Physiological Evidence Indicates Lungfish as a Sister Group to the Land Vertebrates

Abstract

Abstract Current research tends to support that lungfish (Dipnoi) and land vertebrates (Tetrapoda) form a sister group, which has stimulated an interest in these animals. The extant lungfish include: Protopterus, the African lungfish (four species) and the South American lungfish (Lepidosiren paradoxa) (one species). The African and South American lungfish have well-developed lung and reduced gills, while the Australian lungfish (Neoceratodus forsteri) is highly dependent on the gill ventilation, and its lung is one of the simplest among vertebrates. Lungfish and land vertebrates share many features of respiratory control. Lepidosiren (and probably Protopterus possess central cerebral CO2 and H+ receptors, which regulate acid–base by increases or decreases in pulmonary ventilation. This regulatory pattern is also valid for land vertebrates, including human beings. By contrast, teleost fish lack central CO2/H+-receptors, which suggests that the lung and the central chemoreceptors evolved together. In this context, any very specific features are common to lungfish and land vertebrates, and these include the Hering–Breuer reflex and the presence of very specific stretch receptors.