What is Orientognathus? Nesting via description, not observation

Orientognathus chaoyngensis (Lü et al. 2015) is a new Late Jurassic rhamphorhynchoid pterosaur known at present from a series of comparative descriptions. No illustration or photograph of the incomplete(?) material is yet known (at least to me at present).

Given these limitations, let’s see how close we can nest this new enigma.

Data provided:

1. toothless tip of dentary, slightly pointed
2. mc4/humerus ratio = 0.38
3. ulna < each individual wing phalanx
4. tibia subequal to femur
5. deltopectoral crest more developed than in Qinlongopterus
6. anterior teeth stouter and longer than in Pterorhynchus
7. teeth are straight and longer than in Jianchangnathus
8. pteroid/humerus ratio = 0.21; pteroid has expanded distal end
9. larger than other rhamphorhynchine pterosaurs from Late Jurassic NE China (measurements not indicated).

Evidently there is not much known of this specimen:
jaw tips and teeth, a pteroid, a humerus, an ulna, a metacarpal 4, a complete (?) wing (doubtful because the phalanx ratios are not compared to one another) and a femur are all that are mentioned here.

Step one: tibia = femur:
In almost all pterosaurs the tibia is longer than the femur. Just a few specimens have this odd sub equal ratio, so that winnows down the long list of pterosaurs to a short list of possible candidates (left me know if I overlooked any other candidates). You can click the name to view the reconstruction.

1. Rhamphorhynchus gemmingi? MYE 13 (von Meyer 1859, No. 75 in the Wellnhofer 1975 catalog)
2. Scaphognathus ( 2 specimens)
3. St/Ei I (JME 1)

Step two: ulna < each individual wing phalanx
That trait removes both specimens of Scaphognathus and the St/Ei (JME 1) specimen, leaving only one candidate.

Step three: A closer look at Rhamphorhynchus MYE 13 (Fig. 1).

1. Toothless tip of dentary, slightly pointed: Yes.
2. mc4/humerus ratio = 0.38  No. = 0.50, but then MYE 13 has a relatively shorter humerus than most Rhamphorhynchus specimens.
3. ulna < each individual wing phalanx Yes
4. tibia subequal to femur  Yes
5. deltopectoral crest more developed than in Qinlongopterus Yes
6. anterior teeth stouter and longer than in Pterorhynchus Yes
7. teeth are straight and longer than in Jianchangnathus Yes
8. pteroid/humerus ratio = 0.21 (but is the pteroid complete?); No. In MYE 13 the ratio is 0.66, but, as above, the humerus is atypically short  AND pteroid has expanded distal end  Yes
9. Larger than other rhamphorhynchine pterosaurs from Late Jurassic NE China
   Maybe. Wing fingers in Rhamphorhynchus specimens are relatively larger than are those in other Late Jurassic pterosaurs, so if only a wing is known it could belong to a relatively smaller skull and torso. Otherwise the mid-sized specimens listed above (except tiny Qinlongopterus) are all about the same size. 

Figure 1. The MYE 13 specimen of Rhamphorhynchus (n75 in the Wellnhofer 1975 catalog is currently the closest match to the Orientognathus description.

So, we’ll test these hypotheses
when the images become available, hopefully with scale bars. Then we’ll do a comparison.

References
Lü J-C, Pu H-Y, Xu L, Wei X-F, Chang H-L and Kundrát M 2015. A new rhamphorhynchoid pterosaur (Pterosauria) from Jurassic deposits of Liaoning Province, China. Zootaxa 3911 (1): 119–129.  http://dx.doi.org/10.11646/zootaxa.3911.1.7

 

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