Term
What are the major types of evidence for life on Earth?
What kinds of information do each provide about ancient life? |
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Definition
Fossils: Actual physical records of life, the original thing or some remnant of the original thing.
Isotopes: Composition of the rock record rivals the fossil record in determining the history of the Earth.
Biomarkers: Groups of organic chemicals that are distinctive of particular groups of life.
Phylogenies: Hypotheses of relationships that give us the relative sequence of events in the history of life. Phylogenies are of equal status and importance in reconstructing the history of life to fossil evidence. |
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Term
| Why should ecologists know something about the history of ecosystems? |
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Definition
| Test ecological models when a time scale of observation longer than that of modern ecological study |
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Term
What is uniformitatianism?
In what respects is this a testable hypothesis for Earth processes? |
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Definition
Uniformitarianism: Processes observed in the modern world have have acted fundamentally the same way in the past.
Testable because: Observation suggests there is physical and chemical law, we can test the hypothesis that basic physics has not changed by comparing estimated rates of radioactive decay on the same rock, cross comparison of methods of dating of independent systems. |
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Term
| What is the difference between progressive (or mechanistic) and contingent (or random-walk) views on the evolution of the Earth? |
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Definition
Progressive (mechanistic) theorizes that the state of organisms today and throughout evolutionary history is inevitable. There are only so many outcomes for the direction of life when considering limited conditions that over a long time scale we would see the same outcomes even if the evolution of life on Earth were to start again. If you replay the tape of life, you would get the same result every time. Frequent occurrences of convergence argues that the number of design solutions for life is small, therefore highly likely that similar designs would arise again and again with the second playing of the tape.
Contingent (random-walk) theorizes that the history of life is a ‘random walk’ fom a left wall. The left wall being a point of the simplest possible life form. From that point, the evolution from small and simple to large and complex is a one way street, happening in a random fashion, and is not likely to be reproduced if the clock were reset. In this view, contingency dictates that we are not an inevitable result of anything. |
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Term
| What are fossils and what kinds of processes commonly are involved that promote the process of fossilization? |
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Definition
Fossils are remnants of an animals body or tracks and trails (trace fossils) that vary enormously in composition, preservation and information content.
Modes of preservation:
Compression by = simple burial (fine grained sediments are best because they provide better detail for fossils and prevent water penetration) amber preservation. Some mode of excluding oxygen.
Permineralization = Minerals (calcite, silica) precipitate into pores of fossil. |
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Term
| Why is microbial degradation of organic remains typically faster on the sediment surface than in the subsurface? |
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Definition
More oxygen and typically more water at the surface which allows for rapid organic matter decomposition. As you go deeper down, there is less oxygen because oxygen provides for the most efficient metabolic system and is used up quickly. The succeeding metabolic systems are in the order of: Nitrate, manganese, iron, sulfate, methane, which are less efficient and thus there is less decomposition of organic material.
Most of organic degradation occurs where oxygen and nitrate are available. Thereafter, preservation is likely.
Rapid burial = likely to have preservation |
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Term
| What role does skeletal mineralogy play in preservation of fossils? |
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Definition
Mineralogy of preservation:
Best = silica (chert), cryptocrystalline quartz, calcite, apatite, cellulose, lignin, sporopollenin
Eh = opal, high Mg calcite
Worst = aragonite, lipids |
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Term
| What are some useful features and challenges posed by time averaging and sampling when interpreting the fossil record? |
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Definition
Sampling bias:
Best preserved fossils are the most preferred and most collected samples. Have a better record of the things that preserve better than others. When collecting samples, it is often difficult to identify all species in the area because some species are rare. Need to create a collector’s curve in which you plot how many species are found for every sampling. Once your curve starts to level out where you find very few species per sampling, you can be pretty certain you have almost all of the species in the area.
Time averaging:
A function of sedimentation rate and burrowing depth (bioturbation) and transportation. When sed rates are slower time averaging increases.
Pros: a wider variety of fossils accumulate in the same strata over the extended time period.
Con: Extended exposure to oxygen and scavengers results in a smaller percentage of preservation
Better dead than alive: sampling dead population shows a wider variety of species. |
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Term
| Why can we use stable isotopes to infer metabolism of extinct life, or patterns of burial of organic matter? |
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Definition
Heavier isotopes are generally not used in metabolism because they are slower to react. Metabolic activities will discriminate against larger isotopes and thus a larger Carbon 12 to Carbon 13 ratio indicates metabolic activities.
13C/12C ratio = -25 to -28% for photosynthesis and -60% for methanogenesis. Abiotic contributors like volcanoes = -6%
delta Sulfur 34: -10% = S fermentation, -8 to -50% = sulfate reduction
Organic matter being buried means Carbon 12 is being buried. This means that there will be a larger amount of Carbon 13 in the sediments. And when there is erosion going on, there will be more Carbon 12 being exposed and thus more Carbon 12 will be in the sediment. |
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Term
Discuss evidence from both geology and phylogeny for the nature of the first life on Earth?
When did life likely become possible, and what kinds of environmental conditions would it have occurred in? |
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Definition
Direct evidence of body fossils.
Biomarkers tied to extant bacterial or archeal groups.
Trace fossils, such as stromatolites.
Isotopes: C13 rations. S34 ratios, life fractionates sulfer isotopes during sulfate reduction.
Oldest life:
Became possible ~900 Ma after world was cool enough for life. Some form of plankton found in Greenland deep sea sediments.
3.87 Ga - geochemical evidence for photosynthesis and methanogenesis
3.465 Ga - apex chert with body fossils of kerogen, segmentation, isolated strands of similar sizes. Heavily implied that this is not biogenic.
3.48 Ga - pillow basalts, microbial borings indicative of thermophilic communities. Modern analogs found in deep biosphere. |
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Term
Stromatolites are famously contentious when it comes to being interpreted as evidence of early life. Why is this?
What kinds of features provide strong evidence that these structures were built by microbial communities? |
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Definition
Because the laminated sediments they form in can also be formed by inorganic methods.
Features:
Diversity of shapes,
Are soft
Distinctive of different depositional environments
Contorted laminae
Kerogen-rich laminae
Lenses of desiccated fragments. |
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Term
| How are stromatolites built and what kinds of organisms do the building? |
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Definition
| Stromatolites are formed by microbial communities that grow on sediment. The “sticky” microbial mats capture sediment, and they keep growing on top of the sediment that accumulates on top of them. Also may have secreted own calcareous stuff around itself. |
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Term
| Discuss the geologic, isotopic, and environmental evidence for and against the claim that the oldest rocks on Greenland hold evidence of early life? |
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Definition
Plankton from organic material in deep sea sediments (turbidites) from Greenland.
Organic carbon metamorphosed to pure graphite crystals and graphite inclusions. Appear in banded iron formations, marble, metamorphic slate, and lithic sandstone.
Negative delta13 ratios from graphite inclusions in apatite grains
Life fractionates carbon isotopes (marine Corg has del13 of 25% while inorganic C does not exceed 10%)
Delta13=-40% cannot be achieved without life. Some suggest the negative delta13 can be caused by breakdown of carbonate rocks at high temp metamorphism
-others dispute age of rocks themselves
-some report delta13=-19% from graphite flecks in better preserved metasediments. Clearly not from breakdown of carbonates: could be remains of plankton
-gneisses of cross-cut dikes at 3.8 Ga dikes suggest sed are older than 3.8 |
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Term
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Definition
Radioactive Isotopes.
Sedimentary rocks by the presence of fossils of a known time range. That will get you a minimum age. |
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Term
What are some key pieces of evidence that provide strong evidence for evolution of different metabolic systems during the Archaean?
What are specific examples and how what is the quality of these examples in making the case for different metabolic systems? |
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Definition
Evidence for first life:
Biomarkers, isotopic indications of metabolism (see question Lecture 2 #5), trace fossils (wrinkle marks from microbial mats, cementation by stromatolites, flat pebble conglomerates)
3.87 Ga:
Geochemical evidence for photosynthesis and methanogenesis (Greenland)
3.465 Ga:
Apex chert
Thermophylic community
Body fossils of kerogen, segmentation, isolated strands of similar sizes
Heavily implied that this is not biogenic
3.48 Ga:
African pillow basalts
Microbial borings indicative of thermophilic communities
Modern analogs found in deep biosphere
3.465:
Strelly Pool Chert
Photosynth community, lithotrophs
2.72
(1) Tumbiana Formation – lakes, O2 photosynthesis
(2) δ13C = -40‰ to -50‰ à methanogenesis
2.6 – 2.68
Biomarkers in oil
Cyanobacteria evidence; O2 photosynthesis
2.3 – δ34S = -10‰ à sulfate reduction |
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Term
| What kinds of information can be used to create a phylogenetic hypothesis? |
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Definition
Morphology,
Genetics,
Behavior,
Biogeography |
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Term
| What are some potentially confounding issues (that may prevent us from arriving at a well supported phylogeny) that we face doing phylogenetic inference? |
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Definition
Determining the polarity, or rooting, of a clade: Which characters evolved first and which evolved last?
