Available at Extinction: past, present, future Gwen Raitt BCB 705: Biodiversity

 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. What is Extinction?

 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. The Fossil Record – Key to the Past The Occurrence of Fossil-Bearing Rocks

 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. The Fossil Record – Key to the Past An Incomplete Record

 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. The Fossil Record – Key to the Past Problems with Interpretation and Classification

The Geologic Time Scale

 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. Background Extinction and Extinction Events

Some Quantified Effects of Mass Extinctions Extinction EventAge (x10 6 years) b Families (%) Genera (%)Species (%) c End Cretaceous65.016—1747—5076 ± 5 End Triassic200.0— —2348—5380 ± 4 End Permian245.0— —5782—8495 ± 2 Late Devonian360.0— —2250—5783 ± 4 End Ordovician435.0— —2757—6085 ± 3 Table 6.1: The Effects on Skeletonized Marine Invertebrates of the ‘Big Five’ Mass Extinctions (modified a 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.

 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. Causes of Mass Extinctions

 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. End Ordovician 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. Late Devonian 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. End Permian 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. End Triassic 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. End Cretaceous 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  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 For a visited Hyperlink use this colour which is NISL  Keep within the frame … this ensures it will not get clipped when projecting.  Use Bullet Points as indicated (Square colour is ) Present Mass Extinction

 Dark green font Arial at least 18 point this colour is  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  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 For a visited Hyperlink use this colour which is NISL  Keep within the frame … this ensures it will not get clipped when projecting.  Use Bullet Points as indicated (Square colour is ) Human Extinction?

 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  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 For a visited Hyperlink use this colour which is NISL  Keep within the frame … this ensures it will not get clipped when projecting.  Use Bullet Points as indicated (Square colour is ) Conclusions – the Future?

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.