Air-breathing evolved in fishes during the Silurian, prior to the conquest of terrestrial environments, as the first air-breathing groups were still aquatic forms. Among fossil fishes and stem-tetrapods, the air-breathing behaviour was described based on anatomical structures and organs, such as spiracles, skeletal buccal pump components, cranial ribs, well-developed pleural ribs, integumentary dermal skeleton, choanae and calcified lungs. However, due to the rarity of soft tissue preservation in the fossil record, the presence of lungs is mostly described among fossil coelacanths, which present a pulmonary complex covered by ossified lung plates throughout its length. Here, we describe the main differences among fossil coelacanth lungs, review some of the accessory air-breathing structures in fossil fishes and stem-tetrapods and discuss the air-breathing evolution that enabled the rise and development of early vertebrates on the terrestrial environment.

Introduction

Fossil fishes are abundant in the Nova Olinda Member of the Crato Formation, where the ichthyofauna is dominated by the gonorynchiform Dastilbe crandalli (Figures 12.1b, 12.3c, 12.4a–12.4e). Fishes also occur, but more rarely, in the transition beds beneath the Nova Olinda Member at Cascata. Other fish taxa include the ophiopsid Placidichthys bidorsalis, the ichthyodectiform Cladocyclus gardneri, an undescribed amiiform, and rare occurrences of the semionotiform cf. Araripelepidotes sp. and the coelacanth Axelrodichthys sp. Except for Dastilbe and the amiiform, all the taxa cited above are well known and considerably more abundant in the slightly younger Romualdo Member of the Santana Formation of the same basin.

Recent collecting has yielded the semionotiform Lepidotes sp., a single specimen of the aspidorhynchiform Vinctifer longirostris and rare specimens of the tiny ostariophysan Santanichthys sp.

Many of the fishes occur as fully articulated skeletons with scales intact, and occasionally with in situ stomach contents. Partially articulated portions of fishes occur and may represent the relics of prey items, or portions from partially decomposed individuals. Isolated bones and scales also occur. Fishes are most frequently found preserved in left or right lateral view, with examples only rarely occurring in dorsal or ventral aspect. Bedding planes may contain several individuals of the same size (usually juveniles), suggestive of mass-mortality assemblages.

Introduction

The Anura – frogs and toads of common parlance – comprise about 5,250 extant species with a near world wide distribution, excluding only Antarctica, the highest latitudes of the Northern Hemisphere and the marine realm. Their unique morphology, physiology and behavioural adaptations allow anurans to inhabit a wide range of environments, from the arctic tundra to hot arid deserts. However, they achieve their maximum diversity in the Neotropical rainforests (Duellman and Trueb, 1994; Hofrichter, 2000), where they prefer moist environments. Most species are required to return to freshwater environments for the development of their larvae.

Their temporal range begins in the Triassic if the pro-anurans of Madagascar and Poland are considered anurans. True anurans are relatively scarce in the Mesozoic, only becoming common and diverse in the Cenozoic (Roček, 2000). The earliest occurrence of a true anuran is Prosalirus bitis Shubin and Jenkins, 1995, from the Lower Jurassic of Arizona. This taxon achieved the basic anuran body plan that has persisted without significant modification for approximately 200 myr. Of the present 33 anuran families, five have a fossil record extending to the Mesozoic (Leiopelmatidae, Discoglossidae, Pipidae, Pelobatidae and Leptodactylidae), and one family, † Palaeobatrachidae, is exclusively Mesozoic. All but the † Palaeobatrachidae occur in Gondwana (Roček, 2000; Gao and Chen, 2004).

Anurans were first reported in the Crato Formation by Kellner and Campos (1986), where they occur only in the Nova Olinda Member (see Maisey, 1991: 325 for figure).