Usually done with an outgroup and paleotological evidence
Issue of fossilization: use comparative anatomy to reconstruct the primordial form
Assumption of constant clocks: rate of mutation is roughly constant on long time scales, temp of evolution is stable
Extinct or missing taxa
Lateral gene transfer- microbes love to trade genes
Convergent evolution- rare, but still reduces confidence |
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Term
| What are the basic types of metabolism and how do these map onto the tree of life? |
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Definition
Oxygenic metabolism.
Sulfate reduction.
Nitrate reduction.
Methanogenesis. |
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Term
| What are the main branch points in the tree of life? |
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Definition
Bacteria.
Archaea.
Eukarya. |
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Term
| Why is it so difficult to reconstruct the roots of the tree of life? |
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Definition
Very limited evidence as you go farther back into history of life.
i.e. skeletons are not developed, mostly biomarkers or trace fossils are what you have to deal with. |
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Term
| In what respects are cyanobacteria “hyperspecialists” and what are the evolutionary consequences and paleontological evidence of this specialization? |
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Definition
Hyperspecialists - utilize resources very efficiently but only under certain conditions
a. pretty much all different morphologies of cyanobacteria originated > 2 billion years ago
b. Morphologically stable: Single, simple cells, fragments, some with specialized cells...
c. Why do cyanobacteria not have to change for about 2 billion years?
1. they can turn off because metabolic rates are really low
2. no competition
3. efficiency |
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Term
| Conversely, what does Knoll mean when he argues that microbes specialize in doing nothing? |
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Definition
Bacteria are specialists.
They “specialize in doing nothing” meaning they are ready to turn on when conditions are favorable and go into stasis when conditions are unfavorable. |
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Term
| What is meant when we describe the diversification of life as a “left wall” or “Evolutionary ratchet” process? |
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Definition
a. get most basic metabolisms early (perhaps several times, if life was extinguished by heavy bombardment) then see regular expansion of life away from the most basic types of metabolisms to increasingly energetic systems
b. implies that few basic metabolisms have been lost (and probably have been discovered multiple times) and also implies there may be prebiotic life out there to be found
c. Implies a strong directionality to the record of life |
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Term
| What are the main processes that contribute to the formation of an oxic atmosphere and the reduction of free oxygen in the atmosphere? |
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Definition
a. Formation:
i.escape of hydrogen to space - UV light breaks up H2O in the atmosphere; when H escapes to space, O2 is enriched in the atmosphere
ii.Photosynthesis - uptake of CO2 and production of O2
iii. Burial of Organic Carbon - increasing ATM O2 since carbon cannot combine with O2 to form CO2
iv. Volcanism: both a source of O2 (through production of water from the mantle) and a loss function through formation of carbonic acid and SO4 - sulfuric acids and then to weathering rocks
b. Reduction:
i. Rock weathering: Oxygen is lost to the biosphere - particularly through oxidation and formation of Fe-oxides
ii. Respiration in surface environments - uptake of O2 by combination with organic matter to form CO2
iii. Exhumation of buried carbon |
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Term
| What lines of evidence are commonly cited that show when in the Preecambrian the atmosphere became at least partly oxygenated? |
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Definition
a. Sedimentary uraninite (UO2), siderite (FeCO3) and pyrite (FeS2) pebbles found unoxidized in sediments older than 2.3 to 2.6 Ga but none afterward
b. the dates of the first red beds are not known exactly - the soils are cut by intrusive dikes and sills with 2.2, 2.1 and 2.06 Ga dates, so they must be somewhat older than 2.2 Ga
c. Stromatolites become diverse and common after 2.5 Ga suggesting diversification associated with oxygenic photosynthesis and perhaps with eukaryotic communities
d. Carbon isotopes show period (2.8-2.3 Ga) when organic C dominated by methanogenesis - suggest little O2 around to oxidize methane before about 2.3 Ga
e. 2.3 Ga - same time when large scale organic carbon deposition starts allowing O2 to build up in atmosphere instead of oxidizing organic carbon
i.evolution of larger cells - sink better
ii. problem is that prokaryotes are small and so when they die they don’t sink much - microbial food loop - recycles organic matter almost entirely within the surface ocean - little sinks into the depths
iii. marine snow analog - allows better carbon export from surface ocean
iv. greater metabolic efficiency of oxygen metabolism compared to other metabolisms = more organic matter
v.see a change
vi. in TOC deposition in carbon isotopes
f. Increased SO4 fractionation - when there is little SO4 in sea water there is little fractionation - get SO4 from weathering of pyrite by O2
i. see more fractionation starting about 2.5 Ga (consistent with disappearing pyrite pebbles)
g. Banded Iron Formations (BIFs) - common between 2-2.5 Ga
i. Fe+2 is soluble in seawater but when oxidized to Fe+3 becomes insoluble (red)
ii. cyanobacteria - O2 (blooms) = laminations in BIFs |
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Term
| What are some of the main consequences of oxygenating the atmosphere for changing the composition of the ocean? [see also notes for Lecture 7]. |
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Definition
a. change in nutrient composition of the oceans
b. O2 oxidizes any H2S and inhibits Bacterial Sulfate Reduction by reducing the concentration of H2S in seawater
c. Canfield suggests that although the surface ocean may have become oxic by about 2.3 Ga the deep oceans did not become oxic until about 800 Ma = intermediate state between totally anoxic Archaean oceans and oxic latest Precambrian oceans was an anoxic and sulfitic ocean with an oxic surface ocean
d. by 2 Ga the sulfate reduction exceeded Fe delivery from weathering on land
e. allows seawater S to precipitate all of Fe out of seawater - big BIF deposition |
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Term
| What are the main lines of evidence that chroloplasts and mitochondria were once independent microbes? |
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Definition
a. chloroplasts and mitochondria both have DNA, RNA and ribosomes and a double membrane
b. They are semi-automous. reproduce separately via binary fission (not by mitosis like the eukaryotic cell itself) |
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Term
| How do we know that symbioses were established repeatedly and that not only prokaryotes but also eukaryotes were taken as symbionts of different lineages of eukaryotes? |
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Definition
i. show primary and secondary engulfing that leads to different structures
1. chloroplasts surrounded by four membranes in Cryptophyta
ii. Nucleomorph - debris of the nucleus and other cellular material/structure of an alga that was assimilated by the cell that became the Cryptophytes
iii. Tertiary engulfings as well
Page 130 Knoll. |
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Term
| What kinds of criteria are used to recognize eukaryotes in the fossil record and how reliable are these pieces of evidence? |
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Definition
a. Size of the cells - eukaryotic cells are quite bigger than prokaryotic cells
b. distinctive morphology - ornamentation can be very useful for distinguishing different organisms
i.spines, flanges, knobs, all on surface of cells that are strong indication of eukaryotic organization
c. Have preservable walls - early eukaryotes often appear to be cysts that were designed to protect a resting cell
d. Prokaryotes can have a-c individually but are not known to have all three characteristics in one cell
e. Multicellular differentiation - not totally perfect as some cyanobacteria can have different and be sort of multicellular, but multicellular eukaryotes have development of a body |
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Term
| Sketch the history of the eukaryotic fossil record |
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Definition
a. 2.7 Ga Biomarkers - cholesterols (indicative of eukaryotes)
b. 1.8 Ga have first Acritarchs - simple, often large, crushed bags with a split in them that could be eukaryotes but could be prokaryotes too
c. 1.85 Ga- Grypania - macroscopic comma or spiral shaped organic compression fossils from Montana, China up to 13 mm long and 2 mm wide
d. 1.5 Ga - start to get good fossils including the Roper group in Australia
e. 1.2 Ga - Sommerset Island cherts - clear red algal filaments (tells us that reds and greens separated from each other more than 1.2 Ga)
f. 1.0 Ga -Lakhonda Formation - simple branching filaments of Heterokont algae - complex life cycle
g. 800-700 mya - Grand Canyon shales and also Spitzbergen - green algae almost able to identify to genus level - green algae are primary engulfing of a cyanobacterium unlike the multiple engulfing origins of red algae
h. 635 mya - Doushantuo Formation in southern China |
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Term
What may explain the long delay between the advent of oxygenic photosynthesis and the advent of an O2 rich atmosphere?
