Final Flashcards
1
Q
Bryozoans
A
-found in freshwater & marine environments
–vast majority are marine
–few species from Phylactolaemata & all of Stenolaemata are freshwater
-freshwater forms have few hard parts to their skeleton and don’t have much of a fossil record
-only found in colonies
-individuals are called zooids
-organ-level organization
-U-spahed digestive tract
-reproductive organs (gonads)
-open circulatory system
-primitive digestive system
-fossils fragment quite easily
2
Q
Lophophore
A
-filter feeding organ found in tube worms, byrozoans, and brachiopods
-structure varies between groups, consists of long, ciliated strands
-cilia pass particles back to a mouth for ingestion
3
Q
Bryozoan zooids
A
-have specialized forms
-autozooids and heterozoids
-zooid compresses, pressure pushes out lophophore
4
Q
Autozooids
A
-are feeding zooids
-much larger than other zooids within a colony
-prominent lophophore that is used to comb water for food
-muscles can withdraw lophophore into zooid for protection beneath a hardened lid called operculum (done when stressed)
5
Q
Heterozoids
A
-much smaller than autozooids
-do not feed and depend on autozooids for nutrients
-different types of heterozoids
–Aviculara - deter preators
–Vibracularia - remove sediment, also likely provide an early detection system for predators
–Kenozooids - reinforce the skeleton of the colony
-these different zooids produce different skeletal morphologies
-also reflected in fossil bryozoans
6
Q
Bryozoan Skeletal Morphology
A
-calcite skeleton is present in forms with a skeleton
-in comparison with corals
–zooid (polyp): the fleshy animal itself
–zoecium (corallite): the hole that the animal lives in
–zoarium (corallum): the group of zooecia that comprise a colony
-zooids live in a zoecia that form a zoarium
7
Q
Bryozoan colony morphology
A
-bryozoan colonies take on a variety of forms
-related to living environment as well
–robust forms in high-energy settings
–branching & fenestral forms in low-energy settings
8
Q
Class Phylactolaemata
A
-class of bryozoans
-exclusively freshwater
-no mineralized skeleton
9
Q
Class Gymnolaemata
A
-class of bryozoans
-mostly marine
-includes most modern bryozoans
-some have mineralized skeleton of delicate, box-like calcareous zoecia that have relatively good fossil record
-Jurassic to recent
10
Q
Class Stenolaemata
A
-class of bryozoans
-mostly marine
-produce calcareous skeleton of cylindrical elongate zoecia that fossilizes well
-Ordovician to recent
-majority of fossil bryozoans from ordovician to cretaceous belong to this group
-important orders include:
–Cyclostomatida
–Cystoporata
–Treptostomata
–Cryptostomata
–Fenestrata
11
Q
Bryozoan Ecology
A
-most attach to seafloor (fixosessile)
–root themselves in soft sediment
–cement themselves to hard substrates
-some are unattached & free-lying on seafloor (librosessile)
-fed on by fish, arthropods, sea urchins in modern oceans
-encrusting forms commonly cement themselves to shell debris
–encrust surface of shell
–use shell as an anchor
–may take advantage of feeding currents produced by other animals
12
Q
Bryozoan contribution to sediments
A
-substrate stabilizer
–binding & trapping loose sediment
–forming hard pavements on seafloor
-carbonate sediment contributor
–skeletal grains
–biostromes & patch reefs in cool-water carbonate settings
–easily fragmented, but fragments accumulate
-reef builders
–don’t rely on photosynthetic symbionts
–can colonize deep marine environments, turbid water, variable environmental conditions
–occupy cavities in coral reefs
–very important reef communities during late ordovician
13
Q
Bryozoans in cool-water carbonates
A
-along w/ mollusks & red algae, an important component of cool-water carbonate environments
-bryozoans aren’t as dependent on warm waters as corals are
-important component of cool-water carbonates
14
Q
Bryozoans Summary
A
-colonial animals that filter feed using lophophore
-gymnolaematans dominate today, but most fossil groups belong to sternolaematans
-bryozoans difficult to classify based on morphology of colony & key diagnostic features can sometime only be visible via microscope
-only common as component of cool water carbonate platforms today, important reef builders during late ordovician intervals
15
Q
Corals
A
-phylum Cnidaria
16
Q
