Not Another Rhamphorhynchus Growth Series Without a Phylogenetic Analysis!

Prondvai et al. (2012) reported on the bone histology of five Rhamphorhynchus specimens of various sizes (Fig. 1). They concluded “The initial rapid growth phase early in Rhamphorhynchus ontogeny supports the non-volant nature of its hatchlings, and refutes the widely accepted ‘superprecocial hatchling’ hypothesis. We suggest the onset of powered flight, and not of reproduction as the cause of the transition from the fast growth phase to a prolonged slower growth phase.”

Regarding the bone histology of the specimens, Prondvai et al. (2012) reported, “The ontogenetic validity of the smallest size category of Bennett is clearly supported by the overall microstructure found in the bones of the three small specimens BSPG 1960 I 470a, BSPG 1877 X I, CM 11433.”

Earlier Bennett (1995) reported on a growth series with distinct stages for Rhamphorhynchus.

A list of Rhamphorhynchus specimens studied by Prondvai et al. (2012).

Figure 1. A list of Rhamphorhynchus specimens studied by Prondvai et al. (2012). They said this was an ontogenetic series, but the feet (Fig. 2) tell another tale. Note, some specimens were actually headless. One, the IPB specimen, is a single hind limb. In an apparent bid to completely ignore morphological distinctions, all these reconstructions are identical, simply scaled larger or smaller. The largest is 5x the size of the smallest. Pterosaur adults are typically 8x larger than hatchlings.

Not Ontogenetic, But Phylogenetic
Unfortunately and without realizing it, Prondvai et al. (2012) employed a phylogenetic series, not an ontogenetic one. None of their large and small specimens were virtually identical to one another.That’s a requirement for an ontogenetic series in which the taxa grew isometrically as demonstrated by all known pterosaur embryos and several juvenile pterosaurs including Tupuxura and Pteranodon. The allometric growth hypothesis is not supported by phylogenetic analysis or detailed anatomical studies (see Fig. 2). Like Bennett (2007) before them, Prondvai et al. (2012) did not perform a phylogenetic analysis to determine whether or not their study specimens were conspecific or not. Such an analysis is critical. The lack of such an analysis places doubts over the results.

Rhamphorhynchus feet

Figure 2. Click to enlarge. These are the feet of the five Rhamphorhynchus specimens employed as an ontogenetic series by Prondvai et al. (2012). As you can see, the various proportions are not close enough in morphology to possibly be an ontogenetic series. Some have longer metatarsals, others have distinct ratios among the phalanges. Instead, these represent samples from the small and large phylogenetic species within Rhamphorhynchus. PILs are continuous in most sets. Not to scale with one another.

The Feet Are Like Fingerprints
As we learned earlier, if the feet were identical to one another, or nearly so, they would be more closely related as in Pterodaustro, but here, in Rhamphorhynchus, they are not. The specimens were found in different areas at different times. They were not part of a single nesting colony. They were not an ontogenetic series. Prondvai et al. (2012) was evidently not aware that the traditional allometric growth hypothesis cannot be supported except by the power of tradition. So, unfortunately, the Prondvai et al. (2012) study ended up comparing different species, some small, precocious and fast-growing, others larger and slower growing, just like various birds of various sizes. Click here to see what other sister Rhamphorhynchus specimens looked like in lateral view in phylogenetic order. You’ll notice several other non-conspecific differences. Descriptions and comparative differences are included there.

Could The Small Ones Fly?
Regardless of their ontogeneic age, did the smallest Rhamphorhynchus specimens fly? Prondvai et al. (2012) say no. They said the small pterosaurs needed a certain “somatic maturity to get airborne.” The fact that the small rhamphs had immature bone tissue is not unexpected. They became sexually active at an earlier stage than their larger sisters, both preceding and succeeding them. They never got big. Their eggs would have been correspondingly small. They likely did not live as long, but produced more eggs earlier. Their wings were not shorter and their sternal complexes were not smaller. They present specimens were as able to fly as their larger sisters.

Rhamphorhynchus hatchlings (especially the hatchlings of small adults), however, were not able to fly (due to the threat of desiccation) until reaching the critical size of the smallest known adult pterosaur, B St 1967 I 276, Wellnhofer’s No. 6, as described earlier.

You can read Dr. Hone’s interview with Dr. Edina Prondvai here.

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
Bennett SC 1995. A statistical study of Rhamphorhynchus from the southern limestone of Germany: year classes of a single large species. Journal of Vertebrate Paleontology 69: 569–580.
Prondvai E, Stein K, Ösi A, Sander MP 2012. Life History of Rhamphorhynchus Inferred from Bone Histology and the Diversity of Pterosaurian Growth Strategies. PlosOne. online pdf

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