Download Notes: This nautilus lives in waters at a depth of 600

Notes: This nautilus lives in waters at a depth of 600 to 800
meters. Often their habitat is at the bottom of a steep slope
under coral reefs.
At night they use their natural jet propulsion to maneuver up
over 325 meters to feed.
Why an “explosion”?
• What were conditions like at the end of the
Proterozoic?
Supercontinent was breaking up
climate warming after glacial period
Increased oxygen in atmosphere
More coastal habitat – shelf environments
Eukaryotic cells added to diversity
Stage was set for larger cells, specialized cells, and multi-celled
organisms
Sexual reproduction allowed for shuffling of alleles increasing
variation within species
Result? Rapid diversification of life forms and
numbers of families and species occurred during
the early Paleozoic. No “explosion” – it took
millions of years.
Burgess
Shale
• Diorama of
the
environment
and biota
– of the
Phyllopod
bed of the
Burgess
Shale,
• British
Columbia,
Canada
Burgess Shale Soft-Bodied Fossils
• On August 30 and 31, 1909,
– Charles D. Walcott,
• geologist and head of the Smithsonian Institution,
– discovered the first soft-bodied fossils
– from the Burgess Shale,
– a discovery of immense importance in deciphering
the early history of life
– beautifully preserved on bedding planes
More Complete Picture of a Middle Cambrian
Community
• a rare glimpse into a world previously almost
unknown
– that of the soft-bodied animals that lived some
530 million years ago
• a much more complete picture
– of a Middle Cambrian community
– than deposits containing only fossils of the hard
parts of organisms (the bias of the fossil record
favors hard parts to be preserved)
Sixty Percent Soft-Bodied
• 60% of the total Burgess Shale assemblage
– of more than 100 genera is composed of softbodied animals,
– a percentage comparable to present-day marine
communities
• What conditions led to the remarkable
preservation of the Burgess Shale fauna?
• The site of deposition of the Burgess Shale
– was located at the base of a steep submarine
escarpment
Reason for the Preservation
• The animals lived in and on mud banks
– that formed along the top of this escarpment
• Periodically, this unstable area
– would slump and slide down the escarpment as a
turbidity current
• At the base, the mud and animals carried with
it were deposited in a deep-water anaerobic
environment devoid of life, predators, and O2.
Carbonaceous Impressions
• In such an environment,
– bacterial degradation did not destroy the buried
animals
– and they were compressed by the weight of the
overlying sediments
– and eventually preserved as carbonaceous
impressions
Study of Paleozoic Life
• Evolution and plate tectonics forcing:
Early Paleozoic characterized by
– The opening and closing of ocean basins, (Wilson
Cycles)
– transgressions and regressions of epeiric seas,
• as evidenced by Cratonic Sequences
– the formation of mountain ranges,
• Orogenies that formed Mobile Belts
– and the changing positions of the continents
– had a profound effect on the evolution
– of the marine and terrestrial communities
Tremendous Biologic Change
• appearance of skeletonized animals
– near the Precambrian-Cambrian boundary
• marine invertebrates
– began a period of relatively rapid evolution of body
types
– Paleozoic marine invertebrate community greatly
diversified
– Actually the “explosion” had taken place over
millions of years during the Early Cambrian Period
The Cambrian Explosion
• At the beginning of the Paleozoic Era,
– animals with skeletons appeared rather abruptly in
the fossil record
Microscopic, then larger, visible shelly fauna
Lower Cambrian Shelly Fossil
• A conical sclerite* of Lapworthella from
Australia
* a piece of
the armor
covering
– This
specimen
is several
millimeters
in size
Lower Cambrian Shelly Fossil
• Archaeooides, an enigmatic spherical fossil
from the Mackenzie Mountains, Northwest
Territories, Canada
– This
specimen
is several
millimeters
in size
What are advantages of an
Exoskeleton
• :
(1) It provides protection against ultraviolet
radiation, allowing animals to move into shallower
waters;
(2) it helps prevent drying out in an intertidal
environment;
(3) it provides protection against predators
– Recent evidence of actual fossils of predators
• and specimens of damaged prey,
• as well as antipredatory adaptations in some animals,
• indicates that the impact of predation during the
Cambrian was great
Cambrian Predator