Cnidaria body plan
A
-true tissue level organization
–endoderm & ectoderm enclosing mesoglea
17
Q
Enteron
A
-part of corals
-sec-like body cavity capable of extracellular digestion of food
18
Q
Zooxanthellae
A
-symbionts common in some cnidarian groups
-unicellular alage that live within body of cniderian
-use nitrate-rich waste from corals
-use carbs from zooxanthellae
-not present in all corals
19
Q
Coral bleaching
A
-occurs when coral subjected to low or high temps, H2O pH, salinity, pollution, or runoff
-can be caused by a change of only a few degrees
-expel zooxanthellae, losing their colour
-if not killed, weakens corals - more susceptible to disease
-coral reefs slow to recover, hence fossil reef gaps
20
Q
Polyps
A
-individual coral animals
21
Q
Corallites
A
-individual skeletal elements
22
Q
Corallum
A
-colony of coral
23
Q
Class Anthozoa
A
-contains corals
-most diverse class by far
-2 subclasses
24
Q
Subclass Octocorallia
A
-subclass of Anthozoa class of corals
-largely organic skeleton
-most groups have poor fossil record
25
Subclass Zoantharia
-subclass of Anthrozoa class of corals
-sea anemonies & true corals, entirely marine
26
Order Tabulata
-order of subclass Zoantharia
-paleozoic colonial corals
-calcite skeleton
-early ordovician to permean
27
Order Rugosa
-order of subclass Zoantharia
-paleozoic solitary & colonial corals
-calcite skeleton, favours good fossilization
-exclusively paleozoic (middle ordovidian to permean)
-peak abundance in diversity in silurarian & denovian
-colonial rogosans were important framebuilders of paleozoic coral-stromatoporid reefs
28
Order Scleractinia
-order of subclass Zoantharia
-mesozoic & cenozoic colonial corals
-solitary & colonial corals
-aragonite skeleton
-middle triassic to present
29
Rugose corals morphology
-epitheca
-calice
-septa, major & minor
-tabula
-tabularium
-dissepiments
-dissepimentarium
30
Epitheca
-outer calcareous layer
-typically wrinkled in solitary forms
-lost in some colonial forms
31
Calice
-basin-shaped depression formed by top portion of epitheca & top tabula
32
Septa
-prominent vertical partisions
-spaces are fossula
-septa literally means wall
33
Major septa
-dark, thick lines
-extending to or near center, symmetrical through cardinal & counter cardinal septa
34
Minor Septa
-shorter & thinner, inserted sequentially during growth in each quadrant against counter-lateral septa
35
Tabula
-horizontal divison
-typically warped & fragmented, rarely flat & don't extend from wall to wall
36
Tabularium
-axial zone of differentiated & more crowded tabulae
37
Dissepiments
-bubble-like, convex-up plates
-usually best developed along edge
38
Dissepimentarium
-peripheral zone of dissepiments
-enhancing strength for corallites w/ minimum amount of biomineralization
39
Low flat corals
-adapted to soft substrates & low energy environments
40
Cone/cylindrical corals
-adapted for higher energy environments
41
Phaceloid
-tube-like forms
-usually have connecting processes
-dendroid (tree-like) forms where corallites branch from each other are rare
42
Tabulate corals
-tabulate = to have a plane surface
-calcite skeleton, similar to rugose corals
-only colonial forms known
-exclusively paleozoic with peak abundance in silurian and devonian (like rugosans)
-important framebuilders of paleozoic coral-stromatoporid reefs
43
Tabulate corals morphology
-tabulae (well developed & regular, extend across corallite)
-epitheca (flat, not wrinkled, perforated by mural pores)
-septa (weak, only visible on edge of corallum as septal spines, don't extend to center of corallite)
-mural pores
-loosely bound coralla
-massive coralla
44
Mural pores
-connect adjacent corallites
-often form linear patterns along either planar surface of corallite or vertices
-unknown function, probably permitted transfer of nutrients between polyps or communication
45
Loosely bound coralla
-corallites grow in loose networks connected side by side or connected by horizontal tubes
-in dendroid forms, corallites branch off one another, upright or along a surface
46
Massive coralla
-corallites grow in contact with one another, adapted to higher energy environments
-can also grow surround in a dense network of tubes or porous tissue
-can grow in sheets overlying one another
47
Tabulate corals: functional morphology
