Range of Paleontology (or Paleobiology) - Interdisciplinary (“Fossils bring life to geology”)
All types of life (record of organisms living today plus all those that have become extinct)
All of geologic time since life first appeared on earth (at least 3,500 mill. years ago)
All aspects of organisms and their existence (both the pattern of the empirical record and the inferred
processes that may have produced it)
Subdivisions of Paleontology
Invertebrate paleontology - Fossil invertebrates (~ 15 phyla, ~ 200,000 fossil species)
Vertebrate paleontology - Fossil vertebrates (most of Chordates, ~ 25,000 fossil species)
Micropaleontology - Fossil microorganisms (~ 10 phyla & divisions, ~ 25,000 fossil sp.)
Paleobotany - Fossil algae and plants (~ 15 divisions, ~ 30,000 fossil species)
Types of Fossils (definition) - Any evidence of past life preserved in rock (usually sedimentary)
Body fossils - Skeletons or hard parts of multicellular fossil organisms (> 1-2 mm)
Trace fossils - Evidence of an organism’s activity (footprints, trails, root traces, coprolites)
Microfossils - Skeletons of tiny or unicellular fossil organisms (< 1-2 mm)
Extraordinary fossils - Soft part preservation in fossil organisms (rare)
Biases in the fossil record
Usually need skeletons (shell, bone, woody tissue) to be preserved in the record; rarely get soft parts
or soft-bodied organisms (preservation and completeness bias)
Need to be buried in sediment to be preserved (deposition > erosion), so different depositional environments have different preservabilities (environmental & time bias)
~99% of all fossils in last 12% of geologic time (Phanerozoic) vs. only ~1% of
fossils in first 88% of geologic
tim
(Precambrian) (Phanerozoic bias)
Named and described fossils <1% of what has lived in the past (small sample bias)
Need to find and collect fossils in the field, and prepare, reconstruct, describe, & illustrate
them back in the lab (bias in amount of paleontological systematics done)
How much useful information do fossils provide? - one fossil fragment in a 1,000 m section
- vs. better-known living organisms with DNA?
Both fossils and living organisms have excellent information on skeletal morphology.
Living organisms have much better information on soft parts, physiology, behavior, ecology,
growth and development, and molecular differences for at least some members of many taxa
Fossil have much better deep time control (hundreds of time planes vs. only one in Recent).
Different uses of paleontological information
Biostratigraphy - Use of fossils to tell time and date sedimentary rocks (1st use of fossils)
Law of Faunal Succession (1797), relative age dating, correlation, geologic time
scale (1822-1841), zones, index fossils vs. facies fossils
Paleoecology - How fossil organisms work and interactions with their environments
“Way of life”, niches, comparisons with related living organisms, interpreting depositional
environments (where located, water depth, currents), taphonomy (what happened after organism died,
preservation, diagenetic changes)
Evolution - Changes in living organisms through geologic time
“Descent with modification”, natural selection, speciation rates (slow continual vs. fast but rare),
diversity, radiations, extinctions (background vs. mass & causes)
Paleogeography - Geographic distribution of fossil organisms, migration, plate movements
Paleoclimatology - Climatic distribution of fossil organisms, climatic zones
Biogeochemistry - Isotopic analysis of fossils (temperature, salinity, growth rates)
Biostratigraphy – Using fossils to tell time.
Why are fossils useful for dating? 1) Common in sedimentary rocks; can date these rocks directly.
2) Fossils change through time; each time interval has characteristic
assemblage of fossils.
Correlation – Two units have the same age based on fossil content.
Relative age dating – Plug new fossil fauna into a known sequence of time units, a time scale.
Basic terminology – Zone – The smallest time unit usually used for correlation and age dating.
Types of zones – 1) Biozone – The total world-wide stratigraphic range of a
species whether preserved or not.
2) Teilzone - The total regional stratigraphic range of a
species whether preserved or not.
3) Range zone – The preserved regional range of a species.
Usually work with assemblage range zones – Overlapping range zones for many taxa in a fauna.
What are boundaries for different types of zones? Typically first appearance, last appearance, or maximum abundance.
Index fossils – Fossils that are especially good for long-range correlalation.
Common, diagnostic, widely distributed geographically, occur in many facies, evolve rapidly (short biozone), often swimmers or floaters up in the water column. vs.
Facies fossils – Fossils that are especially good at idenitifying environments.
Common, diagnostic, widely distributed geographically, occur in only one facies, evolve slowly (long biozone), often benthic or burrowers in the bottom sedinment.
Rest of Time, Time-rock, and Rock terms from Chart.
How good are assemblage range zones in telling time? Almost as good as using radiometric age
dating (1-2 mill. yrs. back to the Jurassic, 2-5 mill. yrs. back to the Cambrian).
Ecologic time – Few years to few thousand years vs. Geologic time – 100,000 to billions of years.
Setting up zones in a region: Have several sections around the region with stratigraphic ranges and
abundance data for numerous taxa. Set up Composite Section with summed ranges and
abundances, subdivide into several zones based on tops and bottoms of ranges or where
maximum abundance occurs.
