extinction • The second of the five mass extinctions. • Happened about 365 million years ago. • Impacts on life forms: • Insects and tetrapods had not yet developed so they were not affected. • Plants: the rhyniophytes decreased. • Marine organisms affected: ammonoids, brachiopods, corals, agnathan fish, placoderm fish, ostracods and trilobites. • Suggested causes include: • Climate change, • Multiple asteroid impacts.

12. End Permian Mass Extinction • The third and biggest of the five mass extinctions happened about 245 million years ago. • Impacts on life forms: • Plants: the previously dominant Ottokariales (glossopterids) became extinct. • Insects: about two thirds of the insect families became extinct and six insect orders disappeared. • Tetrapods affected: amphibians and mammal-like reptiles • Marine organisms affected: benthic foraminifera, brachiopods, bryozoans, echinoderms, 44% of fish families, all graptolites, solitary corals and all trilobites. • Suggested causes include: climate change, a drop in sea level, massive carbon dioxide (CO2) poisoning, oceanic anoxia, the explosion of a supernova, asteroid or comet impacts, plate tectonics during the formation of Pangea and high volcanic activity.

13. End Triassic Mass Extinction • The fourth of the five mass extinctions. • Happened about 210 million years ago. • Impacts on life forms: • Plants: several orders of gymno-sperms were lost and the Umkoma-siales (Dicroidium) became extinct. • Insects: not severely affected. • Tetrapods affected: some reptile lineages – the mammal-like reptiles (therapsids) especially. • Marine organisms affected: ammonites, ammonoids, bivalves (Molluscs), brachiopods, corals, gastropods and sponges. • Suggested causes include: one or more asteroid/comet impacts, climate change and volcanic activity.

14. End Cretaceous Mass Extinction • The final and best known of the five mass extinctions. • Happened about 65 million years ago. • Impacts on life forms: • Plants: debatably up to 75% of species. • Insects: not severely affected. • Tetrapods affected: 36 families from 3 groups (dinosaurs (all non-avian), plesiosaurs and pterosaurs. • Marine organisms affected: ammonites, ammonoids, cephalopods, bivalves, foraminifera, icthyosaurs, mosasaurs, plackton and rudists. • Suggested causes include: asteroid/comet impact, climate change and volcanic activity. • The occurrence of an impact event has been verified.

15. Present Mass Extinction • There is evidence that the extinctions on New Zealand and the Pacific Islands after human colonization were ultimately caused by humans (Caughley & Gunn 1996). • Use animation and the effects of BLINDS for TEXT and DISSOLVE for IMAGES– they are quick and effective and bring in by paragraph and then dim after mouse click to a mid grey colour 150 150 150 • Give each slide a header … there is space in the top and it also uses the colour 150, 150, 150 this uses Word Art and can be stretched. Use VIEW / MASTER/ SLIDE MASTER to access • If you need to hyperlink such as this is the URL for NISL if you use this as a template the colour is already set and is 96 132 113. For a visited Hyperlink use this colour which is 204 102 0 • Keep within the frame … this ensures it will not get clipped when projecting. • Use Bullet Points as indicated (Square colour is 128 128 0 )

16. Human Extinction? • Dark green font Arial at least 18 point this colour is 70 70 0 • Use animation and the effects of BLINDS for TEXT and DISSOLVE for IMAGES– they are quick and effective and bring in by paragraph and then dim after mouse click to a mid grey colour 150 150 150 • Give each slide a header … there is space in the top and it also uses the colour 150, 150, 150 this uses Word Art and can be stretched. Use VIEW / MASTER/ SLIDE MASTER to access • If you need to hyperlink such as this is the URL for NISL if you use this as a template the colour is already set and is 96 132 113. For a visited Hyperlink use this colour which is 204 102 0 • Keep within the frame … this ensures it will not get clipped when projecting. • Use Bullet Points as indicated (Square colour is 128 128 0 )

17. Conclusions – the Future? • If mass extinctions do occur periodically, the next natural mass extinction should occur in the next 10 million years. • Use animation and the effects of BLINDS for TEXT and DISSOLVE for IMAGES– they are quick and effective and bring in by paragraph and then dim after mouse click to a mid grey colour 150 150 150 • Give each slide a header … there is space in the top and it also uses the colour 150, 150, 150 this uses Word Art and can be stretched. Use VIEW / MASTER/ SLIDE MASTER to access • If you need to hyperlink such as this is the URL for NISL if you use this as a template the colour is already set and is 96 132 113. For a visited Hyperlink use this colour which is 204 102 0 • Keep within the frame … this ensures it will not get clipped when projecting. • Use Bullet Points as indicated (Square colour is 128 128 0 )

18. Links to Other Chapters Chapter 1 Biodiversity: what is it? Chapter 2 The evolution of biodiversity Chapter 3 Biodiversity: why is it important? Chapter 4 Global biodiversity and its decline Chapter 5 Biodiversity: why are we losing it? Chapter 6 Extinction: past, present, future. I hope that you found chapter 6 informative.