L05: Early Fossil Record

What is the earliest fossil?

Bacteria—>not mineralized—>fossils formed differently

What is geobiology?

Field of geology that studies (micro)organism-geology interactions

SQ: What kinds of fossils record early life?

Bacteria is the earliest fossil

Types of evidence(tells microorganisms present):

1. Body fossils

2. Preserved interactions between microorganisms and geology (trace). Ex: ooids and stromatolites

3. Chemical biomarkers (chemicals only living org can produce)

SQ: What is an ooids? How do ooids form?

Ball shaped mud, mud balls that form around something in the middle (like microorg or colony in the middle).

• Oblate (ellipsoid) grains of mud, calcium carbonate, or others

• Form: sediment accumulates around the pellet(microorg or colony), increasing in size as it falls through the mud

• Microorganisms can serve as the nucleus of the pellet

SQ: What are stromatolites and why are they important?

• Fossilized bacterial colony(solid rock)—>layered sedimentary rock formations built by photosynthetic cyanobacteria

• Formed by photosynthetic cyanobacteria (but stromatolite is home to many types of bacteria)

• Colony is home to many others

• Earliest evidence of life, ~3.7 billion years old

• Still found today

Importance: Oldest/Earliest evidence of life

SQ: How do stromatolites form?

Formed by alternating layers of bacteria and trapped sediment

Covered by sediment, cyanobacteria builds over it bc it needs sunlight, so like climbs out under the sediment to get the sunlight, and the cycle repeats as more sediment is added, leading to alternative layers of different bacteria and sediment(cyanobacteria just the builders)

These are microscopic layers

Bacteria + sediment—>covered by sediment—>cyanobacteria builds new colony—>alternating layers

SQ: What kinds of fossils record early metazoans(animals)?

1. Soft-bodied fossils

Body imprints(molds): before the evolution of hard parts; body fossils

2. Skeletal fossils

Once mineralized hard parts evolved—>Bones—>Cloudina (oldest known skeletal fossil), very close to the Proterozoic- Cambrian boundary

3. Trace fossils

None present until 570 MYA.

Before 570 MYA: Fine layers of silt turned into a rock, laminated silt (fine sediments) from 1.3Ga.

After 570 MYA: BURROWS: Get burrows that mix up sediments, Borehole (bite marks) by predatory snails, coprolites

4. Chemical Biomarkers or Molcular fossils

Molecules produced by specific organisms (chemical stuff)

Ediacara and Doushantuo Lagerstatten(locations)

• Dates back to the Ediacara period: 635-542 Ma

• Named after the Ediacara Ridge, South Australia

• Earliest fossil record of metazoans—> Earliest fossils (animals) found here, community of org found during this period

• No hard parts preserved—> SUPER IMPORTANT

• Doushantuo Formation, South China

SQ: Which metazoans first showed up in the Ediacaran periods?

ALL SOFT BODIED FOSSILS, all body imprints

1.Sponge—>from Doushantuo lagerstatte, earliest community we have in Ediacarian, Demosponges + Calcisponges

• Swimming just above sea floor

2.Cnidarians—> found in earliest fossil (found soft bodied), among earliest org that evolved. (ex: jellyfish)

• Swimming just above sea floor

• Cycomedusa and Mowsonites

3. Ancestral Bilaterians—> Bilaterally symmetric animals, relationship to other bilaterians(the clade contains all bilaterally symmetric animals, so all are related bc under 1 clade, Ex: humans, mammals, fish, shark, reptile)

• Charna: Attached to sea floor

• Dickosonia and Kim: walking around sea floor and filtering movements

Most not that complex—>either attached to sea floor, walking around sea floor and filtering nutrients, or swimming just above sea floor

What is a bilaterian?

Bilaterally symmetric animals, relationship to other bilaterians(the clade contains all bilaterally symmetric animals, so all are related bc under 1 clade, Ex: humans, mammals, fish, shark, reptile)

SQ: What are Charnia, Dickinsonia, and Kimberella? When did they show up?

These are all ancient bilaterians(all common, bilaterally symmetric)—>Showed up during the Ediacaran period

Charnia: leaf looking animals—>absorption feeders (absorb nutrients from sea),

• A leaf-like, fractal-branching frond that anchored itself to the dark, deep ocean floor. First recognized Precambrian fossil.

• Immobile (Sessile)- stood upright and absorbed organic nutrients directly from the water via osmosis.

