Lecture 13A: Paleozoic Life
Single-celled organisms dominated Earth (Archean bacteria)
Early Proterozoic
Eukaryotic cells were a milestone in evolution.
Late Proterozoic
Exceptional preservation of soft-bodied organism that vaguely resemble jellyfish, sea pens, and wormlike animals.
Show older evolutionary history for our modern metazoans (multicellular animals).
Neoproterozoic
Phylums Cnidaria (jellyfish, sea pens) and Echinodermata (starfish, sea urchins)
Fauna might go as far back as 800-900 Ma, but not enough evidence.
Widespread between 545-670 Ma.
Small Shelly Fauna
Very first mineralized elements in fossil record (600-550 Ma).
Preserved around the world (Esmeralda County, NV).
Fossils suggest biological pathways for secreting a mineral were in place before Cambrian.
Although mechanism to form shell was there, not really being used
Cloudina
Cloudina: One of earliest known animal fossil with mineralized skeleton.
Metazoan of Neoproterozoic (Ediacaran) to Cambrian.
Can be describe as a “tube-dwelling worm”.
First “shelly” critter.
Bore Holes in Shells
Implying there was at least some form of carnivore in Ediacaran.
Comes from predation.
Likely some sore of sponge
Sponges were the apex predator at the time (top of the food chain).
Non-Vertebrates
Non-vertebrate: Animals that do not have a backbone or spine. This group includes creatures like insects, worms, jellyfish, and snails.
Phylum: A major category in the classification of living organisms, grouping together related classes.
Porifera - the sponges
Cnidaria - corals, jellyfish, sea anemones
Arthropoda - insects, spider, trilobites
Mollusca - clams, oysters, snails, octopods
Echinodermata - sea urchins, star fish
Important Cambrian Biology
Cambrian Explosion (seemingly instantaneous appearance of many varied animals)
Trilobites (index fossil)
Treptichnus pedum (trace fossil)
Burgess Shale Lagerstatten (one of the major lagerstatten)
Anomalocaris (apex predator)
Defining the Cambrian
First period of Paleozoic Era and Phanerozoic Eon
Phanerozoic → ancient Greek, “visible life”
We now have a “visible” Ediacaran biota
Why is Ediacaran not a period of Phanerozoic?
Traditionally base of Cambrian was not defined by “visible life”.
It was defined by first occurrence of Trilobites.
Trilobites
Phylum: Arthropoda
Older and older trilobites kept being found, so the boundary kept having to be moved.
Good index fossil
Led to a Debate
Russian/Chinese scientist wanted Cloudina to define Cambrian.
U.S. scientists anted to keep Trilobite.
Canadians proposed a trace fossil.
Treptichnus pedum → preserved worm burrow.
Occurs above Cloudina but below Trilobites.
The treptichnus pedum defines the base of the Cambrian.
Cambrian Explosion
Cambrian Explosion: Refers to the seemingly instantaneous appearance of many varied animals in the early to middle Cambrian.
It’s more like a slow fuse, this life didn’t suddenly appear.
New phyla appears: Arthropoda, Chordata, Mollusca.
What’s Going On?
Changes attributed to Cambrian Explosion.
Hard parts are evolving as a defense against predation.
Justification: phenomenon occurs across several unrelated phyla same time thus, it must be a reaction to an ecological stress.
Sea water chemistry changed to the point that secreting a shell out of carbonate or phosphate was not metabolically overly expensive.
Justification: phenomenon occurs across several unrelated phyla same time thus, chemistry must have changed or else all these groups would have evolved hard parts sooner.
Take away → Cambrian explosion doesn’t really have a good explanation for why it happened when it did.
Lagerstatten
Lagerstatten: An environment where fossils are exceptionally well-preserved, often including soft tissues.
An instance of exceptional preservation.
Environments give us immaculate pictures of prehistoric life.
Some are preserved in three dimensions.
Many remains of animals lacked hard parts.
Burgess Shale
Discovered in 1909 on an expedition to collect Cambrian trilobites in the Canadian Rockies by Charles Walcott.
One of the major lagerstatten.
Lack of Oxygen (Burgess Preservation)
Mudslides and anoxic water (no oxygen)
Cambrian Life
Simple in structure, ecologically diverse.
Archaeocyathids and other reef building Porifera (sponges).
Archaeocyathids: An extinct group of ancient marine sponges that lived during the Cambrian period; some of the earliest known reef-building organisms.
Trilobites
Brachiopods, Mollusca, and others
Top Cambrian Predator
Top predator was the arthropod Anomalocaris.
