Nyctosaurus gracilis, the Field Museum specimen

Nyctosaurus gracilis FMNH 25026 (Williston 1902a,b) was derived from a sister to Nyctosaurus bonneri and phylogenetically preceded the Nebraska specimen of Nyctosaurus, UNSM 93000.

Distinct from the N. bonneri, the skull of N. gracilis had a slightly deeper rostral tip and a straighter dorsal margin without the posterior downturn, as in Muzquizopteryx. The mandible was probably thinner, but it is crushed dorsoventrally.

The cervicals were slightly smaller. The sacrals were relatively larger. The gastralia were the fewest and thickest among all pterosaurs, forming ventral support to counteract the large moment arm the developed from the fulcrum at the dorsal/sacral interface.

The sternal comnplex had a larger cristospine and sharper corners. The scapula was smaller than the coracoid. The deltopectoral crest of the humerus was strongly pinched. The pteroid was enlarged. Manual 4.1 was relatively longer. Manual 4.4 was shorter.

The pelvis was larger and the pubis contacted the ventrally expanded ischium leaving a large circular obturator foramen between them. The hind limb and foot were larger, as in Muzquizopteryx.

The family tree of the Ornithocephalia and Germanodactylia is here. The expanded family tree of the Pterosauria is here.

YPM 2501 - Big Nyctosaurus? or Pteranodon?

A giant unfused extensor tendon process of YPM 2501. There is only one large example of an unfused extensor tendon process that I am aware of. The question is: does it belong to Nyctosaurus? Or Pteranodon? At present the lack of fusion and general morphology of the elements places this specimen with Nyctosaurus. However the relatively large size of metacarpals 1-3 and the large size of the elements overall nudges this specimen over with Pteranodon. The elements in YPM 2501 are actually larger than those in all but the very largest Pteranodon specimens, in which the extensor tendon process is fused (example O in yellow in the figure below.) On the other hand, it is only a rumor that the metacarpals were tiny in all Nyctosaurus. Actually only the UNSM specimen had vestigial fingers, so far as we know. A little confusing at present, but I think YPM 2501 is a really big Nyctosaurus -- with robust fingers -- which means it was probably primitive and crestless.