The move to Land / Amphibians Flashcards
1
Q
Features already evolved + needed for land
A
- 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
2
Q
Early Evolution Recipe for Terrestrial Tetrapods:
A
- Air-breathing adaptations
- Internal nares (nostrils; chemoreception, connected to pharynx)
- Air filled cavity (Vascularized lungs for effective gas exchange) - Double circulation
(lungs -> heart -> body -> heart -> lungs) - Bigger limbs
- Ossified paired limbs, for bearing weight
3
Q
“Amphibians”
A
- 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
4
Q
Superclass tetrapoda -> Crown Tetrapods
A
- Lissamphibia
5
Q
Lissamphibia
A
- living amphibians
- Frogs, toads, salamanders, newts, caecilians
- The “perfect water/land transition”
6
Q
Major Characteristics of Lissamphibia
A
- Still need water
- Eggs and larvae
- Thin skin! - Respiration can occur across the skin
- Ectothermic (body temp reliant on ext env)
7
Q
Skeleton: Adapted for Land
A
- Strong vertebrae with little flexibility
- Protection and muscle attachment
- Jumping and swimming
8
Q
Double Circulation
A
- 3-chambered heart
- 2 atria and 1 ventricle
- blood flows in both directions in ventricle
- Not as efficient
8
Q
Respiratory Mechanisms
A
- 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 - Buccopharyngeal breathing
- Vascular nets in mouth exchange O2 and CO2 - 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.) - At varrious stages, they may have external gills
- In general, larvae depend on gills for respiration
- Some adults too; e.g., axolotl, mudpuppy Necturus
9
Q
Hearing in air
A
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!
10
Q
Modern Lissamphibia Orders
A
- Order Gymnophiona
- Order Caudata
11
Q
Order Gymnophiona (AKA Apoda)
A
- “naked + of snake”
- The caecilians; > 200 spp.
- Limbless
- Internal fert
- oviparity and viviparity
- Burrowing, leaf litter
- Dark, moist
- Tropical
12
Q
Order Caudata (AKA Urodela)
A
- “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
13
Q
Salamander Reproduction
A
- 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
14
Q
Salamanders -> Newts
A
- Subfamily Pleurodelinae
- Still salamanders
- Aquatic with 3 developmental stages / 2 metamorphoses
