Final Flashcards
Bryozoans
-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
Lophophore
-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
Bryozoan zooids
-have specialized forms
-autozooids and heterozoids
-zooid compresses, pressure pushes out lophophore
Autozooids
-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)
Heterozoids
-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
Bryozoan Skeletal Morphology
-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
Bryozoan colony morphology
-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
Class Phylactolaemata
-class of bryozoans
-exclusively freshwater
-no mineralized skeleton
Class Gymnolaemata
-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
Class Stenolaemata
-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
Bryozoan Ecology
-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
Bryozoan contribution to sediments
-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
Bryozoans in cool-water carbonates
-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
Bryozoans Summary
-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
Corals
-phylum Cnidaria
Cnidaria body plan
-true tissue level organization
–endoderm & ectoderm enclosing mesoglea
Enteron
-part of corals
-sec-like body cavity capable of extracellular digestion of food
Zooxanthellae
-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
Coral bleaching
-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
Polyps
-individual coral animals
Corallites
-individual skeletal elements
Corallum
-colony of coral
Class Anthozoa
-contains corals
-most diverse class by far
-2 subclasses
Subclass Octocorallia
-subclass of Anthozoa class of corals
-largely organic skeleton
-most groups have poor fossil record
Subclass Zoantharia
-subclass of Anthrozoa class of corals
-sea anemonies & true corals, entirely marine
Order Tabulata
-order of subclass Zoantharia
-paleozoic colonial corals
-calcite skeleton
-early ordovician to permean
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
Order Scleractinia
-order of subclass Zoantharia
-mesozoic & cenozoic colonial corals
-solitary & colonial corals
-aragonite skeleton
-middle triassic to present
Rugose corals morphology
-epitheca
-calice
-septa, major & minor
-tabula
-tabularium
-dissepiments
-dissepimentarium
Epitheca
-outer calcareous layer
-typically wrinkled in solitary forms
-lost in some colonial forms
Calice
-basin-shaped depression formed by top portion of epitheca & top tabula
Septa
-prominent vertical partisions
-spaces are fossula
-septa literally means wall
Major septa
-dark, thick lines
-extending to or near center, symmetrical through cardinal & counter cardinal septa
Minor Septa
-shorter & thinner, inserted sequentially during growth in each quadrant against counter-lateral septa
Tabula
-horizontal divison
-typically warped & fragmented, rarely flat & don’t extend from wall to wall
Tabularium
-axial zone of differentiated & more crowded tabulae
Dissepiments
-bubble-like, convex-up plates
-usually best developed along edge
Dissepimentarium
-peripheral zone of dissepiments
-enhancing strength for corallites w/ minimum amount of biomineralization
Low flat corals
-adapted to soft substrates & low energy environments
Cone/cylindrical corals
-adapted for higher energy environments
Phaceloid
-tube-like forms
-usually have connecting processes
-dendroid (tree-like) forms where corallites branch from each other are rare
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
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
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
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
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
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
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
Hermatypic
-if corals have zooxanthellae
Ahermatypic
-solitary scleractinians usually found in deep-water
-lack zooxanthellae
Fungia
-common in tropical reefs
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
Factors that influence coral reef distribution
-sunlight & H2O depth
-H2O temp & chem
-salinity
H2O turbulence
-siliciclastic sedimentation
-phosphate & other inorganic nutrients
-bioerosion
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
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
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
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%
Stenohaline
-grow best in sea water of normal salinity (35%)
-can survive lower (25%)
-hermatypic corals
Why do corals prefer turbulence/energetic waters?
-introduces nutrients
-removes waste
-prevents sediment build up
-corals will grow toward waves
Sedimentation
-increases turbidity
-decreases solar penetration
-buries corals
-can come from anthropogenic sources or natural
-corals don’t find this bussin
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
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
Talus
-debris
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
Lagoon (back reef)
-low energy zone protected by reef crest
-lots of sunlight
Reef crest
-peak of reef exposed to waves
-very high turbulence
-lots of sunlight
Reef front
-oceanward side of reef
-diverse reef-building organisms
Fore reef
-deeper portion of reef beyond reef front
-below zone of coral & algal growth
-lower turbulence & less sunlight
Coral reef zonation
-different factors in different parts of the reef select for different forms
Surface area for photosynthesis
-forms grow wider at shallower depths
-grow more vertical in deeper depths
Optimal skeleton strength to resist turbulence
-high turbulence at reef crest necessitates robust, dense form
-low turbulence produces branching, tabular, & columnar forms
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
Coral reef types
-fringing reefs
-barrier reefs
-patch/platform reefs
-atolls
Fringing reef
-shallow water reef that forms around island or on tropical shorelines
-variable in size, shape, and distribution
Barrier reefs
-form at edge of continental shelf
-often long & linear features
-strongly stratified due to changing environmental conditions with depth
-crow towards ocean
Patch
-platform reefs
-typically form in shallow lagoon settings on continental shelf
-patchy distribution throughout lagoon
-little to no zonation
-grow in all directions
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
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
Brachiopods
-phylum brachiopoda
-bilaterally symmetrical (symmetry through middle of each shell)
-2 asymmetrical hard shells encase flesh of organism
Pedicle
-fleshy extensionof animal that extends from ventral valve
Mantle
-soft part of brachiopod involved in biomineralization
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
Dorsal Valve
-usually shown in figures as upper valve
-previously referred to as brachial valve
-where lophophore attaches to
Ventral Valve
-often shown in figures as lower valve
-previously referred to as pedicle valve
-contains opening for pedicle
Growth Lines
-concentric ridges that develop as shell grows
Ribs
-crenulations across shell surface parallel to direction of growth
-sometimes simple, sometimes split
-sometimes multiple orders
Spines
-extend from shell surface
-visible on some brachiopod groups
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
Fold & Sulcus
-distinctive abrupt deflection at front in some forms
-may be used for directing water
Calcite Shells
-present in most brachiopods
-good preservation under most conditions
-can often see original shell fabric in fossils
Aragonite shells
-very rare for brachiopods
-few have them
-aragonite does not preserve well in fossil record
Impunctate
-no microstructures
-solid shell without any structures that penetrate either the inside or outside of structure
Epipunctate
-perforations open only to shell exterior
-likely served as sensory function
-became isolated & atrophied as shell grew
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
Punctate
-perforations through shell
-contain extensions of the mantle
-terminate just inside external surface of shell
-function uncertain
Brachiopods 3 sets of muscles
-adductors: close the shell
-diductors: open the shell
-adjustors: twist the shell/pedicle
Scars
-attachment points of muscles
-muscles usually not preserved
Hingeline
-formed by 2 joints near posterior of shell in rhynchonelliformean brachiopods
-teeth (ventral valve) insert into sockets (dorsal valve)
2 types of hingelines
-strophic: long, linear hingeline
-astrophic: short/pointed hingeline
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
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
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
Class Strophomenata
-middle cambrain to late permean
-generally have strophic hingelines
Class Rhynchonellata
-early cambrian to recent
-generally have astrophic hingelines
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
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
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
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
Mollusks
-phylum mollusca
-second most diverse metazoan phylum
-entirely solitary organisms
-wide variety of habitats & life styles
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
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
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
Foot (bivalves)
-can be used for burrowing, locomotion, etc.