“Odd shrimp”
Mouth plates used for crushing prey captured by these appendages.
Trilobites with bite marks in fossil record.
Evolutionary Patterns
Cambrian marks a time when Metazoans were ecologically experimenting.
The Cambrian marks diversification of Phyla, but Family / Genus/ Species diversity remained low.
Only 1 Phylum (Bryozoans) originated after Cambrian but Family diversity explodes in the subsequent Ordovician → GOBE
Important Ordovician Biology
Great Ordovician Biodiversification Event (GOBE) (tripling of global diversity)
Coral reefs (Rugose and Tabulates)
Nautiloids and sea stars (top predators of the Ordivician)
Vertebrate radiation (earliest = jawless fish; reptiles, mammal, fish, birds, and amphibians)
Ordovician mass extinction event (first great Mass Extinction; caused by global cooling)
GOBE
Great Ordovician Biodiversification Event
Mid-Ordovician (over ~25 million years geologic time)
Unlike Cambrian diversification (new phyla), this was characterized by an increase in species, genus, family, and order.
Tripling of global diversity.
Consistent throughout Paleozoic.
Simple Cambrian food chain of deposit and suspension feeders replaced by more complex food web.
Causes of Ordovician Radiation
Late Cambrian extinctions left niches (function) available.
A time of continental fragmentation and sea-floor spreading.
Which may have provided nutrients
High sea levels created vast shallow warm seas (Tippecanoe).
Oxygen levels reaching modern levels.
Evolution of new predators
Robust calcite shells evolve
Brachiopods
During Paleozoic, thousands of different species in near-shore and deep-sea.
Found in Cambrian but became abundant in Ordovician (calcite becoming more commonplace).
Useful for biostratigraphic correlation.
Bryozoans
First show up in the Ordovician.
Filter feeding “Moss Animals”
Colonial organism which supported 100’s of little animals.
Build coral-like structures.
Cousins of the brachiopods
Crinoids
Known as “Sea lilies”
Stalked echinoderms (phylum includes sea stars, sea urchins, etc.)
Sessile (immobile); modern ones are mobile.
Arms used as long filter-feeding fans.
Bodies suspended by long stalks rooted to sea bed.
Rarely preserved
Corals
Sponge reefs occurred during Cambrian.
Ordovician marks first coral reefs.
Rugose Corals: Horn corals
Tabulates: Honeycomb corals
Stromatoporoids
Extinct group of mound-building (reef) sponges.
Common during Ordovician-Devonian
Difficult to interpret (enigmatic); used to think these were stromatolites, but these are animals, not cyanobacteria.
Grew in association with corals, brachiopods, and other reef-dwellers.
Top Predator(s)
Cambrian: largest predator arthropod Anomalocaris.
Ordovician: Cephalopod nautiloids reached up to 10 m.
Living relative is the Chambered nautilus
The other new predator were sea stars.
Gastropods
Evolve in Cambrian
Snails
Predators of the stromatolites
Diversify in the Ordovician
Show abilities to scavenge
Predation
Graze (results in decline of stromatolites)
Graptolites
Ordovician index fossils
Greek for “writing in the rocks”
Colonial animals composed of interconnected system of tubes.
Filter feeders
Extinct
Vertebrates
Ordovician marks the biodiversification (or radiation) of our own subphylum → the Vertebrates.
Fossil discoveries (in China) can place back to the Cambrian.
Earliest vertebrates were jawless fish.
Reptiles, mammals, fishes, birds, amphibians
Agnathans
Ancient Greek for “no jaws”
Oldest known discovery was in the Lower Cambrian, but diversification in Ordovician.
Relatives exist today.
Conodonts
Class of agnathans
Group of well-known, small, tooth-like fossils composed of the mineral apatite (calcium-phosphate).
Evolve in Cambrian but become abundant in the Ordovician
Become excellent index fossils for the Ordovician.
Extinct at end of Triassic
First Life on Land
Seeing small signs that life existed on land.
Life invades land
Land plants ~475 Ma
First land colonizers were likely micro-biotic crusts.
Communities of fungi, bacteria, and algae.
Advantages:
Light abundant (photosynthesis)
Nutrients supplied directly to soils (weathering).
First fossils of spores and tissues of simple land plants in later Ordovician.
Ordovician Extinction
The first great Mass Extinction
Global cooling caused the Ordovician mass extinction event.
>100 families of marine animals did not make it to Silurian.
Half of all brachiopods and bryozoans died out.