(see also lecture notes for Lecture 5) |
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Definition
a. drawdown of O2 by weathering so need life to maintain an O2 atmosphere
b. evolution of O2 photosynthesis is not enough to make an oxygenated atmosphere - need an additional perturbation to cause O2 to rise - explains why O2 photosynthesis evolved >300 my before the Great Oxidation without causing the atmosphere to become oxic
c. The early Earth was an extremely reducing environment due to the previous lack of ATM O2. So there was a considerable buffering capacity. |
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Term
| Some definitions: “Pelagic”, “nekton”, “plankton”, “remineralization”. |
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Definition
Pelagic - open ocean >200m depth
Nekton - capable of swimming against currents
Plankton - just let the current take them wherever, can’t swim.
Remineralization - Being put back into the ocean system after being deposited |
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Term
| What is the carbon pump and what how has it evolved from the days of microbial food loops to the “fecal pellet express”? |
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Definition
Carbon pump is the pumping of carbon from surface ocean to the deep ocean. When only the microbial food loop, very little organic carbon ma de it down to the deep ocean where it could be buried or recrystallized because the microbes didn’t excrete heavy organic waste and were not heavy themselves so most of the organic carbon got recycled in surface waters before it could sink to the sea floor. During this time (younger than 543 mya) the sediment was non-burrowed, and the amount of carbon that made it to the bottom accounted for the net burial of carbon.
Later, the presents of metazoans altered the carbon pump by contributing large fecal pellets (leading to the fecal pellet express) and had much larger bodies than the previously dominant microbes, which sunk in the water column fast enough to make it to the bottom before being fully scavenged. the organic carbon was sent to deeper ocean quickly and thus was able to be buried and stored. During this time, burrowing organisms were present in the sediment, and played a key role in recycling nutrients (mixing sed to return nutrients to the water column and fixing other nutrients).
→ As Forams and Coccoliths (CaCO3) make it to the sea floor and get buried, oxygen in the ocean increases (making production and activity greater), nutrient cycling increases, and increased burial acts as a climate buffer. |
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Term
| How does weathering and atmospheric O2 affect the composition of nutrients in the oceans? |
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Definition
| Weathering brings nutrients like Mo and SO4 (from pyrite) into the ocean. Atmospheric O2 precipitates nutrients like Fe and P out of the water, making it unavailable to organisms. The SO4 causes Fe and Mo to be precipitated out of the water. |
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Term
Is molybdenum a “limiting nutrient” today?
When and why has Mo been a limiting nutrient in the past? |
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Definition
Molybdenum is not a limiting nutrient today. Molybdenum gets precipitated out by SO4 and is used in N fixation. Mo is more abundant today due in part to increased weathering.
1. Most Mo is in the form of sulfides that are weathered efficiently in an O2-rich ATM (like pyrite)
2. Mo and Fe, for example play a key role in nitrogen fixation (perhaps by nitrogen fixing bacteria and archaea, as in today’s ocean)—a process that really gets started with development of more-or-less oxic ocean by ~1-1.5 Ga.
3.In Archean have low Mo due to low weathering, low Fe too and low sulfate (since pyrite and Mo-sulfides are not weathered in anoxic atmosphere. As O2 builds up in ATM, the high sulfate delivered to the oceans by pyrite weathering into a low O2 deep ocean in the mid Proterozoic deep oceans (like the modern Black Sea) would tend to strip bio-essential metals from surface seawater like Fe and P ( as Fe and P-oxides) or metals like Mo, Zn, Cu from deeper anoxic waters (as Mo, Cu and Zn-sulfides) |
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Term
| Kennedy et al 2002 suggest that the development of a terrestrial biota, in the form of lichens and cyanobacteria had a major impact on metazoans in the oceans. What are the connections between terrestrial life and the rise of metazoan oceanic life? |
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Definition
→ the presents of terrestrial life created a “clay factory” in the ocean. “before the late precambrian, clay minerals deposited in marine sediments were probably not substantial until the evolution and colonization of the terrestrial env’t by some form of primitive land biota”... Land biota increase clay production b/c they “stabilize soil profiles, retain water, enhance weathering rates, drive chemical differentiation, and provide chemically adsorptive organic matter”. One reason that there may have been an increase in metazoan life is that there was an increase in oceanic oxygen due to increased burial of organic carbon by the “clay factory”. → check this!
→ clay-driven increase in OC burial resulted in a six-fold increase in O2 retention in the atm
→ land biota caused increased weathering intensity, increased PCM formation, increased OC burial and oxygen accumulation. |
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Term
Sketch the evidence and likely driving mechanisms behind the development of an oxic ocean.
How have changes in ocean chemistry contributed to changes in biotic evolution? |
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Definition
C-org burial, O2 metabolism, O2 ATM
Anoxic ocean from Archean buries 50% of the C-org produced → rapid increase in O2 in the atmosphere .
Increased weathering from O2 atmosphere delivers SO4 to the oceans, sulfate builds up in the oceans due to pyrite weathering→ sulfitic ocean ~2.5Ga
High sulfate in the ocean strips bio-essential metals (as Fe and P-oxides) from surface water and metals (as Mo, Zn, Cu-sulfides) from deeper anoxic water. Result: maximum of nutrients near oxic-anoxic boundary in ocean.
Fe and P become limiting in the surface ocean, oxic-anoxic boundary gets lowered, creates a more oxic ocean.
With a more oxic deeper ocean, C-org burial slows, the ratio of burial:exhumation is stabilized, C-org production is low because nutrients in the ocean have become limiting (note the flat section of d13C graph for the Mesoproterzoic)
C-org production rises again at ~700-800 mys due to (1) Fecal Pellet Express (2) Marine Snow (3) Continental Break-up (4) clay |
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Term
| What are the major lines of geologic evidence that the Earth became widely (if not entirely) glaciated several times during the Precambrian? What does evidence from the fossil record indicate about the geographic extent of these glacial events? |
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Definition
Glacial tills during that time period are found at mid latitude.
Till is found in current tropical and subtropical areas of the earth, indicating widespread glaciation |
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Term
| What are the main types of metazoan body plan organization in terms body layers and functionality? |
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Definition
Ecotoderm - outer layer, endoderm - inner layer,
Mesoderm - in between layer, forms organs and stuff.
Coelem - a cavity inside the organism can be compressed and decompressed. Used for digging/burrowing.
Sponges - No tissues, only differentiated cells that perform diff functions
Diploblastic - 2 tissue layers (ectoderm, endoderm).
Radial symmetry
Triploblastic - 3 tissue layers (ecto, endo, mesoderm).
Bilateral symmetry (distinct front and back) |
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Term
| 4 What are Stem and Crown metazoans, what role does paleontology play in recognizing them, and what does the existence of stem groups imply about the process of evolution? |
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Definition
Stem metazoans
Extinct forms that diverged before the crown
Crown Metazoans
The Last Common Ancestor of all the LIVING members of a clade plus all its descendants.
Paleontology gives us fossils that help identify what the stem groups may have looked like and what characteristics they had. The fossils can be used as tools to give a relative sense of when the stem groups diverged off from the branch that includes the living crown groups. The existence of stem groups implies that the process of evolution is gradual and follows several different paths at a time, not all of which survive. |
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Term
| How does a molecular clock work? |
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Definition
Molecular phylogenies generally suggest divergence times between the protostome (like arthropods, annelids, flatworms) and the deuterostomes (including vertebrates and echinoderms) between ~670-1500 Ma (Levinton 2001).
a. How does this work? Need to have dates on divergences in the younger parts of the tree; then extrapolate back assuming constant rates of molecular evolution to determine when the major early splits occurred.
b. Use a fairly conservative gene with slow rate of evolution. Why? So that there will be a fair number of molecular homologies between even distantly related groups.
c.The big assumptions are that
i. rates are constant,
ii. the fossil dates are accurate and represent maximum ages; although there are some methods that allow a range of dates.
a. The results strongly depend upon:
i. What dated events are used,
ii. How many dates you have,
iii. How close those dates are the event you want to date and
iv. How many gene systems are used.
a. Even then, you don’t actually date the divergences between body plans because body plans are composed of many different parts controlled by different genes. |
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Term
| What are the main differences between the results of molecular clocks and the fossil record when it comes to interpreting the origins and rates of evolution in the metazoans? |
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Definition
A Key Observation:
While some authors have arrived at molecular dates similar to the fossil record, these assume minimum dates for the various dated nodes;
1. Most molecular clock estimates are older than the fossil record suggests.
2. This is expected if the molecular dates are dating divergence times in gene systems (which they are supposed to do) rather than divergence times of fully formed body plans (e.g. Valentine 2003, Origin of Phyla, U. Chicago Press). |
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Term
| What evidence (other than molecular data) supports the conclusions of molecular clock analyses for a prolonged evolution of metazoans long before they turn up in the fossil record? |
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Definition
| The sponge biomarker record matches up well with the dates provided by molecular clock analyses, providing support for molecular clock analyses in general. |
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Term
| In what respects is the Cambrian and “explosion” and in what respects is it not explosive at all? |
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Definition
Huge diversity of organisms found during this time. May just be an explosion of skeletons though. We may just be finding a lot of fossils of different organisms because of better preservation of skeletons. Ediacaran organisms don’t get preserved well, which are what came before the “explosion”
Cambrian explosion occurs in the space of 33 my |
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Term
| What is the significance of the first trace fossils for the evolution of metazoans? |
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Definition
They developed a coelem, which indicated burrowing behavior → Corg getting exhumed. Helped create a C pump that stabilized the Earth’s atmosphere?
metazoans had to pass through two “Snowball” events. |
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Term
| Outline the major events in the fossil record of plankton from the Archean to the Mesozoic. |
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Definition
3.87 Ga - Greenland - deep water plankton, speculative.
1.8 - 1.5 Ga - Acritarchs found, galgae, fungi, protist.
