One group of bony fishes, the lobe-finned fishes (Sarcopterygii), developed strong, muscular fins
that allowed them to crawl along dry stream beds during times of desiccation. Their lungs allowed them to
breathe air when stranded out of water, and their development of nasal passages (choanae) with
internal nares allowed them to breathe air without opening their mouths. It was from these lobe-finned
fishes that the first amphibians evolved.
The Amphibia develop from gill-breathing aquatic larvae that usually undergo metamorphosis
into air-breathing adults. Early amphibians had a sprawling posture still seen in modern salamanders. Many early
amphibians were well-armored, but their modern descendents all have skins that must be kept moist and slippery.
- Subclass Sarcopterygii
- Air-breathing adaptations
- Lungfishes
- Crossopterygii
- Preadaptations and the transition to land
- Class Amphibia
- The earliest amphibians: Ichthyostegids, Acanthostegids
- Adaptations for living on land
- Limb posture
- Vertebrae and support
- Temnospondyls
- Anthracosaurs: Embolomeres and reptile ancestors (Seymouriamorphs)
- Lepospondyls
- Modern amphibians: salamanders and caecilians
- Modern amphibians: anurans
Illustrations
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