-colony shape adapted to environment conditions
-massive, tabular, domal colonies are common in shallow & turbulent waters
-horizontal growth exceeds vertical growth
--some tabular & domal forms adapted to soft, muddy substrates
-cylindrical, digitate, & delicately branching forms are only found in low-energy environments
--growth primarily in vertical direction
48
Scleractinian corals
-stony corals
-only corals with robust stony skeleton alive today
-triassic to present
-aragonite skeleton, only coral with aragonite skeleton
-usually colonial, sometimes solitary
-lack true tabulae
49
Hermatypic
-if corals have zooxanthellae
50
Ahermatypic
-solitary scleractinians usually found in deep-water
-lack zooxanthellae
51
Fungia
-common in tropical reefs
52
Focused septal growth
-trait of scleractinian corals
-focused septal growth
-some forms lose their epitheca to focus growth on septa
-no definitive calices, difficult to differentiate individual corallites
-commonly referred to as brain corals
53
Factors that influence coral reef distribution
-sunlight & H2O depth
-H2O temp & chem
-salinity
H2O turbulence
-siliciclastic sedimentation
-phosphate & other inorganic nutrients
-bioerosion
54
Photic zone
-in clear water
-100-200m in depth
-reefs grow best in water less than 50m deep
-zooxanthellae thrive best here
--require photosynthesis --> light
55
Hermatypic corals
-with zooxanthellae
-reef building
-need sunlight for photosynthesis
-live in clear shallow water
-temp 18-29°C
--ideal temp is 25-29°C
-high temps cause bleaching
--corals expel zooxanthellae, lose ability to photosynthesize & colour
56
Ahermatypic corals
-lack symbiotic algae/zooxanthellae
-commonly live at much greater dephts than hermatypic corals
-solitary corals may not have required sunlight; may have been ahermatypic
--tradeoff between benefit of zoohanthellae & sunlight for deeper, more nutrient-rich waters
-can survive below 0°C in deep ocean
--most abundant at 5-10°C
57
Coral ecology: Salinity
-few reefs near mouths of large river systems
-large fresh water input events cause significant salinity fluctuations
-high siliciclastic sediment loads can bury corals & cause murky water
-ideal range for tropical corals is ~25-35%
58
Stenohaline
-grow best in sea water of normal salinity (35%)
-can survive lower (25%)
-hermatypic corals
59
Why do corals prefer turbulence/energetic waters?
-introduces nutrients
-removes waste
-prevents sediment build up
-corals will grow toward waves
60
Sedimentation
-increases turbidity
-decreases solar penetration
-buries corals
-can come from anthropogenic sources or natural
-corals don't find this bussin
61
Phosphate & other inorganic nutrients
-phosphorous & nitrogen
-too many inorganic nutrients results in eutrophication
-detrimental to corals
-algal blooms consume all O2
-other organisms die off
-can smother coral reefs
62
Bioerosion
-coral reefs broken down by starfish, coral eating fish, encrusting boring sponges
-contributes to reef by destroying parts of it
--talus builds up at base of reef & fortifies reef
--must be balanced so that erosion doesn't outpace ability of reef to grow
63
Talus
-debris
64
Requirements for coral reef to become established:
-carbonate shelf
-not too deep (sunlight, H2O temp, turbulence)
-tropical (H2O temp, supersaturation of CaCO3)
-not near major river (normal marine salinity, low organic nutrients, low siliciclastic input)
-not near rising mountain chain (low siliciclastic input)
-limited bioerosion
65
Lagoon (back reef)
-low energy zone protected by reef crest
-lots of sunlight
66
Reef crest
-peak of reef exposed to waves
-very high turbulence
-lots of sunlight
67
Reef front
-oceanward side of reef
-diverse reef-building organisms
68
Fore reef
-deeper portion of reef beyond reef front
-below zone of coral & algal growth
-lower turbulence & less sunlight
69
Coral reef zonation
-different factors in different parts of the reef select for different forms
70
Surface area for photosynthesis
-forms grow wider at shallower depths
-grow more vertical in deeper depths
71
Optimal skeleton strength to resist turbulence
-high turbulence at reef crest necessitates robust, dense form
-low turbulence produces branching, tabular, & columnar forms
72
Shedding sediments
-wide flat forma are able to collect more sunlight but also collect sediments