1.1 Ga - Biomarkers for dinoflagellates found
1 Ga - 800 Ma - Increase in acritarch diversity. |
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Term
| What are some major transitions in the evolution of the carbon pump and remineralization of organic carbon in the oceans? |
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Definition
Archean - low energy metabolisms → low Corg production
Proterozoic - higher energy metabolisms develop due to oxygen, but the ocean is too oxic and very few nutrients are available due to their oxidation → low Corg production
In the Neoproterozoic, have the evolution of the “Fecal-pellet express” which Appearance of multicellular organisms
(a)Increases O2 by burying Corg,
(b)Increases nutrient gradients in the surface ocean by creating a strong “carbon pump” (and similar pump for all limiting nutrients)
(c)BUT: there is no way to recycle buried organic matter and nutrients before the evolution of large burrowing animals
In the Cambrian: see a great expansion of suspension feeding in shallow shelf waters—they are eating something, but the food is probably non- skeletonized plankton
(a)See a great expansion of burrowing—re-exposing previously buried nutrients back into the ocean.
(b)Indeed, Mary Droser (UCR) showed that burrowing intensity increases a lot across the Cambrian-Precambrian boundary; the depth and intensity of burrowing goes way up, so nutrient recycling from sediments goes up too.
(c)This Cambrian expansion of nutrient recycling from sediments adds the final touch to the nutrient system in the oceans (previously consisting of the ‘microbial food loop’ and the ‘fecal pellet express’).
1. But we do see a great increase in carbonate skeletons deposited on the shelf in the form of reef sediments. The burial of carbonates releases CO2 whereas the dissolution or erosion of carbonate takes up CO2 from the ATM and so moderates global climate. In the Mesozoic, see the evolution of calcifying plankton (foraminifera, nannoplankton). Evolution of radiolarians and calcifying plankton lead to more burial of Corg because they were heavier so when they died, they were more likely to sink to the bottom before getting brought back into the microbial food loop. |
|
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Term
| What lines of evidence do we have for the oxygenation of the oceans in the Phanerozoic (the last 500 myrs)? |
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Definition
This turns out not to be too easy to figure out…. One approach has been to use Mo isotopes (Dahl et al. 2010 PNAS 107 (42) 17911-17915. This suggests:
1. Neoproterozoic pO2 = 1-2% present atmospheric level (PAL = 21% O2 in modern atmosphere) of O2
2. ~15-50% PAL by Ediacaran time
3. 20-60% PAL in the early Paleozoic (Cambrian-Silurian)
4. ~40% PAL (or more) in Devonian when Earth starts to make coal
5. Eventually 100% PAL by the Cenozoic if not earlier.
A take home point: If you have more places to store carbonates (shelf and now deep sea) you stabilize ATM CO2—no longer see the wild swings in CO2 associated with “snowball” events [Ridgwell et al., 2003].
THE BIG BOTTOM LINE: In the end, the planetary metabolism is jacked up as the ocean becomes better oxygenated and the ATM does too. O2 metabolism is now EVERYWHERE. |
|
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Term
| How does the evolution of calcifying plankton in the deep ocean affect the greenhouse gas concentration in the atmosphere and the level of acidity in the oceans? |
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Definition
In the Mesozoic, see the evolution of calcifying plankton (foraminifera, nannoplankton). These organisms:
1. Transfer a great deal of carbonate to the deep sea
2. So now, even when sea level falls there is still a lot of carbonate being buried in the ocean;
3. The buried deep ocean carbonate can, in turn, be dissolved by CO2 invading the ocean form the atmosphere, so carbonate dissolution in the deep ocean modulates atmospheric CO2 and global climate!
4. The deep sea now becomes a major part of the system stabilizing CO2 in the atmosphere. |
|
|
Term
| What do we mean by “diffusional processes” and “constraints” in evolution? How about stochastic or contingent processes? |
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Definition
A) evolution can be seen as a diffusional process in which it fills available ‘evolutionary space’ assuming life can occupy all ecological “space”
B) Some fundamental constraint (like limits on how small an animal can be and still function) limit the lower size bound. If the upper bound is not similarly constrained we can see a tendency for evolution to fill out the range of permissible body sizes.
C) ? |
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Term
| What is the significance of conodonts and ‘amphioxus’ in early vertebrate evolution? |
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Definition
The conodonts appear in the early Cambrian ~525 Ma still lack bone but have
1. mineralized tooth-like elements arranged in 7 batteries of specialized structures.
2. Wear patterns suggest they were used as teeth rather than supporting a feeding structure and
3. they range from stabbing forms at the front of the mouth to crushing forms at the rear, further demonstrating their use as teeth;
However conodont animals had no jaws. Large eyes suggest these were visual predators. Conodonts were likely pelagic predators since they:
1. are very widespread (and used for biostratigraphy)
2. small (a few centimeters, max),
3. are found commonly in relatively deep ocean sediments |
|
|
Term
| When do sharks and modern bony fish diversify and what are some innovations in these groups? |
|
Definition
Sharks appear about 420 Ma (Silurian [although there are probable Ordovician shark teeth]) and develop many modern features including:
1. Partly calcified cartilage
2. A heterocercal tail (in which the notochord beds into the upper limb of the tail)
3. Two sets of pectoral and pelvic fins located under dorsal fins.
The modern bony fishes are the major group to radiate in the Jurassic and Cretaceous. The bony fishes:
1. not only have bone in the skeleton,
2. but also develop a free premaxilla.
3. In advanced bony fishes (Teleosts) the premaxilla can swing forward to increase the suction of the mouth. This strategy permitted a major radiation of the bony fishes.
Gills formed muscles by them so that they could swing open (expand volume quickly) to make suction feeding strategy better. The gills slowly migrated forward to form the jaws of many fish species. |
|
|
Term
| What are some innovations in marine reptiles and whales for a marine existence? |
|
Definition
Changes involve development of:
1. underwater hearing,
2. echolocation in the toothed whales, and
3. loss of the hind limbs
4. oil-filled bones (like marine reptiles)
5. Stiff vertebral column and many-boned fingers (also like Marine reptiles)
6. elongation of the skull (like marine reptiles)
7. migration of the nasal passages to the top of the skull (like marine reptiles)
8. Baleen (in the baleen whales) appears in the Oligocene ~30 Ma; initially in animals with teeth.
9. Get big: Large body size helpful to conserve heat, O2, and energy for
a. deep dives, and
b. long distance swimming to exploit distant food sources.
c. You guessed it: like marine reptiles! |
|
|
Term
| Why do marine vertebrates consistently develop deep diving and exploitation of the oxygen minimum zone? |
|
Definition
The O2 minimum is a great place to hunt because:
1. initially, the nautiloids (a group of cephalopod molluscs) were shelled and their gas-filled shells make great targets for echolocation (there is a very strong return pulse)
2. the cephalopods cannot move around much in the mid water because of O2 limitation—a whale with large body size does not have the same problem (can store O2 in blood for long-diving).
3.Notably, cephalopod diversity takes a dive when echolocating whales come on the scene[Lindberg and Pyenson, 2007].
4.See this today not only in whales but also deep diving seals (like elephant seals) which tracking experiments repeatedly visit the O2 minimum during foraging dives. |
|
|
Term
| What are the likely ancestors of whales and what are some other terrestrial groups that have gone back to the sea? |
|
Definition
Whales: Once, this transition was very poorly documented, but there is now a wealth of fossil evidence for the transition from terrestrial hippo-like mammals to whales.
1. Start with tetrapod wolf-like animal (Pachycetids),
2. then evolve forms with large webbed feet and
3. then evolve tail flukes with vestigial hind limbs.
a.Still see just the pelvic girdle in compete skeletons of Sperm Whales; the rest of the hind limbs are gone. |
|
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Term
| Outline the major events in the fossil record of plankton from the Archean to the Mesozoic. |
|
Definition
O2 → Better metabolism → stronger MFL, so more cycling at the surface ocean.
