Revisão do Ramo Gondwânico da família Mawsoniidae (Sarcopterygii: Actinistia: Coelacanthiformes)

Abstract

Represented at the present with only two species: Latimeria chalumnae and Latimeria medadoensis, the coelacanth (Infraorder: Actinistia) were once a very numerous and prolific group since their dawn in the Lower Devonian. Amongst the Actinistia, the family Mawsoniidae stands out for harboring the biggest species in the group, some reaching three meters in length. The entry of the Mawsoniidae family on the Gondwana continent happened during Upper Jurassic, period attributed to the species Parnaibaia maranhoensis from the Parnaíba basin (Maranhão). During the Cretaceous, the family branched into two distinct genus: Mawsonia (known from Brazil and Africa) and Axelrodichthys (a Brazilian genus with unconfirmed African occurrences). The goal of this work was to make a redescription and comparison of six species of the Gondwana branch of the Mawsoniidae family: Parnaibaia maranhoensis, Axelrodichthys araripensis, Mawsonia gigas, M. minor, M. lavocati e M. brasiliensis. The specimens are located in eight institutions: three nationals and five internationals. After a thorough anatomical description of the specimens, characters were selected for a phylogenetic analysis, restricted to the group. The results of the anatomical observations revealed several structures not described in previous literature, including the first medial element of the appendicular skeleton of the Mawsoniidae family ever to be observed, aside from differences and affinities between the six species. P. maranhoensis presented a set of plesiomorfic characters that were interpreted as being the result of a neotenic event, something not yet described in the specialized literature. Every species of the genus Mawsonia showed diagnostic characters that validate their respective status as a distinctive species. The phylogenetic analysis resulted in two trees equally parsimonious. Both agreed with the position of Parnaibaia, at the base of the group. However, differ in relation to the position of Axelrodichthys as a genus separate from Mawsonia. It is concluded that Parnaibaia is the most plesiomorfic genus of the group being at the base of the Gondwana branch of the family. Axelrodichthys represents the link of Parnaibaia and the other species of the group.