Pterosaur reproduction and gender identification – SVPCA talks

Two upcoming SVPCA talks worth discussing:
Kellner et al and Unwin + Deeming both discuss pterosaur reproduction, growth and gender.

Key notes from the Kellner et al. (2015) abstract: All eggs show depressions, clearly indicating their overall pliable nature. SEM analysis shows that the eggshell structure is similar to some squamates. SEM analysis of [another] eggshell did not reveal an external calcareous layer suggesting that it was either removed due to taphonomy or not present at all. Histological section of the femur lacks medullary layer, a bone tissue reported in avian dinosaurs during ovulation and egg-laying phase. Those specimens, associated with experimental taphonomic studies, show that pterosaurs had two functional oviducts and laid eggs even smaller than previously thought, indicating that they have developed a reproductive strategy more similar to basal reptiles than to birds.”

Like I’ve been saying since 2007 and before.
Pterosaurs are non-squamate lepidosaurs. Egg shell morphology is just one more clue to this.

Unwin and Deeming abstract:
“Sexual dimorphism is common in extant vertebrates and almost certainly occurred in extinct species as well, but identifying this phenomenon in fossils is difficult. Meeting two key criteria: a large sample size in which all ontogenetic stages are present; and independent evidence of gender, is rarely possible, but has now been achieved for the early Upper Jurassic pterosaur Darwinopterus modularis. This pterosaur is represented by over 20 individuals ranging from hatchlings through juveniles to mature adults (ontogenetic status determined from osteological, histological and morphometric data). One example, ‘Mrs T’, is preserved with two eggs and thus clearly a female. Approximately half the mature individuals of Darwinopterus exhibit a cranial crest and several of these individuals have a relatively narrow pelvis. The remainder lack a cranial crest and in two cases, including Mrs T, have a relatively broad pelvis. All immature individuals lack a crest, an observation that applies to other species of pterosaur in which immature individuals are known. This pattern of morphological variation shows that the cranial crest and pelvis of Darwinopterus modularis are sexually dimorphic. Datasets for other pterosaurs are less complete and/or lack independent evidence of gender, but many species including Ctenochasma gracile, Germanodactylus cristatus and Pteranodon longiceps, exhibit directly, or closely, comparable patterns of anatomical variation to Darwinopterus and are likely to have been sexually dimorphic. We conclude that the spectacular variability in the shape and size of pterosaur cranial crests was likely generated by sexual selection rather than processes such as species recognition.”

Unfortunately
other than with the presence of eggs in association, sexual dimorphism has not been determined in other pterosaurs in which a large sample size is present (Rhamphorhynchus, Pteranodon, Germanodactylus, Pterodactuylus), even without eggs in association. This is widely recognized, hence the excitement level in the abstract for Darwinopterus. Rather speciation of these taxa has been determined through phylogenetic analysis. Speciation has also been determined for the several Darwinopterus specimens. Currently published specimens don’t divide neatly in two. If that changes with the addition of 15 more, I’ll be happy to note that. Unwin and Deeming do not mention phylogenetic analysis in their abstract. If this is a clue to their methods such laziness in skipping phylogenetic analysis is becoming more and more common, especially when it suits a false paradigm. You can’t just eyeball these things. You have to put your data through analysis. Otherwise the work will always be doubted and you’ll be ‘pulling a Bennett’ (assertion of association without cladogram evidence). The purported hatchlings noted by Unwin and Deeming also need to be run through analysis. Are they examples of phylogenetic miniaturization or actual juveniles? Adding hatchlings and embryos along with tiny adults to analysis has been online for more than four years, so there is no excuse for avoiding it.

Tiny wukongopterids are welcome news, by the way. This clade is one of a few that currently lacks any tiny representatives and that lack is the current best reason why wukongopterids left no descendants in the Cretaceous.

The bone originally identified as an ischium on Mrs. T was a misidentified displaced prepubis. The actual ischia were preserved in the counter plate and they were relatively narrow.

Unwin does not support isometric growth during ontogeny, which is otherwise a well established fact in pterosaurs. So he may be accepting dissimilar morphologies as juvenile examples (pulling another Bennett). Very dangerous. As in all other pterosaurs, like Pteranodon, you have to evolve crested derived forms from non-crested basal forms. Unwin and Deeming, if you’re reading this: before you publish your paper, send me your data, if you don’t want to do the analysis yourself. I’ll send back the recovered cladogram. Don’t make the same mistakes again. However, if the juveniles are isometric copies of the adults, then congratulations and remember to give credit where credit is due.

References
Kellner  AWA et al. 2015. Comments on pterosaur reproduction based on recently found specimens from the Jurassic and Cretaceous of China. Among the most spectacular pterosaur finds done in recent years is the bone-bed from the Tugulu Group (Lower Cretaceous) discovered in the Hami area, Xinjiang Uyghur Autonomous Region of China. SVPCA 2015 abstracts.
Peters D 2007. The origin and radiation of the Pterosauria.
Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27
Unwin DM and Deeming CD 2015. New evidence for sexual dimorphism in the basal monofenestratan pterosaur Darwinopterus. SVPCA 2015 abstracts.

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