New findings of the coelacanth Mawsonia Woodward (Actinistia, Latimerioidei) from the Late Jurassic – Early Cretaceous of Uruguay: Novel anatomical and taxonomic considerations and an emended diagnosis for the genus

Abstract

New findings of Mawsonia from the Juro-Cretaceous Tacuarembó Formation (Uruguay) are presented. The new materials have taphonomic and anatomic significance, considering the biofabric and state of preservation of most of the bones. The most complete specimen studied is represented by several cranial and postcranial remains found in spatial association, including skull roof, cheek bones and opercula, neurocranium, palate, lower jaw, branchial and hyoid apparatuses; and also part of the shoulder and pelvic girdles. The present record is also complemented through the finding of several isolated bones from other individuals. General morphology of the bones, postparietal shield configuration and external ornamentation of dermic bones, allow to refer all the specimens to the species Mawsonia gigas. It is considered that the most complete specimen studied in this work constitutes one of the anatomically most informative records referable to this species, and to the genus, considering the following arguments: The presence of complete bones scarcely represented in previous records due to its delicate configuration, and the fact that all the remains are three-dimensionally preserved (being completely released from their sedimentary matrix). The new information provided by the comparative analyses is used for the following purposes: Bring a critical anatomical description, complement the diagnosis of the genus, and discuss previous taxonomic and ontogenetic hypotheses. The comparative analyses support previous taxonomic proposals, regarding the existence of morphological, size and ornamental variabilities, which as a whole characterize M. gigas and place it as the only recognizable species referable to this genus in South America.