Name zones based on distinctive fossil confined to the zone or whose maximum abundance occurs
within the zone. Example: Salenia texana Zone in the Glen Rose Fm. (Lower Cretaceous). Zone can either be named after a genus or a species.
Examples of Late Devonian zones based on goniatite ammonoids and on “fingerprint” ostracods.
Plotting range tops & bottoms of fossil taxa in two local sections X and Y – Shaw Range Diagrams
1) Sections start at same time and have equal rates of deposition – Get straight-line plot at 45º.
2) Sections start at same time and have unequal rates of deposition – Get straight-line plot at >
or < than 45º slope.
3) Sections start at same time and have change in rate of deposition so that X > Y followed by
Y > X – Get “kink” in range diagram with < 45º slope followed by > 45º slope.
4) Have unconformity at base of section X followed by equal rates of deposition – Get
horizontal segment in plot followed by straight-line plot at 45º.
5) Have unconformity in middle of section Y, with equal rates of deposition before and after –
Get vertical segment in middle of straight-line plots at 45º.
6) Have unconformity in middle of both sections X and Y, with equal rates of deposition
before and after – Get straight-line plot at 45º with cluster of range tops and bottoms where
unconformity occurs.
Use of Correlation Indices: Numerical method of comparing two faunas based on # of taxa present.
# of taxa in common
Simpson’s Index of Comparison = ------------------------------- X 100 (S.I.C. range from 0 – 100)
# of taxa in smaller fauna
Do internal comparison between local sections first to get likely range in S.I.C. values for same age (say 80) and different ages (say 40). Then do long-range comparison to test how well two formations or zones correlate numerically compared to this expected range.
Problems trying to do correlation work:
1) Migration time – usually short within a faunal province
2) Different environments and facies – few organisms occur in very different environments; problems with facies fossils
3) Different climatic zones – hard to compare across several climatic zones; more problems during Icehouse times (3 zones) vs. Greenhouse times (2 zones)
4) Distance and Geography – barriers and filters for marine & terrestrial organisms – wide deep oceans, big continents, unfavorable environments (deserts, mountains)
Biomeres – Repeated extinctions, migrations, and radiations in Cambrian trilobites
Example of Iterative Evolution pattern
Caused by changes in thermocline depth (temperature boundary near edge of shelf)?
Ranges of Major Groups (Handout) – Talk about these more in lab and on field trips.
Become familiar with characteristic faunas for different parts of Phanerozoic (Early, Middle,
and Late Paleozoic, Early and Late Mesozoic, and Cenozoic).
Introduction to Paleoecology (definition) - Interactions of fossil organisms and their environments - how they functioned (both organ systems and whole organisms), how organisms interacted with each other, where they lived in different environments, etc.
Also Taphonomy (definition) – What happened to the remains of these fossil organisms after death; how did remains get preserved in the fossil record?.
“Basic needs” of organisms – nutrients and/or energy, oxygen for respiration, circulation system for moving nutrients, oxygen, and wastes, elimination of wastes, protection from the environment, ability to reproduce, sensing activity in the environment, other needs?
Specific needs in different environments – Marine environments (first to be colonized, easiest to live in), fresh water environments (low ionic concentrations), terrestrial environments (need water).
Concept of a niche (definition) – An n-dimensional space including all the physical and biotic components of the organism’s environment. These form the limits for an organism to exist vs. the optimal conditions where an organism does really well (coral reef example).
Where do organisms live? Terms for aquatic environments (planktic, nektic, benthic; epifaunal vs. infaunal) and terrestrial environments (flying, surface living, burrowing in soil)
Major ways of getting nutrients: producers using photosynthesis (algae and multicellular plants), consumers using ingestive feeding (some protists and multicellular animals), reducers using extracellular absorption (many monerans, some protists, and fungi).
Types of animal ingestive feeding (herbivores, carnivores, scavengers, parasites, detritus & deposit feeders (nutrients or bacteria in sediment), suspension & filter feeding (nurrients or microorganisms from water column), others?
“Ways of Life” using 2-6 descriptors – mobility, where live, how get nutrients or feed.
Environments for organisms to live
– Continental and oceanic environments diagram
– Preservability - deposition vs. erosion, continental vs. oceanic crust
– Shallow-water marine > Lowland terrestrial > Deep sea > Upland terrestrial
– Represents a “Time Bias” for these environments and their fossils
Specific environments (how common?, how thick?, how fossiliferous?)
Shelf profiles – Ramp (clastic and carbonate deposition) vs. Platform (carbonate deposition)
Where do organisms occur in the marine environment?
Heckel’s (1972) environmental diagrams – Salinity, Water depth, Substrate type
Also Oxygen content, other factors?
Distribution of fossil groups (from Lab, Field Trips) in Ramp and Platform transects
Abstract Project – Topic for this year
– How to write an abstract for a meeting (like GSA)
– Follow formatting instructions (margins, 12-pt. Times, title, author [you], UT address, body of abstract, key words)
– Do this, don’t do that
Objectives of Paleoecologic Analysis – 6 item list in Handout
Methods used in Paleoecologic Analysis – 5 item list in Handout
Examples of these – Swimming position of Nautiloids and Ammonoids
– Living position of brachiopods, feeding currents in brachiopods
– Pore rhombs in rhombiferan cystoids
– Trilobite molts and injuries
– Burrowing depth in heart urchins
– Zoophycos worm feeding methods
– Dimetrodon sail on back
– Living position of Early Cambrian echinoderm – lucky find
– Fossilized eggs in abnormal hydrospires of a Pennsylvanian blastoid – lucky find
Community – Any natural assemblage of organisms living together in a given environment
over a long time period.
