Paleontology Final

phylum porifera

sessile, benthic filter feeders with porous bodies

lack tissues & organs

some of the earliest, most basal metazoans (diverged 700 - 800 Ma)

3 groups of porifera

demospongea - common sponges

hexactinellida - glass sponges

calcarea - calcareous sponges

2 hypotheses of porifera relationships

1. paraphyletic - calcarea is separate

2. monophyletic - 1 common sponge ancestor

porifera morphology

body structure mostly made of spongin

skeletal structure made of spicules

body is sack-shaped with central opening (spongocel) and small pores (ostia)

spicules

made of calcite or silica

calcite spicules evolved convergently multiple times

can be fused into a rigid skeletal structure

most likely element to fossilize

porifera feeding

1. pump water into their bodies through ostia

2. water is moved by choanocytes (cells with flagella)

3. food is digested by amoeboid cells

4. water is expelled from spongocel through osculum (large opening)

porifera reproduction

1. asexual - budding

2. sexual - spawning

porifera distribution

global distribution

live in marine and fresh water

can live at almost any depth

75% of Antarctic benthos

sponge ecology

can produce boring trace fossils

some encrusting forms can ‘crawl’

some deep-sea forms w/ large spicules are carnivorous

very few natural predators - spicules deter predation

porifera evolution

first fossil may date to 890 Ma

appeared en masse in the Cambrian

began thin walled with unfused spicules

later evolved rigid bodies suitable for reef building

demosponges dominated by the Ordovician

stromatoporoid

mound or sheet shaped organisms with calcareous skeletons

classified as poriferans

stromatoporoid morphology

found exclusively in shallow marine waters (carbonates)

components of reef systems in the early Phanerozoic

grew together in bioherms or biostromes

often hosted other species

stromatoporoid morphology

densely layered calcite skeletons, most with no spicules

morphologies were reflective of the environment

upper surface have bumps called mamelons

cracks on upper surface = astrorhizae for expelling water

horizontal laminae and vertical pillars w/ galleries in between

stromatoporoid evolution

first occurance in the early Cambrian

extinct by late Devonian

some possible younger specimens, and some modern poriferans resemble their organization

archeocyathids

mysterious group of cup-shaped organisms thought to be poriferans

evolved early Cambrian, reached global distribution quickly

extinct by end-Cambrian

great for biostratigraphy

cnidaria

least complex of the true metazoans

radially symmetrical

only a few true tissues

may be in Ediacaran biota, appeared by Cambrian

3 main cnidarian groups

hydrozoa - jellyfish, fire corals

scyphozoans - moon jellies, compass jellies

anthozoa - sea anemones, sea fans, sea pens, corals

common cnidarian traits

carnivorous

stinging cells (cnidoblasts)

live as polyps (sessile) or medusae (free swimming)

often exist as both during their life cycle

cnidarian morphology

open body cavity (enteron) with single opening for mouth, anus, reproduction

mouth surrounded by tentacles with nematocysts

body made of endoderm and ectoderm with gelatinous mesoglea in between

important anthozoa groups

rugosa (extinct)

tabulata (extinct)

scleractinia (extant)

rugosa

solitary or colonial

calcite skeletons

robust, usually horn-shaped

prominent septa

middle Ordovican - end Permian

tabulata

colonial (many corallites living together)

calcite skeletons

reduced septa but prominent tabulae

middle Ordovician - end Permian

scleractinia

solitary or colonial

aragonite skeletons

prominent septa, tabulae usually absent

all modern corals

Triassic - present

coral ecology

all corals are benthic

most are reef building organisms that provide habitat and shelter

some natural predators

2 types of modern coral ecology

1. hermatypic - have symbiotic algae called zooxanthellae (dinoflagellates)

2. ahermatypic - no symbiotic algae, grow slowly in deep water

coral distribution

global distribution

predominantly live in shallow (<100 m), warm (>18C), marine waters within the tropics

modern reef distribution

between 30S and 30N

almost exclusively on east coasts of continents

¼ of ocean biodiversity

11×10¹² kg/year OM productivity

reef accommodation space

reef depth limited by surface light availability

upward limitation of coral growth is base of intertidal zone

when upward growth is no longer possible, reefs sometimes begin to grow and expand laterally

reef types in relation to sea-level changes

1. keep-up reefs: track rising sea levels

2. catch-up reefs: show shallowing features as they reach low tide

3. give-up reefs: cannot keep pace and drown

Darwin’s 3 types of reefs

fringing reef

barrier reef

atoll

coral atoll

circular to oval reefs outlining the protected lagoon

fringing reef develops around a volcano - becomes a barrier reef as volcano subsides - atoll once volcano is sunken

sandy atoll reef surfaces are covered with plants

Daly’s glacial control theory

during glacial periods, reefs die due to cold waters

shorelines unprotected by coral are eroded into platforms

when water warmed, coral flourished on platforms

this formed most Caribbean continental shelf reefs

carbonate platform

buildups of older reef material and carbonate sediments

reef anatomy

highly zoned from onshore to offshore

each reef zone has characteristic features and populations

coral groupings by zone are distinctive - single species can show variation due to environmental conditions

