Anurognathus
Anurognathus is a genus of small pterosaur that lived during the Late Jurassic period (Tithonian stage). Anurognathus was first named and described by Ludwig Döderlein in 1923.[1] The type species is Anurognathus ammoni. The genus name Anurognathus is derived from the Greek αν/ an- ("without"), оυρα/ oura ("tail"), and γναθος/ gnathos ("jaw") in reference to its unusually small tail relative to other "rhamphorhynchoid" (i.e. basal) pterosaurs.[2] The specific name ammoni honours the Bavarian geologist Ludwig von Ammon, from whose collection Döderlein had acquired the fossil in 1922.
The genus is based on holotype BSP 1922.I.42 (Bayerische Staatssammlung für Palaeontologie und Geologie), found in the Solnhofen limestone near Eichstätt. It consists of a crushed, relatively complete skeleton on a slab. The counterslab is missing and with it most of the bones: much of the skeleton is only visible as an impression.
Anurognathus had a short head with pin-like teeth for catching insects and although it traditionally is ascribed to the long-tailed pterosaur group "Rhamphorhynchoidea", its tail was comparatively short, allowing it more maneuverability for hunting.[3] According to Döderlein the reduced tail of Anurognathus was similar to the pygostyle of modern birds.[2] Its more typical "rhamphorhynchoid" characters include its elongated fifth toe and short metacarpals and neck.[2] With an estimated wingspan of fifty centimetres (20 inches) and a nine centimetre long body (skull included), its weight was limited: in 2008 Mark Paul Witton estimated a mass of forty grammes for a specimen with a 35 centimetre wingspan.[4] The holotype was redescribed by Peter Wellnhofer in 1975.
Later a second, smaller specimen was found, probably of a subadult individual. Its slab and counterslab are separated and both were sold to private collections; neither has an official registration. It was described by S. Christopher Bennet in 2007. This second exemplar is much more complete and better articulated. It shows impressions of a large part of the flight membrane and under UV-light remains of the muscles of the thigh and arm become visible. It provided new information on many points of the anatomy. The skull was shown to have been very short and broad, wider than long. It transpired that Wellnhofer had incorrectly reconstructed the skull in 1975, mistaking the large eye sockets for the fenestrae antorbitales, skull openings that in most pterosaurs are larger than the orbits but in Anurognathus are small and together with the nostrils placed at the front of the flat snout. The eyes pointed forwards to a degree, providing some binocular vision. Most of the skull consisted of bone struts. The presumed pygostyle was absent; investigating the real nine tail vertebrae instead of impressions showed that they were unfused, though very reduced. The wing finger lacked the fourth phalanx. According to Bennett a membrane, visible near the shin, showed that the wing contacted the ankle and was thus rather short and broad. Bennett also restudied the holotype, interpreting bumps on the jaws as an indication that hairs forming a protruding bristle were present on the snout.[5]
Anurognathus was assigned by Oskar Kuhn to the family Anurognathidae in 1937. In the modern clade Anurognathidae, Anurognathus is the sister taxon of the clade Batrachognathinae, which contains the species Batrachognathus, Dendrorhynchoides and Jeholopterus. In 2021, a phylogenetic analysis conducted by Xuefang Wei and colleagues recovered Anurognathus within the subfamily Anurognathinae, a subfamily within the family Anurognathidae. Anurognathus was found to have been the sister taxon to Vesperopterylus in the study.[6] Below is a cladogram representing their phylogenetic analysis:
