Bergamodactylus wildi (Wild 1978, Kellner 2015; MPUM 6009) Norian, Late Triassic, ~210 mya, was similar in size to Longisquama and was originally considered a juvenile Eudimorphodon ranzii. Later Dalla Vecchia (2009) considered this specimen congeneric with Carniadactylus, but the morphological differences are far too great. Often called "the Milan specimen" Bergamodactylus is a distinct taxon and the most primitive known pterosaur following the analysis of (Peters 2007).
Distinct from Longisquama, the skull of the Milan specimen was proportionately larger. The antorbital fenestra was larger, reaching the top of the skull. The mandible was more gracile.
Atypical for pterosaurs, but similar to Longisquama, the cervicals were relatively short but much more robust. The dorsal series was compressed. The caudals were more slender.
The sternal complex had posterior indentions marking the contributions of the clavicles and sternum. The coracoid retained its quadrant curve, but was more robust. The hand was relatively smaller, but manual digit IV was hyper-elongated to form the spar for a wing membrane. Complete folding of digit IV against the ulna was possible. due to the torsion of metacarpal IV. Manual digit V was a tiny vestige but retained two phalanges plus an ungual.
The ilium was slightly shorter. The pubis and ischium were ventrally separated. The femoral head was inturned but no distinct neck is visible. The prepubis extended halfway to the knee. The hind limb was relatively the longest among pterosaurs, similar to that of Longisquama. The digitigrade pes was smaller. Pedal 5.2 and p5.3 were fused and preserved folded against p5.1, which is straight. The digit V ungual is present.
Cranial and dorsal plumes were similar to those in Cosesaurus, but smaller than in Longisquama. The wing membranes extended along with the wing finger. More on pterosaur wings here and here.
A better flyer than Longisquama, MPUM 6009 had wing proportions more like those of other pterosaurs. It is doubtful that MPUM 6009 was a quadruped owing to the relative limb lengths.
Many of the evolutionary changes from Longisquama to MPUM 6009 (i.e. larger skull, shorter torso) may have been the result of paedomorphosis or they may have been the result of natural selection in a flyer, rather than a leaper, with certain traits (long legs, elevated tail, short neck) retained. The pelvic aperture and posterior sacrals indicate a relatively larger egg could have been delivered. |
