1. Paleozoic Life:
Invertebrates
Burgess Shale

2. Paleozoic Life Geology drove biology Evolution affected by
evolution and plate tectonics
Evolution affected by
the opening and closing of ocean basins
transgressions and regressions of epeiric seas
formation of mountains
changing positions of the continents

3. Tremendous Biologic Change
Dramatic biologic change in Paleozoic
appearance of skeletonized animals
marine invertebrates adaptive radiation and evolution
diversification and extinction
culminating at the end of the Paleozoic Era in the greatest mass extinction in Earth history
Archaeooides, an enigmatic spherical Cambrian fossil from the Mackenzie Mountains, Northwest Territories, Canada – specimen is several millimeters in size

4. Cambrian Explosion Beginning of the Paleozoic Era
animals with skeletons appeared abruptly in the fossil record
Sudden and rapid appearance of new animals in the fossil record
rapid, however, only in the context of geologic time
millions of years during the Early Cambrian Period
How many million?

5. Not a Recent Discovery
Early geologists observed sudden appearance of skeletonized animals
Charles Darwin addressed this problem in On the Origin of Species
such an event was difficult to reconcile with his newly
expounded evolutionary theory

6. Sharp Contrast The sudden appearance of shelled animals
contrasts sharply with the biota living during the preceding Proterozoic Eon
Up until the evolution of the Ediacaran fauna
Earth was populated primarily by single-celled organisms
The Ediacaran fauna
consists primarily of
multicelled soft-
bodied organisms
Restoration of the Ediacaran Environment

7. Time Between Long time period assumed to have existed
between the extinction of the Ediacaran fauna
and the evolution of the first Cambrian fossils
That gap has narrowed in recent years
with the discovery of more fossils
known Proterozoic fossil assemblages continue right to the base of the Cambrian
recent work from Namibia indicates that Ediacaran-like fossils are even present above the first occurrence of Cambrian index fossils

8. Triggering Mechanism Hypotheses about triggers:
critical threshhold
both biological and geological
Environmental trigger (Snowball Earth):
Earth was glaciated one or more times during the Proterozoic
followed by global warming during the Cambrian
Evolutionary trigger:
appearance of Hox genes
(how do we know this?)

9. Snowball Earth Shallow seas formed as supercontinents broke up
organic matter could be produced rapidly -and- decomposition was restricted
atmospheric O2 goes up; CO2 and CH4 go down;
Usually when glaciers form, their formation stops CO2 consumption by rock weathering
thwarted by equatorial continents
eventually volcanoes outgassed enough CO2 to melt the Snowball

10. Hox genes
all metazoans (animals except sponges + algae) have the same genetic controls on body organization
Hox genes: master switch in body pattern creation (‘put a leg here and an eye there’)
these genes first appeared in the Cambrian

11. When Hox genes mutate...

12. Skeletons
(1) protection against ultraviolet radiation, allowing animals to move into shallower waters
(2) prevent drying out in an intertidal environment
(3) protection against predators
recent evidence of actual fossils of predators
and specimens of damaged prey
indicates that the impact of predation during the Cambrian was great

13. Cambrian Ecology Reconstruction of Anamalocaris
a predator from the Early and Middle Cambrian
about 45 cm long and probably fed on trilobites
gripping appendages presumably carried food to its mouth

14. Wounded Trilobite
Wounds to the body of the trilobite Olenellus robsonensis
wounds have healed suggesting predation

15. Cambrian Marine Community
Body plans
Most documented evolutionary experiments
Almost all the major invertebrate phyla evolved during the Cambrian Period
many were represented by only a few species
Majority of Cambrian skeletonized life:
trilobites
brachiopods
archaeocyathids

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

17. Trilobites
Most conspicuous element of the Cambrian marine invertebrate community
about half of the total fauna
benthonic
mobile
sediment-deposit feeders
Appeared in the Early Cambrian, and rapidly diversified,
reached their maximum diversity in the Late Cambrian,
and then suffered mass extinctions near the end of the Cambrian, never fully recovered

18. Trilobite Extinctions
No consensus on what caused the trilobite extinctions
plate tectonics -> changed ecological niches
increased competition
rise in predators
A cooling of the seas may have played a role
particularly for the extinctions that took place at the end of the Ordovician Period

19. Cambrian Brachiopods Cambrian brachiopods
not abundant until the Ordovician Period
Ordovician Brachiopod

20. Archaeocyathids Archaeocyathids, an extinct group of sponges
benthonic sessile suspension feeders
constructed reeflike structures
The rest of the Cambrian fauna consisted of representatives of the other major phyla,
including many organisms that were short-lived evolutionary experiments

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

22. Burgess Shale Soft-Bodied Fossils
1909, Charles D. Walcott
Smithsonian Institution,
first soft-bodied fossils from the Burgess Shale
a discovery of immense importance in deciphering the early history of life
Walcott and his collecting party split open blocks of shale
yielding the impressions of a number of soft-bodied organisms
beautifully preserved on bedding planes

23. Burgess Shale
Presented a much more complete picture of a Middle Cambrian community
What conditions led to the remarkable preservation of the Burgess Shale fauna?

24. Reason for the Preservation
Animals preserved in the Burgess Shale
lived in and on mud banks
that formed along the top of a steep submarine escarpment
Periodically, this unstable area would slump
slide down the escarpment as a turbidity current
mud and animals carried with it were deposited in a deep-water anaerobic environment

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

26. Rare Preservation: Burgess Shale
Wiwaxia, a scaly armored sluglike animal

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

28. Rare Preservation: Burgess Shale
Waptia, an anthropod

29. How Many Phyla arose during the Cambrian?
At the center of that debate are the Burgess Shale fossils
Early hypothesis: most Burgess Shale organisms are part of existing phyla
Competing hypothesis: Cambrian had many more phyla

30. Burgess Body Plans Highly diverse Gould: more diverse than ever before
Evolutionary experimentation

31. Ordovician Marine Community
A major transgression that began during the Middle Ordovician (Tippecanoe sequence)
resulted in the most widespread inundation of the N. A. craton
This vast epeiric sea, which experienced a uniformly warm climate during this time
opened numerous new marine habitats
soon filled by a variety of organisms

32. Striking Changes in Ordovician
Both sedimentation patterns and fauna underwent striking changes
Ordovician was characterized by the adaptive radiation of many animal phyla
brachiopods
Bryozoans
corals
with a consequent dramatic increase in the diversity of the total shelly fauna

33. Middle Ordovician Seafloor Fauna
Cephalopods, crinoids, colonial corals, trilobites, and brachiopods

34. Brachiopods Brachiopods present since the Cambrian
began a period of major diversification
in the shallow-water marine environment during the Ordovician

35. Graptolites Excellent guide fossils
especially abundant
most graptolites were planktonic
most individual species existed for less than a million years
Due to the fragile nature of their organic skeleton
most commonly found in black shales

36. Conodonts well-known small toothlike fossils
composed of the mineral apatite
(calcium phosphate)
the same mineral that composes bone
Cahabagnathus sweeti, Copenhagen Formation
Middle Ordovician, Monitor Range, Nevada

37. Mass Extinctions
End of the Ordovician a time of mass extinctions in the marine realm
> 100 families of invertebrates became extinct
What caused such an event?
another massive glaciation?

38. Silurian and Devonian Marine Communities
Ordovician extinction -> rediversification, recovery of:
brachiopods, bryozoans, gastropods, bivalves, corals, crinoids, and graptolites

39. Massive Reef Builders
Silurian and Devonian were times of major reef building
While most of the Silurian radiations of invertebrates represented repopulating of niches
Organic reef builders diversified in new ways
building massive reefs
larger than any produced during the Cambrian or Ordovician

40. Middle Devonian Reef
corals, cephalopods, trilobites, crinoids, and brachiopods

41. Ammonoids Excellent guide fossils !
for the Devonian through Cretaceous periods
with their distinctive suture patterns
short stratigraphic ranges
widespread distribution
Imitoceras rotatorium (DeKoninck), an ammonoid cephalopod
from the Lower Mississippian Rockford Limestone, near Rockford, Indiana

42. Another Mass Extinction
Another mass extinction occurred near the end of the Devonian
worldwide near-total collapse of the massive reef communities
were most extensive in the marine realm

43. Another Mass Extinction
The tropical groups were most severely affected
in contrast, the polar communities were seemingly little affected
Apparently, an episode of global cooling
was largely responsible for the extinctions near the end of the Devonian
WHY?

44. Actors in Extinctions
During such a cooling, the disappearance of tropical conditions
would have had a severe effect on reef and other warm-water organisms
Cool-water species, on the other hand, could have simply migrated toward the equator
The closing of the Iapetus Ocean and the orogenic events of the Late Devonian
undoubtedly also played a role in these extinctions
by reducing the area of shallow shelf environments where many marine invertebrates lived
Remember the connection between the tectonic and faunal changes!

45. Carboniferous and Permian Marine Communities
The Carboniferous invertebrate marine community (Mississipian and Pennsylvanian)
responded to the Late Devonian extinctions
in much the same way as the Silurian invertebrate marine community responded to the Late Ordovician extinctions
that is, by renewed adaptive radiation and rediversification

46. Mississippian Marine Life
blastoids
lacy bryozoans
crinoids
brachiopods
small corals

47. Restricted Permian Marine Faunas
The Permian invertebrate marine faunas resembled Carboniferous faunas
not as widely distributed
restricted size of the shallow seas on the cratons
reduced shelf space along the continental margins

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

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

50. The Permian Marine Invertebrate Extinction Event
Greatest recorded mass-extinction event
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

51. Phanerozoic Diversity
Diversity of marine invertebrate and vertebrate families
3 episodes of Paleozoic mass extinction are visible
with the greatest occurring at the end of the Permian Period

52. Permian Mass Extinction
Potential causes:
(1) a meteorite impact (like the end of the Cretaceous Period)
(2) a widespread marine regression resulting from glacial conditions
(3) volcanic eruptions -> CO2 -> warming -> collapsed ocean circulation -> anoxia -> euxinia

53. Permian Mass Extinction
It appears that the Permian mass extinction
took place over an 8-million-year interval at the end of the Permian Period
which would seemingly rule out a meteorite impact: see reading for essay three for more discussion of this

54. Biota Dramatically Changed
Regardless of the ultimate cause of the Permian mass extinctions,
the fact is that Earth's biota was dramatically changed
Triassic marine faunas were of low diversity
but the surviving species tended to be abundant
and widely distributed around the world