Lucky Number 13.

Wellnhofer’s (1970) catalog of “pterodactyloid” Solnhofen pterosaurs included a putative Pterodactylus specimen B St 1878 VI 1 (Zittel 1882) to which he applied the number “13.” Earlier we discussed the hypothesis that the genus “Pterodactylus” was a taxonomic wastebasket, that included several taxa within the genus Pterodactylus and several that did not. One of the latter that stands alone is #13. In the present tree, it was derived from the SMNK 6592 specimen of Germanodactylus and was basal to Nyctosaurus, Pteranodon, Eopteranodon and Eoazhdarcho (Figure 2).

B St 1878 VI 1, #13

Figure 1. B St 1878 VI 1, #13 in the Wellnhofer (1970) catalog.

Not a Pterodactylus but a Reduced Germanodactylus
The single large tooth at the tips of the jaws, the (albeit tiny) posterior skull crest, the ventral keel of the mandible, the shapes of the pelvis and sternum, and the proportions of all ten digits are traits separating #13 from the genuine Pterodactylus clade. Moving #13 back to Pterodactylus adds 35 steps in the large pterosaur tree. The reduced size of #13 is a common, if not typical pattern preceding morphological change (contra Hone and Benton 2006). In this case the change produced Eopteranodon and Eoazhdarcho on one branch and Muzquizopteryx plus Nyctosaurus on the other. Note the hatchet-shaped deltopectoral crest (as in Nyctosaurus) on #13. The lack of scapulocoracoid fusion in #13 (a biproduct of phylogenetic size reduction) gave rise to a clade with a similar lack of fusion up to but not including the KJ nyctosaurs.

 No. 13 and its sisters

Figure 2. No. 13 and its sisters, Germanodactylus, Muzquizopteryx and Eopteranodon. Click to enlarge.

The Size Thing
Figure 2 shows #13 with its successors, Muzquizopteryx and Eopteranodon, to scale and two to three times its height. In like manner, the Germanodactylus successor, a basal Pteranodon, was three times its size. The hyper-elongated metacarpus of Nyctosaurus finds its origins in Muzquizopteryx and Eopteranodon. The same trait in Pteranodon owes its origin either to a sister to Eopteranodon or to an unknown transitional series derived from Germanodactylus following a convergent evolutionary pattern.

Successors were Toothless
The phylogenetic successors of both Germanodactylus and #13 were all toothless. How this came to be is not illustrated in the fossil record, but generally the teeth become more numerous and smaller prior to disappearance.

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 and Benton 2006. Cope’s Rule in the Pterosauria, and differing perceptions of Cope’s Rule at different taxonomic levels. Journal of Evolutionary Biology 20(3): 1164–1170. doi: 10.1111/j.1420-9101.2006.01284.x
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
Zittel KA 1882.  Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Palaeontographica 24: 47-81.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.