• Reconstruction of Anamalocaris
– a predator from the Early and Middle Cambrian
– It was about 45 cm long and probably fed on
trilobites
– Its gripping appendages presumably carried food
to its mouth
Wounded Trilobite
• Wounds to the body of the trilobite Olenellus
robsonensis
– The wounds have healed, demonstrating that they
occurred when the animal was alive and were not
inflicted on an empty shell
Advantages of an Exoskeleton
• With predators playing an important role
– in the Cambrian marine ecosystem,
– any mechanism or feature
– that protected an animal
– would certainly be advantageous
– and confer an adaptive advantage to the organism
(4) A fourth advantage is that
– a supporting skeleton, whether an exo- or
endoskeleton,
– allows animals to increase their size
– and provides attachment sites for muscles
Planktonic organisms
• Plankton are mostly passive and go where
currents carry them
– Plant plankton
• such as diatoms, dinoflagellates, and various algae,
– are called phytoplankton and are mostly microscopic
– Many are photosynthesizers
– Animal plankton are called zooplankton and are
also mostly microscopic
• Examples of zooplankton include foraminifera,
radiolarians, and jellyfish
Nektonic organisms
• The nekton are swimmers
– and are mainly vertebrates
• such as fish
– the invertebrate nekton
• include cephalopods -- chambered, coiled shellfish
Benthic organisms
• Organisms that live
– on or in the seafloor make up the benthos
• They can be characterized
– as epifauna (animals) or epiflora (plants),
• for those that live on the seafloor,
– or as infauna,
• which are animals living in and moving through the
sediments
Sessile and Mobile
• The benthos can be further divided
– into those organisms that stay in one place,
– called sessile,
– and those that move around on or in the seafloor,
– called mobile
Marine Ecosystem
Infauna:
worm,
bivalve
Mobile epifauna: gastropod,
Marine Ecosystem
• Where and how animals and plants live in the
marine ecosystem
Plankton:
Sessile epiflora:
seaweed
Jelly fish
Nekton: fish
cephalopod
Sessile epifauna:
Benthos: d-k
bivalve
coral
crinoid
Cambrian Skeletonized Life
• Although almost all the major invertebrate
phyla
– evolved during the Cambrian Period
– many were represented by only a few species
• While trace fossils are common
– and echinoderms diverse,
• the organisms that comprised the majority of
Cambrian skeletonized life were
– trilobites,
– inarticulate brachiopods,
– and archaeocyathids
Cambrian Marine Community
• Floating jellyfish, swimming arthropods,
benthonic sponges, and scavenging trilobites
Reconstruction
Trilobites
• Trilobites were
– by far the most conspicuous element
– of the Cambrian marine invertebrate community
– and made up about half of the total fauna
• Trilobites were
– benthonic
– mobile
– sediment-deposit feeders
– that crawled or swam along the seafloor
Trilobites
• They first appeared in the Early Cambrian,
– rapidly diversified,
– reached their maximum diversity
– in the Late Cambrian,
– and then suffered mass extinctions
– near the end of the Cambrian
– from which they never fully recovered
• As yet no consensus exists on what caused the
trilobite extinctions
Trilobite Extinctions
– possible reduction of shelf space,
– increased competition,
– rise in predators
• cooling of the seas may have played a role,
at the end of the Ordovician Period
Cambrian Brachiopods
• Cambrian brachiopods
– were mostly primitive types called inarticulates
• They secreted a chitinophosphate shell,
– composed of the organic compound chitin
– combined with calcium phosphate (like teeth)
• Inarticulate brachiopods
– also lacked a tooth-and-socket-arrangement
– along the hinge line of their shells
Articulate Brachiopods
• The articulate brachiopods,
– which have a tooth-and-socket arrangement,
– were also present
– but did not become abundant
– until the Ordovician Period
Archaeocyathids
• The third major group of Cambrian organisms
– were the archaeocyathids
• These organisms
– were benthonic sessile suspension feeders
– that constructed reeflike structures
Cambrian Reeflike Structure
• Restoration of a Cambrian reeflike structure
built by archeocyathids
Back to the Burgess Shale….
• The diversity of organisms preserved in the
mud that is now the Burgess Shale shows
– Most modern phyla are represented
– Additional organisms cannot be placed in the
evolutionary tree
– A primitive chordate may have existed – “Pikaia”
Pikaia, chordate
ancestor of vertebrates??