Reef communities decimated; did not bounce back until late Silurian.
Nautiloids were decimated.
Trilobites declined further
Likely cause was a global glaciation event
Created a dramatic drop in sea-level eliminating much habitat along continental shelved.
Concentrated on tropical groups (most warm water invertebrates were gone).
Cold or deep water adapted groups weathered the storm best.
Early Silurian Seas were dominated by low diversity widespread taxa; by the Late Silurian and into the Devonian, life had recovered.
Were there general names for specific periods and/or eras (e.g., Age of Fish)?
Age of Fish: Devonian
How did life change from Precambrian into (and through) the Paleozoic?
Life evolved from simple, single-celled organisms in the Precambrian to more complex, multicellular forms in the Paleozoic.
The Cambrian Explosion led to a rapid increase in biodiversity and the evolution of major animal groups.
By the end of the Paleozoic, life had colonized land, but the era ended with a mass extinction.
What was the Cambrian explosion?
Cambrian Explosion: Refers to the seemingly instantaneous appearance of many varied animals in the early to middle Cambrian.
New phyla appears: Arthropoda, Chordata, Mollusca.
What is a Lagerstatten? Why was the Burgess Shale important? Who discovered it?
Lagerstatten: An environment where fossils are exceptionally well-preserved, often including soft tissues.
Burgess Shale is one of the major lagerstatten.
Discovered by Charles Walcott on an expedition to collect Cambrian trilobites in the Canadian Rockies.
What were dominant predators, new organisms, and index fossils for specific Periods?
Paleozoic:
Apex predator: Sponge
Cambrian:
Apex predator: Anomalocaris
Index fossil: Trilobites
Trace fossil: Treptichnus pedum
Ordovician:
Apex predator: Cephalopod
Index fossil: Graptolites, conodonts
What was the evolutionary path of life from marine to land?
Early signs of life on land.
Life invades land with plants around 475 Ma.
Microbiotic crusts (fungi, bacteria, algae) were likely the first colonizers.
Advantages: abundant light for photosynthesis and nutrients from soil weathering.
First fossils of simple land plants appear in the late Ordovician.
What were the mass extinction event(s)? When did they occur? What caused them?
Ordovician mass extinction event
First great mass extinction
Global glaciation event (global cooling)
Single-celled organisms dominated Earth (Archean bacteria)
Early Proterozoic
Eukaryotic cells were a milestone in evolution.
Late Proterozoic
Exceptional preservation of soft-bodied organism that vaguely resemble jellyfish, sea pens, and wormlike animals.
Show older evolutionary history for our modern metazoans (multicellular animals).
Neoproterozoic
Phylums Cnidaria (jellyfish, sea pens) and Echinodermata (starfish, sea urchins)
Fauna might go as far back as 800-900 Ma, but not enough evidence.
Widespread between 545-670 Ma.
Small Shelly Fauna
Very first mineralized elements in fossil record (600-550 Ma).
Preserved around the world (Esmeralda County, NV).
Fossils suggest biological pathways for secreting a mineral were in place before Cambrian.
Although mechanism to form shell was there, not really being used
Cloudina
Cloudina: One of earliest known animal fossil with mineralized skeleton.
Metazoan of Neoproterozoic (Ediacaran) to Cambrian.
Can be describe as a “tube-dwelling worm”.
First “shelly” critter.
Bore Holes in Shells
Implying there was at least some form of carnivore in Ediacaran.
Comes from predation.
Likely some sore of sponge
Sponges were the apex predator at the time (top of the food chain).
Non-Vertebrates
Non-vertebrate: Animals that do not have a backbone or spine. This group includes creatures like insects, worms, jellyfish, and snails.
Phylum: A major category in the classification of living organisms, grouping together related classes.
Porifera - the sponges
Cnidaria - corals, jellyfish, sea anemones
Arthropoda - insects, spider, trilobites
Mollusca - clams, oysters, snails, octopods
Echinodermata - sea urchins, star fish
Important Cambrian Biology
Cambrian Explosion (seemingly instantaneous appearance of many varied animals)
Trilobites (index fossil)
Treptichnus pedum (trace fossil)
Burgess Shale Lagerstatten (one of the major lagerstatten)
Anomalocaris (apex predator)
Defining the Cambrian
First period of Paleozoic Era and Phanerozoic Eon
Phanerozoic → ancient Greek, “visible life”
We now have a “visible” Ediacaran biota
Why is Ediacaran not a period of Phanerozoic?