fore reef slope (zone 10)

below storm wave base

platy corals to catch sunlight

fore reef escarpment (zone 9)

most seaward part of the reef

mostly storm derived coral rubble

barren zone (zone 6)

lowermost part of the reef crest

exclusively elkhorn corals in caribbean reefs

reef crest (zone 5)

highest part of the reef

may be exposed during low tide

back reef (zone 3)

begins where reef slopes downward into lagoon

continues to where the reef flattens

coral knobs, patch reefs

lagoon (zone 2)

floored by fine calcareous mud

• derived from breakdown of coralline algae

can also be covered by sea grass

ecology

the study of:

adaptations of animals and plants to their habitats

interactions b/w organisms and their environment

flow of energy through communities

dynamic interactions over short time intervals

paleoecology

the study of ancient organisms in the context of their environments

deciphering the lifestyles of organisms and their relationships to each other

static data over long periods of time

actualism

interpretations of the past informed by the ecology of modern organisms

carboniferous trophic structure

Joggins, NS

detritovores are primary consumers

autoecology

studying the ecology of the individual organism (lifestyle, behavior, etc.)

synecology

studying the interactions between organisms and their environment (ecosystem, community, etc.)

paleoautoecology

relies on functional morphology to understand behavior and lifestyle

can be informed by trace fossils

stable isotopes can be used to infer diet, migration, etc

tooth wear can indicate diet preferences and chewing mechanisms

paleosynecology

can be conducted at different levels:

• population

• community

• ecosystem

• macroecology

ecotone

unique environment formed in the transitional area between habitats

diversity is usually low, but species that are present are abundant

e.g. foraminifera are highly zoned in a salt marsh - sea level

ecological niche

the ecological space an organism occupies - its role in the community and its place in the habitat

fundamental niche - where a species can live

realized niche - where a species actually does live

trophic levels

producers - autotrophs, use solar energy to make food

consumers - heterotrophs, primary-tertiary

decomposers - directly consume dead organisms

detritovores - consume detritus, dead organisms, organic waste, etc.

biomass

the amount of living matter in the ecosystem or at a specific trophic level

decreases with each trophic level

horizontal species distribution

important for understanding terrestrial ecology

in marine species, controlled by sediment, salinity, turbulence, etc.

vertical distribution

important for marine species

light is the primary factor

photic zone

portion of the water column penetrated by light where photosynthesis occurs

can reach 200m depth, but more than 90% of photosynthesis occurs in the top 100m

types of pelagic organisms

pelagic = in the water column

nektic - active swimmers

planktic - transported by waves or currents

• phytoplankton - microscopic floating ‘plants’

• zooplankton - microscopic floating ‘animals’

types of benthic organisms

epifaunal - living on substrate

infaunal - living in substrate

vagile - capable of locomotion

sessile - immobile

stratification of ecosystems

tiering can occur within communities due to competition for resources

vertical ecological structure

marine tiering became more complex throughout the Phanerozoic

4 marine feeding groups

grazers - pick organics off the substrate

deposit feeders - feed on seafloor deposits

suspension feeders - select microorganisms and detritus from the water column

carnivores - feed on other animals

biocoenosis

life assemblage - the organisms that truly lived together and interacted while alive

thantocoenosis

death assemblage - organisms found together after death and decay

taphocoenosis

fossil assemblage - fossils preserved together in a single horizon/locality

paleocommunity

assemblages or associations of organisms that are inferred to have interacted with one another

effect of taphonomy on assemblages

fossil material is altered or lost due to taphonomy

taphocoenosis not a perfect reflection of biocoenosis

time averaging

makes things appear synchronous in the geologic record that were not in reality

increases diversity of the death assemblage

taphocoenoses from different depositional environments have different temporal and spatial resolutions

fidelity

how well the death or fossil assemblage matches the living assemblage

assessed experimentally and using lagerstatten

main macroevolutionary changes

1. Ediacaran fauna

2. small shelly fauna

3. Cambrian explosion

4. Great Ordovician biodiversification

5. nekton revolution

ediacaran biota

oldest assemblage of large complex organisms

soft bodies, high surface to volume ratios, radial/bilateral symmetry

most species had worldwide distributions

predators and scavengers yet to evolve in great numbers

ediacaran ecology

life restricted to epifaunal benthos

short food chains dominated by suspension and deposit feeders

tiering of benthos (evolution of stalks)

small shelly fauna

first evidence of hard skeletonization

some thought to be worms or worm-like organisms

some evidence of predation and scavenging

likely mobile and sessile forms

oceanic shift

changes to the oceans between the late Proterozoic and early Phanerozoic

evolution of planktonic suspension feeders changed the water quality of the oceans

opened new ecospaces

Cambrian explosion

rapid appearance of new body plans, diversification of Bilateria

Cambrian substrate revolution indicates the evolution of a new feeding ecology and increased tiering