Modern examples – Terrestrial plant communities (Biomes)
– Petersen’s (1913) shallow marine and brackish communities around
Denmark
Features of communities – Associated on a statistical basis (dominant vs. rare species)
– Basic environmental controls (abiotic, external) plus
– Biotic interactions (biotic, external), food pyramid with trophic levels
– Last for long time (short geologic); more stable than included taxa
– Recur whenever same environmental conditions return
– Show short-term succession whenever environment disturbed (colonizing species ––> successional stages ––> climax community), low to high diversity, reach equilibrium?
– Show r vs. K selection (opportunists, generalists vs. specialists)
– Often show partitioning of the environment (divide up food resources), along with tiering (feeding height above or below the substrate)
Identifying fossil communities: Ziegler’s (1968) early work on Paleozoic communities
Setting – Silurian shelf and slope communities in Wales
– Ramp – gradual increase in water depth offshore
– Slow transgression during time of study
– Fine clastic sediment but no big river input
Found 5 brachiopod-dominated communities arranged parallel to shoreline plus graptolites in deep water furthest offshore; implies simple environmental setting results in simple community distribution on ramp-type shelf.
Later fossil community studies: Broadhead’s (1975 UT MA, 1976) study in Late Paleozoic
Setting – Late Mississippian shelf communities in NW Georgia
– Platform – shallow area nearshore with carbonate banks offshore
– Several delta progradations and sea-level changes
– Considerable clastic input nearshore plus carbonates offshore
Found 5 brachiopod-, mollusk-, bryozoan-, crinoid-, and coral-dominated communities in a complex arrangement from prodelta muds and nearshore environments to carbonate banks furthest offshore; implies complex environmental setting results in complex community distribution on platform.
Use this study as a model for interpreting communities on our Brownwood field trip next month because north-central Texas has a similar setting and is only slightly younger (Middle Pennsylvanian – Early Permian).
Preview of Saturday Austin area Field Trip – Setting, objectives, stops, field equipment, “beer fossils”
Review for 1st Hour Exam next Tuesday – What cover, types of questions, last year’s exam
Trace Fossils (Ichnofossils) – fossilized remains of an organism’s past activity or presence but not the organism itself or its skeleton (body fossil)
Examples: Tracks, trails, burrows, borings, bite marks, drill holes, corprolites (fecal material), fecal pellets, root traces, nests, galls, etc.
Distinctive trace fossils are usually given taxonomic names just like body fossils (Scolithos, Zoophycus), but we often don’t know what animal, or even type of animal, made many of these trace fossils. It’s rare to find a trace fossil and its maker (a body fossil) together in a bed.
Depth zonation of trace fossils – Ichnofacies
Skolithos-Cruziana ichnofacies – shallow-water, high energy nearshore
Zoophycos ichnofacies – below wave-base offshore shelf
Chondrites-Nereites ichnofacies – quite deep water slopes or basins
Amount of bioturbation in section – Ichnofabric (Ichnofabric index from 1-5)
Pass back and review 1st hour exam, distribution of grades, answers to questions.
Paleobiogeography – Distribution of organisms in the past - distribution
- diversity -# taxa/larger group
- morphological differences
Observation – Diversity in most groups increases toward the equator in both marine and terrestrial environments – many possible reasons for this
Controlling factors – temperature, ocean currents, stability of environment (recent glaciation), more trophic levels (predators and parasites), evolution of new species there?
Plotting present-day and past diversity – Frank Stehli’s work (1960’s-1970’s) trying to recognize past climatic zones (problems with this)
Island Equiblibrium Model – Robert MacArthur and E. O. Wilson (1963, 1967*)
– Islands as a simplified microcosm of the complex, messy, real world (ecologic time, ignore history of island, ignore “cast of characters”)
– Immigration vs. (local) extinction curves for each island
– Equilibrium point where these curves intersect (stable)
– Predictions – Larger islands will have more species at equilibrium
– Nearby islands will have more species at equilibrium
– Daniel Simberloff’s test of model – fumigating tiny islands in Keys
Do small (or even large) continents reach similar equilibrium levels?
– Changes occur over geologic time (millions of years)
– Immigration + evolution vs. (regional) extinction curves for each cont.
– North vs. South American edge collision in Late Tertiary as test case
Banks (Biostromes), Mud mounds, and Reefs (Bioherms) – Structures built by organisms
3 components – frame builders – resistant skeletal framework of bank or reef
– cementing organisms (usually algae)
– detrital fill (fossil debris) in cavities and down flanks
3 facies in reef or mud mound – massive core built up by organisms or mud accumulation
– dipping, bedded, flank deposits of debris from core
– thin interreef mudstones with few fossils
Banks (Biostromes) – Tabular (bedlike), grainstone vs. mudstone
Mud mounds (Bioherms) – Relief (built up), usually wackestone or packstone core with mud-trapping fossils, dipping grainstone flanks, and surrounding mudstone
Reefs (Bioherms) – Relief (built up), usually boundstone or grainstone core with frame builders, dipping grainstone flanks, and surrounding mudstone
These 3 types fit a sequence, implying fair, good, and excellent conditions for reef building?
