Lecture 2: Evolution of Metazoan Biodiversity

Question 1

What are some key questions to ask in Biodiversity?

Answer 1

1. Organismal Relationships: How are organisms connected through evolutionary history?
2. Phenotypic and Genotypic Variation: What are the tempo (rate) and mode (patterns) of variations in traits?
3. Conservation Priorities: Which species/populations are most critical for conservation?
4. Measuring and Protecting Biodiversity: How should biodiversity be quantified and safeguarded?

Question 2

Diversity

Answer 2

Refers to the number of taxa (e.g., species, genera, families).

Question 3

Disparity

Answer 3

The range of differences between taxa.

Question 4

What are some examples of Taxonomic Categories (from Specific to Broad)?

Answer 4

• Homo sapiens (humans)
• Homo & Pan (genus-level group, e.g., humans and chimpanzees)
• Hominoidea (family-level grouping, e.g., apes)
• Primates, Mammalia, Tetrapoda (four-limbed animals)
• Vertebrata (animals with backbones), Deuterostomia, Metazoa (multicellular animals), All life

Question 5

What are the 3 key geological time periods and the evolutionary events associated with them?

Answer 5

1. Paleozoic Era (541–252 million years ago):
   - Early formation of Deuterostomia, Bilateria (bilateral symmetry animals), Metazoa.
2. Mesozoic Era (251–66 million years ago):
   - Development of Amniota (terrestrial vertebrates), Tetrapoda, and Vertebrata.
3. Cenozoic Era (66 million years ago to present):
   - Rise of Homo sapiens, Primates, Mammalia.

Question 6

What are notable fossil sites?

Answer 6

1) Little Dal Fossils Reefs (890 Ma): Early evidence of complex reef structures.

2) Burgess Shale (505 Ma): Known for well-preserved Cambrian fossils and early animal diversification.

3) Mistaken Point (575–650 Ma): Location of Ediacaran fauna (early multicellular life).

Question 7

Origin of Bilateria and Early Animals

Answer 7

1) Urbilaterian (First Bilaterian): Likely possessed:
- Basic brain and central nervous system (CNS)
- Sensory structures (possibly eyes and appendages)
- Segmented body with a circulatory system
- One-way gut

2) First Animal Characteristics: Increasing cell type number over evolutionary time, indicative of growing complexity.

Question 8

What are the two Metazoan Explosion Events?

Answer 8

1. Avalon Explosion (~575 Ma): Emergence of Ediacaran life forms.
   - Have complex feather type arrangement and three-fold symmetry.
2. Cambrian Explosion (~541 Ma): Rapid diversification of animal body plans, driven by ecological factors like predation.

Question 9

What are the noteworthy Cambrian Organisms?

Answer 9

1) Nectocaris: Possibly the first cephalopod.

2) Sanctacaris: Ancestor of Chelicerata (spiders, scorpions).

3) Pikaia: Early chordate (primitive vertebrate).

4) Metaspriggina: Among the earliest vertebrates.

Question 10

Ecological Drivers of Metazoan Radiation

Answer 10

1) Predation and Defence Arms Race:
- Predation required prey to evolve defense mechanisms, such as hard exoskeletons.
- Body segmentation evolved to support complex movements and structures.
- Emergence of novel trophic levels (predator/prey dynamics) enabled complex ecosystems.

2) Examples of Adaptations:
- Eyes: Developed for predator detection and prey targeting.
- Exoskeletons: Led to more sophisticated body plans, musculature, and predator capture adaptations.

Question 11

Main Evolutionary Events and Diversification of Life

Answer 11

1. Great Ordovician Biodiversification Event (GOBE): Major increase in marine biodiversity.
2. Mesozoic Marine Revolution: Rise of predators capable of crushing shells; increased diversity in marine species.
3. Cretaceous Terrestrial Revolution:
   - Origin of flowering plants, co-evolution with pollinators.
   - Development of ecosystems rich in insect-plant relationships.
4. Body Size Evolution in Marine Animals:
   - Expansion in body size throughout the Phanerozoic.
   - By the Devonian, marine organisms reached sizes comparable to modern whales.
5. Evolution of Vascular Plants (Silurian-Devonian):
   - Cooksonia: Earliest known vascular plant, small with stems but no leaves or roots.
   - Prototaxites: Large fungi reaching up to 8 meters, potentially the tallest organisms of its time.

Question 12

Geological Climate shifts and Life’s Impact

Answer 12

1) Silurian-Devonian CO2 and O2 Changes: Phases of global warming and CO2 reductions influenced plant evolution and photosynthesis rates, impacting biodiversity.

Question 13

Evolution Summary and Tree of Life Insights

Answer 13

1. Transition from Ediacaran to Cambrian Fauna:
   - Marked by vast diversification in body plans and species.
   - Expanded geographic distribution, emergence of predation, and establishment of complex ecosystems.
2. Phanerozoic Life Trends:
   - Waxing and Waning of Diversity: Initial explosion of life in the Cambrian, followed by fluctuations in diversity, potentially reaching a carrying capacity in modern times.

Question 14

What are the key takeaways from this lecture, what it was about?

Answer 14

• Biodiversity and Disparity evolve over time through ecological pressures and genetic variation.
• The Cambrian Explosion was a foundational event, establishing nearly all modern animal phyla and some that are now extinct.
• Fossil records from major sites help reconstruct ancestral traits and environmental shifts that shaped early metazoan life.