Pipimorpha and its crown-group Pipidae possess one of the most extensive fossil records among anurans, known since the Early Cretaceous in both Laurasia and Gondwana. Pipimorph diversification may have been driven by the breakup of West Gondwana during the Cretaceous. Numerous fossils from South America have been unearthed in the last decade, documenting this event. Unfortunately, Cretaceous pipimorphs from Africa have been limited to a few wellpreserved taxa from sub-Saharan Africa and the Arabian Peninsula, which hinders our comprehension of pipimorph diversification during this key period. The site of In Becetèn, in south-east Niger, is one of the few mid-Late Cretaceous (Coniacian–Santonian) sites from which a pipid, Pachycentrata taqueti, is known. Here, we describe and name a second pipid from the same locality. This taxon is known by a relatively complete braincase. Phylogenetic analyses confirm its position as a pipid, with pipinomorph affinities. This makes In Becetèn the oldest site with at least two pipids. Phylogenetic results are congruent with recent pipimorph relationships, with the presence of an endemic extinct clade in South America, Shelaniinae. The phylogenetic results also allow us to review the proposed definition for Pipimorpha and its subclades and propose new systematic definitions for them. Temporal calibration of the phylogenetic tree based on the fossil record suggests that pipimorphs diversified in a western Gondwana block and confirms that South America separated from Africa around the mid-Cretaceous. Between these two events, pipids diverged in Africa, giving rise to major extant clades. This study highlights the importance of Africa for early pipid diversification during the Cretaceous and of the opening of the Southern Atlantic Ocean for anuran dispersion and diversification.
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RBINS Staff Publications 2023 OA
An exceptionally well-preserved new acanthothoracid (placoderm fish) presenting complete endocranium and skull roof, from Saudi Arabia (Qasr Limestone Member, Jauf Formation), Early Devonian in age, is described as Arabosteus variabilis n. gen., n. sp. Compared to other Acanthothoraci, the new taxon exhibits a skull roof variable in its dermal plate distribution (e.g., a supernumerary plate: the posterior central plate) and sensory line pattern. Even the different specimens of this taxon show such variability between them. Arabosteus variabilis n. gen., n. sp. enlarges the scope of our knowledge of Acanthothoraci and Placodermi in general. Traditionally, the Arthrodira, one of the historically earliest described groups, provide the standard reference model for the placoderm skull roof pattern. The interpretation of the acanthothoracid skull roof pattern of the Saudi taxon from an arthrodiran model and the establishment of homologies is impossible to resolve unless based on prior assumptions (e.g., hypothesis of fragmentation or fusion for the paranuchal plate complex). The lateral line system of A. variabilis n. gen., n. sp. is unstable (e.g., presence or absence of the postmarginal sensory line canal) making it ambiguous to define bone homology and terminology. Consequently spatial distribution of skull roof plates has been retained for such a task with a minimal reference to the instable features of the sensory line groove distribution.
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