A 4th Finger Imprint in the Haenamichnus Pterosaur Track?

Tracks attributed to pterosaurs are now known worldwide. The largest such tracks have been rightly attributed to giant azhdarchid pterosaurs like Quetzalcoatlus. The  Haenamichnus trackway (Hwang et al. 2002, Fig. 1) leaves no doubt as to the identity of the trackmaker, but the individual impressions differ greatly from one another and are indistinct at best. It must have been a wet, muddy day when these were produced. Sometimes the manus and pes impressions are separate, but often they glob together.

haenamichnus-track

Figure 1. Yellow arrow points to a possible 4th digit imprint in the trackway of Haenamichnus. Note how messy these muddy tracks are. Not much detail in each one. Only the walking pattern (on right) is precise. Note that Step 7 is the only one without a pes imprint, unless that medial shape IS the pes imprint.

Step 7
Among the many Haenamichnus ichnites (Fig. 1), step 7 is interesting because it appears to impress an oddball fourth impression medially between #1 and #3. What could it be?  In other pterosaurs or, for that matter, in other ichnites within this trackway digit 4, the wing finger, did not leave impressions. The wing finger was carried vertically, folded against the arm during terrestrial locomotion and the knuckle was elevated above the substrate. If digit 4 DID make that impression, why was the impression bent and so short? After all, digit 4 was a long straight bone that terminated in a large knuckle.

The first guess: The odd shape is the (otherwise missing) pes impression, blended into the manus impression. And with that, perhaps I need go no further… but I will.

The second guess:  The odd shape is the first impression of manual digit 3 before it was lifted and repositioned, rotated on the axis of the impression of digit 1. If so, the pes did not make an impression. In this case the pes might have hit a dry spot or was later obliterated.

The third guess:  Whatever geological thing that discoloration or dip was, it was there before the pterosaur touched it and remained afterwards.

Don’t be fooled by those who say: four impressions = four digits. Critical thinking, and the lack of similar traces in other pterosaurs argue against such snap judgements.

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
Hwang KG, Huh M, Lockley MG, Unwin DM and Wright JL 2002. New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, southwestern Korea. Geology Magazine 139(4): 421-435.

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