SVP 2018: Reproduction and Growth in Pterosaurs

Unwin and Deeming 2018 report,
“Pterosaur eggshells were pliable and occasionally bounded externally by a thin calcitic layer. Contact incubation seems impractical and eggs were likely buried and developed at ambient temperatures.”

Burial is not only unnecessary, but dangerous
given that pterosaurs are lepidosaurs and therefore able to retain eggs within the mother until just before hatching, something the authors continue to ignore. That’s why the eggs have lepidosaur-like ultra-thin external layers. No tiny fragile pterosaur wants to dig out of a buried situation. Too dangerous for fragile membranes. Unwin and Deeming are clinging to an archosaur hypothesis, ignoring all the data since Peters 2000 that nest them apart from archosaurs.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

The authors report,
“Near term embryos were well ossified and hatchlings had postcranial proportions and well developed flight membranes that indicate a superprecocial flight ability.” 

As in lepidosaurs, not archosaurs.
Overlooked by the authors, cranial proportions are also adult-like in hatchlings (Fig. 1). Lepidosaurs hatch ready to eat and take care of themselves.

Regarding growth, they report,
“The growth rates recovered for pterosaurs are comparable to those reported for extant reptiles and a magnitude lower than in extant birds.” Here the authors are lumping turtles, lizards and crocs, when lizards will do.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Note,
the authors do not address isometric growth in their abstract, as in lepidosaurs, not archosaurs. Nor do they address sexual maturity at half full growth, which facilitates rapid phylogenetic miniaturization or gigantism whenever needed due to changing environs.

We’ve heard this all before. Years ago.

Respecting the embargo
other SVP abstract posts will show up after the 20th. This one made the news, so its embargo is over. That article featured BMNH 42736 (Fig. 3) labeled as a hatchling or flapling. Actually it’s a hummingbird-sized adult female. We know this because it nests with other phylogenetically miniaturized taxa in the large pterosaur tree (not with a larger specimen) and… it’s pregnant.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

References
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Unwin DM and Deeming C 2018. An integrated model for reproduction and growth in pterosaurs. SVP abstracts.

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