Also, larger organisms → sink, escape the MFL, end up in deep sea, included in the sinking is the ballasting of organic matter by clays creatd by terrestrial biota ~800 Ma. O2 at deep sea → burrowing, remineralization of C, gets sent back up to surface. |
|
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Term
| How does the evolution of calcifying plankton in the deep ocean affect the greenhouse gas concentration in the atmosphere and the level of acidity in the oceans? |
|
Definition
| Deep sea calcifying plankton → CaCO3 = buried consistently. CaCO3 = buried → releases CO2 into atmosphere. CO2 + H2O + CO3 ⇐⇒ 2HCO3. This buried CaCO3 can be dissolved again by the CO2 in the atmosphere, which takes up CO2 from the atmosphere. Acts as a buffer to the climate system, and thus keeps acidity in the oceans stable. |
|
|
Term
| What is the significance of conodonts in early vertebrate evolution? |
|
Definition
The conodonts appear in the early Cambrian ~525 Ma still lack bone but have:
1. mineralized tooth-like elements arranged in 7 batteries of specialized structures.
2. Wear patterns suggest they were used as teeth rather than supporting a feeding structure and
3. they range from stabbing forms at the front of the mouth to crushing forms at the rear, further demonstrating their use as teeth;
However conodont animals had no jaws. Large eyes suggest these were visual predators. Conodonts were likely pelagic predators since they:
1. are very widespread (and used for biostratigraphy)
2. small (a few centimeters, max),
3. are found commonly in relatively deep ocean sediments |
|
|
Term
| When do sharks and modern bony fish diversify and what are some innovations in these groups? |
|
Definition
~520 Ma - Agnathans. Not a true vertebrate because no true bones.
~470 Ma Jawed fish with suction feeding, free premaxilla for better suction.
~420 Ma Sharks with teeth, heterocercal tail, pectoral and pelvic fins. |
|
|
Term
| What do we mean by “diffusional processes” and “constraints” in evolution? |
|
Definition
Diffusional processes - diversification occurs in a way that species take up ecological spaces.
Constraints = the things that limit diversification. i.e. Can’t have calcified skeleton if you are going to be motile because its heavy. Evidence = convergent evolution is prevalent. |
|
|
Term
There is a distinct evolutionary trend away from shelled cephalopods in the Paleozoic to the dominance of ‘naked’ cephalopods in the Cenozoic.
Describe this transition and what some of the
constructional and functional constraints are thought to be that govern it. |
|
Definition
| Transition begins with the advent of marine mammals that use echolocation appeared. Shells = easy to target with echolocation and shelled cephalopods were restrained with their movement → easy targets. Constructional constraints = calcified skeleton → modern internal “skeletons” of cephalopods = calcite. Functional constraints = shells were commonly used for buoyancy → you see internal “skeletons” in modern cephalopods that are used for buoyancy regulation. |
|
|
Term
| What are some innovations in marine reptiles and whales for a marine existence? |
|
Definition
Oil filled bones → add buoyancy for life in the sea.
Elongation of skull and migration of nasal passage to top of the head
Hypocercal tails → for long distance travel
Stiff vertebral columns
Fins, flippers
Large size → to be able to exploit oxygen minimum zones to eat slow moving shits |
|
|
Term
| Why do marine vertebrates consistently develop deep diving and exploitation of the oxygen minimum zone? |
|
Definition
| Oxygen minimum zones have a lot of slow moving easy to capture little shits. |
|
|
Term
| What are the likely ancestors of whales and what are some other terrestrial groups that have gone back to the sea? |
|
Definition
Hippos → whales ~55 Ma
Elephants → sea cows ~55Ma
Minks → otters ~25 Ma
Bears → seals ~30 Ma |
|
|
Term
| Where does most of our fossil record come from? Why are epi-continental seas important to the fossil record? Why is it unfortunate that most of our fossil record comes from them? |
|
Definition
From continental shelves. Epicontinental seas were like extended continental shelves that were relatively low energy, so the things that died there typically didn’t get washed down to the deep sea like in modern shelf environments.
Its unfortunate because most of the sea floor is the deep sea floor, so we don’t have a good record of what actually has lived in the past. |
|
|
Term
| What is the history of epifaunal and infaunal tiering? |
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Definition
| Lack of predators → many epifaunal species at first with low burial depths for infaunal species. Advent of predators (Mesozoic Marine Revolution) → less epifaunal species and more infaunal species that bury deeper than before. |
|
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Term
| What are the main differences in composition and ecology between the Cambrian, Paleozoic and Mesozoic “evolutionary faunas” of Jack Sepkoski? What are some alternative approaches to describing Phanerozoic diversity? |
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Definition
Cambrian fauna → Paleozoic fauna → Modern fauna (Mesozoic onward)
Cambrian = low tiering, benthic deposit feeders, grazers, small shelly fauna
Paleozoic = Epifaunal (Brachiopods, bryozoans, corals, cephalopods) Many suspension feeders
Modern = lots of predators, lots of infaunal organisms. Sharks, mollusks, crabs, echinoids, echinoderms. Modern scleractinian corals also appear. |
|
|
Term
| What reasons do we have to doubt the accuracy of taxonomic trends in biodiversity (such as the Sepkoski curve for genera or families)? Conversely, what lines of evidence support the basic inference of increasing biodiversity during the Phanerozoic? |
|
Definition
|
|
Term
| What was the “Mesozoic marine revolution”? |
|
Definition
Period in which there were a ton of predators that appeared, which lead to a lot of innovations by the prey to avoid predation.
Thickened shells, smaller apertures, higher mobility, and deeper burial depths. Changes in shell shapes; etc as well. Lots of skeletons also appear |
|
|
Term
What is a reef and how have they changed over time?
What are some reasons that could account for changes in reef biota? |
|
Definition
Reef characteristics:
-Carbonate structures
-Biological in origin
-Wave resistant
-Life aggregations
-Relief above sea floor
Reef builders:
-Stromatolites
-Sponges
-Archaeocyathans
-Bryozoans
-Corals
-Calcifying algae
Events that killed off reef building organisms could trigger space for new types of reef builders to take over. i.e. sea level changes.
Developments in predation → different reef builders. Scleractinian corals = not very efficient, but are able to dominate because there are a lot of organisms that eat macroalgae and calcifying algae that would otherwise dominate. |
|
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Term
| What kinds of physiological problems did plants and animals have to overcome to become terrestrial? |
|
Definition
| Resistance to desiccation, non-swimming-in-environment reproductive cells, stiffer water-impermeable bodies, transport of fluids in and out, less water wasting waste production, |
|
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Term
| Outline the contrasts between the fossil record and the molecular clock record in deducing the early splits between major groups of terrestrial plants and their marine ancestors. |
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Definition
Molecular clock dates them to be much older like always ~800 Ma. Evidence for this date: Algae/Fungi split ~1Ga, closer. Meandering streams become present around this time (the idea being that need support of soil to create those structures - debated), advent of clays (lots of it), C isotope data in near shore environments indicating plant life (but what if it was actually near shore aquatic?) Also about the same time that animals started diversifying on land as well.
Other molecular clock data suggests younger like ~400-600 Ma (these ones used more genes)
Fossil record dates them to be much younger ~400 Ma, which matches some of the molecular clock data. |
|
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Term
| What kinds of traits did marine plants and animals have that aided their development of terrestriality? |
|
Definition
Marine plants:
-cyclic cellulose for structure
-apical meristems
-branching ability
-flavonoids (UV protection)
-spore bearing structures |
|
|
Term
| What kinds of changes in land plant reproduction, plant tissues and interactions with animals, occurred over the evolutionary history of land plants and when were the major transitions? |
|
Definition
| ~700 Ma or 400-600Ma vascular plants appear. Roots, sporopollenin/spores, more structural support (lignin), split between sexual and reproductive stages of life, waxy cuticles (antidesiccation) |
|
|
Term
| How does the evolution of roots and lignin influence the structure of terrestrial ecosystems and Earth’s biochemistry and climate? |
|
Definition
Roots → more soil stability, more meandering streams, more clay → more water being held.
Lignin → larger structures, forests |
|
|
Term
| Why, in spite of sampling artifacts, do we think that there are true mass extinctions? |
|
Definition
Taken from lecture 16:
Then there is the problem of what could cause mass extinctions in the first place: Here we
have to deal with the limits of imagination….
Appendix: Mass extinction mechanisms
Main problem is to explain why widely distributed species and members of ecologically- dissimilar groups can become simultaneously extinct. Particularly acute for extinctions involving both marine and terrestrial organisms or extinctions which do not appear to be selective.
