ZOO: DSC-354 Practical - IV
Unit 2: Evolution
1. Study of Fossils from Models/Pictures
Fossils are the remains or impressions of prehistoric organisms preserved in petrified form or as a mold or cast in rock. They provide direct evidence of evolutionary history.
Practical Objective
To identify different types of fossils and understand their significance in establishing evolutionary lineages.
Common Examples Studied
- Archaeopteryx: A transitional fossil between non-avian dinosaurs and birds.
- Trilobites: Extinct marine arthropods used as index fossils.
- Ammonites: Extinct marine mollusc fossils.
2. Study of Homology and Analogy
Comparative anatomy helps in understanding the phylogenetic relationships between different species.
A. Homology (Divergent Evolution)
Definition: Organs that have the same fundamental structure and embryonic origin but may perform different functions.
- Example: Forelimbs of vertebrates (Human hand, Wing of a bird, Flipper of a whale, Foreleg of a horse).
- Significance: Indicates common ancestry.
B. Analogy (Convergent Evolution)
Definition: Organs that perform similar functions but have different structural designs and embryonic origins.
- Example: Wing of an insect (chitinous) vs. Wing of a bird (feathers and bones).
- Significance: Indicates adaptation to similar environmental pressures or lifestyles rather than common ancestry.
Exam Focus: Practical Identification & Viva
Exam Tip: During the practical exam, when identifying a specimen for homology, always mention the "fundamental skeletal plan" (e.g., Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges).
Frequently Asked Questions (FAQs)
- Q: What is a "Missing Link"?
A: A fossil organism that exhibits traits common to both an ancestral group and its derived descendant group (e.g., Archaeopteryx).
- Q: How do analogous structures arise?
A: Through convergent evolution where unrelated species occupy similar niches.
- Q: Why are fossils often studied through models?
A: Original fossils are rare and fragile; plaster cast models provide a durable way to study morphology.
Common Error: Do not say homologous organs have "the same function." They often have different functions (e.g., swimming vs. flying) despite the same structure.