increased predation driven by sight

increased biomineralization, nutrient availability, and defense

great Ordovician biodiversification

no new phyla (except bryozoa) but extensive radiation, many crown groups emerge

evolution of the plankton - diversification of acritarchs, development of feeding larvae

diversification of predators led to “evolutionary arms race” and increasingly complex food webs

nekton revolution

oversaturation of ecological space on the seabed drove evolution of nektonic forms

primarily cephalopods and fish

diversification continued well into the Devonian

limiting factor (def. & examples)

a variable in the environment that can restrict the growth, abundance, and distribution of a population of organisms in an ecosystem

e.g. space, environmental conditions, predation, shelter, resource availability

only one factor can be limiting at any one time

Liebig’s law of the minimum

originally applied solely to elemental nutrients

concept that the productivity is limited by the availability of the scarcest nutrient

now applied to any environmental factor

law of limiting factors

biological or ecological processes that depend on multiple factors are limited by the slowest factor

law of tolerance

an organism’s success or survival is dependent on a complex set of conditions with maximum, minimum, and optimal ranges of environmental factors

limiting factors in marine ecosystems

light

oxygen

temperature

salinity

depth

substrate

light as a limiting factor

required for most ecosystems to operate

absorbed by the water column, blue light penetrates deepest

most productivity in the top 10-20 m

major limiting factor for reefs

oxygen as a limiting factor

required by most eukaryotes for metabolism

low biodiversity in oxygen poor environments

oxygen decreases down to 100-500m

small seas and lakes can become stratified w anoxic bottom waters - low diversity

temperature as a limiting factor

varies with latitude, affects geographic distribution of organisms

water temperature decreases with depth

salinity as a limiting factor

low diversity in brackish water, very low diversity in hypersaline water

most organisms have a low range of tolerance for salinity - characteristic species/assemblages can show changes

some organisms change morphology in response to salinity

substrate as a limiting factor

grain size reflects energy levels - correlated to community distribution

deposit feeders prefer mud, suspension feeders like hard ground or sand

depth as a limiting factor

related to many other factors - light, salinity, oxygen, sed size, turbidity, etc

pressure becomes a factor at large depths

carbonate compensation depth limits distribution of organisms w

lophophorates

group including brachiopods and bryozoans

have complex tentacled feeding structures called lophophores

also have similarities in the structure of their body cavities

bryozoans

colonial animals made of individual zooids

some zooids specialized for reproduction, defense, etc

higher level of organization than cnidarians → separate mouth and anus

bryozoan morphology

each zooid encased in a protective covering

zooids connected by tissue chords (funiculus) which extends along the stolon

each zooid has a lophophore

lophophore tentacles gather food and bring to central mouth

u-shaped gut

zooecia

a bryozoan skeleton mineralized with calcite

bryozoan reproduction

reproduce both asexually and sexually

asexual: budding of new zooids, broken pieces rooting

sexual: zooid has sperm and eggs, capture free-swimming sperm to develop eggs internally, produces swimming larvae

bryozoan distribution

sessile benthos, mostly marine (some freshwater forms)

exist in subtidal zone to the edge of the shelf

most common in <200 m, some deep-water forms

bryozoan ecology

variety of body plans linked to different feeding strategies and environments

colony shapes can reflect environmental conditions

zooid size linked to water temperature

species can be facies dependent

bryozoan evolution

first appearance in the lower Ordovician

possible 1st fossil in the early Cambrian

brachiopoda

a.k.a. lamp shells, name means ‘arm foot’

exclusively marine, bilaterally symmetrical, two-valved shells

global distribution: 12000 fossil species, 350 extant species

2 groups: inarticulate and articulate

brachiopod morphology

two shells - brachial (dorsal) and pedicle (ventral) valves

valves are bilaterally symmetrical about the midline of the valve

pedicle valve usually larger than brachial valve

interlocking teeth and cardinal process (in articulate species)

pedicle for anchoring to substrate

muscles for opening and closing shell

where does the lophophore attach in brachiopods?

upper brachial valve

brachiopod feeding

draw water in from sides of shell and expel through the front

lophophore captures food particles, brought to mouth along the brachial groove

not retractable - cartilaginous or hydrostatic support

produces little solid waste

most forms reverse lophophore cilia movement to expel blockages/waste

brachiopod reproduction

release eggs/sperm into water for external fertilization

some have brood chamber for developing embryo

distinct male and female individuals, adults stay the same sex

lingulid larvae swim and filter feed as plankton, then sink as they grow

articulate brachiopods are only planktonic for a few days

brachiopod ecology

suspension feeding benthos

anchor to substrate with pedicle

some infaunal and unattached forms

valve morphology reflective of environment (within species)

some have clasping spines to attach to substrate

stable isotopes in shells reflect environmental conditions

brachiopod origins

old hypothesis: brachiopod fold hypothesis

new hypothesis: evolved from larval valved form of Tommotiids