-in lagoon, branching forms are able to better shed sediments in comparison to tabular forms
73
Coral reef types
-fringing reefs
-barrier reefs
-patch/platform reefs
-atolls
74
Fringing reef
-shallow water reef that forms around island or on tropical shorelines
-variable in size, shape, and distribution
75
Barrier reefs
-form at edge of continental shelf
-often long & linear features
-strongly stratified due to changing environmental conditions with depth
-crow towards ocean
76
Patch
-platform reefs
-typically form in shallow lagoon settings on continental shelf
-patchy distribution throughout lagoon
-little to no zonation
-grow in all directions
77
Atolls
-form around isolated volcanic islands
-forms ring around island near shoreline
-as island subsides, coral continues to "keep up" to sea level
--results in circular barrier reef with shallow interior lagoon
78
Corals in geology
-stratigraphic indicators
--long temporal ranges, wide geographic ranges, rock type dependent
-poor tools for biostratigraphic correlation
--occasionally useful regionally for correlation
-very useful for determining paleoenvironmental conditions
-important component of reef ecosystems throught phanerozoic
--dominant reef builders in silurian and devonian with stromatoporoids
-still one of dominant reef builders today
-corals & stromatoporids commonly closely associated in paleozoic rocks
-form laterally extensive metazoan reef complexes
-sometimes closely associated as endosymbionts
79
Brachiopods
-phylum brachiopoda
-bilaterally symmetrical (symmetry through middle of each shell)
-2 asymmetrical hard shells encase flesh of organism
80
Pedicle
-fleshy extensionof animal that extends from ventral valve
81
Mantle
-soft part of brachiopod involved in biomineralization
82
Organization of Brachiopod
-most of brachiopod is empty space
-organism itself occupies posterior of shell
-most of anterior consists of mantle cavity
-cavity contains lophophore
83
Dorsal Valve
-usually shown in figures as upper valve
-previously referred to as brachial valve
-where lophophore attaches to
84
Ventral Valve
-often shown in figures as lower valve
-previously referred to as pedicle valve
-contains opening for pedicle
85
Growth Lines
-concentric ridges that develop as shell grows
86
Ribs
-crenulations across shell surface parallel to direction of growth
-sometimes simple, sometimes split
-sometimes multiple orders
87
Spines
-extend from shell surface
-visible on some brachiopod groups
88
Commissure
-plane along which shells open
-sometimes forms flat plane, but often deflected due to shell shape
-zig-zag ones evolved as filtering grids to prevent entry of large harmful particles
89
Fold & Sulcus
-distinctive abrupt deflection at front in some forms
-may be used for directing water
90
Calcite Shells
-present in most brachiopods
-good preservation under most conditions
-can often see original shell fabric in fossils
91
Aragonite shells
-very rare for brachiopods
-few have them
-aragonite does not preserve well in fossil record
92
Impunctate
-no microstructures
-solid shell without any structures that penetrate either the inside or outside of structure
93
Epipunctate
-perforations open only to shell exterior
-likely served as sensory function
-became isolated & atrophied as shell grew
94
Pseudopunctate
-structures within shell
-columnar features with in shell
-warping of shell fabric to create bumps on inner shell surface
-uncertain function
-characteristic of strophomenide brachiopods
95
Punctate
-perforations through shell
-contain extensions of the mantle
-terminate just inside external surface of shell
-function uncertain
96
Brachiopods 3 sets of muscles
-adductors: close the shell
-diductors: open the shell
-adjustors: twist the shell/pedicle
97
Scars
-attachment points of muscles
-muscles usually not preserved
98
Hingeline
-formed by 2 joints near posterior of shell in rhynchonelliformean brachiopods
-teeth (ventral valve) insert into sockets (dorsal valve)
99
2 types of hingelines
-strophic: long, linear hingeline
-astrophic: short/pointed hingeline
100
Linguliformea
-subphylum of brachiopods
-pohsphatic inarticulates
-early cambrian to recent
-still found worldwide
-became especially adapted to very difficult environment
-tend to have longer larval periods & stay in water column
101
Craniiformea