Examples from field work and GEO 660 – E. Ord. and Penn. mounds in C. and W. Texas
– E. Miss. Muleshoe Mound, Alamogordo, N.M.
– Penn. Dry Canyon Reef, NE Alamogordo, N.M.
1st lecture in evolution block – Nomenclature, Linnaean classification, species
Fossil record is one of best sources for information about evolution – who lived when in past, major changes in whole faunas (diversity levels, radiations, extinctions), gradual changes in single lineages (adaptations, speciation events).
What’s available in fossil record – mostly skeletal morphology (+ reconstructed soft parts)
– additional information (age, geographic occurrence, inferred way-of-life)
– 99% of preserved fossil record in last 12% of geologic time (Phanerozoic)
Nomenclature and classification – “Classical” system dates from Linnaeus (1758) in 10
Ed. of his “Systema Naturae”
Organisms classified into a hierarchy of category levels – higher taxa (named organisms) down to lower taxa – Typical levels used today (~half from Linnaeus, ~half added later):
Kingdom – major basic groups of organisms (3-5 groups now) Animalia
Phylum – major groups sharing similar morphology Echinodermata
Class Blastoidea
Order Spiraculata
Family Pentremitidae
Genus Pentremites
Species godoni
The scientific name of a species is a combination of the generic name and the specific name (two lowest levels in the hierarchy above), often accompanied by the author of the species and the date of publication (like a bibliographic citation):
Homo sapiens Linnaeus, 1758 or Pentremites godoni (deFrance), 1808.
Author’s name is put in parentheses (deFrance) when species has later been moved to a different genus from what the species-name author originally used. This type of two-word naming system is called Binomial Nomenclature, and has been the standard system for naming both living and extinct organisms since 1758.
Species level has its own biological species definition: Species – A group of actually or potentially interbreeding populations which are reproductively isolated from other such groups under natural conditions (Mayr, 1963).
Rules for naming and classifying Linnaean species are governed by several Codes including the International Code of Zoological Nomenclature (4th Ed., 2000). 3 major features:
1) There should by one species name for each organism – uniqueness
2) The same species name should be accepted by everyone – universality
3) The species name should stay the same through time – stability
Achieve stability by using oldest validly described and published name – priority
Two models available for how speciation (formation of one or more new species from an existing one) takes place in the fossil record (or today):
1) Phyletic Gradualism (a type of sympatric speciation) – from classical paleontology.
An entire lineage undergoes a gradual change through geologic time from 1 species to
another because of a slow accumulation of mutations, slowly changing environmental
conditions, etc. Features: Slow (geologic time), all members of species populations gradually change everywhere, happening all the time, lots of intermediates, “breaks” between species represent interruptions in deposition. Slow continuous change within large widespread populations, sloping pattern with moderate rates of evolution.
2) Punctuated Equilibrium (a type of geographic or allopatric speciation) – from modern biology.
New species arise very rapidly in small isolated populations (peripheral isolates) because of
adaptations to local conditions, fixing of genes, inbreeding, etc., then spread out over an
entire area usually displacing the previous species. Features: Fast (ecologic time), local, rare, few intermediates, “breaks” between species real (no time loss), reproductive isolation develops even though relatively little morphologic change, almost no morphologic change (oscillations) within large populations. Equilibrium with almost no change (stasis) punctuated by rapid but rare speciation events producing a rectangular pattern of evolution.
New model published in 1972 symposium volume by Niles Eldredge and Stephen J. Gould – caused huge controversy first within paleontology, then by early 1980’s spread to evolutionary biology, hundreds of papers written both pro and con (What features change by phyletic gradual-ism? Do you ever see punctuation? What happens when one species suddenly appears and replaces another? Is stasis really common in fossil lineages?). One of rare cases where a paleontological theory became a major controversy in biology. Neither side has won out over the other, probably both types of speciation occur in nature, big question now becomes which one is more common and important. This 1972 paper the most important paper written in paleontology in the past 35+ years?
Higher Taxa – Generic level on up to kingdoms.
Uses of Classification – For grouping together (emphasizes similarities, but needs to be based on
multiple characters, not just one key character, such as trilobite facial sutures)
– For identification (emphasizes differences)
– But should also express evolutionary relationship (evolution from a common ancestor) – underlying reason why higher taxa show similarities.
– Numerical Taxonomy (Phenetics) – Consider only amount of
divergence during evolution (based on overall similarity).
– Phylogenetic Systematics (Cladistics) – Based only on order of
branch points (genealogical relationship).
Types of diagrams used in different philosophies:
Evolutionary systematics – Phylogenetic (or spindle) diagrams – Shows both time of
splitting (vert.) and amount of change and diversity of descendent groups (horiz.).
