Abstract
The non-mammalian therapsids comprise a paraphyletic assemblage of Permian-Jurassic synapsids closely related to mammals that includes six major clades of largely unresolved phylogenetic affinity. Understanding the early evolutionary radiation of therapsids is complicated by a gap in the fossil record during the Roadian (middle Permian) known as Olson’s gap. Because of its early stratigraphic occurrence and its primitive features, Raranimus dashankouensis, from the Dashankou fauna (Rodian), Qingtoushan Formation (China), is currently considered the best candidate to fill this gap. However, it is known from only a single specimen, an isolated snout, which limits the amount of usable phylogenetic characters to reconstruct its affinities. In addition, understanding of the stratigraphy of the Qingtoushan Formation is poor. Here, we used CT scanning techniques to digitally reconstruct the bones and trigeminal canals of the snout of Raranimus in 3D. We confirm that Raranimus shares a high number of synapomorphies with more derived therapsids and is the only therapsid known so far to display a “pelycosaur”-like maxillary canal bearing a long caudal alveolar canal that gives off branches at regular intervals. This plesiomorphic feature supports the idea that Raranimus is basal to other therapsids.
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Acknowledgements
We acknowledge the help of Dr. Jörg Fröbisch, Dr. Adam Huttenlocker, and Dr. Kenneth Angielczyk for their helpful reviews and comments on the manuscript, and Prof. Matthias Waltert for his help in the review process.
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This research is supported by the African Origins Program of the National Research Foundation, the DST-NRF Centre of Excellence in Palaeosciences, the Postgraduate Merit Award of the University of the Witwatersrand, and the Strategic Priority Research Program of Chinese Academy of Sciences (XDB26000000).
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Communicated by: Aurora Grandal-d’Anglade
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Miss Alienor Duhamel wrote the manuscript. Dr. Julien Benoit, Prof. Bruce Rubidge, and Dr. Jun Liu made extensive corrections and comments during the writing process. Dr. Jun Liu wrote the geological section.
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Original scan data (data sets IVPP V 15424.CT01) for the specimen are available by request from the Collection House of IVPP (bbg@ivpp.ac.cn) or on ADMorph: http://dx.doi.org/10.12112/R.0006.
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Duhamel, A., Benoit, J., Rubidge, B.S. et al. A re-assessment of the oldest therapsid Raranimus confirms its status as a basal member of the clade and fills Olson’s gap. Sci Nat 108, 26 (2021). https://doi.org/10.1007/s00114-021-01736-y
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DOI: https://doi.org/10.1007/s00114-021-01736-y