Lecture 6: Life beneath the Palaeozoic ocean wave Flashcards
As we’ve moved into the Proterozoic?
communities become more structured (things are starting to live in different places and eating in different ways).
more ecological interactions
Pelagic organisms (live in the water column):
Can be divided into…
planktonic -drifters/floaters
nektonic - active swimmers
Benthic (or benthonic) organisms, the bottom dwellers:
Can be divided into…
Epifaunal- live ON sediment surface and can be…
- sessile/ anchored
- mobile
Infaunal- live IN the sediment
What are Trilobites?
Three lobed…
- head
- body
- tail
Mainly Benthic…
Arthropods
Among first to…
Develop vision
Sensitive to motion (prey)
some had stereoscopic vision (distance away)
rigid crystalline calcite lenses
good depth of focus and corrected spherical aberration
schizochroal eyes – fewer lenses
development of camouflage/ colour patterning
…accelerated evolution?
Arthropods
soft tissues
legs gill and antennae
roll up for protection- jointed
The first (Cambrian) reefs
Sponges made of calcium carbonate.
appear ~525 Ma
became extinct by end of the Cambrian
Corals arrive
Phylum Cnidaria
jellyfish, sea anenomes, corals Cup shaped with tenticles Benthic Sessile Much folded gut wall – increases digestive ability
Echinoderms
sea urchins, starfish
major components of reefs
disarticulate after death: produce crinoidal limestones
Brachiopods (Lamp shells)
all benthic (lowest point in water)
sessile filter
anchored by ‘stalk’
feeders (‘sit and suck’)
Molluscs
‘soft tissue’
Class Cephalopoda- most common (‘head foot’)
chambers: regulate buoyancy
First cephalopods were…
nautiloids (simple chambers)
had straight shells- cumbersome, buoyancy regulation difficult
‘orthocones’
Winding you up through the paleozoic…
Nautiloids into goniatites- had more and more coiled shells
Easier to move around (better buoyancy regulation)
More complex internal divisions
Written in stone
graptolites
resistant organic colonies (collagen)
filter feeders
earliest were sessile
later ones planktonic- didn’t have to attach
Palaeozoic plankton
as they evolve they reduce no. of branches (‘stipes’)
many 4
Ordovician: two stipes (“tuning fork graptolites”)
Silurian: one stipe (monograptids)
first macroscopic plankton
High ocean drifters
graptolite facies: defined association / environment
black shales
deep water, low O2
no benthos, preserved laminations, pyritic (FeS2)
dead graptolites drift through water column undisturbed
Biological organisms are classified using
a hierarchical system
Highest level of classification is into 3 domains:
Archaea, Eubacteria, Eukaryota
The Eukaryota is divided into 4 kingdoms:
Protista, Fungi, Plantae, Animalia
Classification system
Kingdom Phylum Class Order Family Genus Species
Lower levels of classification include…
the genus and species
these use “Linnean binomials” (i.e., two names)
NOTE: species names are italicised when typed (if you write them by hand they should be underlined: Homo sapiens)
NOTE also that family, order, class, phylum names are NOT italicised, nor are informal names, such as ‘hominids’
Biostratigraphy: 1
environmentally controlled fossils can be used…
To trace similar environmental conditions through time
but these are no good for dating sediments.
Biostratigraphy: 2
What properties make a a fossil useful for dating rocks?
rapid evolution/extinction
abundance
distinctive, easily identified
facies independence
mostly pelagic (or pelagic larval stages)
e.g., Silurian graptolite biostratigraphy
Benthic (or benthonic) organisms, the bottom dwellers:
Infaunal
Live IN soft sediment (burrowers), or bore INTO hard substrates
Something that lives within the water column is referred to as…?
Pelagic
Something that lives in the bottom of the water is referred to as…?
Benthic
How do arthropods grow?
By moulting their exoskeleton
What were reefs in the precambrian like?
Reef systems made out of stromatolites.
These started to get eaten away by the browsers and grazers as we move into the Cambrian.
Benthic meaning
Something that lives in the bottom of the water
Sessile meaning
Anchored to ground
Planktonic
drifters/floaters
Nektonic
active swimmers
