From Devonian Radiation to the Breakup of Gondwana: 400 Million Years of Lungfish Evolution

Oct 4

6 min read

Today, lungfishes are restricted to Africa, South America, and Australia, with only six living species. Early in their history, however, lungfishes underwent a remarkably rapid burst of morphological evolution. They later shifted from predominantly marine environments into freshwater, while their diversity rose and fell through time. By the Mesozoic, the progressive breakup of Gondwana further isolated the surviving lungfish lineages, eventually leaving them separated across three widely distant continents.

Lungfishes (Dipnoi) are sarcopterygians, or lobe-finned fishes, and living lungfishes form the sister lineage to tetrapods. Their evolutionary history therefore offers an important window into how early sarcopterygians reorganized the skull and feeding apparatus during the early stages of their diversification.

The Early Devonian lungfish Diabolepis speratus, discovered in Yunnan, China, and dating to the late Lochkovian around 415 million years ago, possesses a striking mixture of primitive and lungfish-like features. Parts of its skull still resemble those of more basal sarcopterygians, whereas its palate and lower jaw already show clear specializations associated with lungfishes. Diabolepis has consequently been placed very close to the base of lungfish evolution, and later phylogenetic analyses have generally regarded it as one of the earliest and most morphologically primitive known lungfishes. Even at this early stage, Diabolepis already possessed a well-developed feeding apparatus associated with durophagy. Its upper and lower jaws bore radiating tooth plates composed of non-shedding teeth, its mouth provided a broad palatal biting surface, and its lower jaw was relatively short, with the two halves firmly united at the mandibular symphysis. Together, these features would have been well suited for crushing hard-shelled prey or prey protected by a tough exoskeleton.