Traditionally base of Cambrian was not defined by “visible life”.
It was defined by first occurrence of Trilobites.
Trilobites
Phylum: Arthropoda
Older and older trilobites kept being found, so the boundary kept having to be moved.
Good index fossil
Led to a Debate
Russian/Chinese scientist wanted Cloudina to define Cambrian.
U.S. scientists anted to keep Trilobite.
Canadians proposed a trace fossil.
Treptichnus pedum → preserved worm burrow.
Occurs above Cloudina but below Trilobites.
The treptichnus pedum defines the base of the Cambrian.
Cambrian Explosion
Cambrian Explosion: Refers to the seemingly instantaneous appearance of many varied animals in the early to middle Cambrian.
It’s more like a slow fuse, this life didn’t suddenly appear.
New phyla appears: Arthropoda, Chordata, Mollusca.
What’s Going On?
Changes attributed to Cambrian Explosion.
Hard parts are evolving as a defense against predation.
Justification: phenomenon occurs across several unrelated phyla same time thus, it must be a reaction to an ecological stress.
Sea water chemistry changed to the point that secreting a shell out of carbonate or phosphate was not metabolically overly expensive.
Justification: phenomenon occurs across several unrelated phyla same time thus, chemistry must have changed or else all these groups would have evolved hard parts sooner.
Take away → Cambrian explosion doesn’t really have a good explanation for why it happened when it did.
Lagerstatten
Lagerstatten: An environment where fossils are exceptionally well-preserved, often including soft tissues.
An instance of exceptional preservation.
Environments give us immaculate pictures of prehistoric life.
Some are preserved in three dimensions.
Many remains of animals lacked hard parts.
Burgess Shale
Discovered in 1909 on an expedition to collect Cambrian trilobites in the Canadian Rockies by Charles Walcott.
One of the major lagerstatten.
Lack of Oxygen (Burgess Preservation)
Mudslides and anoxic water (no oxygen)
Cambrian Life
Simple in structure, ecologically diverse.
Archaeocyathids and other reef building Porifera (sponges).
Archaeocyathids: An extinct group of ancient marine sponges that lived during the Cambrian period; some of the earliest known reef-building organisms.
Trilobites
Brachiopods, Mollusca, and others
Top Cambrian Predator
Top predator was the arthropod Anomalocaris.
“Odd shrimp”
Mouth plates used for crushing prey captured by these appendages.
Trilobites with bite marks in fossil record.
Evolutionary Patterns
Cambrian marks a time when Metazoans were ecologically experimenting.
The Cambrian marks diversification of Phyla, but Family / Genus/ Species diversity remained low.
Only 1 Phylum (Bryozoans) originated after Cambrian but Family diversity explodes in the subsequent Ordovician → GOBE
Important Ordovician Biology
Great Ordovician Biodiversification Event (GOBE) (tripling of global diversity)
Coral reefs (Rugose and Tabulates)
Nautiloids and sea stars (top predators of the Ordivician)
Vertebrate radiation (earliest = jawless fish; reptiles, mammal, fish, birds, and amphibians)
Ordovician mass extinction event (first great Mass Extinction; caused by global cooling)
GOBE
Great Ordovician Biodiversification Event
Mid-Ordovician (over ~25 million years geologic time)
Unlike Cambrian diversification (new phyla), this was characterized by an increase in species, genus, family, and order.
Tripling of global diversity.
Consistent throughout Paleozoic.
Simple Cambrian food chain of deposit and suspension feeders replaced by more complex food web.
Causes of Ordovician Radiation
Late Cambrian extinctions left niches (function) available.
A time of continental fragmentation and sea-floor spreading.
Which may have provided nutrients
High sea levels created vast shallow warm seas (Tippecanoe).
Oxygen levels reaching modern levels.
Evolution of new predators
Robust calcite shells evolve
Brachiopods
During Paleozoic, thousands of different species in near-shore and deep-sea.
Found in Cambrian but became abundant in Ordovician (calcite becoming more commonplace).
Useful for biostratigraphic correlation.
Bryozoans
First show up in the Ordovician.
Filter feeding “Moss Animals”
Colonial organism which supported 100’s of little animals.
Build coral-like structures.
Cousins of the brachiopods
Crinoids
Known as “Sea lilies”
Stalked echinoderms (phylum includes sea stars, sea urchins, etc.)
Sessile (immobile); modern ones are mobile.
Arms used as long filter-feeding fans.
Bodies suspended by long stalks rooted to sea bed.
