A well-preserved pterosaur humerus
from the Late Jurassic of Thailand has just been documented (Buffetaut et al. 2015; Fig. 1). The authors considered the humerus an azhdarchoid (traditionally tapejarids + azhdarchids, but those clades are not related to each other in the large pterosaur tree). They report, “On the basis of such an isolated specimen, a very accurate identification is hardly possible. However, the long, parallel-sided crista deltopectoralis differs from that of basal pterosaurs, which is usually shorter and broader proximodistally. The general morphology of the bone, especially its proximal region, agrees with that of azhdarchoids (sensu Witton, 2013). To sum up, the humerus from Phu Noi shows clear azhdarchoid characters, and may belong to anazhdarchid.”`
To test the affinities
of the new humerus to taxa in the large pterosaur tree, I first eliminated all non-pterosaurs, then eliminated all pterosaurs with a straight humeral shaft. Then I eliminated all warped deltopectoral crests. Some taxa are known from skulls only, and they were also eliminated. That left me with about 22 taxa which I then visually compared to the new Thai humerus. Two taxa were most similar (Figs. 2, 3), neither related to azhdarchids or tapejarids. One comparable (a. M. No. 4072; Fig. 2) was much too small. The other (Fig. 3), is a dorygnathid nesting at the base of the azhdarchids and protoazhdarchids (SMNS 50164; Figs. 3, 4), appeared similar to the Thai pterosaur, but occurred in Mid-Jurassic strata.
The tiny proto-germanodactylid, n12, a. M. No. 4072, was as tall overall as the new Thai humerus was long, so it is not a good candidate despite the similarity in numeral shapes – unless a larger version of this taxon lived in Thailand.
The derived Dorygnathus specimen (SMNS 50164) has a similar humeral shape, but occurs too early in Europe (Mid-Jurassic). However, it is possible that some dorygnathids survived in Thailand until the Late Jurassic and if so, this may be evidence of this.
The large azhdarchids (Fig. 3) have a warped deltopectoral crest, and the small ones have a straight humeral shaft or other traits not found in the Thai humerus, so azhdarchids were dropped from consideration in the present analysis. The new Thai humerus displays several traits that were not considered in the large reptile tree. Perhaps a skull-only taxon is the closest match, but we’ll never know until more complete Late Jurassic specimens of these are found.
Also note: there is tremendous convergence within the Pterosauria. The two closest matching taxa are not related to each other. And the Thai humerus may not be related to either.
Buffetaut E, Suteethorn V, Suteethorn S, Deesri U and Tong H 2015. An azhdarchoid pterosaur humerus from the latest Jurassic (Phu Kradung Formation) of Phu Noi, north-eastern Thailand. Research & Knowledge 1:43-47.
Witton, M.P. 2013. Pterosaurs. Princeton University Press, Princeton and Oxford, pp. 291.