You heard it here first: no gender differences detected in pterosaur pelves

A new paper on wukongopterid crests
(Cheng et al. 2017) reports, “We also show that there is no significant variation in the anatomy of the pelvis of crested and crestless specimens. We further revisit the discussion regarding the function of cranial structures in pterosaurs and argue that they cannot be dismissed a priori as a valuable tool for species recognition.”

The subject of gender differences
in pterosaur pelves was examined here, here and here. While the subject of gender differences in pterosaur crests was examined here, here and here in previous posts going back several years (Fig. 1).

Female Pteranodon?

Figure 3. Pteranodon (left) and Nyctosaurus (right) pelves. KUVP 933 (I)  is closer to Nyctosaurus in morphology. It is not a female Pteranodon. It belongs to a big Nyctosaurus. Note the HUGE individual variation presented here among putative congeneric specimens.

Nice to see published work
rejecting the hypotheses by Bennett 1992 that linked crest size to pelvic canal size. Bennett did not realize the large opening pelvis was that of a large nyctosaurid (Fig. 1), as in all specimens of Nyctosaurus. Cheng et al. report, “there is no direct association of the skulls and pelves that could back this hypothesis (e.g., Kellner and Tomida 2000). Re-evaluation of several specimens attributed to Pteranodon has shown that in some cases there are sufficient morphological differences other than the shape and size of the cranial crest, supporting a larger taxonomic diversity within what can be called the Pteranodon-complex (Kellner 2010).” Here (Fig. 2) smaller more primitive Pteranodon specimens have smaller crests, just as smaller more primitive tapejarids do.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen 'w' = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen 'z' = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen ‘w’ = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen ‘z’ = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Then there is the Hamipterus association…

According to Cheng et al. “Hamipterus tianshanensis bears a  premaxillary crest that, in similar sized individuals, showed consistently two distinct morphotypes: one with larger and more robust crests, and the second with smaller and more delicate crests. These morphotypes were tentatively regarded as males and females, respectively (Wang et al. 2014a). This occurrence constitute, to our knowledge, the best argument favoring sexual dimorphism expressed by cranial crests.” Of course these could be different ages, alpha and beta individuals (= individual variation leading to rapid phylogenetic changes), tribes (familial clades), or male and female. Pterosaurs have been competing for mating privileges since before they had wings, in Cosesaurus, for instance.

And there is Caiuajara
where Cheng et al. report, “Caiuajara (admittedly very distantly related to the Wukongopteridae), there seems a continuum in the appearance and development of the cranial crest, present in this taxon at a very young ontogenetic stage (Manzig et al. 2014).”

Cheng et al. conclude: “the variation in shapes and sizes of cranial crests that are found in pterosaurs, associated with other morphological features, should not be understated as being a powerful tool for understanding their diversity.”

No images or reconstructions
were offered of the pelves under study (as provided in Fig. 3). Precise measurements in a series of tables were presented. No phylogenetic analysis was attempted by Cheng et al., but you can see the results of such a test here, at the large pterosaur tree where five specimens attributed to Darwinopterus and additional others attributed to other wukongopterids lump and separate without loss of resolution.

As reported earlier
I have not found two Rhamphorhynchus specimens that score the same, except for a juvenile of the largest species. That goes the same for Pterodactylus, Germanodactylus, Pteranodon (Fig. 2), Darwinopterus (Fig. 3) or any other genus represented by a large number of individual specimens. They all nest in phylogenetic order, lumped and split by a variety of traits. Note the HUGE individual variation presented here among putative congeneric specimens.

Figure 1. Click to enlarge. The five specimens of Darwinopterus to scale and in phylogenetic order preceded by six more primitive taxa. The ZMNH 8802 specimen is a female associated with an egg. The others genders shown are guesses by Lü et al. 2011a. Note the skull did not elongate, it actually shrank in the vertical dimension, probably reducing its weight. The female is crestless because it is the most primitive of the five known Darwinopterus specimens. The odds that the remaining four specimens are all males is relatively small.

Figure 3. Click to enlarge. The five specimens of Darwinopterus to scale and in phylogenetic order preceded by six more primitive taxa. The ZMNH 8802 specimen is a female associated with an egg. The others genders shown are guesses by Lü et al. 2011a. Note the skull did not elongate, it actually shrank in the vertical dimension, probably reducing its weight. The female is crestless because it is the most primitive of the five known Darwinopterus specimens. The odds that the remaining four specimens are all males is relatively small.

References
Cheng X, Jiang S-X, Wang X-L and Kellner AWA 2017. Premaxillary crest variation within the Wukongopteridae (Reptilia, Pterosauria) and comments on cranial structures in pterosaurs. Anais da Academia Brasileira de Ciencias. http://dx.doi.org/10.1590/0001-3765201720160742

Advertisements

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 )

Twitter picture

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

Facebook photo

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

Google+ photo

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

Connecting to %s