|Figure 1: The variation of cranial crest within the Wukongopteridae.|
Kunpengopterus sinensis (IVPP V 16047), (a) complete skull and (b) close-up of the area in the white frame of a, showing the flat crestless skull roof;
holotype of Darwinopterus linglongtaensis (IVPP V 16049), (c) complete skull and (d) close-up of the area in the white frame of c; new specimen (IVPP V 17957), (e) complete skull (inverted), and (f) close-up of the area in the white frame of e; IVPP V 17959 (g) complete skull (inverted), and (h) close-up of the area in the white frame of g, with arrow 1 pointing at the low premaxillary crest and arrow 2 pointing at the crestless middle portion of the premaxilla;
Darwinopterus robustodens (holotype, HGM 41HIII-0309A) (i) complete skull based on Lü et al. 2011b), and (j) close-up of the area in the white frame of i.
Scale bar: 50mm in a, c, e, g, i; 10mm in b, d, f, h, j.
Cheng, Jiang, Wang & Kellner, 2017. DOI: 10.1590/0001-3765201720160742
Cranial crests show considerable variation within the Pterosauria, a group of flying reptiles that developed powered flight. This includes the Wukongopteridae, a clade of non-pterodactyloids, where the presence or absence of such head structures, allied with variation in the pelvic canal, have been regarded as evidence for sexual dimorphism. Here we discuss the cranial crest variation within wukongopterids and briefly report on a new specimen (IVPP V 17957). 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.
Key words: Wukongopteridae; Pterosauria; cranial crest; sexual dimorphism; China
The function of cranial crests in pterosaurs will be a matter of contempt until more material becomes available. Although the comparisons of the pelvic elements of wukongopterids is interesting, one cannot overemphasize the reduced number of specimens on which this and other studies are based. Variations introduced by taphonomy, allied with morphological differences as a result of ontogeny and other factors cannot be adequately assessed with three or so individuals. Notwithstanding these shortcomings, the explanation of the evolutionary function of cranial crests as sexual dimorphism (including mutual sexual selection, Hone et al. 2012) should not be used as the default option. As has been pointed out before (e.g., Kellner and Campos 2002a, 2002b), it seems quite unlikely that once a pterosaur developed a cranial crest (as perhaps the so called “bizarre structures” in other reptiles), this structure could not have performed a variety of functions. Despite the limitation of the available data, it seems difficult not to acknowledge that these quite distinct anatomical features have played a major role in species recognition, as has been put forward for other reptiles (e.g., Padian and Horner 2011). This has been shown to be true at least for some material of the Pteranodon-complex and seems also to have been the case for the Wukongopteridae. Perhaps more detailed studies of deposits with large amount of specimens that might have been part of the same or closely related populations like the occurrences of Caiuajara dobruskii and Hamipterus tianshanensis (and others that might come to light) have the potential to provide a step further into the discussion of several paleobiological questions concerning flying reptiles, including sexual dimorphism and ontogeny (Kellner 2015). Meanwhile 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.
Xin Cheng, Shunxing Jiang, Xiaolin Wang and Alexander W. A. Kellner. 2017. Premaxillary Crest Variation within the Wukongopteridae (Reptilia, Pterosauria) and Comments on Cranial Structures in Pterosaurs. Anais da Academia Brasileira de Ciências. [An. Acad. Bras. Ciênc.] 89(1); Epub Feb 09, 2017. DOI: 10.1590/0001-3765201720160742