-subphylum of brachiopods
-calcareous inarticulates
-early cambrian to recent
-still found worldwide
-became especially adapted to very difficult environment
-tend to have longer larval periods & stay in water column
102
Rhynchonelliformea
-subphylum of brachiopods
-articulates
-early cambrain to recent
-during cenozoic, shifted to cool water habitats
-still found worldwide, generally overshadowed by bivalves in shallow tropical ecosystems
-have very short larval periods & settle out quickly
-2 classes, strophomenta & rhynchonellata
103
Class Strophomenata
-middle cambrain to late permean
-generally have strophic hingelines
104
Class Rhynchonellata
-early cambrian to recent
-generally have astrophic hingelines
105
Brachiopod paleoecology
-variety of lifestlyes
-many attach to substrate via pedicle (fixosessile)
-many librosessile when fully grown
-few groups cemented to seafloor
-some have spines to anchor themselves or use soft parts of mantle to hold themselves in place
-1 group is infaunal, limited motility due to large bedicle & complex muscle system
-rest are entirely epifaunal
106
Brachiopods good ecological & environmental indicators for paleozoic?
-yes
-very abundant across wide range of marine environments
-very diverse form ordovician to permean
-calcite shells often preserved with minimal alteration
-form distinctive assemblages that depend on movement
107
Time frame of Brachiopods
-first appear in cambrian
-diversify extensively at order level during ordovician
-almost extinct during permean mas extinction
-minor component of mesozoic shelly benthos
-diversifying in template & cool-water settings in cenozoic
108
Brachiopods & bivalves
-brachiopods only found in marine settings
-mollusks found in freshwater & marine
--also have higher metabolism, thought to be more resilient
-shift from brachiopod dominated to bivalve dominated between paleozoic & mesozoic
109
Mollusks
-phylum mollusca
-second most diverse metazoan phylum
-entirely solitary organisms
-wide variety of habitats & life styles
110
2 types of feeding mollusks
-suspension & deposit feeding via gills, siphons, labial palp
--bivalves
-herbivory & carnivory by means of radula
--numerous teeth, grinding
--gastropods & cephalopods
111
Bivalves
-class of mollusks
-mainly filter feeders
-symmetry between valves, shells
-mantle secretes calcareous (aragonite) shell & forms siphons for infaunal filter feeding
--inhalent siphon takes in water, exhalent one releases wastes
112
Beak (bivalves)
-first part of shell that forms
-umbo is sometimes used synonymously, but mainly used to describe hump part
--umbo projects to anterior side, which is shorter
--umbo also on dorsal side
113
Foot (bivalves)
-can be used for burrowing, locomotion, etc.
114
Paleosinus
-indicates retractible siphon/position of siphon
115
Relaxation of adductors (bivalves)
-external ligament opens shell
-ligament stretches when closed, relaxed when open
116
Dentition
-teeth of bivalves
-how fossils are distinguished
--also use ligament insertion area, adductor scars, pallial line, shell shape, shell fabric
117
Taxodont dentition
-short teeth
-straight or chevron pattern
-most frequently inclined
-arranged along entire dorsal edge below umbo
118
Dysodont dentition
-row of teeth along hingeline
-reduced strength in comparison to taxodont
-strong ligament
119
Isodont dentition
-very large teeth on either side of central ligament pit
120
Heterodont dentition
-2 or 3 wedge shaped teeth centered near umbo
-radiate from beak
121
Desmodont dentition
-teeth replaced by large resilifer
-attachment for enlarged internal ligament
122
Bivalves shell structures
-outer surface may be smooth, ribbed, or spiny
--offers protection, stabilization
-concentric growth lines & lamellae are generally prominent
-ribs, ridges, & bulges are variable
--assist in digging & strengthening shell
123
Bivalves shell mineralogy
-most are aragonite
-calcite in oysters & scallops
-mix of aragonite & calcite are rare
124
Bivalves ecology
-can be infaunal or epifaunal
--infaunal: shallow or deep, most have siphons
--epifaunal: free lying, cemented, or attached by byssal therads (collagen threads from byssal notch)
-some can swim via rapid contraction of adductors
-few can bore into rock with foot
125
How are bivalves' shell form related to lifestyle?
