Lab 11: Vertebrate Homologies

Lab 11: Vertebrate Homologies

Objectives

  • Explore the structures/functions of a teleost fish.
  • Compare skeletal homologies of vertebrates.
  • Investigate vertebrate dentition as a function of diet.

Overview of Chordates

  • General characteristics:
    • Bilaterally symmetrical
    • Deuterostomes
    • Unique combinations of features present at some developmental stage:
    • Notochord
    • Dorsal tubular nerve cord
    • Pharyngeal slits/pouches
    • Post-anal tail

Taxonomic Classification

  • Phylum Chordata includes:
    • Subphylum Urochordata (tunicates)
    • Subphylum Cephalochordata (lancelets)
    • Subphylum Craniata:
    • Infraphylum Hyperotreti (hagfishes)
    • Infraphylum Vertebrata
      • Jawless (Agnatha: lampreys)
      • Jawed (Gnathostomes: includes most fish, amphibians, reptiles, birds, mammals)

Major Classes of Fish

  • Cartilaginous fishes (Chondrichthyes): sharks, skates, rays.
  • Bony fishes (Osteichthyes):
    • Class Sarcopterygii (lobe-finned fishes including lungfishes and coelacanths)
    • Class Actinopterygii (ray-finned fishes such as sturgeon, paddlefish, teleosts)

Fish Anatomy: Yellow Perch Dissection

  • Key structures include:
    • Nostril, gills, swim bladder, heart, liver, stomach, intestines, gonads, etc.
    • Gill anatomy vital for understanding gas exchange.

Gas Exchange in Bony Fishes

  • Countercurrent exchange:
    • Water and blood flow are opposite.
    • Maintains a favorable concentration gradient across the lamellae, enhancing oxygen extraction.

Homologies in Vertebrate Limbs

  • Definition of homology: Characteristics shared due to common ancestry.
    • Homologous structures may serve different functions.
  • Vertebrate forelimbs consist of the same foundational bones:
    • Examples: humerus, radius, ulna, carpals, metacarpals, phalanges in various animals such as humans, birds, and bats.

Dentition

  • Types of teeth:
    • Incisors, canines, premolars, molars.
  • Dental formula calculation:
    • E.g., Pig (Sus scrofa): I3/3 C1/1 P4/4 M3/3
    • Total = (3 + 3 + 1 + 1 + 4 + 4 + 3 + 3) x 2 = 44 teeth.

Comparisons of Dental Formulas in Animals

  • Common Examples:
    • Dog: I3/3, C1/1, P4/4, M2/3 = 42
    • Cat: I1-3/3, C1/1, P3/2, M1/1 = 30
    • Pig: I1-3/3, C1/1, P4/4, M3/3 = 44
    • Cow/Sheep: I1-0/4, C0/0, P3/3, M3/3 = 32.

These notes summarize the expected objectives, anatomical observations, important classifications, and key biological concepts related to vertebrate homologies and dentition as designed for Lab 11.