Paleosinus
-indicates retractible siphon/position of siphon
Relaxation of adductors (bivalves)
-external ligament opens shell
-ligament stretches when closed, relaxed when open
Dentition
-teeth of bivalves
-how fossils are distinguished
–also use ligament insertion area, adductor scars, pallial line, shell shape, shell fabric
Taxodont dentition
-short teeth
-straight or chevron pattern
-most frequently inclined
-arranged along entire dorsal edge below umbo
Dysodont dentition
-row of teeth along hingeline
-reduced strength in comparison to taxodont
-strong ligament
Isodont dentition
-very large teeth on either side of central ligament pit
Heterodont dentition
-2 or 3 wedge shaped teeth centered near umbo
-radiate from beak
Desmodont dentition
-teeth replaced by large resilifer
-attachment for enlarged internal ligament
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
Bivalves shell mineralogy
-most are aragonite
-calcite in oysters & scallops
-mix of aragonite & calcite are rare
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
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
Pallial sinus/game in shell interior
-indicates presence of siphon
Mucus tubes
-used by infaunal bivalves that lack siphon
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
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)
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
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
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
Whorl
-shell fragments
-separated by sutures
-last whorl is largest; where organism lives
Siphonal canal
-where siphon would extend out of small notch
Radula
-used to scrape at surfaces back & forth for feeding
-surfaces could be algae on seafloor or drilling through hard shell
Prosobranchiata
-subclass of gastropoda
Columella
-axis on which the shell is twisted on
-may be twisted towards a point forming a spire (top is usually called apex)
Gastropods shell structure
-thin outer coating of organic material
-thick carbonate later almost entirely aragonite
-some shells have separate layers of calcite & aragonite
Planispiral
-whorls are aligned within a plane
Conispiral
-whorls are not aligned within a plane
-high-spire forms (long) and low spire forms
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)
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)
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
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
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
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
Longicone
-long shells
Brevicones
-short shells
Orthoconic
-straight shells
Cyrtoconic
-curved shells
Evolute
-applies to curved shells
-younger whorls do not overlap earlier whorls
Convolute
-applies to curved shells
-younger whorls partially overlap earlier whorls
Involute
-applies to curved shells
-younger whorls completely overlap earlier whorls
Subclasses of Cephalopods
-Nautiloidea (late cambrain to present)
-Ammonoidea (devonian to cretaceous)
-Coleoidea (carbonifeous to present)
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
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
Nautiloids ecology
-top predator in ordovician & silurian seas
-less than 1cm in late cambrian
-10m in ordovician
Modern Nautilus
-slow swimmer
-only active at night
-found in moderately shallow waters
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)
3 main types of ammonoids
-Goniatitic: devonian to permean
-Ceratitic: Triassic, differentiation of lobes
-Ammonitic: Jurassic & Cretaceous
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
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
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
Arthropoda body plan
-segmented body
-jointed appendages
-chitinous exoskeleton
-simple & compound eyes
-open circulatory system
Segmented body
-characteristic of arthropoda
-cephalon (head), thorax, abdomen (pygidium)
-some segments more well developed in some groups than others
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
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
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
3 Lobes in trilobite body division
-axial: runs down middle lengthwise
-2 pleural lobes: flank axial lobe
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
Trilobites eyes
-consist of calcite lenses
-2 main types, holochoral & schizochoral
-some trilobites had stalked eyes, some were blind
Holochoral eyes
-more primitive
-consist of many small biconvex lenses covered by a continuous cornea
-smooth glossy appearance
-ancestral form
Schizochoral eyes
-consist of small number fo calcite lenses
-individual cornea covering each lens
-derived form
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
Trilobites Thorax
-composed of many articulated & flexible segments
-divided into axial ring & 2 pleura
-each pleuron has groove that acts to strengthen it
Growth stages of trilobites
-protaspid: cephalon develops
-meraspid: pygidium differentiated from cephalon
-holaspid: all segments fully developed
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
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
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
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
Late Ordovician Mass Extinction
-caused by glaciation in Gondwana suring Hirnantian Stage
-extinction occurred for ~500k years
-~86% species lost
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
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
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
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