-infaunal forms tend to be rounded & elliptical with pronounced pallial sinus
-epifaunal forms variable in shell shape, sometimes have different shaped valves
-swimmers are flattened with extended ear-like extensions along hinge line
-borers are cylindrical & elongate
126
Pallial sinus/game in shell interior
-indicates presence of siphon
127
Mucus tubes
-used by infaunal bivalves that lack siphon
128
Bivalves fossil record
-cambrian to recent
-generally not well-preserved in fossil record due to their aragonite shells
--usually recrystallizes to calcite
--commonly dissolves completely
129
Bivalves vs brachiopods
-bivalves competed with brachiopods as filter feeders
-bivalves had several physiological advantages
--larger, thicker shell
--some evolved to become infaunal
--most were mobile
--wider range of ecological tolerances (especially salinity)
130
Rudists
-extinct group of cementing bivalves
-late jurassic & cretacious
-highly modified form resembling coral
--right valve became conical
--left valve often perforated, flatteend
-important mesozoic reef builders
-evolved into 2 forms:
--elevator forms: densely packed colonies, similar to colonial corals
--recumbent forms: free-lying on seafloor similar to solitary rugose corals
131
Bivalves good index fossils?
-no
-stratigraphic ranges too long to be useful as index fossils other than few specialized groups (rudist)
-gryphaea is one of few that can be used as index fossil in triassic and jurassic
132
Gastropods
-class of mollusks
-head w/ eyes, mouth, tentacles
-large foot for locomotion
-torsion of body
-gills/lungs for respiration underwater/on land
-growth lines on shell exterior common
-no septa on inside of shell - one continuous chamber
133
Whorl
-shell fragments
-separated by sutures
-last whorl is largest; where organism lives
134
Siphonal canal
-where siphon would extend out of small notch
135
Radula
-used to scrape at surfaces back & forth for feeding
-surfaces could be algae on seafloor or drilling through hard shell
136
Prosobranchiata
-subclass of gastropoda
137
Columella
-axis on which the shell is twisted on
-may be twisted towards a point forming a spire (top is usually called apex)
138
Gastropods shell structure
-thin outer coating of organic material
-thick carbonate later almost entirely aragonite
-some shells have separate layers of calcite & aragonite
139
Planispiral
-whorls are aligned within a plane
140
Conispiral
-whorls are not aligned within a plane
-high-spire forms (long) and low spire forms
141
Gastropod feeding strategies
-4 major feeding strategies
-herbivores
-carnivores (use radula for drilling into prey or injecting venom)
-detritus feeders (deposit feeding & scavengers)
-suspension filter feeders (restricted to unusual fixosessile worm-like gastropods)
142
Gastropods ecology
-ultimate generalists - occupy almost every niche imaginable
-benthic: most are vagile/free-living, few are fixosessile worm-like forms
-planktonic: pteropods
-Epiplanktonic: attached to floating seaweed or detritus
-Nektonic: swimming nudibranchs
Terrestrial: found in variety of habitats ( have to keep moist)
143
Gastropods fossil record
-long stratigraphic ranges generally make them poor index fossils
-phylogeny of fossil groups difficult & poorly defined
-aragonite shell usually dissolves or recrystallizes
144
Scaphopods
-aka tusk shells
-common by carboniferous, still found today
-unusual type of partially infaunal marine mollusk
--live with pointed end sticking out of sediment
--tiny tentacles would grab foraminifera
--locally common in cretaceous shales of western north america
145
Cephalopoda
-class of mollusks
-evolution of body shape for mobility (streamlined, buoyancy control, modified foot into cone jet propulsion)
-advanced NS with well developed head (cephalization)
-have septa that divide shell into chambers, form suture patterns where they meet shell
-some very large
146
Cephalopods shells
-most modern forms lack shells, most fossils had shells
-shell divided by septa with siphuncle
--siphuncle removes water from unoccupied chambers & replaces it with gas, used to adjust buoyancy
-septal foramen calcified, readily preserved, support structures for siphuncle
-peristome: edge of opening of shell
147
Longicone
-long shells
148
Brevicones
-short shells
149
Orthoconic
-straight shells
150
Cyrtoconic
-curved shells
151
Evolute
-applies to curved shells
-younger whorls do not overlap earlier whorls
152
Convolute
-applies to curved shells
-younger whorls partially overlap earlier whorls
153
Involute
-applies to curved shells
-younger whorls completely overlap earlier whorls
154
Subclasses of Cephalopods
-Nautiloidea (late cambrain to present)
-Ammonoidea (devonian to cretaceous)
-Coleoidea (carbonifeous to present)
155
Nautiloids
-cambrain to present
-shell straight or coiled
-composed of aragonite
-simple septa that are flat or arched but not wrinkled
-siphuncle often large & located near central axis of shell
-cameral & siphuncular deposits common
--camera: chamber
-relatively diverse through ordovician & silurian
-only 1 order through most of mesozoic & today (Nautilida)
-significantly affected by permian mass extinction
-trend of increasing degree of coiling
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How did nautiloids evolve to be more mobile swimmers?
