Deep Time - Evolution Lecture 21 Study Notes

Deep Time – Evolution Lecture 21

Fossils

  • Definition: Fossils are the preserved remains or traces of ancient organisms.

    • Context: Charles Darwin was aware of fossils and their significance, yet paleontology as a science was relatively new during his time.

    • Incompleteness of Fossil Record:

    • Darwin correctly hypothesized that the fossil record is incomplete.

    • Question Posed: Why is the fossil record incomplete?

Studying Fossils

  • Key Insights: Paleontologists derive a substantial amount of knowledge about organisms from studying their fossils.

Examples of Fossils

  • Mating Turtles: Fossils demonstrate instances of turtles dying while mating.

  • Aquatic Dinosaurs: Some aquatic dinosaurs are indicated to have given live birth instead of laying eggs.

  • Fish Behavior: Modern fish are still observed dying in similar predatory situations as their ancestors did.

Live Birth

  • Image Source:

    Live Birth

Trilobite Growth Rates

  • Graph Analysis:

    • Measurement of maximum cephalic width (B) in relation to total cephalic length (A).

    • Important for inferring organismal growth rates across different time periods.

    • Help infer global temperatures and other environmental conditions.

Coloration in Dinosaurs

  • Feather Pigmentation: Using scanning electron microscope images to identify different types of melanosomes.

    • Melanosomes correspond to specific pigments, helping provide information on the coloration of dinosaur feathers.

    • Knowledge of melanosomes allows paleontologists to infer the colors of extinct species.

  • Countershading Techniques: Various methods are used to analyze how species, including dinosaurs, were countershaded.

Animal Mass and Predatory Dynamics

  • Current Research Findings:

    • Data indicates that no extant (living) predators have a mass comparable to the largest herbivores, such as rhinos and elephants.

  • Graph Analysis: Ratio of body mass to percentage of species that exhibited countershading.

    • Reference: Zimmer/Emlen, "Evolution: Making Sense of Life, 3e, 2020 W. H. Freeman and Company."

Hadrosaur Crests

  • Physiology Insights: Hadrosaurs had unique crests located on the back of their heads.

    • CT Scanning: Fossil examinations revealed that these crests are associated with nasal cavities.

  • Acoustic Predictions: Crests likely utilized for sound production, with predictions of sound frequency based on their shape.

    • Research indicates that ear morphology suggests these dinosaurs were adapted to hear the sounds generated by their crests.

Chemical Analysis of Rocks

  • Rock Chemistry and Age:

    • Rock chemical composition can provide insights beyond dating, such as the biological origins of carbon.

    • Analysis of isotopes:

    • Key Isotopes: 12C and 13C.

    • 13C is less absorbed by plants compared to 12C, reflecting a lower ratio of 13C/12C in plant matter compared to the atmosphere.

  • C3 and C4 Plants: Difference in isotope ratios helps identify dietary sources for animals.

    • C3 Plants: Examples include forbs, with a specific isotopic signature.

    • C4 Plants: Examples include grasses, which have a different isotopic ratio, facilitating inferences about animal diets.

Hominin Diet Trends

  • Dietary Evolution: Early hominins initially consumed more C3 plants (akin to modern chimps).

    • Gradual shift towards C4 plants over generations, indicating dietary adaptability in response to environmental changes.

Trace Fossils

  • Definition of Trace Fossils: Often, the fossilized evidence studied is not from the organism itself but marks of its activity.

    • Examples: Follow animal movement through tracks, nests, or waste rather than the remains themselves.

  • Stromatolites: Ancient structures formed by microbial mats, indicative of early life on Earth.

    • Date of Fossil Stromatolites: Approximately 3.8 billion years old, reflecting parallels with modern stromatolites.

    • Image Reference: [Stromatolites](https://globalchange.umich.edu/globalchange 1/current/lectures/complexlife/complexlife .html)

Animal Movement Evidence

  • Burrowing Evidence: Specific fossils indicating burrowing patterns of ancient worms and animal movements.

  • Footprints: Footprints from approximately 390 million years ago have been preserved and studied for insights into prehistoric animal behavior.

Concept of Deep Time

  • Understanding Depth of Time in Evolution:

    • Example: Counting time sequentially to understand the immense duration of evolutionary history.

    • Hypothetical Examples: How long would it take to count to 1,000,000? To a billion? To 4.567 billion years?

  • John McPhee's Metaphor:

    • McPhee provides a relatable metaphor for deep time by comparing Earth's history to a yardstick. A small action (like filing a nail) could represent the erasure of entire human history. This metaphor emphasizes the vast scale of geological time.

24-Hour Timeline of Earth History

  • Visualization of Earth's History:

    • The first appearance of Homo sapiens is metaphorically represented at 11:59:30 P.M. on a 24-hour time scale.

    • Significant Events in Geological Timeline:

    • Age of Dinosaurs: between 1-2 billion years ago.

    • Oldest Multicellular Fossils: around 1 billion years ago.

    • Origin of Earth and the oldest known rocks: Approximately 4.567 billion years ago.

    • Each second on this timeline equates to about 52,000 years.

Measuring Deep Time in Distance

  • Reflecting on Distance:

    • Hypothetical exercise of measuring Earth’s age in physical distance (e.g., 100 meters) to determine "years per meter".

    • Calculating: 0.04567 billion years per meter, leading to 45.67 million years per meter.

    • Purpose: To examine pivotal moments in Earth’s history using this continuous scale to appreciate the longevity of evolutionary processes.