Abstract Joseph Mawson, a nineteenth-century British railway engineer and businessman in Brazil, discovered fossils from the Cretaceous of Bahia that were described by E. D. Cope and Arthur Smith Woodward. A biographical outline of Mawson is presented. Mawson’s discoveries (especially the giant coelacanth fish Mawsonia , named after him by ASW) are interpreted today in the light of modern geological investigations. Mawsonia apparently lived in fluvial, lacustrine and brackish-water habitats in western Gondwana at the time South America separated from Africa. From the Late Jurassic until the Barremian, Mawsonia was widespread across western Gondwana, but its Aptian–Cenomanian records in South America are restricted to northeastern Brazil (including the Borborema tectonic province and adjacent areas to its north). In contrast, Mawsonia remained widespread in the Aptian–Cenomanian of Africa. Recently published data suggest that northeastern Brazil was still contiguous with Africa in the Aptian/Albian, although it was probably separated from the rest of South America by an epicontinental seaway that apparently followed an unconventional course across the Brazilian interior rather than along the present-day coastline. Aptian–Cenomanian records of Mawsonia and other non-marine taxa (including tetrapods) in northeastern Brazil may therefore represent ‘African’ rather than ‘South American’ biotas.

Abstract The Cretaceous actinistian Mawsonia is represented by more than 360 dissociated, but well-preserved, bones obtained from the Areado Group in the Sanfranciscana Basin of Minas Gerais, Brazil. These are among the oldest records of Mawsonia (Berriasian, Lower Neocomian) and include previously undescribed or poorly known skeletal elements (e.g. splenial, dentary, autopalatine, zygals). The new material is referred to the type species, M. gigas . Morphological variation in the sample blurs some of the distinctions formerly drawn between nominal species of Mawsonia , and species level diversity in the genus is difficult to establish. Mawsonia ubangiensis , M. libyca , and M. brasiliensis are considered to be junior subjective synonyms of M. gigas. Mawsonia gigas probably appeared prior to the separation of S America and Africa and became widespread throughout much of western Gondwana (including parts of Africa), even surviving briefly on both continents following their separation. Mawsonia tegamensis is a morphologically distinctive Late Cretaceous African species with no evident fossil record in Brazil and which probably arose by vicariant speciation following isolation of a local Mawsonia population during the later stages of rifting between Northern Africa and the rest of Western Gondwana. Similarities between Axelrodichthys , Lualabaea (here regarded as Early Cretaceous in age) and recently described fossils from Morocco, Niger, and Madagascar suggest the presence of a second endemic Cretaceous mawsoniid lineage in northeastern Brazil and Africa.