Cladistics – Cladograms – Show array of taxa (usually horiz.) vs. branching order (usually
vert.).
Higher taxa classified in different classification philosophies:
Monophyletic taxa – An ancestor and all of its descendants (Evol., Phenetics, Cladistics)
Paraphyletic taxa – An ancestor and some (but not all) of its descendants (Evol., Phenetics)
Polyphyletic taxa – A group of organisms but not their most recent common ancestor (none
of philosophies)
Phylogenetic patterns present in the fossil record:
Adaptive Radiation – Rapid Divergence of small group followed by Diversification into
much larger, long-lived, and more successful group – Likely origin of major higher
taxa; these often show Mosaic Evolution where some features change quickly, some
slowly, others not at all.
Convergence – Two groups converging on the same morphology from different ancestors.
Iterative Evolution – Repeated evolution of the same morphologic features (Biomere exam.)
Arrested Evolution – Almost no evolutionary change through a long period of geologic time
(many living fossils).
Extinctions – Happening all the time, most species (> 99%) that have ever lived are now extinct, along with most genera (> 98%) and many families (~ 73%).
Standing diversity (at any time) = Number of originations in past minus number of extinctions in past. For Phanerozoic marine metazoan families:
3,300 originations – 2,400 extinctions = 900 living families (~ 27%)
Implies that extinction is an important process in determining diversity both in the fossil record and today.
Two types of extinction in the fossil record – Background Extinction and Mass Extinction
Background extinction – Dropping out of species (and higher taxa) one-by-one during rela-tively normal times. Most of these would represent endangered species with low population size and limited geographic range, and would disappear because of local disturbance, competition for resources, disease, etc. Background extinction was thought to occur throughout the fossil record at a low constant rate (but see below).
Mass extinction – Many species (and higher taxa) disappearing all at the same time during unusual times, perhaps catastrophic events affecting a large part of the Earth. Most of these unusual events probably represent a physical (or biologic) trigger followed by a regional or world-wide collapse of the ecosystem, followed by a slow recovery from very low diversity levels.
Raup and Sepkoski (1982, 1984) work on extinctions – used diversity data for Phanerozoic marine families (and later genera) to plot the extinction level for 85 time intervals (stages). 5 medium-to-large drops in the diversity curve represent the 5 largest mass extinctions in the marine environment. These “outliers” occurred during 8 stages at the following times:
5) Cretaceous-Tertiary boundary (11% drop) – ammonoids†, most marine reptiles†
Most likely cause is meteorite or comet impact in Yucatan.
4) Triassic-Jurassic boundary (12% drop) – ammonoids, conodonts†, some reptiles
Possible cause is meteorite or comet impact.
3) Permo-Triassic boundary (2 stages with 52% drop) – fusulinids†, rugose and
tabulate corals†, many brachiopods, many crinoids. Most likely cause is assembly of Pangaea and drop in sea level as ocean spreading stopped.
2) Last 3 stages of Devonian (14% drop) – reef corals, brachiopods, foraminifera
Likely cause is change to Icehouse climate & overturn of deep ocean waters
1) Ordovician-Silurian boundary (12% drop) – trilobites, graptolites, brachiopods
Likely cause is brief Hirnantian glaciation in middle of Greenhouse interval.
Most of these mass extinctions were located at Era or Period boundaries because early workers chose these times as boundaries between Eras or Periods because the marine faunas changed so drastically here. Fossil groups that were most prone to big drops in diversity or extinction include dominant groups before the extinction or groups that were relicts, restricted geographically, or restricted ecologically.
The other 77 stages had relatively low levels of background extinction and represented relatively “normal times”, but the mean values for background extinction was not constant but slowly fell during the Phanerozoic to about half its starting value, a somewhat surprising result. Analysis of this pattern led to the following causes:
1) Marine organisms slowly became better adapted to their environments.
2) Organisms most prone to extinction were wiped out early, leaving more resistant organisms for later times, causing extinction rates to fall.
3) A “pull of the Recent” effect has decreased Mes. and Cen. extinctions.
4) Average stage length has decreased during the Phanerozoic, causing apparent extinction rates to fall (less time per stage = fewer extinctions).
Preview for Brownwood field trip next Saturday
6 stops in Pennsylvanian to Early Permian, bring 8-9 small-medium bags.
Setting is shallow platform with deltas building out from SE + offshore banks.
Looking at most marine and fossiliferous parts of the section.
Chance to collect trilobites, crinoids, and other possible “reward fossils”.
Emphasizing paleoecology and depositional environments on this trip.
Best model for communities is Broadhead (1976) work on Late Mississippian.
Size and growth of organisms and their skeletons
Growth during Ontogeny (lifetime of an organism)
Growth during Phylogeny (lineage of ancestral and descendent organisms)
Correlation of organism size and other features (numbers of organisms, length of life).
Types of growth that are available to organisms:
1) Accretion – Small increments added around edges of old skeleton.
2) Modification – Type of specialized accretionary growth in vertebrate bones.
3) Addition of new parts – Serially add new parts to increase a skeleton’s size.
4) Molting (arthropods +?) – break out of old skeleton, grow, secrete new one.
5) Combinations of the above – Accretion + new parts, molting + new parts.
