The Family Tree of the Pterosauria 14 – Nyctosaurus

Earlier we looked at the base of the Protopteranodontia, a clade that originated with a private specimen incorrectly referred to Germanodactylus cristatus. The clade also included No. 13, Eopteranodon and Eoazhdarcho and the Pteranodontia (Nyctosaurus + Pteranodon).

Here we look at Muzquizopteryx and the variety within the genus Nyctosaurus.

Nyctosaurus clade

Figure 1. The clade of Nyctosaurus and kin. Click to enlarge.

Muzquizopteryx
At the base of the genus Nyctosaurus is the smallest, newest and most primitive member of the nyctosaur clade, Muzquizopteryx (Frey et al. 2006). Overall larger than and distinct from No. 13, the skull of Muzquizopteryx had a longer rostrum, a shorter antorbital fenestra. The crest was shorter. The orbit was smaller, the lateral temporal fenestra was larger. The cervicals were more robust and shorter with higher neural spines. The cristospine was longer, The scapula was no longer than the coracoid. The deltopectoral crest was expanded distally. The pteroid was right angled. Fingers 1-3 were larger.The ischium was narrower. The prepubis fenestra was expanded beyond the anterior rim creating an anterior and ventral process. The femur and tibia were shorter. The foot was larger with longer toes. Pedal digit 5 was a vestige. It is not know whether Muzquizopteryx had jaw rim teeth or not.

Nyctosaurus bonneri, the Fort Hays specimen
Nyctosaurus bonneri FHSM VP 2148 (Bonner 1964, Miller 1972) Coniacian, Late Cretaceous was Overall larger than and distinct from Muzquizopteryx, the skull of Nyctosaurus bonneri was downturned anterior to the antorbital fenestra. No crest was present. The postorbital process of the jugal was gracile. The mandible was nearly as deep as the skull. No jaw rim teeth were present. The cervicals were shorter and more robust. The sacrum was coosified. The sternal complex was shorter and wider. The scapula and coracoid were more robust. The deltopectoral crest was greatly enlarged. The metacarpus was elongated. Fingers 1-3 were vestiges, probably because they could not touch the ground. Compared to Eopteranodon, the wing was longer. The distal wing phalanges were relatively longer. The pelvis was relatively smaller. The hind limb and foot were relatively shorter. The increase in wing length and decrease in leg length means this Nyctosaurus probably spent more time flying. The short crest sometimes applied to this specimen is an artifact made of putty.

YPM 2501
Size-wise and according to Bennett (1991, 2001) YPM 2501 is a Pteranodon distal metacarpus and proximal portion of the manual 4.1 (the wing finger). The strange thing is, this specimen is larger than virtually all — if not all — known specimens of Pteranodon — AND — the extensor tendon process is not fused. This specimen is a problem for Bennett (1991, 2001) and most other current pterosaur workers because an unfused extensor tendon process, to them, means an immature specimen (following archosaur growth pattern traits). However, following lizard growth patterns and phylogenic patterns this is probably a Nyctosaurus, because Pteranodon fuse the ETP. Crestless nyctosaurs don’t. This specimen also had larger fingers than later, more derived taxa.

Nyctosaurus nanus
The smallest Nyctosaurus (about the size of Muzquizopteryx) is N. nanus, known only for a humerus and pectoral girdle.

Nyctosaurus gracilis, the Field museum (Chicago) specimen
Distinct from the N. bonneri, the skull of N. gracilis (Williston 1902a, b) FMNH 25026 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.

Nyctosaurus sp. the Lincoln Nebraska state museum specimen 
Distinct from Nyctosaurus gracilis, the dorsals of the Nebraska specimen (Brown 1978, 1986) UNSM 93000, were relatively shorter. The scapula and coracoid were more robust. The deltopectoral crest of the humerus most closely resembled that of Muzquizopteryx. Fingers 1-3 were tiny vestiges. Manual 4.1 extended to mid ulna when folded. Manual 4.4 was probably fused to m4.3 or it was missing and m4.3 became curved. The pubis and ischium did not touch, as in more primitive nyctosaurs. It would have been impossible for the forelimb to develop thrust during terrestrial locomotion. It was likely elevated or used like a ski-pole.

