3D eggs and a new ornithocheird – Hamipterus

A recent paper
by Wang et al. (2014) introduced us to a new ornithocheirid, Hamipterus (Fig. 1) — AND it’s three-dimensional eggs (Fig. 2). The preservation is atypical: several dozen disarticulated specimens of many sizes were jumbled together, likely following a sudden flood. A Pterodaustro colony was preserved similarly. This sort of preservation can be a blessing and a curse. The parts are buried quickly and we can compare individual and strongly associated elements with those of other pterosaurs, but we cannot create a complete reconstruction except by estimation, especially since so many sizes are represented.

Hamipterus — what is it?
Adding Hamipterus to the Wang et al. pterosaur family tree resulted in 324 MPTs with loss of resolution at Hamipterus and elsewhere. Unfortunately they found toothless Pteranodon and Nyctosaurus were the outgroup taxa. Their problem is a result of yet another instance of taxon exclusion.

Let’s correct that by adding taxa.
Adding Hamipterus to the large pterosaur tree resulted in a single MPT. Hamipterus nested between Boreopterus + Zhenyuanopterus and Arthurdactylus + all higher ornithocheirids. Among them only Coloborhynchus has a completely fused pubis and ischium, just like Hamipterus (Fig. 3). None of these were included in the Wang et al. study.

Eggs
Wang et al. report a total of five eggs were recovered. Most are 59 to 65x34mm in size. One egg was smaller: 30x22mm and considered, “not fully developed.” The shell was pliable, with an ultra-thin calcareous layer followed by a thinner shell membrane, a structure the authors considered similar to that of snakes. (Hmm, and snakes are lepidosaurs!!!). Unfortunately the authors suggest Hamipterus, “likely made its nesting grounds on the shores of freshwater lakes or rivers and buried its eggs in sand along the shore, preventing them from being desiccated.” Of course, another way for them to prevent egg desiccation is to carry eggs within the female until just prior to hatching. Wang et all report that “the eggs are not part of the same clutch and were likely laid by different females, since they were found apart from each other, mixed with bones and subjected to limited transportation.” Of course this would require that buried eggs were excavated before transportation — or they could have been carried within the mother, like many lizards do. Then there’s the half-size egg. That is most likely explained by having a half-sized mom pterosaur. Chinsamy et al. (2008) reported that Pterodaustro reached sexual maturity at half the final adult size. Half-sized moms had half-sized pelves and half-sized eggs.

Ontogeny
Figure S4 in Wang et al. 2014 shows three ulnas with “no significant variation during ontogeny.” Similarly, the small skulls demonstrate no shorter rostra or larger orbits. This confirms the isometric ontogenic patterns shown by Zhejiangopterus, contra the allometric ontogenetic patterns generally accepted by pterosaur workers. It’s just too bad the flood that killed the flock didn’t arrive several weeks later, otherwise we’d see some ossified hatchlings mixed in.

References:
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Wang X et al.*, 2014. Sexually Dimorphic Tridimensionally Preserved Pterosaurs and Their Eggs from China, Current Biology. http://dx.doi.org/10.1016/j.cub.2014.04.054

*et al includes: Alexander W.A. Kellner, Shunxing Jiang, Qiang Wang, Yingxia Ma, Yahefujiang Paidoula, Xin Cheng, Taissa Rodrigues, Xi Meng, Jialiang Zhang, Ning Li and Zhonghe Zhou