Examples of these in different organisms and their skeletons.
Growth through a large size range – Development of Surface/Volume problems
If length = L, surface area = L2, volume = L3 in cubes growing from L =1 to 10, Surface/Volume drops to 1/10 its original value during this much growth.
Solving Surface/Volume problems – 1) Dividing and remaining small (microorganisms)
2) Becoming long and thin (tapeworm solution)
3) Developing complicated internal structures (insect trachea)
4) Allometric growth – accelerated growth of one body part over other parts
General equation for Allometric Growth – Y = CXk, symbols, spectrum of k values
k < 0, k = 0, 0 < k < 1, k = 1 (Isometric Growth), k > 1, k > 2 or 3
Plot of k values found in nature; why peaks at k = 1 and k = 1.5? Why no k values above 2 throughout life? (can’t be maintained; crayfish example)
Phylogenetic growth by changing ontogenetic factors – Plotting phylogeny vs. ontogeny
Model with length of life, somatic body form change, and sexual maturity through many generations (a lineage) – hold two factors constant, change one.
No changes – outcome 80% of the time (vs. other 10 and 10%)
Move time of somatic change back = Recapitulation (add new adult stages to end)
“Ontogeny recapitulates phylogeny” – Ernst Heckel (1866)
Move time of somatic change forward = Paedomorphosis (discard old adult stages)
Moderate to drastic change in organism in ecologic time – more important?
How make these changes? Mutations of regulatory genes
Living and fossil examples of paedomorphosis
Raup’s shell coiling – Most 1 or 2-valved shells in living or fossil organisms show isometric growth (no change in shape during increase in size) along a geometric spiral.
Why so common in organisms? 1) It’s easy to grow a shell like this; just keep growing
along an already established trajectory.
2) The organism doesn’t have to change its way of life if
the shape doesn’t change during growth.
Features of a geometric spiral – Aperture of shell grows in size while spiraling around (and often moving down) a coiling axis. Can describe all of these features mathematically (hard) or graphically (easier), and can program a computer to reproduce these shell patterns.
Shell coiling parameters – S = Shape of generating curve for aperture (often a circle).
– W = Whorl expansion rate, growth of generating curve per
revolution around axis.
– T = Translation rate of generating curve down axis per revolution.
– D = Distance factor describing slow movement of generating
curve away from axis per revolution.
Hold S=a circle constant, plot 3 other factors as axes of a cube (W from 1-106, T from 0-4,
D from 0-1), and plot where actual living and fossil organisms fit into this figure.
Actual organisms occupy only a small part of this cube.
(Implies some shell designs very inefficient or weak, and not used, or that evolution
hasn’t had time to generate all the possible shell designs for organisms - unlikely.)
Different groups of organisms tend to occupy non-overlapping parts of this cube.
(Example – bivalves and brachiopods in different parts of the lower right corner based
on different T and D values.)
All univalved organisms occur near the top front of the cube with low W and whorl overlap;
all bivalved forms occur below this region where W is high and whorls don’t overlap.
Deviations from isometric growth with constant S, W, T, and D values in coiled shells (rare)
1) Start growing high-spired juvenile snail shell with high T, then drop T value to much lower level to produce much more compact adult shell (like dropping k value in allometric equation) (few snails).
2) Grow high-spired snail shell, then drop off early parts of shell and seal opening (common Austin-area land snails).
3) Change shell shape between juvenile and adult stages and drop off juvenile stages (slightly curved Silurian ascocerid nautiloids).
4) Grow straight juvenile ammonoid shell, then change all of growth parameters to produce completely different coiled or irregular shell around this (family of Japanese Cretaceous ammonoids).
Not many fossils known from Precambrian, only about 150 occurrences, and most fossils from Precambrian are either stromatolites (layered domal or columnal structures) or simple unicellular prokaryotic or eukaryotic cells in chert deposits (rarely phosphorite) until latest Proterozoic when first metazoans appear.
Big question is whether this observed Precambrian fossil record is in fact what really happened or is so highly distorted and biased that it’s giving us the wrong answer. The Precambrian contains about 87% of geologic time (about 4.07 billion years), but represents only about 10% of the outcrops exposed on the continents, probably less than 25% of these Precambrian outcrops are sedimentary to low-grade metamorphic rocks that have a chance of preserving fossils, and less than 1% of all the fossils that have ever been described and named are of Precambrian age.
Stromatolites – First appearance about 3.5 billion years ago in Middle Archean, but only
slowly became more common throughout rest of Archean.
– Built mostly by blue-green algae along with bacteria, green algae, and (in living
examples) forams and diatoms.
– Blue-green algal filaments either trap carbonate particles each tidal cycle or secrete
carbonate particles to cover their top surface, producing a layered structure.
– Stromatolites become much more common and diverse in Proterozoic where they
are the dominant fossil group. Peak diversity is about1.0 billion years ago,
followed by a steep decline in latest Proterozoic probably caused by climatic
deterioration, competition from green algae and seaweeds, and grazing by
earliest metazoans.
– Stromatolites rare after Early Ordovician, but survived Phanerozoic and are still
alive today in hypersaline intertidal bays (Shark Bay, W. Australia) and some current–swept subtidal channels (Bahamas).
