The smallest known Devonian tetrapod shows unexpectedly derived features

• Published in: Royal Society Open Science
• Main Authors: Ahlberg, Per E., Clack, Jennifer A.
• Format: Text
• Language: English
• Published: The Royal Society 2020
• Subjects: Organismal and Evolutionary Biology; Britta Dal; Fang; Fossa; Greenland; Stensiö Bjerg; East Greenland
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7211834/; https://doi.org/10.1098/rsos.192117

A new genus and species of Devonian tetrapod, Brittagnathus minutus gen. et sp. nov., is described from a single complete right lower jaw ramus recovered from the Acanthostega mass-death deposit in the upper part of the Britta Dal Formation (upper Famennian) of Stensiö Bjerg, Gauss Peninsula, East Greenland. Visualization by propagation phase contrast synchrotron microtomography allows a complete digital dissection of the specimen. With a total jaw ramus length of 44.8 mm, Brittagnathus is by far the smallest Devonian tetrapod described to date. It differs from all previously known Devonian tetrapods in having only a fang pair without a tooth row on the anterior coronoid and a large posterior process on the posterior coronoid. The presence of an incipient surangular crest and a concave prearticular margin to the adductor fossa together cause the fossa to face somewhat mesially, reminiscent of the condition in Carboniferous tetrapods. A phylogenetic analysis places Brittagnathus crownward to other Devonian tetrapods, adjacent to the Tournaisian genus Pederpes. Together with other recent discoveries, it suggests that diversification of ‘Carboniferous-grade’ tetrapods had already begun before the end of the Devonian and that the group was not greatly affected by the end-Devonian mass extinction.