Rarely preserved
Corals
Sponge reefs occurred during Cambrian.
Ordovician marks first coral reefs.
Rugose Corals: Horn corals
Tabulates: Honeycomb corals
Stromatoporoids
Extinct group of mound-building (reef) sponges.
Common during Ordovician-Devonian
Difficult to interpret (enigmatic); used to think these were stromatolites, but these are animals, not cyanobacteria.
Grew in association with corals, brachiopods, and other reef-dwellers.
Top Predator(s)
Cambrian: largest predator arthropod Anomalocaris.
Ordovician: Cephalopod nautiloids reached up to 10 m.
Living relative is the Chambered nautilus
The other new predator were sea stars.
Gastropods
Evolve in Cambrian
Snails
Predators of the stromatolites
Diversify in the Ordovician
Show abilities to scavenge
Predation
Graze (results in decline of stromatolites)
Graptolites
Ordovician index fossils
Greek for “writing in the rocks”
Colonial animals composed of interconnected system of tubes.
Filter feeders
Extinct
Vertebrates
Ordovician marks the biodiversification (or radiation) of our own subphylum → the Vertebrates.
Fossil discoveries (in China) can place back to the Cambrian.
Earliest vertebrates were jawless fish.
Reptiles, mammals, fishes, birds, amphibians
Agnathans
Ancient Greek for “no jaws”
Oldest known discovery was in the Lower Cambrian, but diversification in Ordovician.
Relatives exist today.
Conodonts
Class of agnathans
Group of well-known, small, tooth-like fossils composed of the mineral apatite (calcium-phosphate).
Evolve in Cambrian but become abundant in the Ordovician
Become excellent index fossils for the Ordovician.
Extinct at end of Triassic
First Life on Land
Seeing small signs that life existed on land.
Life invades land
Land plants ~475 Ma
First land colonizers were likely micro-biotic crusts.
Communities of fungi, bacteria, and algae.
Advantages:
Light abundant (photosynthesis)
Nutrients supplied directly to soils (weathering).
First fossils of spores and tissues of simple land plants in later Ordovician.
Ordovician Extinction
The first great Mass Extinction
Global cooling caused the Ordovician mass extinction event.
>100 families of marine animals did not make it to Silurian.
Half of all brachiopods and bryozoans died out.
Reef communities decimated; did not bounce back until late Silurian.
Nautiloids were decimated.
Trilobites declined further
Likely cause was a global glaciation event
Created a dramatic drop in sea-level eliminating much habitat along continental shelved.
Concentrated on tropical groups (most warm water invertebrates were gone).
Cold or deep water adapted groups weathered the storm best.
Early Silurian Seas were dominated by low diversity widespread taxa; by the Late Silurian and into the Devonian, life had recovered.
Were there general names for specific periods and/or eras (e.g., Age of Fish)?
Age of Fish: Devonian
How did life change from Precambrian into (and through) the Paleozoic?
Life evolved from simple, single-celled organisms in the Precambrian to more complex, multicellular forms in the Paleozoic.
The Cambrian Explosion led to a rapid increase in biodiversity and the evolution of major animal groups.
By the end of the Paleozoic, life had colonized land, but the era ended with a mass extinction.
What was the Cambrian explosion?
Cambrian Explosion: Refers to the seemingly instantaneous appearance of many varied animals in the early to middle Cambrian.
New phyla appears: Arthropoda, Chordata, Mollusca.
What is a Lagerstatten? Why was the Burgess Shale important? Who discovered it?
Lagerstatten: An environment where fossils are exceptionally well-preserved, often including soft tissues.
Burgess Shale is one of the major lagerstatten.
Discovered by Charles Walcott on an expedition to collect Cambrian trilobites in the Canadian Rockies.
What were dominant predators, new organisms, and index fossils for specific Periods?
Paleozoic:
Apex predator: Sponge
Cambrian:
Apex predator: Anomalocaris
Index fossil: Trilobites
Trace fossil: Treptichnus pedum
Ordovician:
Apex predator: Cephalopod
Index fossil: Graptolites, conodonts
What was the evolutionary path of life from marine to land?
Early signs of life on land.
Life invades land with plants around 475 Ma.
Microbiotic crusts (fungi, bacteria, algae) were likely the first colonizers.
Advantages: abundant light for photosynthesis and nutrients from soil weathering.
First fossils of simple land plants appear in the late Ordovician.
What were the mass extinction event(s)? When did they occur? What caused them?
Ordovician mass extinction event
First great mass extinction
Global glaciation event (global cooling)
