Zool 406 -Amphibian developement, morphology & origins

What lifestyle do most amphibian larvae have?

• Free living

• Most feed, but some need yolk

• All aquatic larvae (some exceptions)

How are Caecilian and Salamander larvae similar?

• Juveniles resemble adults

• Metamorphosis gradual

What is the morphology of amphibian larvae?

• Large, lidless eyes

• Non-valvular nares

• Muscular trunk and tails

• Cartilagenous

• Lateral line system

T/F amphibian larvae have gills?

True,

They can have pharyngeal slits, external gills or internal gills

What does metamophoss look like in amphibians?

• Hind limbs appear late in development (non functional until metamorphosis)

• Operculum grows over gills = spiracles

• @ metamorphosis front legs break through operculum

What are the various styles of feeding (oral disk) in tadpoles?

• Ventral horizontal (suctorial, anchor and scrape)

• Dorsal horizontal (surface grazing)

• Round to dumbbell shaped

• Keritinous beaks or rows of keratinous denticles

• Large oropharyngeal cavity; pumps water for gills

What is the morphology of Caecilians?

• Limbless; Lost pectoral and pelvic girdle elements

• Cylindrical, segmented bodies

• Blunt head, underhung lower jaw

• Degenerate eyes

• Tail short or absent

• Most fossorial others aquatic

What is the morphology of caudata?

• Low-slung bodies, moderate limb length and long tail

• Broad head, with distinct neck

• Distinct eyes

• Half are terrestrial, half are aquatic

• Some are aquatic with reduced limbs

What is the morphology of anura?

• Completely adapted for saltatory locomotion

• Short body, broad head, no neck, no tail

• Well-developed limbs

• Few entirely aquatic, most terrestrial or semi-terrestrial

What is the morphology of Rhidistian fishes?

• Notochord prominent, ossified arches

• Lobe fins

• Shallow water habitat

• Cranial kinesis

• Labrynthodont teeth

What is the morphology of Labrinthodonts?

• Bony Scales

• Lateral Line System

• Labyrinthodont teeth

—> Contains Temnospondyls; Ichthyosterga, Aconathostega

What traits do temnospondyls share with amphibians?

Metamorphosis

What is Romers gap?

A 30 million year gap between Acanthostega type forms and fully terrestrial forms

When did Lissamphibia (monophyletic) arise? what did they look and act like?

Arose ~200 mya in the Early Jurassic period

• Terrestrial but lay eggs in the water and have aquatic larvae

• No extra-embryonic membranes in egg

• Small, cutaneous respiration

What are the four hypothesis for the origin of amphibians from Lissamphibia?

1. Each amphibian group comes from different fossil groups

2. Two different origins: temnospondyls and microsaurs

3. Monophyletic lissamphibia from temnospondyls

4. Monophyletic lissamphiba from leposondyls

Explain the hypothesis that each lissamphibia group comes from a different fossil group?

• Temnospondyls → frogs

• Microsaurs → Caecillians

• Different microsaurs → Salamanders

Probably not correct

Explain the hypothesis that there are two different origins of lissamphibians?

• Dissorophoid temnospondyls → frogs and salamanders

• Microsaurs → Caecilians

Explain the hypothesis for monophyletic lissamphibians from temnospondyls?

Pedicellate teeth, open palate

Shares:

• With frogs a large orbit, circumorbital bones and stumpy ribs

• With salamanders inferred ossification patterns

• With caecilians maybe heavy closed caecilian skull

Explain the hypothesis for monophyletic lissamphibians from Lepospondyls?

Reduced skulls, absence of labyrinthodont teeth, reduced limbs and girdles

What was the earliest form of Caudata? when did they appear?

Karaurus sharovi

• Late Jurassic ~152 mya

What was the earliest form of Gymnophiona? when did they appear?

Eocaecilia micropodia

• Early Jurassic

What was the earliest form of Anura? when did they appear?

Vicerella 

• first modern type

• Early Jurassic

Triadobatrachus 

• Link between dissorophids and primitive frogs

• Early Triassic

Whatis distinct about the group Albanerpetondidae?

• Stem Caudata, Batrachia (F+S) or Lissamphibia

• Middle Jurassic – Early Pliocene ~170 mya

• Salamander-like appearance, characteristics of salamanders + caecilians