Require global mechanisms:
1. bolide impact—nuclear winter scenario: dust injection, cooling, food chain collapse
2. hypercampnea-elevated CO2 acts as a narcotic, decreasing O2 uptake, and change in acid-base balance in CaCO3-secreating organisms during biomineralization.
3. Massive volcanic eruptions injecting the atmosphere with CO2 (causing global warming) or Sulfate aerosols (causing global cooling or toxicity).
Prompted by hypotheses that LIPs (Large igneous provinces) are linked with mass extinctions. Modeling suggests this is a difficult mechanism to get to work unless the gas is injected on time scales of less than 1000 years. Hard to see how LIPs could do this.
4. continental coalescence causing gradual loss of habitat. Clearly inadequate to explain abrupt extinction
5. Other potentially global mechanisms: Loss of ozone, cosmic ray damage from nearby supernova
1. Mechanisms of regional significance or may cause protracted extinction:
Anoxia-O2 consumption by organic matter consumption, stratification and
reduced ventilation, or oxidation of methane; Related effects would be draw-
down in redox-sensitive trace metals and increase in denitrification (Erbacher
and Thurow 1997).
2. Circulation changes that alter regional O2, nutrient, substrate; could reflect
gateway changes, sea level changes (affecting sill depths), could be ocean wide
but seem unlikely to kill cosmopolitan taxa or terrestrial species
3. Knock-on effects of removal of key members of the ecosystem. Could remove
a few taxa, but marine ecosystems are not thought to be so highly structured that
species would be under severe threat if other members of the ecological web
were removed.
4. Non-instantaneous climate/circulation change that reduces population sizes and ability to survive modest perturbations.
5.habitat loss from gateway openings, and disappearance of frontal systems between water masses (reducing niche diversity).
6.Viruses or other disease organisms—could appear nearly instantaneous from a geological perspective. |
|
|
Term
| What are some examples of “pressed” and “pulsed” extinctions and how might their causes be separated, or confused, in looking at the fossil record? |
|
Definition
Pressed = prolonged. Pulsed = immediate.
Pleistocene mass extinction: ~160 Ka Africa, 80 Ka Australia, 50 Ka Europe, 11 Ka North America caused by human migration = Pressed extinction.
K/Pg and P/T extinctions = pulsed. K/Pg = bollide impact. P/T = in question: Siberian traps or supervolcano.
Pulsed extinction >1 Myrs
Pressed extinction <1 Myrs
Causes may be confused because of regional extinctions. i.e. human migration induced mass extinction is a series of regional extinctions. End Ordivician mass extinction may be regional extinction not global.
When you look at the fossil record for an extinction boundary you oftentimes see taxa starting to peter out before the boundary. This is due to a faulty fossil record many times rather than a prolonged press extinction. |
|
|
Term
| What kinds of traits serve to predict the likelihood of extinction in a given taxon? |
|
Definition
| Large size, small geographic range, small population, specialist, low reproductive rate, low dispersal ability, low genetic diversity |
|
|
Term
| What is the essential contrast between the arguments that extinctions relate to “Bad genes” or “Bad luck”? |
|
Definition
Bad luck = holy shit a meteor hit me in the face
Bad genes = holy shit its so fucking cold because of all of this ash in the air thats blocking out the sun and I have no hair to keep me warm I fucking suck. |
|
|
Term
| What does the observed pattern of biodiversity imply about the kinds of processes that regulate diversity on Earth? |
|
Definition
| Observed pattern of diversity = Increased #families over time with dips in between that indicate extinctions. Mass death → opens up spaces for other species to dominate, which are derived from the survivors of the extinctions. There is an observed evolutionary pressure to become larger and have similar body plans. Everyone has the same constraints. |
|
|
Term
| Why is it difficult to determine causality in many (perhaps all) extinction events? Put another way, what kinds of sampling artifacts plague our ability to deduce the pace, magnitude and duration of an extinction event? |
|
Definition
Main problem is to explain why widely distributed species and members of ecologically- dissimilar groups can become simultaneously extinct. Particularly acute for extinctions involving both marine and terrestrial organisms or extinctions which do not appear to be selective.
For extinction events, some species disappear way below the impact line, and some disappear closer to it. How can we tell which disappearances are due to the extinction event? |
|
|
Term
| What is the history of evolution of such morphological traits as four limbs, upward pointing eyes and lungs in the evolution of tetrapods and what kind of environment did they originate in? |
|
Definition
~410 Ma lobe finned fishes → fins eventually became the four limbs. These lobed fins were used to “walk” around in clogged waterways where they would hide and ambush prey. These areas can get hypoxic → many developed air-breathing.
Upward looking eyes were retained.
~327 Ma lungs and feet evolved |
|
|
Term
| What is the pattern of ecological evolution of tetrapods and what kinds of innovations were needed for them to become fully terrestrial? |
|
Definition
| Pattern of ecological evolution = ate arthropods at first (easier access to nutrients because no cell wall), and then herbivory developed. Air-breathing (lungs), amniote. |
|
|
Term
| Why, (in phylogenetic terms, at least) should we have some respect for the chicken in our “KFC bucket”? |
|
Definition
| Because they are more derived than us. |
|
|
Term
| What are the major traits involved in the evolution of synapsids, therapsids and mammals and when do these innovations appear in the diversification of the whole group? |
|
Definition
Synapsids (Lillegraven 1979; Hopson 2001)
Includes mammals, and so called “mammal-like reptiles”
1. First appear in late Carboniferous ~310 Ma as Pelycosaurs—“Sail-backed Synapsids”—most are predators, but first herbivores by ~300 Ma (Kemp 1982)
a. Clearly ectotherms with food requirements about 1/10th that of modern mammals
b. No palate—probably bolt their food without chewing
c. Undifferentiated stabbing teeth
d. Lower jaw composed of multiple bones, all of which other than the dentary become parts of the ear in mammals. (Allin 1992)
e. Sprawling gait forcing the animals to suspend breathing while running.(Carrier 1987)
i. Both actions were controlled by same muscle groups and lungs were compressed by the side-to-side motion of the body in sprawl-gaited animals
ii. Therapsids moved the legs under the body separating locomotion from breathing
iii. Dinosaurs did this by being bipedal (like us)
2. Followed by the late Permian Therapsids (~260 Ma)
a. Had upright stance
b. Everything from high plant biomass browsers to insectivores to large animal predators (Rybczynski 2001)
c. Show tooth differentiation (specialization) from the front to the back of the jaw suggesting diverse diets and food handling.
d. Have a palate—suggesting a more endothermic ecology
e. Cynodonts a derived group of Therapsids with a complete palate
i. Have an external ear supported by jaw bones; not yet the internal ear of mammals (Manley 2000)
ii. A tympanic ear—capable of perceiving higher frequencies than the simple cochlear ear of stem amniotes and amphibians (evolves independently in lepidosaurs, turtles and derived archosaurs; 75 Ma after Lepidosaur/Archosaur split and 100 ma after mammal-archosaur split; 150 my after origin of amniotes)
iii. Suffer extinction [the really big one] in late Triassic ~210 Ma
iv. Survivors are the modern monotremes which have a primitive post-cranial skeleton like Cynodonts (Kielan-Jarorowska 2004)
1. Sprawling limb posture, hind claw (similar to that in other Cretaceous mammal groups)
2. Have origin in early Cretaceous with modern groups appearing in the Paleocene.
3. Mammals appear after the Triassic extinction (~210 Ma) and diversify in Jurassic and Cretaceous. (Olsen 1987)
a. Include Morganucodon with only two phases of tooth replacement— milk teeth and adult teeth (instead of regular replacement) (Crompton 1979)
b. Had hair as indicated by Harderian gland near eye
c. Probably the first to lactate (allows birth of young separate from seasonal food supply)
d. Mainly insectivorous and omnivorous
e. Became fairly diverse but remained small until dinosaur extinction-got to otter and small pig size.
