Chapter 10 - Salamanders, Anurans, and Caecilians

Question 1

Important Extinct Species in the Movement to Land - Tiktaalik

Answer 1

• Intermediate between fish and tetrapods (not a true tetrapod)
• Well-developed gills
• Poorly ossified vertebrae
• Long body
• Large overlapping ribs (more necessary for terrestrial movement)
• Pectoral fin could bend

Question 2

Important Extinct Species in the Movement to Land - Acanthostega

Answer 2

• Early tetrapod that was mostly aquatic in nature

- Short ribs, wrists, and ankles making it incapable to bear complete weight on land

Question 3

Important Extinct Species in the Movement to Land - Ichthyostega

Answer 3

• early tetrapod with modifications for living both an aquatic and terrestrial life
• Ribs at base of tail for swimming (First three adaptations for water)
• Robust paddle like hind-limbs
• Ear specializations for hearing under waters
• Distinct thoracic and lumbar regions of the spine (Last three - adaptations for land)
• Robust overlapping ribs
• Bendable, weight supporting elbow

Question 4

Tetrapoda Synapomorphies

Answer 4

• Tetrapody - having four limbs; two connected to the pectoral girdle and the other two connected to the pelvic girdle
• Pentadactly - possession of five digits
• Modified pectoral and pelvic girdle - allows for the weight of the body to be transferred to the limbs
  • Supracleitherum is absent causing the connection to the skull to be lost (bone that connects pectoral girdle to the skull - lost)
  • Scapula is enlarged for attachment of limbs
  • Pelvic girdle is greatly enlarged

-Two skeletal modifications that allow for greater mobility of the skull:

 - Atlas - (first cervical vertebrae) is modified on its anterior surface to form atlantal condyles, which are two cup-shaped structure that form joints with occipital condyles 
 - Development of two occiptal condyles on the posterior end of the skull (Both of these adaptations allow for the movement of the head - up and down)

• Rib Modifications
  • Cervical ribs are short
  • Thoracic ribs are elongated and connected to the sternum (to form a protective cage for lungs/heart)
  • Lumbar ribs are short or absent
  • Sacral ribs are connected to pelvic girdle and are immobile
• Dermal body armor is greatly reduced or absent
• Muscular tongue allows for feeding out of water
• Middle ear components: Tympanum and Stapes allow for transmission of sound
• Eyelids to protect the eye and keep in moisture