1. Notes: This nautilus lives in waters at a depth of 600 to 800 meters
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.

2. 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.

3. Burgess Shale Diorama of the environment and biota
of the Phyllopod bed of the Burgess Shale,
British Columbia, Canada

4. 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

5. 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)

6. Sixty Percent Soft-Bodied
60% of the total Burgess Shale assemblage
of more than 100 genera is composed of soft-bodied 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

7. 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.

8. 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

9. 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

10. 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

11. 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

12. Lower Cambrian Shelly Fossil
A conical sclerite* of Lapworthella from Australia
* a piece of the armor covering
This specimen is several millimeters in size

13. Lower Cambrian Shelly Fossil
Archaeooides, an enigmatic spherical fossil from the Mackenzie Mountains, Northwest Territories, Canada
This specimen is several millimeters in size

14. 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

15. 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

16. 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

17. 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

18. 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

19. Nektonic organisms The nekton are swimmers and are mainly vertebrates
such as fish
the invertebrate nekton
include cephalopods -- chambered, coiled shellfish

20. Benthic organisms Organisms that live They can be characterized
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

21. 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

22. Marine Ecosystem Infauna: worm, bivalve
Mobile epifauna: gastropod, starfish

23. Marine Ecosystem
Where and how animals and plants live in the marine ecosystem
Plankton:
Jelly fish
Sessile epiflora:
seaweed
Nekton: fish
cephalopod
Sessile epifauna:
bivalve
Benthos: d-k
crinoid
coral

24. 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

25. Cambrian Marine Community
Floating jellyfish, swimming arthropods, benthonic sponges, and scavenging trilobites
Reconstruction

26. Trilobites Trilobites were by far the most conspicuous element
of the Cambrian marine invertebrate community
and made up about half of the total fauna
benthonic
mobile
sediment-deposit feeders
that crawled or swam along the seafloor

27. 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

28. 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

29. 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

30. Articulate Brachiopods
The articulate brachiopods,
which have a tooth-and-socket arrangement,
were also present
but did not become abundant
until the Ordovician Period

31. Archaeocyathids The third major group of Cambrian organisms
were the archaeocyathids
These organisms
were benthonic sessile suspension feeders
that constructed reeflike structures

32. Cambrian Reeflike Structure
Restoration of a Cambrian reeflike structure built by archeocyathids

33. 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”

34. Pikaia, chordate ancestor of vertebrates??

35. Rare Preservation: Burgess Shale
Ottoia, a carnivorous worm

36. Rare Preservation: Burgess Shale
Wiwaxia, a scaly armored sluglike creature whose affinities remain controversial

37. Rare Preservation: Burgess Shale
Hallucigenia, a velvet worm

38. Rare Preservation: Burgess Shale
Waptia, an anthropod

39. 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

40. 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

41. Middle Ordovician Seafloor Fauna
Recreation of a Middle Ordovician seafloor fauna with cephalopods, crinoids, colonial corals, trilobites, and brachiopods

42. 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

43. 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

44. 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

45. Middle Devonian Reef
Reconstruction of a Middle Devonian reef from the Great Lakes area
with corals, cephalopods, trilobites, crinoids, and brachiopods

46. Silurian Brackish-Marine Scene
Restoration of a Silurian brackish-marine bottom scene
near Buffalo New York
with algae, eurypterids, gastropods, worms, and shrimp

47. Ammonoids Ammonoids are excellent guide fossils
for the Devonian through Cretaceous periods
with their distinctive suture patterns,
short stratigraphic ranges,
and widespread distribution

48. 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

49. 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

50. Permian Period
Paleogeography of North America during the Permian Period

51. Permian Patch-Reef Community
From Glass Mountains of West Texas
including algae, productid brachiopods, cephalopods, sponges, and corals

52. 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

53. 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

54. 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,

55. 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