Diversity of Lissamphibians

Question 1

What does the clade amphibians include? What are two organisms that are amphibians but not part of Lissamphibia?

Answer 1

Amphibians are a paraphyletic clade, they are anamniotes, they contain all extant and fossil tetrapods except amniotes. The temnospondyls and the lepospondylys are two basal amphibians that lie outside of Lissamphibia

Question 2

What does the clade Lissamphibia include? What are the three clades contained within it?

Answer 2

Lissamphibia is a monophyletic clade that contains the last common ancestor of all extant amphibians and all its descendants and it is split into three clades. Anura, Urodela as well as Gymnophiona, and we are unsure of which is the most basal. They are all carnivorous and have diverse reproductive/parental strategies

Question 3

What are the three types of developmental regulation found in Lissamphibia? Describe them.

Answer 3

Heterochrony: changing the timing of developmental events, such as paedomorphosis which is retaining larval features as an adult, there are two types: Neoteny (deceleration of development) and progenesis (accelerated development of the reproductive organs)
Heterotrophy: changing the location of developmental events
Heterometry: changing the magnitude of developmental events (different morphologies)

Question 4

What are the diagnostic features of Lissamphibians? (5)

Answer 4

1. Thin/moist skin with reduced or absent keratinized layer, facilitates cutaneous respiration and had skin covered in mucus and poison glands
2. Pedicellate teeth, have two cusps and a flexible connections between the crown and the root, sometimes break in order to prevent damage to the jaw
3. Eye with green rods, specialized cells in the retina, facilitate blue/violet light detection, sensitive in low light conditions
4. Eye with m. levator bulbi muscle, which is a thin sheet of muscle ventral to eyeball, pulls eyes into oral cavity to facilitate swallowing
5. Inner ear with two types of papilla, basilar papilla (gathers air vibrations via the tympanic membrane), and the accessory papilla (gets vibrations from the ground through the operculum)

Question 5

What are the diagnostic features of Gymnophiona? (6)

Answer 5

1. Limbless
2. Eyes reduced or poorly developed
3. Pair of protrusible tentacles: moved by eye muscles and there is a moist gland called the Harderian gland which lubricates them, they are likely used to deliver odor molecules to the vomeronasal organ
4. Dual jaw closing mechanism using 2 muscles (m. adductor mandibularis, and m. interhyoideus)
5. Venom gland along jaw (pressure on teeth causes release of toxins)
6. Annuli rings all over body that mark the position of the ribs and have keratinized scales within them

Question 6

What are the two types of parental care seen in Gymnophiona? Which one do most species engage in?

Answer 6

1. Oviparous: 25% of species, lay eggs and make underground nests guarded by female, and they have a larval stage OR direct development, and females likely provide SOME nutrients after young are hatched
2. Viviparous: 75%, live birth, mother provides nutrients to the young via uterine milk (matrotrophy) or via lipid rich skin (dermatotrophy), and they make/guard the nest

Question 7

What is it called when mothers provide nutrients to their young in the form of uterine milk? What is is called when mothers provide nutrients to their young through lipid rich skin?

Answer 7

Matrotrophy and dermatotrophy