-crowded septa to increase phragmocone weight
-reduction in cone length
-calcareous deposits inside shell (siphuncular & cameral deposits)
-flattening & coiling of shell
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Nautiloids ecology
-top predator in ordovician & silurian seas
-less than 1cm in late cambrian
-10m in ordovician
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Modern Nautilus
-slow swimmer
-only active at night
-found in moderately shallow waters
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Ammonoids
-most are coiled & commonly ribbed
-unlike nautiloids, siphuncle simple in structures & located on edge of shell
-complex suture patterns, especially in ammonitic ammonoids
-evolved from straight-shelled nautiloids in early devonian
-extinct at end of cretaceous
-important index fossils for late paleozoic & mesozoic rocks
--rapid evolution = short stratigraphic scales
--nektonic lifestyle = wide geographic distribution
-sutures mark contact between septa & inner shell surface (can be traced across shell as suture line)
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3 main types of ammonoids
-Goniatitic: devonian to permean
-Ceratitic: Triassic, differentiation of lobes
-Ammonitic: Jurassic & Cretaceous
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Evolution of ammonoids
-some evolved into long straight shell, similar to earlier nautiloids
-mixed results on why more complex sutures evolved
--resistance to predators, increase shell strength, support to enable diving deeper, buoyancy control
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Coleoids
-some forms have internal shells
-gladius: rigid internal structure composed of chitin
-cuttlebone: thin chambered internal shell
-some have lost shell (octopus)
--adaptation for faster movement & greater agility
-many evolved complex colour-changing abilities (chromatophores)
-some have photophores for bioluminescense
-Belemnites: Jurassic to Cretaceous, developed thick guard of prismatic calcite
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Arthropods
-phylum arthropoda
-most abundant & diverse metazoan phylum
-extremely under-represented in geological record due to poor preservation potential
-conquered water, land, air
-fill variety of niches in many different ecosystems
-body sizes range from mciroscopic to giants
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Arthropoda body plan
-segmented body
-jointed appendages
-chitinous exoskeleton
-simple & compound eyes
-open circulatory system
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Segmented body
-characteristic of arthropoda
-cephalon (head), thorax, abdomen (pygidium)
-some segments more well developed in some groups than others
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Chitinous skeleton (carapace)
-characteristic of arthropoda
-composed of complex chains of polysaccharides
-initially soft after molting (ecdysis) but quickly rehardens
-generally does not preserve well in fossils
-many fossils are probably molted exoskeletons
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Trilobites
-subphylum trilobitomorpha
--subphylum of arthropoda
-evolved in earliest cambrian & went extince before end of permean
-well preserved due to chitinous exoskeleton being fortified by CaCO3 (dorsal only)
-lack any internal growth lines
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3 Groups of Trilobites
-agnostids: small & blind forms common in deep-water deposits
-cambrian trilobites: abundant in cambrain, less diversity
-paleozoic trilobites: more diversity but uncommon
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3 Lobes in trilobite body division
-axial: runs down middle lengthwise
-2 pleural lobes: flank axial lobe
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Trilobites head anatomy
-contains important diagnostic features
-axial part forms raised glabella
-cheeks located on either side of glabella
--may be cut by facial suture that divides cheeks into fixed inner cheeks & free outer cheeks
-suture probably marked where exoskeleton breaks free during molting
-some have pitted cephalic fringe: must have served sensory function given lack of eyes or some filtering function
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Trilobites eyes
-consist of calcite lenses
-2 main types, holochoral & schizochoral
-some trilobites had stalked eyes, some were blind
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Holochoral eyes