Rare Preservation: Burgess Shale
• Ottoia, a carnivorous worm
Rare Preservation: Burgess Shale
• Wiwaxia, a scaly
armored sluglike
creature whose
affinities remain
controversial
Rare Preservation: Burgess Shale
• Hallucigenia, a velvet worm
Rare Preservation: Burgess Shale
• Waptia, an anthropod
Cambrian Phyla
• Thus, the phyla of the Cambrian world
– were viewed as being essentially the same in
number
– as the phyla of the present-day world,
– but with fewer species in each phylum
• According to this view, the history of life
– has been simply a gradual increase in the diversity
of species
– within each phylum through time
• The number of basic body plans
– has therefore remained more or less constant
– since the initial radiation of multicelled organisms
Striking Changes in Ordovician
• The Cambrian invertebrate community
– was dominated by trilobites, inarticulate brachiopods, and
archaeocyathids,
• the Ordovician was characterized
– by the adaptive radiation of many other animal
phyla,
• such as articulate brachiopods, bryozoans, and corals
Middle Ordovician Seafloor Fauna
• Recreation of a Middle Ordovician seafloor
fauna with cephalopods, crinoids, colonial
corals, trilobites, and brachiopods
Mass Extinctions
• The end of the Ordovician
– was a time of mass extinctions in the marine realm
• More than 100 families of marine
invertebrates became extinct,
• and in North America alone,
– approximately one-half of the brachiopods and
bryozoans died out
• What caused such an event?
– Many geologists think these extinctions
– were the result of the extensive glaciation
– that occurred in Gondwana
– at the end of the Ordovician Period
Mass Extinctions
• Mass extinctions,
– those geologically rapid events
– in which an unusually high percentage
– of the fauna and/or flora becomes extinct,
• have occurred throughout geologic time
– for instance, at or near the end of the
•
•
•
•
Ordovician,
Devonian,
Permian,
and Cretaceous periods
– and are the focus of much research and debate
Silurian and Devonian Reefs
• The Silurian and Devonian reefs
– were dominated by
– tabulate and colonial rugose corals and
stromatoporoids
• While the fauna of these Silurian and Devonian
reefs
– was somewhat different
– from that of earlier reefs and reeflike structures,
– the general composition and structure
– are the same as in present-day reefs
Middle Devonian Reef
• Reconstruction of a Middle Devonian reef
from the Great Lakes area
– with corals, cephalopods, trilobites, crinoids,
and brachiopods
Silurian Brackish-Marine Scene
• Restoration of a Silurian brackishmarine bottom scene
– near Buffalo New York
– with algae, eurypterids,
gastropods, worms,
and shrimp
Ammonoids
• Ammonoids are excellent guide fossils
– for the Devonian through Cretaceous periods
– with their distinctive suture patterns,
– short stratigraphic ranges,
– and widespread distribution
Ammonoid Cephalopod
• A late Devonian ammonoid cephalopod
– from Erfoud,
Morocco
– The distinctive suture
pattern, short
stratigraphic range,
and wide geographic
distribution make
ammonoids excellent
guide fossils
Another Mass Extinction
• Another mass extinction
– occurred near the end of the Devonian
– and resulted in a worldwide near-total collapse
– of the massive reef communities
• On land, however, the seedless vascular plants
– were seemingly unaffected,
• Thus, extinctions at this time
– were most extensive in the marine realm,
– particularly in the reef and pelagic communities
Permian Period
• Paleogeograph
y of North
America during
the Permian
Period
Permian Patch-Reef Community
• From Glass Mountains of
West Texas
– including algae, productid
brachiopods, cephalopods,
sponges, and corals
The Permian Marine Invertebrate
Extinction Event
• The greatest recorded mass extinction event
– to affect Earth
– occurred at the end of the Permian Period
• Before the Permian ended,
– roughly 50% of all marine invertebrate families
– and about 90% of all marine invertebrate species
became extinct
Phanerozoic Diversity
• Diversity for marine invertebrate and
vertebrate families
– 3 episodes
of Paleozoic
mass
extinctions
are visible
– with the
greatest
occurring at
the end of
the Permian
Period
Mass Extinction
• What caused such a crisis
– for both marine and land-dwelling organisms?
• Various hypotheses have been proposed,
– but no completely satisfactory answer
– has yet been found
• Some scenarios put forth to explain the
extinctions include
– (1) a meteorite impact such as occurred at the end
of the Cretaceous Period
– (2) a widespread marine regression resulting from
glacial conditions,
Permian Mass Extinction
– (3) a reduction in shelf space due to the formation
of Pangaea,
– (4) oceanographic changes such as anoxia, salinity
changes, and turnover of deep-ocean waters
• It appears that the Permian mass extinction
– took place over millions of years
– at the end of the Permian Period,
– which would seemingly rule out a meteorite
impact