A late Jurassic pterosaur humerus from Thailand

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.”`

Figure 1. The new Late Jurassic Thai pterosaur humerus, PRC 64. 112 mm long.

Figure 1. The new Late Jurassic Thai pterosaur humerus, PRC 64. 112 mm long.

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.

Figure 2. A tiny proto-germanodactylid, n12 in the Wellnhofer 1970 catalog is as tall as the new Thai humerus, but has a similar shape to its own humerus.

Figure 2. A tiny proto-germanodactylid, n12 in the Wellnhofer 1970 catalog is as tall as the new Thai humerus, but has a similar shape to its own humerus. Not a likely candidate, but a larger descendant is a possibility.

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.

Figure 3. The derived Dorygnathus specimen, SMNS 50164 has a similar humerus of the right size and right age.

Figure 3. The derived Dorygnathus specimen, SMNS 50164 has a similar humerus of the right size but too early with regard to age. Not all Dorygnathus specimens have a similar humerus shape.

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.

Azhdarchids and Obama

Figure 3. Click to enlarge. Here’s the 6 foot 1 inch President of the USA alongside several azhdarchids and their predecessors. Most were knee high. The earliest examples were cuff high. The tallest was twice as tall as our President. This image replaces an earlier one in which a smaller specimen of Zhejiangopterus was used.

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.

References
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.

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