Prokaryotic cells – First appearance about 3.5 billion years ago in Middle Archean, but
uncommon throughout rest of Archean. Gradually became more common
in Proterozoic, first eukaryotic cells appear about 2.0 billion years ago (by symbiotic association of prokaryotes – Margulis model) in Gunflint Chert (S. Canada), both cell types became more common in Middle-to-Late Proterozoic (Bitter Springs Chert, Australia), and have continued to the Recent as Monera and unskeletized Protista.
First Metazoans – Ediacara Fauna, S. Australia, about 570 million years old. Soft-bodied,
multicellular invertebrates that resemble coelenterates, annelids, or possibly arthropods, preserved in fine sandstone with fairly large trace fossils, now known from scattered occurrences almost world-wide.
Tommotian Small-Shelly Fossils – 1-2 mm sized sclerites, spicules, and pieces of skeletons
of sponges, worms, onychophorans, other metazoans. Also round embryos with cell clusters and segmentation from some of these Early Cambrian metazoans, such as sponges, or algae.
Possible reasons for rapid increase in metazoan diversity (“Cambrian Explosion”)
– Rapid evolution of new metazoan groups (adaptive radiation)
– First development of skeletons leads to much better fossil record
– More oxygen in atmosphere plus ozone layer (occurred earlier?)
– Development of higher levels in food pyramid (herbivores, carnivores)
Models in Paleobiology – Why are there so many models in this field?
1) Paleobiology is interdisciplinary – at the junction of Biology (life) and Geology (rocks) – the record of life preserved in rocks needs models from both areas.
2) Trying to interpret process from pattern (What caused this fossil crinoid to become extinct at this time?)
3) Geologic lengths of time (deep time) are beyond human experience; need to model long period events.
4) Paleobiology is a historical science – fossil record has already occurred and can’t be rerun to see what would happen if conditions changed, so have to model why observed changes occurred in this record.
Stochastic modeling – Raup, Gould, Schopf, and Simberloff (1973) diversity modeling paper (what else are these four authors known for?)
Sepkoski (1981 & many subsequent) papers on evolutionary faunas
Sprinkle’s echinoderm work
Why does a researcher work on the topics that he (or she) does?
Ability, interest, availability of material to collect or study, gaps in previous research
Echinoderm history and evolution – Early 2-part diversification, later reduction in diversity,
lots of convergence in designs, only 5 classes survived Permo-Triassic extinction and all still living today
Early research – Field work slides from Rocky Mountains
Collecting early echinoderms
Surprise discovery with Dick Robison in July, 1968: 1st carpoids from North
American Middle Cambrian, then discovery of new class called ctenocystoids (published Science, 1969)
Recent research on origin of earliest crinoids with Tom Guensburg (published 2003)
Sepkoski, 1981 (& many subsequent papers) on Evolutionary Faunas – Way of organizing
diversity into groups of organisms that dominated different parts of the fossil record.
What are Evolutionary Faunas? Definition – Class-sized groups of macroscopic marine animals
that reached their maximum diversity (number of families or genera per time interval [stage
or substage]) at different times during the Phanerozoic.
Three Evolutionary Faunas
1. Cambrian Evolutionary Fauna – Classes that reached their maximum diversity during the Cambrian. Trilobites, inarticulate brachiopods, few others. Most now extinct, few others relicts.
2. Paleozoic Evolutionary Fauna – Classes that reached their maximum diversity during the
post-Cambrian Paleozoic. Articulate brachiopods, rugose and tabulate corals, nautiloids,
crinoids. Many relicts today, some extinct.
3. Modern Evolutionary Fauna – Classes that reached their maximum diversity during the
Mesozoic or Cenozoic. Bivalves, gastropods, crustaceans, echinoids, ammonoids, ray-finned
bony fish, marine reptiles, marine mammals. Many dominant today, few relicts or extinct.
Patterns shown by Evolutionary Faunas:
1. New groups appear and rise to their maximum diversity at different times.
2. Increase in overall diversity through time (Camb. < Paleo. < Modern).
3. Increase in ecosystem packing in marine environments through time.
4. Increase in extinction resistance through time.
5. Migration of groups from onshore to offshore through time (origination, spread, retreat)
Problems with Evolutionary Faunas
1. Based on maximum diversity of taxa within a group.
2. Interpreting environments on the shelf (shelf profile used).
3. Didn’t use microfossil groups (no taxa < 5 mm maximum size).
4. Didn’t use any specialized environments (reefs, hardgrounds, etc.).
5. Emphasis on intrinsic causes (extinction resistance) vs. extrinsic environmental causes.
Extraordinary Fossils – Unusual preservation of soft parts of skeletized organisms or soft-
bodied organisms that usually are not preserved under normal conditions.
Gives us a “window” into overall faunal diversity and total morphology of skeletized forms
How get preservation of soft parts in extraordinary fossil occurrences?
1) Rapid burial of a fauna under a thick layer of sediment – fairly common
2) Elimination of decay soon after burial so impression of soft parts remain by development of anaerobic conditions or concretion development – much less common.
