The move to Land / Amphibians

Question 1

Features already evolved + needed for land

Answer 1

• Nares, lungs, and limbs already present in Devonian “fishapods” -> punting in and partly out of shallow waters
• More structural support in limps (and ribs) further evolved for possible move on land in the Carboniferous

Question 2

Early Evolution Recipe for Terrestrial Tetrapods:

Answer 2

1. Air-breathing adaptations
   - Internal nares (nostrils; chemoreception, connected to pharynx)
   - Air filled cavity (Vascularized lungs for effective gas exchange)
2. Double circulation
   (lungs -> heart -> body -> heart -> lungs)
3. Bigger limbs
   - Ossified paired limbs, for bearing weight

Question 3

“Amphibians”

Answer 3

• Tetrapods that are NOT Amniotes
• Early Terrestrial Tetrapods and divergence of Toes:
  1. “Lepospondyls”: 5 toes, closely related to Amniotes?
  2. “Anthracosoars” / “Reptiliomorphs”: 5 toes, gave rise to Amniotes?
  3. Temnospondyls: 4 toes, gave rise to Lissamphibians

Question 4

Superclass tetrapoda -> Crown Tetrapods

Answer 4

1. Lissamphibia

Question 5

Lissamphibia

Answer 5

• living amphibians
• Frogs, toads, salamanders, newts, caecilians
• The “perfect water/land transition”

Question 6

Major Characteristics of Lissamphibia

Answer 6

1. Still need water
   - Eggs and larvae
   - Thin skin!
2. Respiration can occur across the skin
3. Ectothermic (body temp reliant on ext env)

Question 7

Skeleton: Adapted for Land

Answer 7

• Strong vertebrae with little flexibility
• Protection and muscle attachment
• Jumping and swimming

Question 8

Double Circulation

Answer 8

• 3-chambered heart
• 2 atria and 1 ventricle
  
  • blood flows in both directions in ventricle
  • Not as efficient

Question 8

Respiratory Mechanisms

Answer 8

1. Cutaneous (skin) respiration important!
   - In general, respiration also occurs across skin in adults
   - Thin skinned! Not a strong barrier like amniote’s skin
   - vascular nest in skin exchange O2 and CO2
   - Mucousy and smooth, easy passage of chemical and water
2. Buccopharyngeal breathing
   - Vascular nets in mouth exchange O2 and CO2
3. Pulmonary respiration
   - O2 and CO2 exchange in lungs (ventilated via buccal pumping)
   - In general, gills are lost and lung are activated in adults
   - Only 1 salamander terrestrial family (Plethodontidae) has no lungs (also caecillian spp.)
4. At varrious stages, they may have external gills
   - In general, larvae depend on gills for respiration
   - Some adults too; e.g., axolotl, mudpuppy Necturus

Question 9

Hearing in air

Answer 9

Tympanum (Anurans)
- Membrane transmits sound to inner ear bone (columella; does not process sound; high frequencies)
- Can also hear with lungs and low frequencies via forelimbs!

Question 10

Modern Lissamphibia Orders

Answer 10

1. Order Gymnophiona
2. Order Caudata

Question 11

Order Gymnophiona (AKA Apoda)

Answer 11

• “naked + of snake”
• The caecilians; > 200 spp.
• Limbless
• Internal fert
  
  • oviparity and viviparity
• Burrowing, leaf litter
  
  • Dark, moist
• Tropical

Question 12

Order Caudata (AKA Urodela)

Answer 12

• “tail + evident”
• Newts + salamanders; > 700 spp
• Limbs at right angles
• Normally small (<15 cm) but can be huge (1.5 m)
• Various ecological traits:
  
  • fully aquatic to terrestrial
  • can regenerate lost limbs
• Mostly in temperate regions

Question 13

Salamander Reproduction

Answer 13

• Internal fert with spermatophores
• no copulation (female inseminates herself)
• Aquatic species lay eggs in clusters or stringy masses
• Completely terrestrial species deposit eggs in small, grape-like clusters under logs or in soft earth
• Terrestrial species undergo direct development
• hatch as miniature adults

Question 14

Salamanders -> Newts

Answer 14

• Subfamily Pleurodelinae
• Still salamanders
• Aquatic with 3 developmental stages / 2 metamorphoses

Question 15

Paedomorphosis

Answer 15

• “child form”
• Reach sexual maturity while retaining gills and other larval characters
• Mudpuppies (Necturus) and axolotls

Question 16

Terrestrial Metamorphosis

Answer 16

• E.g. tiger salamander

Question 17

Order Anura (AKA Salientia)

Answer 17

• “without + tail”
• Frogs & Toads; ~7000 spp.
• All have metamorphosis phases
  
  • egg -> tadpole -> adult
• All have tailed larvae (tadpole)
  
  • all oviparous
  • Become tail-less as adults
  • Tadpoles have a different lifestyle
• Near-global distribution

Question 18

Common Anurans

Answer 18

Family Ranidae
- Most frogs we see in North America
Family Hylidae
- Mostly tree frogs
- Spring Peeper is the only NS Tree Frog!
Family Bufonidae
- Toads!

Question 19

Anuran Feeding

Answer 19

• Sticky slinging tongue, attached to the front!
• Swallow with eyes!

Question 20

Anuran Adaptations for Jumping & Swimming

Answer 20

• Vertebral column lost much flexibility in order to transmit force from limbs to body
• Extremely shortened body
  
  • Only 9 trunk vertebrae & a
    urostyle

Question 21

Frog Mating

Answer 21

• External fert
  
  • Amplexus mating position
• Large masses of eggs
  
  • Jelly expands in water