Nyctosaurus sp. – two private crested specimens
Nyctosaurus sp. private specimens KJ1 and KJ2 (Bennett 2003) were derived from a sister to the Nebraska specimens of Nyctosaurus sp. and represent the last of their lineage with no known descendants. Distinct from the Nebraska specimen, the skull of KJ1 (below) had an enormous bifurcated frontal crest and a longer mandible than rostrum. The upper temporal fenestra was not visible in lateral view. The mandible was extremely sharp and ideal for skim or stab fishing. A notarium (fused dorsal vertebrae) was present. The coracoid was smaller and fused to the scapula. The humerus and deltopectoral crest were robust. The extensor tendon process was fused to the first wing phalanx. The pteroid was longer than in other nyctosaurs. Manual 4.1 was not much longer than the metacarpus. In KJ1 it was no longer than the metacarpus. The pelvis was deeper than shorter. The tibia was shorter. Overall KJ2 was slightly larger than KJ1. Contra Bennett (2003) not all Nyctosaurus had a crest. A crest does not mean these were male specimens.

Other “Big” Nyctosaurus specimens
As shown above (Figure 1), most Nyctosaurus were roughly the same size, but there is evidence of larger specimens. The largest was YPM 2501 (above). Bennett 1992 considered a pelvis, KUVP 993, in the size range of Pteranodon to be a female pelvis, but morphologically it belongs to a very large Nyctosaurus. Bennett (2000) also reported on a very large Nyctosaurus skeleton in an abstract. “…although incomplete, is the largest known specimen of Nyctosaurus with an estimated wingspan of 4.5 m.” Such a Nyctosaurus is shown in gray in figure 1, scaled up from the UNSM specimen.

In Summary
Unlike Pteranodon, the ancestry of Nyctosaurus included a very small taxon, No. 13, mislabeled Pterodactylus by Wellnhofer (1970). After that point all subsequent taxa, no matter how large (including YPM 2501) did not fuse the extensor tendon process or the scapula to the coracoid, until we come to the derived crested and privately held nyctosaurs, KJ1 and KJ2. They alone had a notarium, fused the scapula to the coracoid and fused the extensor tendon process to the first wing phalanx. Thus nyctosaurs, like all other pterosaurs, followed lepidosaur growth patterns as shown by phylogenetic analysis. Some nyctosaurus (and pterosaurs like ornithocheirids) grew to adults without fusion. Others fused certain bones.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References:
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992.
 
Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 2000. New information on the skeletons of Nyctosaurus. Journal of Vertebrate Paleontology 20 (Supplement to Number 3):29A.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153.
Bennett SC 2003. New crested specimens of the Late Cretaceous pterosaur Nyctosaurus.Paläontologische Zeitschrift 77: 61-75.
Bonner OW 1964. An osteological study of Nyctosaurus and Trinacromerum with a description of a new species of Nyctosaurus. Unpublished Masters Thesis, Fort Hays State University, 63 pages.
Brown GW 1978. Preliminary report on an articulated specimen of Pteranodon Nyctosaurus)gracilis. Proceedings of the Nebraska Academy of Science 88: 39.
Brown GW 1986. Reassessment of Nyctosaurus: new wings for an old pterosaur. Proceedings of the Nebraska Academy of Science 96: 47.
Frey E, Buchy M-C, Stinnesbeck W, González AG, and di Stefano A. 2006. Muzquizopteryx coahuilensis n.g., n. sp., a nyctosaurid pterosaur with soft tissue preservation from the Coniacian (Late Cretaceous) of northeast Mexico (Coahuila). Oryctos 6:19-39.
Miller HW 1972. 
The taxonomy of the Pteranodon species from Kansas. Transactions of the Kansas Academy of Science 74: 1–19.
Williston SW 1902a. On the skeleton of Nyctodactylus, with restoration. American Journal of Anatomy 1: 297–305.
Williston SW 1902b. On the skull of Nyctodactylus, an Upper Cretaceous pterodactyl. Journal of Geology 10: 520–531.

wiki/Nyctosaurus

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.