Sedimentology and Palaeontology Lecture 11: The Colonization of Land

Question 1

List all the animal kingdoms and animal phyla

Answer 1

Eukaryote kingdoms:
Animalia, Plantae, Fungi

• Animal phyla: annelida,
  molluscs, arthropods,
  chordates, nematodes,
  nemerteans, flatworms,
  tardigrades, gastrotrichs,
  onychophorans, rotifers

Question 2

What are the various types of physiological adaptations necessary to live on land?

Answer 2

• Water management
• Respiration
• Support and locomotion
• And: digestion,
  temperature control,
  reproduction, dispersal,
  sensory perception

Question 3

What were the barriers to living on land in terms of water managment?

Answer 3

Water management

• Aquatic organisms = live in interstitial water in
  soils
• Cryptic organisms = inhabit environments with
  high humidity such as soil and forest litter
• Poikilohydric organisms = desiccation tolerant
  but require high humidity to function
• Homoiohydric organisms = waterproof cuticles
  and osmoregulation to truly colonize the land

Question 4

What were the barriers to living on land in terms of respiration

Answer 4

Respiration
* Need to switch from obtaining oxygen
from the water to breathing air
* Membranes that allow diffusion of
respiratory gases will leak water
* Respiratory surfaces must therefore be
internalised – lungs, spiracles, stomata

Question 5

What were the barriers to living on land in terms of support and locomotion(moving)?

Answer 5

Support and locomotion

• Without the aid of buoyancy provided by water compared to air
• Arthropods - jointed exoskeleton with
  articulated limbs
• Tetrapods – evolved four limbs from fish ancestors

Question 6

Describe the evidence found for early life on land in hot springs

Answer 6

Pilbara, Australia (3.5 Ga)

• Hot spring and geyser deposits as the terrestrial component of a
  volcanic-hydrothermal system
• Biosignatures – stromatolites,
  microbial fabrics, and gas bubbles

Question 7

Describe evidence for the colonization of land through Molecular clocks and Prokaryote divergence times

Answer 7

Divergence times estimated based on rates of genetic mutations

• Prokaryotes before 4.1 Ga
  (consistent with Nuvvuagittuq and Jacks Hills)
• Colonization of land 3.1-2.8 Ga

Question 8

Describe the evidence of the colonization of land found microbial mats and soils

Answer 8

Microbial mats on top of 3.22 Ga river deposits in South Africa
* Geochemical evidence for the presence of organic matter in 2.6 Ga paleosols in South Africa

Microbially Induced Sedimentary Structures (MISS) through the
Proterozoic

Question 9

Describe evidence for the colonisation of land found in eukaryote fossils

Answer 9

Late Mesoproterozoic and early
Neoproterozoic palaeokarst surfacesin North America

Late Mesoproterozoic lacustrine
deposits in Scotland

Question 10

Describe evidence of land colonization found in fungi

Answer 10

First evidence of fungi thought to be from 503 Ma paleosol in the USA

But now fossils with fungal affinity have been found from 1 Ga old rocks of Canada

Question 11

What are some of inferred reasons that animals colonized the land?

Answer 11

Traces of arthropods, molluscs,
and worm-like animals from
transitional environments
associated with MISS

• Search for food (detritus) and
  lack of competition
• Predator avoidance
• Reproduction

Question 12

Describe evidence for the first Plants to colonise land

Answer 12

Land plants (embryophytes)
includes the liverworts,
mosses, ferns, gymnosperms,
and angiosperms

• Oldest known evidence from
  spores from the Middle
  Ordovician of Argentina
• Probably from a liverwort-like
  plant

Land plants came to prominence
in the Silurian to Devonian

• Small plants like clubmosses
  (430 Ma ago) → trees such as
  Archaeopteris (370 Ma ago)

Question 13

How are ecosystems and environments impacted by the addition of plantlife?

Answer 13

With plants, roots provide structure to sediment creating channel braided river

Unconfined sheet flows → channel-braided rivers

• ↑ mud production and retention by baffling and binding
• ↑ weathering may have ↓ atmospheric CO2 and led to
  global cooling and glaciation at the end of the Ordovician

Question 14

What are the oldest Tetrapod body fossils found on land?

Answer 14

Oldest known are Late Devonian
(Fammenian, 365 Ma) in age

• Acanthostega and Ichthyostega
• Lungs and gills
• Barrel-shaped bodies and ankle
  joints likely too weak to support
  their weight out of water
• Gap in the fossil record of ~30
  Ma (Romer’s Gap) and then see
  fully terrestrially adapted
  tetrapods

A number of trackways have
been attributed to tetrapods
* Some have been reevaluated as being made by
arthropods
* Or may be from tetrapods but
were made in water rather
than fully on land
* Genoa River, Late
Devonian, Australia