Is Bellubrunnus a hatchling or a juvenile?

It’s too bad that the new small pterosaur Bellubrunnus (Hone et al. 2012) was not admitted to a comprehensive phylogenetic analysis. The authors and others considered it a juvenile, if not a hatchling, due to a lack of fusion of various skeletal elements that are fused on other (but not all) pterosaurs. In the large pterosaur tree Bellubrunnus nests as an adult between other small adults.

Let’s imagine that Bellubrunnus is a hatchling or juvenile. 
What can we learn by scaling Bellubrunnus up to adult size?

ellubrunnus to scale

Figure 1. Click to enlarge. Bellubrunnus to scale, imagined as an adult of a hatchling and at other sizes in between. If a hatchling, Bellubrunnus would end up larger than the largest Rhamphorhynchus.

Currently Bellubrunnus is the size of sister taxa. However, if we consider it a hatchling, then at 8x larger an adult becomes the largest taxon in this clade. If we consider Bellubrunnus half grown or quarter grown, then intermediate sizes in blue (Fig. 1) indicate adult size, larger than sisters and more in line with the larger Rhamphs.

As evidenced by pterosaur embryos, pterosaurs hatched as virtual copies of the adult only 8x smaller. Not all small pterosaurs had unfused bones. Not all large pterosaurs had fused bones. Fusion or a lack thereof, follows phylogenetic patterns. This becomes visible when certain taxa are not excluded from analysis a priori. It is likely that Bellubrunnus is an adult because sister taxa are similar in size and shape. However, the adult would have been identical to a 8x smaller hatchling, not quite half as tall as the adult’s standing tibia.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Hone DWE, Tischlinger H, Frey E and Röper M. 2012.
 A New Non-Pterodactyloid Pterosaur from the Late Jurassic of Southern Germany. PLoS ONE 7(7): e39312. doi:10.1371/journal.pone.0039312

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