Reappraisal of the lower actinopterygian Birgeria stensioei Aldinger, 1931 (Osteichthyes; Birgeriidae) from the Middle Triassic of Monte San Giorgio (Switzerland) and Besano (Italy)

Abstract

Classic descriptions and a previous reconstruction of the Middle Triassic ray-finned fish Birgeria stensioei Aldinger, 1931 from the Besano Formation (= Grenzbitumenzone) of Monte San Giorgio (Canton Ticino, Switzerland) and Besano (Lombardy, Italy) relied either on poor material or on a single specimen only. This study of B. stensioei is based on 67 specimens from that region in the Southern Alps including the lectotype of B. stensioei. The reappraisal of B. stensioei indicates that this species differs from the other known species of the genus Birgeria in several respects, most notably in the arrangement of the pterygiophores of the dorsal fin. B. stensioei is also distinct to certain other species of Birgeria in having a largely unossified brain case. Furthermore, the palatoquadrate of B. stensioei is ossified as the autopalatine, the metapterygoid and the quadrate, which are always found separate. An ossified autopalatine and metapterygoid was not described in Birgeria so far. A dermohyal is developed in B. stensioei and this bone is probably also present in the other species of the genus Birgeria.