4. Most stem mammals evolve in the early Cretaceous (possibly in the Jurassic or upper Triassic)
a. First Holotheria (including modern placental and marsupial mammals) appears in the late Triassic (~210 Ma); However fossil record of the major mammalian groups is mostly much younger [e.g. Multituberculates—rodent-like herbivores/omniivores (159 Ma (Clemens 1979)); Triconodonts—carnivores (165Ma), Placentals (~100 Ma), Marsupials (~90 Ma)]
5. Explosively evolve large body size and ecological specialization in Cenozoic after dino extinction |
|
|
Term
| What is the significance of the End Triassic mass extinction and how does it affect the evolution of tetrapods? |
|
Definition
| It killed off almost all of the Therapsids, opening up a chance for dinosaurs to dominate. |
|
|
Term
| What is the phylogenetic placement of dinosaurs within the Diapsids and what other groups of non-dinosaurian diapsids are there? |
|
Definition
Diapsids
Main groups:
1. Lepidosaurs--include marine reptiles and modern lizards + snakes
2. Archosaurs--includes the crocodiles, pterosaurs, dinosaurs and birds
3. Crocodiles a close ‘outgroup’ to dinosaurs
4. Marine reptiles a more distant outgroup
5. Most archosaur diversity also became extinct with synapsids in late Triassic
Major groups of dinosaurian diapsids differentiated (in part) on hip morphology:
1. Saurischian- pubis behind hip joint (ancestral condition)--includes theropod and sauropod dianosaurs + Birds
2. Ornithischian -pubis in front of hip joint--includes armored dinosaurs, duck-bills and ceratopsians
The Dinosaurs (Fastovsky 1996; Sereno 1999)
1. A derived group of archosaur diapsids
2. Ancestral group was bipedal--independently evolved four-legged stance among very large dinosaurs (Sereno 1993)
3. Probably all had parental care and vocalizations since these are present in crocodilians and birds;
a. Evidence for parental care in Dinosaurs comes from living outgroups:
b. Crocodiles (a dinosaur outgroup) and birds (highly derived dinosaurs) both:
c. Build elaborate nests of decaying vegetation
d. Vocalize with young,
e. Protect nests,
f. Care for hatchlings
g. Have fossil evidence of similar nests in extinct dinosaurs
4. emotionally challenged, however, since unable to show emotional range seen in mammals owing to restrictions in facial musculature….
5. Birds highly derived Saurischians
6. Very large body size evolved at least 8 times
7. Only birds survive K/T mass extinction |
|
|
Term
| What kinds of evidence do we have to infer the ecology and pattern of parental care in dinosaurs? |
|
Definition
| Inferred from crocodilian behavior. Create and protect nests, vocalize to young, care for hatchlings. We see similar nests in the fossil record for dinosaurs. |
|
|
Term
| What are some of the morphological and ecological traits of the major dinosaurian groups? |
|
Definition
Major groups of Dinosaurs include (Benton 1990; Sereno 1993; Fastovsky 1996; Fastovsky, Huang et al. 2004):
Ornithischia—armored, horned and duckbilled dinosaurs (Sereno 1986)
United by possessing a fleshy cheek for manipulating food
1.Armored groups include the Stegosaura, Anklosaura, and Pachycepthalosaura—first two of these are Thyreophora—
a. Sister group to the Cerapoda that include ceratopsians and duckbilled Ornithopoda;
b. Thyreopoda have leaf-shaped or flower-shaped teeth for slicing vegetation
c.wide rib cages to support a large hind guts for fermentative reduction of low-nutrient plant material (Farlow 1978).
d. Fed low to the ground,
e. Contrary to early reports did not have two brains [the ‘brain’ between the hips is a swelling to accommodate a ‘glycogen body’ like those found in modern birds—supplies glycogen for neural tissue growth]
1. Both Ceratopsians and Ornithopoda have tooth batteries
a. Ability to shed teeth like a shark,
b. Move the jaws side to side as well as up and down to macerate food before delivering it to the gut.
c. Most were at least partly quadrapedal with hooves on the fore feet, even in Ornithischians like duckbills. However, the digits may also be specialized with an opposable pinkie, three hooves and one stripping claw in Iguanodon.
d. Largely herding groups—suggested by monospecific bone beds
e. Frill (in Ceratopsians) and crest bones (in duckbills) regarded as sexual display and mate competition; both morphologies become more elaborate in more derived forms (Hopson 1975).
f. Saurischia—Sauropod and Theropod dinosaurs
1.Sauropodomorpha—all derived forms are quadrapedal with a ligament supported neck (up to 8.5 m) and a long counter-balancing tail.
a. Most with fore limbs the same length or longer than the hind limbs,
b. unlike most quadrapedal Ornithischians where the fore limbs are relatively short. The long limbs and neck allow large sauropods to reach ~13 m into trees.
c. Like giraffes, large sauropods would have needed a large heart to pump blood into the head, particularly if the animal was standing on its hind legs.
i. In giraffes, the heart is large to produce pressures over 300 mm of Hg with one way valves in muscularized blood vessels
ii. Calculations suggest a full grown Brachiosaurus would need a heart of 400 kg able to pump at pressures of >600 mm Hg.
1.Theropoda—highly diverse group, ranging from small (~1 m; 5 kg) to large (40 m; 7000 kg) animals;
a. remain bipedal (the primitive condition) with a stance like a chicken, but balanced by the long, ligament-supported (in big animals) tail.
b. Most predatory with either ripping teeth or a bill (evolved twice in non-avian theropods)
c. Many also feathered demonstrating that feathers evolved as insulation, brooding or sexual display rather than for flight.
d. Archaeopteix is essentially a Coelosaur dinosaur with primitive features like a tail, minimal keel, teeth and an unfused hand—appears about 155 Ma.
e.Either Archaeopterix is a very primitive form or there was very rapid evolution, since within 10 my (~145 Ma) have Confusiusornis (similar to a crow), and Sinornis, the latter sparrow-sized, and capable of perching |
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Term
| What kinds of stages are commonly observed during recovery from mass extinction and what kinds of geological, ecological, and evolutionary changes are observed in each? |
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Definition
Survival, recovery, and final recovery periods.
Survival - fast growing, rapidly reproducing, short life span, generalist species are left. Series of boom and bust cycles of species may be observed.
Recovery - an increase in biodiversity over a course of several million years that will be derived from the survivors; they will be most related to the survivors. Primary producers begin developing
Final Recovery - Number of taxa begins to plateau out. Consumers begin coming into the mix. |
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Term
| Why, when you take antibiotics, does it take so long for your gut microflora to recover? What is the essential process that delays recovery from major extinctions? |
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Definition
Incumbency, the dominance of the surviving species delays the recovery of the microflora. There are a series of boom and bust cycles of individual or few species that are able to dominate because they are the most competitive out of the survivors. Over time the gut is reworked until the new microflora begin coexisting with the incumbents.
The process that delays recovery is due to incumbency and the domination of certain species over another for short periods of time while new species come into play through evolution or through genetic drift. |
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Term
| What types of “rules” are associated with radiations of many groups of organisms? |
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Definition
Logistic growth rules - the S shaped curve of #species vs time.
Ecological architecture - addition of species enlarges ecospace
-incumbency - slow recoveries
-establish base of food chain first
-starting from high dominance/low diversity communities
Constraints - constructional and functional
Extrinsic communities - imposed by environment i.e. O2 atmosphere |
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Term
| What is the difference between density dependent and density independent evolution? |
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Definition
Density dependent evolution relies on density to occur. With higher density, organisms will be more constrained to resources and will have to compete against each other to get their fair share of resources. This could be resolved by either an evolution of some sort of behavior or a divergent evolution in which one species uses one resource and the new species uses a different resource.
If two populations of organisms are separated by a geographic barrier in two different environments, then density plays no role in the divergent evolution of these species. |
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Term
| Why do we need good time scales to have a prayer of determining causation? |
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Definition
| Good time scales can be used to provide rates and correlations. If you know the rate, you can use that to determine if it is pressed or pulsed. Correlations allow you to determine if the extinction is regional or global. These are both vital for determining a cause. |
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Term
| Good time scales can be used to provide rates and correlations. If you know the rate, you can use that to determine if it is pressed or pulsed. Correlations allow you to determine if the extinction is regional or global. These are both vital for determining a cause. |
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Definition
| Mixing by bioturbation leads to the contamination of layers by material from other layers from different times - zombie species. Sampling leads to an inaccurate depiction of the geologic range of species because you get the majority of the shit from the middle point where there are a shitload of that species but not when it first began appearing or when it started petering out. Signor Lipps effect - faulty fossil record makes it look like a species begins disappearing before it actually does. Especially emphasized in rare species where there isn’t much of a population to preserve to begin with. |
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Term
| Why is it rare to find a record of truly abrupt events? Why do even instantaneous events often appear to have occurred over a significant span of time? |
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Definition
| Signor Lipps effect. Rare species tend to peter out before they disappear because they are rare and you can’t find a solid fossil record for them to begin with, so they look like they’re disappearing before the event. |
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Term
| Why, if you have a strong pattern, may it be possible that there actually is no single underlying cause? |
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Definition
| We go around looking for shit with the expectation of finding a single deterministic reason as the cause because its easier to understand that way. |
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Term
| What is the difference between “Phyletic evolution” (or “gradualism) and “Cladogenetic evolution” (= “Punctuated equilibrium”)? |
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Definition
| Phyletic evolution = one species is subsumed and transformed into another species. No branching. Cladogenetic evolution requires branching; divergent evolution |
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Term
| What is the biological explanation for the pattern of cladogenesis observed in the fossil record? |
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Definition
| What is the biological explanation for the pattern of cladogenesis observed in the fossil record? |
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Term
| What is the difference between allopatric and sympatric speciation? |
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Definition
| Allopatric involves a separation between populations. Sympatric does not. |
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Term
| How is extinction a creative part of speciation? |
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Definition
| Extinction opens up niches and thus more branching of species can occur. |
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Term
| In what respect are there agreements or disagreements between molecular clock estimates and the fossil record about the origins and timing of diversification of mammals and the major orders of mammals? |
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Definition
1. Placental and marsupial mammals appear ~125 Ma according to molecular clocks and ~100 Ma (perhaps as early as 135 Ma) according to fossils.
