mammals day 1

Class Synapsida

  • New class name set to Synapsida.
      - Type of holes in skulls:
        - Synapsids: One hole
        - Diapsids: Two holes
        - Anapsida: Zero holes
      - Purpose of skull openings:
        - For jaw muscles.

  • Example: Coyote skull presented.
      - Key feature: Psychomatic arch - large hole for jaw muscles.
      - Relation to human anatomy: Similar arch present at the cheekbone where jaw muscles pass.

Subclasses of Synapsida

  • Two subclasses identified:
      1. Subclass Prototheria
         - Refers to early or primitive egg-laying mammals.
         - Historically referred to as Monotremata.
         - Examples of living Prototheria today:
           - Platypus
           - Echidna

  2. Subclass Theria
     - Comprised of marsupials (Metatheria) and eutherian mammals (placental mammals).
     - Metatheria: Pouch mammals such as the possum, primarily found in Australia and a few in South America.
     - Historical context of marsupials diversifying during Pangaea.

Evolutionary History

  • Ancestors of Mammals:
      - Most primitive mammals show the first fossilized evidence of synapsids, characterized by one skull opening.
      - First synapsids occurred in the Permian period, at the end of the Paleozoic era, coinciding with the early development of dinosaurs.
      - Synapsids eventually gave rise to therians, appearing early in the Mesozoic era during the Triassic period.

  • Key evolutionary adaptations in mammals:
      - Larger, stronger jaws (notably in males)
      - Greater diversity in teeth (important for mammalian diet).
      - Developments in appendage structure:
        - Quadrupedal mammals show ventrally located appendages for efficient movement; important evolutionary shift from amphibians to reptiles to mammals.

External Morphology

  • General characteristics inspected:
      - Mammalian anatomy uses common terms such as forehead, nose, mouth, etc.
      - Specific skeletal structures will correlate to human anatomy.

Integumentary System

  • Primary covering: Fur and hair in mammals.
      - In contrast to scales in reptiles and feathers in birds.
      - Functions:
        - Protection (first line of defense)
        - Waterproofing (due to keratin structure and oils)
        - Communication (emotional signals through fur standing up)
        - Camouflage (blending into environments)
        - Insulation (subcutaneous fat in cold climates)

  • Adaptive features:
      - Blubber in aquatic mammals like seals and polar bears aids in insulation and buoyancy.

  • Skin structure:
      - Epidermis: Outermost layer continuously lost and replaced.
        - Lives approximately 2 weeks before shedding.
      - Contains melanocytes responsible for producing skin pigment.
        - Individuals have similar numbers of melanocytes; variations in skin tone arise from differences in pigment concentration.
      - Dermis: Deeper, dense connective tissue that does not regenerate itself, leading to scarring.

Hair Structure

  • Components of hair:
      - Hair shaft: Visible part above the skin's surface; primarily dead keratinized cells with no pain sensation.
      - Root: Below the surface; contains living cells.
      - Hair bulb: Base of the root where the hair grows; involved in mitosis.
      - Hair papilla: Stimulates hair growth.
      - Medulla, cortex, cuticle: Layers of hair each with differing roles and structures relevant for pigmentation.

  • Coloration of hair:
      - Primarily linked to melanin levels, with different pigments leading to variations in shades.
      - Aging leads to diminished pigment production leading to gray or white hair, depending on the loss of melanin.

  • Hair anatomy specialization:
      - Differences in hair textures (straight, wavy, curly) due to cross-sectional shape.

Hair Follicle Anatomy and Function

  • Muscle associated with hair:
      - Arrector pili muscle: Causes hair to stand upright in response to stimuli (warming, fear).
      - Leads to goosebumps or piloerection in mammals.
      - Functions as insulation and creates an emotional response visually observed.

  • Hair layers:
      - Medulla: Inner core, predominantly where pigment is found.
      - Cortex: Middle layer containing keratin and pigment.
      - Cuticle: Outermost protective layer with scales resembling reptilian scales, providing structural integrity.

  • Scientific relevance:
      - Hair structure variation can be used for species identification in forensics, based on shape and hair scale patterns.