Introduction

Proterozoic Setup

• 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).

Ediacaran Fauna

• 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

Cambrian

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

Ordovician

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.

Review Questions (All of Lecture 13)

• 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)