Comparative Vertebrate Morphology

Comparative Vertebrate Morphology Notes

Taxonomy

• Definition: Classification of organisms into a hierarchical structure based on morphological similarities.
  • Explore common structures during dissections to understand similarities/differences.

Taxonomy & Evolution

• Common Misunderstandings: Terms such as 'higher' or 'lower', 'advanced' or 'less advanced' are misleading.
  • Understanding Evolution: No species is at the 'top' of evolution. Humans are one of many outcomes of evolutionary processes.

Dissection Species

• Current Week: Shark and Fish
• Next Week: Frog and Pig
• Classes:
  • Chondrichthyes (Sharks and Rays)
  • Actinopterygii (Bony Fish)
  • Amphibia (Frogs)
  • Mammalia (Pigs)
• No species is the direct ancestor of another; they may share a common ancestor.

Simple Cladogram

• Illustrates relationships among species based on shared characteristics such as:
  • Feathers
  • Jaws
  • Lungs
  • Claws/nails
  • Fur and mammary glands

Class Chondrichthyes (Sharks)

• Key Characteristics:
  • Over 500 named shark species
  • Reproduction: Internal fertilization with few large young.
  • Long gestation and maturity periods make them vulnerable to fishing.
  • Cartilaginous skeleton for lightness and flexibility.
  • Buoyancy from liver oil.
  • Morphological adaptations: Dermal denticles (placoid scales), two-chambered heart, heterocercal tail.

Class Actinopterygii (Bony Fish)

• Key Characteristics:
  • About 40,000 species (half of all vertebrates)
  • Bony skeletons, strong yet heavy
  • Buoyancy from swim bladder; opercula (gill covers) allow breathing while stationary.
  • Two-chambered heart.
  • Homocercal tail and various scale types (Ctenoid, Cycloid, Ganoid).

Osmoregulation in Fishes

• Freshwater vs. Saltwater Fish:
  • Marine Fish: Lose water through osmosis but gain salts by drinking seawater.
  • Salt excretion through gills; produce small volumes of salty urine.
  • Freshwater Fish: Gain water through osmosis and excrete large volumes of dilute urine to cope with water excess.

Comparative Anatomy - Class Chondrichthyes

• External Anatomy of a Shark: Key structures include:

  • Nictitating membrane, spiracle, various fins, gill slits, claspers (in males).

• Internal Anatomy of a Shark: Includes organs like the stomach and rectal gland.

Comparative Anatomy - Class Actinopterygii

• External Anatomy of Bony Fish: Features include dorsal fins, nares, caudal fin, operculum, pectoral/pelvic fins, anal fin, and scales.

• Internal Anatomy: Components include muscle, kidneys, gonads, swim bladder, and heart.

Sensory Organs in Fish

• Lateral Line: Detects vibrations and movement in water.
• Ampullae of Lorenzini: Specialized to sense electrical fields generated by living organisms.

Class Amphibia

• Key Characteristics:
  • Evolved from lobe-finned fishes; mainly tetrapods with four limbs.
  • Cutaneous respiration alongside lungs in many species; three-chambered heart.

Class Mammalia

• Key Characteristics:
  • Possess mammary glands (nourishment for offspring).
  • Endothermic (warm-blooded) with four-chambered hearts.
  • Only mammals have hair; primarily for insulation.
  • Most have placentas; give birth to live young (exceptions: marsupials & monotremes).

Anatomy Overview

• Class Amphibia:

  • External Anatomy of Frog: Key structures include limbs, eye, tympanic membrane, external nares.

• Internal Anatomy of Frog: Includes liver lobes, lungs, stomach, intestines, urinary bladder.

• Class Mammalia:

  • External Anatomy of Pig: Male and female reproductive openings.

• Internal Anatomy of Pig: Contains thymus gland, heart, lungs, stomach, intestines, kidneys.