New information on the Eocene frog Thaumastosaurus (Anura, Pyxicephalidae) from the Phosphorites du Quercy, France

Abstract

Abstract We present new disarticulated cranial elements of the Eocene frog Thaumastosaurus from several localities in the Phosphorites du Quercy, France, providing novel information about the variation of its anatomical characteristics. With the use of micro-computed tomography (μCT) scanning technology, we examine and discuss various types of dermal cranial ornamentation in extant Pyxicephalus, the closest extant relative of Thaumastosaurus, in which these features are useful in species diagnoses, paying particular attention to the individual and ontogenetic variation, and sexual dimorphism, as well as interspecific variation among extant species. We suggest that various types of dermal cranial ornamentation in Thaumastosaurus could be potentially used in diagnoses at species level, although ontogenetic variation should be taken into consideration. Apart from ornamentation, the size and general morphology of the maxillae and squamosa in Thaumastosaurus reveal an unexpected disparity of morphotypes, which suggests the potential presence of cryptic taxa. Some squamosa reveal that their processus zygomaticus extended up to the postnasal wall, so their associated maxillae were excluded from the orbital margin, whereas others were short and their respective maxillae participated in the formation of the orbital margin. Thaumastosaurus is envisaged as the product of an Early Palaeogene direct, potentially overseas, dispersal from isolated Afro-Arabia to Europe.