Pterosaur remains from uppermost Lower Cretaceous (Albian) of China, with comments on the femoral osteological correlates for thigh muscles

Abstract

Pterosaurs, an extinct group that ruled Mesozoic skies, flourished during the Cretaceous. Knowledge about their radiation largely comes from several Lagerstätten, especially in China and Brazil. Despite their abundance and diversity in other continents during the latest Early Cretaceous, pterosaurs from East Asia in this period are extremely rare, rendering their evolutionary history still unexplored. Here we redescribe pterosaur remains from the Albian Doushan Formation of Laiyang, Shandong Province, China, to refine such gap. The most completely preserved element, a femur, can be assigned to the Azhdarchoidea, a clade achieving global distribution by the end of the Early Cretaceous, based on combination of derived and plesiomorphic characters including the triangular and anteriorly curved ‘greater trochanter’, a deep ‘intertrochanteric fossa’ with a pneumatic foramen, presence of a bulbous ridge and a pulley-like lateral condyle. Moreover, osteological correlates for thigh muscles on the femur are identified here using the Extant Phylogenetic Bracket method. The general pattern of these osteological correlates is conservative when compared with other basal ornithodirans. The pterosaurian ‘greater trochanter’ is not homologous to the lesser trochanter in other archosaurs as previously suggested. M. femorotibialis internus is subdivided into two parts in some pterosaurs, probably representing a derived trait.