Examples of extraordinary fossil occurrences – ~20 of these distributed throughout Phanerozoic fossil record.
Specific examples – Chengjiang Fauna (E. Camb.), Burgess Shale (M. Camb.), Mazon Creek-Essex Faunas (M. Penn.)
How has the diversity of marine life increased throughout Phanerozoic time?
Valentine (1969, 1985; also Sepkoski, 1981) plotted empirical pattern – Phyla, classes, and
orders peaked in Mid Paleozoic; families, genera, and species (inferred) peaked in Recent (2-10X higher?).
Raup (1972) objections – Biases are more important than observed empirical record; biases
distort actual pattern to produce much different observed record? Species diversity reached equilibrium in Paleozoic that has continued to today, or peak in Paleozoic that has not been exceeded since then?
Bambach (1975) compromise – Determined diversity levels within well-studied communities,
onshore communities showed no increase in diversity (Raup pattern correct?) vs. offshore communities
showing big increase in diversity (Valentine pattern correct?)
Bob Bakker’s arguments about warm- vs. cold blooded dinosaurs
Observed pattern– Dinosaurs (L. Trias.-L. Cret.) dominated the Mesozoic terrestrial environments as both medium-large herbivores and carnivores vs. mammals (M. Jur.-Rec.) that remained small and not very diverse; this was not the expected pattern if dinosaurs were “normal” cold-blooded reptiles in contrast to more advanced, warm-blooded mammals. This implies that dinosaurs were in some ways more advanced than early mammals, and that mammals didn’t radiate to large body size and become dominant until after dinosaurs had become extinct at the end of the Mesozoic.
Main argument – Bakker argues that dinosaurs were in fact advanced, active, homeothermic endotherms like living birds (warm-blooded, constant temperature animals using internal heat production) and not homeothermic ectotherms (constant temperature, cold-blooded animals using external heat) or poikilothermic ectotherms (variable temperature, cold-blooded animals using external heat) like living tropical or temperate reptiles.
Bakker’s arguments – 1) Dinosaurs had an advanced fully-erect gait like living birds and
most living mammals (advanced gait = high activity?).
2) Dinosaurs had Haversian canals in their bones for strength and fast ion ex-
change, and Air sacs in their long bones for heat exchange to solve problem of
heat loss (a size-dependent feature?).
3) Dinosaurs had low Predator/prey ratios similar to living warm-blooded mammals (difficult to determine this accurately from fossil death assemblages).
4) Archaeopteryx argument: origin of birds from theropod dinosaurs implies these (and perhaps all dinosaurs?) may also have been warm-blooded, and some small theropods may have already had insulating downy feathers to prevent heat loss.
Counter arguments – Dinosaurs have low Brain weight/body ratios similar to those of living
reptiles (cold-blooded), and not high ratios like those of living mammals and birds (warm-blooded) (intelligence goes along with high activity levels?).
Paul Martin’s (1973) arguments about humans causing big extinction of large mammals and flightless birds at the end of the Pleistocene (last 65,000 years).
Extinctions occur at different times in different places coinciding with arrival of advanced Paleolithic humans from Africa (where originated) or southern Asia (reached by Late Pleistocene about 100,000 years ago). Reached Australia ~ 65,000 years ago from SW Asia, reached southern Europe ~ 40,000 years ago from Middle East, reached North America as Pleistocene glaciers were melting ~ 12,000 years ago from Asia across Bering Land Bridge, reached South America from N. Amer. ~11,000 years ago, reached Mada-gascar from Africa and New Zealand from Australia ~ 2,000 years ago, and reached Pacific islands from Australia? ~ 1,500 years ago. Appearance of these advanced big-game hunters recognized by first occurrence of Paleolithic Clovis Point spear points and arrowheads.
Martin’s “overkill” or “blitzkrieg” model for extinction: “wave” of big-game hunters swept through North and then South America between 12,000 and 10,000 years ago causing major extinction of larger Plains mammals, such as mammoths, giant bison, ground sloths, horses, camels, and saber-toothed cats. No humans in front of wave, just rich Pleistocene large-mammal fauna, high density of humans (0.4 humans/square km) in wave front where best hunting and extinction occurred, low density of humans (0.04 humans/square km) and depauperate fauna behind wave where hunting more difficult. Wave front took about 10 years to pass through any particular area; humans probably kept moving camps toward south where hunting was better every 5-10 years. Model implies not much chance of getting human remains associated with extinct mammals (such as a Clovis Point stuck in mammoth rib) because humans and mammoths only associated for about a 10 year period (out of ~12,000 yrs. in Recent) during which the extinction occurred. But human remains and Clovis Point artifacts should appear in an area at about the same time that the larger mammals and flightless birds became extinct there; implies carbon-14 dating of these first and last appearances is the best way to test this model. Dating does agree with this model; slightly younger dates for South American extinctions than North American ones.
Biggest problem with Martin’s model is scattered dates for very early human remains in this hemisphere (> 13,000 years). Model doesn’t work so well if some humans already here before big-game hunters arrived.
Alternate model is that stress from big climatic changes, from cool wet to warm dry, was cause of extinctions – Ernie Lundelius, retired paleontologist at UT, a big advocate of this theory.