PRACTICE QUESTIONS MIDTERM EXAM: ANSWERS.

NOTE THAT I HERE LINK TO ONLINE SOURCES OF ANSWERS, BUT YOUR TEXT BOOK AND THE READINGS ALSO HAVE MUCH OF THIS INFORMATION.

PART 1. QUESTIONS WITH SHORT ANSWERS (about 1 page in blue book or less); 5 points each; expect about 5 of these.

1. How does a trilobite grow from larva to adult (growth processes)? How large do you think the largest trilobite could have been, and what would have limited its growth?

By addition of elements (segments) to an initial single head-shield, as well as by growth of segments later in life. Trilobites, like modern crustaceans, molt, and are limited in size because the soft-bodied form during molting must be able to survive (Attenborough movie); largest where about a soup-plate size (reading; length about 1 foot).

Trilobite reading, trilobite lab handout, also chapter 2 text book on growth, p. 20.

2. What are 'lagerstätten' and under what conditions do they form?

Localities where fossils are preserved unusually well, with traces of soft body parts. They form under conditions where predators did not disturb the fossils remains, such as under non-oxygenated waters (Burgess shale, Solnhofen limestone) or in ice (frozen mammoths).

text book chapter 1, notes lecture 1.

3. In which major aspects do Cnidaria differ from Porifera? In which respects are they similar?

Cnidaria and Porifera are both organisms without body cavities (acoelomates), and are both not bilaterally symmetrical. Porifera are organized at the cellular level (do not have true organs), Cnidaria are more complex and have organs. There are more things (e.g., alternation of polyps and medusae in Cnidaria, not in Porifera), but these are the most important.

textbook chapter 12; notes lecture 4.

4. What are Vendobionta, in what type of ecosystem did they live, and when did they live?

What are included in 'Vendobionta' are various organisms. Jellyfish or sea anemones, frond-like organisms, possibly related to modern soft corals and worms. There are also trace fossil (shallow burrows) maybe made by worms. Then there are unusual forms (quilted mattress structure, no mouth, gut or anus). All were either suspension feeders (taking particles from water), detritus feeders (picking up bacteria from sea floor), or lived on bacterial symbionts. There were no predators (no jaws), no burrowing up old organic matter ('Graden of Ediacara'). They lived from before the Cambrian revolution (starting at 650 Ma or so) into the Cambrian.

notes lecture 10.

5. What is the main point of punctuated equilibrium theory, and how is it related to the theory of allopatric speciation?

See lecture 6 notes; pages 74-76 text book. Punctuated equilibrium: in the evolution of species long periods of time in which nothing happens to the morphology of a species (stasis) alternate with relatively short periods of rapid morphological change (punctuations). We would expect this if allopatric speciation is common and most species originate by allopatric speciation: species originate in marginal areas of the species where few specimens are present, then migrate widely if they become reproductively isolated from their parent-species. It is only the widespread species which are commonly found.

PART 2: QUESTIONS WITH LONGER ANSWERS (2-3 pages of blue book); expect about 3 of these, 25 points each.

Question 1. Define what a mass extinction is and speculate on its possible causes. What were the two largest mass extinctions of the Phanerozoic? When did these happen? Were animals and plants equally hard hit? Which abundant groups of organisms became extinct at these two major mass extinctions? (See textbook chapter 6 and notes lecture 8; P/T extincton; K/T extinction) .

During a mass extinction many unrelated forms of life (adding up to a significant fraction of the total biota on Earth), living in many habitats all over the world become extinct within a geologically short period (maybe ~ 10,000 years or so). In order to do this, the global environment must have changed so severely and so rapidly that biota could not adapt by evolution or moved away by migration (as they did during the ice ages). Terrestrial causes: large scale volcanism leading to cooling (explosive volcanism) or warming (flood basalts exhaling CO2); possible indirect effects: warming results in low oxygen conditions in the oceans; cooling may lead to ise sheet formation and sea-level fall. Extraterrestrial causes: impacting asteroids or comets, exploding supernovae.

Permostriassic (P/T) extinction, about 250 million years ago (end of Paleozoic); Trilobites, Paleozoic corals (Rugosa, tabulata); many crinoids (sea lilies; Echinodermata) ; many brachiopods; many bryozoa; many sponges; large foraminifera (fusilinids); ancestors of Dinosaurs and mammals. Plants show short-term ecological disturbance, no major extinction.

Cretaceous/Tertiary (K/T) extinction, about 65 million years ago (end of Mesozoic). Plants show short-term ecological disturbance, no major extinction. Extinct: dinosaurs, oceanic organisms such a ammonites and mosasaurs, oceanic phytoplankton without resting spores; organisms with photo-symbionts (corals, reefs); filter feeders (feed on phytoplankton).

Question 2. Darwin first published 'The Origin of Species' in 1859. Present-day ideas about evolution contain concepts described by Darwin, as well as concepts added later (even much later). Describe Darwin's theory of evolution, additions that make up the so-called 'Modern Synthesis', and additions made after the formulation of the 'Modern Synthesis'; See notes lecture 6 ; textbook chapter 5.

Components of Darwinism as Darwin knew it: 1).Evolution occurred; 2) Common descent: all life on Earth has a single ancestor; 3)Multiplication of species: number of species increased during earth history; 4) Gradualism: evolution occurs gradually; 5. Natural selection is main cause

Natural selection:

  • All individuals of a species are slightly different
  • These differences are heritable
  • Not all young of a species survive into adulthood and reproduce
  • The individuals who are best adapted to their environment leave most offspring
  • Individuals who leave most offspring transfer their heritable characteristics into the next generation

Neodarwinism: 'The Modern Synthesis' combines Darwin's concepts with the concepts of Mendelian inheritance (1865 -1900), as well as with these of population genetics (Fisher, Haldane, Sewall Wright), genetics: (Dobzhansky), population field studies: (Mayr ), and paleontology (Simpson), with later added the information on the structure of genetic material (DNA-RNA) 1953 (Watson & Crick).

Problems can be classified under several headings, particularly the following:

  • Reductionism: genes say all there is to say about an organisms
  • Panselectionism: natural selection of individuals is the only cause of evolution.
  • Extrapolationism: small scale evolution is the same as large scale evolution.
  • Gradualism: all evolutionary change is gradual.

Question 3. Describe how ones does classical taxonomy, phenetic taxonomy and cladistic taxonomy, and problems with each. Describe how cladistic classification differs from 'traditional' classification of vertebrates that have eggs with an 'amnion' (Amniota). What is the major advantage of cladistic classification? (see notes lecture 5, textbook chapter 3, p. 53).

Problem: subjective (lumpers and splitters)

Problem: Homologous  versus Analogous structures: how can we distinguish these? Parallel evolution?

Problem: morphology not taken into account, thus classification may become counter-intuitive; number of categories becomes very large and cumbersome.

Traditional classification: Reptiles (cold blooded, scales, eggs); Birds (warm-blooded, feathers, eggs); Mammals (warm blooded, hair, internal development embryo).

Cladistics: Mammals are in one group (actually, together with 'mammal-like reptiles); Birds are in the same group as 'Reptilia' (including turtles, lizards and snakes, crocodiles, dinoaurs); birds are most closely related to dinoaurs and are included in one group (non-avian dinosaurs, avian dinosaurs-birds) .

Advantages of using cladistics: it provides testable hypothesis. Each cladogram is a hypothesis to-be-tested: it predicts characters that should be seen if further groups are studied, or if different study methods are used; one is thus forced to state very clearly what assumptions have been made. From the cladogram one can make predictions about what charcaters should be found in as yet not studied organisms: testable hypotheses.