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The dentition of lungfish is conspicuously different from that of any other vertebrate group. Odontodes on the palate and lower jaws develop in a series of rows to form a fan-shaped occlusion surface. These odontodes then wear to form a uniform crushing surface. In several groups, including the modern lepidosireniformes, these ridges have been modified to form occluding blades.
The modern lungfishes have a number of larval features, which suggest paedomorphosis. They also demonstrate the largest genome among the vertebrates.
Modern lungfish all have an elongate body with fleshy paired pectoral and pelvic fins and a single unpaired caudal fin replacing the dorsal, caudal, and anal fin of most fishes.
African and South American lungfish are capable of surviving seasonal drouts by burrowing into mud and estivating throughout the dry season. Changes in physiology allow the lungfish to slow its metabolism to 1/60th of the normal metabolic rate, and protein waste is converted from ammonia to less-toxic urea (normally, lungfish excrete nitrogenous waste as ammonia directly into the water). Burrowing is seen in at least one group of fossil lungfish, the Gnathorhizidae.
Lungfish are best-known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Today, they live only in Africa, South America, and Australia. While vicariance would suggest this represents an ancient distribution limited to the Mesozoic supercontinent Gondwana, the fossil record suggests that advanced lungfish had a cosmopolitan freshwater distribution and that the current distribution of modern lungfish species reflects extinction of many lineages following the breakup of both Pangea and subsequently Gondwana and Laurasia.
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