Dickinsonia: extracts nutrients from sea floor, clam looking thing

• A flat, oval-shaped organism with a ribbed, quilted design that looked like a bathmat or a large leaf.

• Moved using rhythmic muscular contractions to creep over microbial seafloor mats, secreting digestive enzymes to absorb nutrients through its underbelly.

Kimberella: early mollusc, like an abalone shell, from sea floor

• A slug-like or mollusc-like bilateral creature with a tougher, hood-like outer shell.

• Highly Mobile. It had a true mouth and a functional internal digestive tract. It crawled across the sea floor, using a scratchy tongue-like organ (radula) to graze on green algae and bacteria.

Dickinsonia?

Dickinsonia: extracts nutrients from sea floor, clam looking thing

• A flat, oval-shaped organism with a ribbed, quilted design that looked like a bathmat or a large leaf.

• Moved using rhythmic muscular contractions to creep over microbial seafloor mats, secreting digestive enzymes to absorb nutrients through its underbelly.

Kimberella?

Kimberella: early mollusc, like an abalone shell, from sea floor

• A slug-like or mollusc-like bilateral creature with a tougher, hood-like outer shell.

• Highly Mobile. It had a true mouth and a functional internal digestive tract. It crawled across the sea floor, using a scratchy tongue-like organ (radula) to graze on green algae and bacteria.

Cambrian Biota

• Cambrian period: 551-490 Ma

• First appearance of hard parts (lots of fossils)

• Exceptional preservation of soft-bodied organisms and trace fossils

• Lagerstatten: Burgess Shale, Canada and Chenjiang, China

What is the complex paleoecology that appeared in the Cambrian Biota? What was this due to?

Due to evolution of hard mineralized parts

Complex paleoecology:

• Free Swimmers (more of them)

• Communites becomes more complex

• Deposite feeders(crawl on sea floor) started to burrows deep (this wasn’t present in Edia)

• Predators with claws and spines

• Prey with spines and armor

SQ: Which metazoans first showed up in the Cambrian period?

Early Cambrian (542 Ma)

• Small shelly fossils dominate (like cloudina: mineralized shealth animals live in)

• Archaeocyathid sponges(ancient sponges) that formed large reefs as a habitat for other animals (fake coral)—>extinct by the end of Cambrian period

Mid Cambrian (520 Ma)

• Rapid increase in abudnance, size, and complexity of shells

• Brachiopods(fake clam), trilobites(arhropods) and echinoderms dominate, mollusc(bivalve), “worms”-fake worms with long soft body, like velvet worm), chordates

• Some other worms: priapulid (voracious predatory worms burrow in sediment)

• Chordates: has a stiff organ in body that allows them to whip body side to side, gils, and tail. This is basc vertebrate.

• So more complex bivalves appeared.

• Echinoderms, hemichordates, chordates, arthropods, priapulids, bryozoans, annelids, brachiopods, and mollsuks (lots of radiation)

Ediacaran vs. Cambrian

As you can see, complex bivalves came in cambrian

SQ: What innovation differentiates the Cambrian fauna from the Ediacaran fauna?

HARD MINERALIZED PARTS, that is how the boundary is formed

Also, more complex paleoecology due to these hard parts.

Also—> complex active mobility (burrowing and swimming), and predator-prey interaction

SQ: How did the evolution of hard parts contribute to the apparent Cambrian radiation(what made look so diverse)? What did hard parts enable?

Likely due to evolution hard parts and resulting perservation bias (hard parts having enabled better preservation)

Bc better preservation due to hard parts, it appeared like a lot of species just spawned out of nowhere.

Structural support(due to hard parts):

• Enabled larger, more complex bodies (high O2 content allows for this)

• Higher mobility—>bc muscles attach to hard parts

• Predator-prey arms race(better protection/tools for predator and prey)

What is the predator-prey arms race? What did this lead to?

Both evolved parts to protect themselves or eat the prey

Ex: has shell(prey), evolve teeth(pred)

Led to greater diversity and complexity—> Contributed to huge increase in diverse animal clades

SQ: What environmental conditions helped preserve the Cambrian lagerstatten?

Preservation bias:

• Hard parts preserve better in the fossil records (possible edia also diverse, but don’t preserve well. So since Cambria preserved well, it looks more diverse as have more evidence).

• Lagerstatten characterized by low energy, hypoxic (low O2) preservation conditions(good at preserving fossils; suggest more fossils formed)