2. Molecular phylogenies suggest that the major groups of mammals diverge before the K/Pg boundary, with Cretaceous origins of groups like bats (not known as fossils until early Eocene), horses (E. Eocene), Primates (E. Paleocene), Rodents (Middle Eocene), pigs (and other artiodactylids—E. Eocene).
a. In short the fossil record suggests much later originations for most Mammal orders than the molecular phylogenies. Fossils suggest that most Cretaceous mammals were generalized small insectivores.
b. Suggestion that these insectivores may be stem groups of modern mammals (since there are small, generalized insectivores in several extant orders (the “Long fuse model”) or that diversification occurred somewhere with a bad fossil record (like Africa, Australia or India)
c. Have a foraminifer example—the Neogene globorotaliids also start from small globular ancestors that diverge into the more distinctive members of five different clades only after a ~7 million year run as independent globular lineages.
3. Early mammals radiate explosively in body size and form (even if the basic groups were established before the K/Pg mass extinction)—Have 23 species of K/Pg placental mammals and 60 species 5 million years later. Most of these Paleocene mammals are still small and insectivorous.
4. By Early Eocene, have nearly all modern groups—Europe, Asia and N. America have similar groups—horses, primates, horses and rhinos in forests and the brontotheres, bats, rodents, and artiodactyls; Africa gets first elephants and S. America has a marsupial fauna in common with Antarctica and Australia.
5. Extensive mammalian migration associated with the abrupt warming of the Paleocene-Eocene Thermal Maximum (~55 Ma) as seen in the continental sediments of the Bighorn Basin, Wyoming (and elsewhere). The abrupt warming of 5-7°C over a few thousand years apparently allowed extensive forests to develop on high northern latitude land bridges between Europe and N. America aiding the spread of mammals faunas. |
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Term
| What are some examples of climate or tectonic events that fostered the migration and interchange of mammal faunas? Why may it have been easier for North American mammals to invade South America than the reverse during the “Great American Interchange”? |
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Definition
1. The Eurasian Flood
a. By around this same time (~20 Ma) see a major change in mammalian assemblages (Kemp 2005)
b. Numerous east Asian groups invade Europe and N. America associated with the draining of the Turgai Strait—a seaway that bisected eastern Europe and isolates Europe from Central Asia
c. Demise of the Turgai Strait and docking of Africa against S. Europe (via the Arabian peninsula) allows immigration to Africa as well. Includes archetypal African groups like giraffes, Rhinos, pigs, horses (Zebras), big cats, —all in all, 29 new families invade Aftrica to accompany the 14 mammal families already there.
d. A reverse migration also occurs with elephants and primates moving out of Africa.
American Interchange:
1. S. America is an island continent since ~80 Ma,
a. Invaded only by groups like rodents (35 Ma), monkeys (25 Ma) bats, and a few oddities like raccoons (8 Ma).
b. The rest of the fauna consists of diverse marsupial fauna (from ‘horses’ to large predators, to possums) that were already there since the late Cretaceous.
2. Formation of Panama Isthmus creates a land connection by ~3 Ma and an island chain before this. Leads to major interchange of mammals from S. America into N. America and vice versa.
3. S. American invaders of the North include the armadillos, new world monkeys, sloths, porcupines, and flightless (and large) predatory birds {Phorusrhacids).
4. N. American invaders of the S. American land mass include skunks, peccary, horses, dogs, cats, bears, deer, elephants, camels, deer and shrews.
5. The asymmetry of the respective invasions may be explained by
a. The limited rain forest in N. America limiting dispersal of rain-forest S. American species to the North, and
b. The periodic appearance of grassland in central S. America when glacial cycles dried out the rain forest (creating habitat for N. American savanna dwellers). |
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Term
| What is the history of habitat evolution of the Northern Continents during the Cenozoic? When do the major grasslands develop and what is the evidence? |
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Definition
1. Spread of Grasslands
a. Evidence from phytoliths (opal structures formed mostly by grasses) show that basal-group grasses evolved in the late Cretaceous consistent with molecular clock estimates
b. Up to the late Oligocene, phytoliths suggest
i. the dominant groups of grasses were forest species—bamboo, understory grass
ii. whereas by the Oligocene-Miocene boundary (22.9 Ma) in Wyoming and the late Early Miocene in Idaho there was a switch to dominant occurrence of open grassland species.
c. These changes are approximately coincident with the appearance of hypsodont and mesohypsodont teeth in ungulates;
i. possibly earlier evolution of grasslands in S. America where the switch to high-crowned teeth occurs in the M. Eocene.
d. Ungulates see their peak diversity in the late Early Miocene (~16 Ma) and then the diversity of browsers begins a steady decline.
e. Christine Janis suggests that peak browser diversity is associated with elevated plant production during the low seasonality, warm early Miocene/late Oligocene; at least today in Africa, ungulate diversity is correlated with rainfall (itself used as a proxy for productivity).
f. Traditionally, the evolution of grasses has been identified as a consequence of aridification of the continents;
i. However, Stromberg notes that grasses evolve long before the development of grasslands (such as bamboo and other forest grasses)
g. Initial appearance of grassland evolution may be linked to
i. aridity or
ii. possibly to higher O2 levels and increased incidence of fire that would discourage woody vegetative growth.
iii. Higher O2 associated with decrease in ATM CO2 (Vaguely suggested by Pearson & Palmer’s Boron Isotope work-dubious in my opinion). |
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Term
| Contrast the pattern on genetic diversity of the modern great apes. What does this pattern imply about the processes of speciation and extinction in these groups and how is that related to the hominoid fossil record? |
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Definition
Less branches (twiggy) → extinctions/bottlenecking
More branches → no extinctions |
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Term
| What happened about 2.5 MA and what does this figure so prominently in the evolution of the hominid tree? |
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Definition
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Term
| There are substantial differences in the apparent timing of the diversification of “archaic Homo sapiens” between mitrochondrial and Y-chromosome data. Why, and what does this imply both about human behavior and rates of extinction? |
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Definition
Differences attributed to a higher rate of extinction of y-chromosome lines due the large differences in reproductive success between men and women;
i. Suggests a few men are very productive (many matings) and so swamp the genetic variation with their genetics
ii. In contrast women produce a smaller, but consistent number of kids than men. |
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Term
| Modern humans are reckoned to have appeared about 40 kyr based upon the spread of human tool kits and art into Europe. Why is this data likely too young based upon technological events in other parts of the world? |
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Definition
| Human population was low enough that human fossils are very rare before the Holocene. |
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Term
| Modern humans are reckoned to have appeared about 40 kyr based upon the spread of human tool kits and art into Europe. Why is this data likely too young based upon technological events in other parts of the world? |
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Definition
| Human population was low enough that human fossils are very rare before the Holocene. |
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Term
| Why did agriculture not become widespread before 11,500 yrs BP, even as domestication of dogs and advanced tool kits had evolved earlier? |
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Definition
The climate was
i. Too cold
ii. CO2 too low
iii. Environment too variable on a year to year basis to support agriculture before ~11,500 years. |
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Term
| What are contrasting models and evidence to explain the loss of the Pleistocene “Megafauna” on all the continents except Africa? |
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Definition
i. Extermination by humans.
Evidence: Persistence of certain island megafauna for several millennia past the disappearance of their continental cousins.
Africa being an exception due to animals there being naturally wary of humans since they evolved together.
ii. Climate change: Retreat of polar ice cap
How can we explain the extinction of small, non-target species like mice and little birds by a “humans-did it” model?
Loss of habit. Possibly domestication of cats and dogs. “safe” from predators |
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Term
| Finally, what is likely to be the strongest evidence of our time on Earth as an industrial society? |
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Definition
Geochemical changes.
Large magnitude negative 13C excursion (from buring 12C-rich fossil fuels). This carbon would persist in the environment for ~150 kyr. Mass extinctions? |
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