-more primitive
-consist of many small biconvex lenses covered by a continuous cornea
-smooth glossy appearance
-ancestral form
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Schizochoral eyes
-consist of small number fo calcite lenses
-individual cornea covering each lens
-derived form
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Enrollment
-some later trilobites were able to enroll, protecting softer underside from predators/environment
-enroll during molting process
-could also have occured after death
-only found in mid-Paleozoic trilobites
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Trilobites Thorax
-composed of many articulated & flexible segments
-divided into axial ring & 2 pleura
-each pleuron has groove that acts to strengthen it
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Growth stages of trilobites
-protaspid: cephalon develops
-meraspid: pygidium differentiated from cephalon
-holaspid: all segments fully developed
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Trilobites paleoecology
-most were benthic to nektobenthic & vagile
-likely were deposit feedes, feeding on organic matter on seafloor or within sediments
-ones with large eyes may have adapted to more nektonic lifestyle
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What period are trilobites good index fossils for?
-cambrain
-widespread distribution
-periodic extinctions serve as biostratigraphic boundaries
-somewhat useful in ordovician, less common in paleozoic, meaning less useful
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Biodiversification events
-intervals of rapid evolution across multiple evolutionary lineages
-often new body plans evolve during these events
-3 major ones:
--cambrian explosion
--great ordovician biodiversification event
--mesozoic marine revolution
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Mass extinction events
-periods of high extinction rates across several evolutionary lineages
-may result in disappearance of higher-level taxa
-5 major ones:
--late ordovician
--late devonian
--late permean
--late triassic
--late cretaceous
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Late Ordovician Mass Extinction
-caused by glaciation in Gondwana suring Hirnantian Stage
-extinction occurred for ~500k years
-~86% species lost
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Devonian Mass Extinction
-21% marine families lost
-57% genera & 75% of species across entire extinction
-multiple pulses over last 20 mill years of Devonian
-probably multiple causes, not as well understood as other mass extinctions
-tropical reef ecosystems devastated, stromatoporoids go extinct
-planktonic graptolites, most jawless fish, placoderms extinct (benthic ones still chilling)
-shelly benthos less severly affected
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Permean Mass Extinction
-75% of species on land, 95% of species in marine environments disappear
-devastated all environments
-pulse driven, 2 main pulses in late permian
-spanned 10mill years
-Siberian Traps erupted, releasing CO2 & SO2
-sudden rise in CO2 & drop in O2 -- widespread anoxia in ocean
-terrestrial & oceanic ecosystems severely affected
--loss of many early tetrapods
--most groups that dominated the paleozoic oceans either went extinct or became minor part of marine ecosystem
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Triassic Mass Extinction
-initial rifting of pangaea in late triassic triggered volcanism along rift
-also may have been linked to impact event in manicouagan
-relatively minor in comparison to other Big 5 mass extinctions
-increased CO2 from volcanism: = temp & ocean pH increase
-Primative archosaurs went extinct
-large amphibians that survived Permean mass extinction finally disappeared
-one of the few extinctions that had major impact on plants
-mollusks severely affected & conodonts disappear
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Cretaceous Mass Extinction
-15% marine families, 75% species
-dinos, large reptiles affected along with some early birds
-rudist bivalves, ammonites, belemnites become extinct in ocean with several lineages of large cartilaginous & bony fish
-Bolide impact: lots of iridium at impact site, lead to theory of asteroid
--shocked quartz also supports this theory
-sudden shift in plankton & pollen
-fern spike recorded in sediments dating to after impact
--ferns are first to thrive in an environment
