New Nyctosaurus LACM 51130 (Perez 2012)

A recent paper, poster and online presentation by Teresa Perez (2012) introduced us to a new Nyctosaurus (LACM 51130) known from an articulated but incomplete post-crania sans cervicals (Fig. 1). Perez doesn’t indicate whether this is a ventral or dorsal presentation, but the exposure of the posterior tuberosity of the humerus, the layering of the radius slightly below the ulna, the layering of the coracoid on top of the scapula and the exposure of the prepubes on top of the left ilium indicate a ventral exposure.

Nyctosaurus (Perez 2012) LACM 51130.

Figure 1. Nyctosaurus (Perez 2012) LACM 51130. Note the original false scale bar (20cm) has been repaired here (0-2-10cm) in concert with published bone length data.

LACM 51130 was described by Perez as immature due to an unfused ETP (extensor tendon process), but that is a phylogenetic trait (contra Bennett 1991, 2001), not an ontogenetic one, as we noted earlier. (All basal Nyctos have unfused ETPs. Only derived crested forms fuse the ETPs.)

As noted by Perez, the specimen is about the same size as the other Nyctosaurus (Fig. 2) specimens, but morphologically not identical to any one of them. Thus it is probably an adult like the others are.

Figure 2. Reconstructions of several Nyctosaurus including UNSM 93000 and LACM 51130. To the right are three Nyctosaurus humeri showing morphological and size change toward the crested form, KJ2.

Figure 2. Click to enlarge. Reconstructions of several Nyctosaurus including UNSM 93000 and LACM 51130. To the upper right are three Nyctosaurus humeri showing morphological and size change toward the crested form, KJ2.

In the LACM specimen the humerus and antebrachium are shorter and more robust than in the UNSM 93000 specimen — yet the humerus of the LACM specimen is longer and not as robust as in the KJ2 specimen (Fig 2). Thus the LACM specimen appears to be a transitional taxon between these two previously known sister taxa. Perhaps it had a short skull crest in life, but all skull material is missing.

Or is it…????
There’s an interesting unidentified curved flat bone that disappears beneath the left manual 4.1(flipped to the right in ventral view). This gives every indication that it is a small portion of a crest of unknown length, likely smaller than in other crested Nyctosaurus based on its apparent cross section.

Perez considered the two preserved pectoral elements to both be coracoids, but they are different shapes and one is nearly identical to the scapula of UNSM 93000. Lack of fusion in the scapulocoracoid is also another crestless Nyctosaurus trait. Note that crested Nyctosaurus are no larger than crestless specimens and yet the humerus is smaller (Fig. 2). Odd that…

So not all Nyctosaurus had a crest. Not all had just three wing phalanges. Not all lost their free fingers. So far, every Nyctosaurus featured at is a distinct species (Fig. 2). The LACM specimen appears to be a basal crested specimen. These comparisons probably could not have been determined without making a reconstruction or two, a practice that focuses the eye and clarifies subtle differences and is, unfortunately, deemed to difficult for professional palaeontologists and their students to attempt.

That’s why I’m here.
And here’s yet another case in which I have not even seen the fossil yet am able to make small corrections and contributions. Photos, tracings and a catalog of reconstructions have value.

Perez T 2012. Diagnosis of an Immature Nyctosaurus (Pterosauria) Specimen. The Dinosaur Institute, Natural History Museum of Los Angeles County. Online here.


Leave a Reply

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

You are commenting using your 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.