Finding the foot of Yi qi

The fossil scanoriopterygid bird,
Yi qi (Xu et al. 2015) is infamous for purporting to have a long extra bone (the so-called ‘styliform element’) somehow anchored to the wrist (see below) that many experts, including Dr. Kevin Padian (2015, see below), regarded as acting like a bat finger to stretch and support a bat-like wing membrane (not feathers). No sister taxa, all of them scansoriopterygid birds, have even a hint of such a bone. Here at pterosaurheresies alone that bone was determined to be a displaced radius on one wing and a displaced ulna on the other. Without these displaced bones, the forearms do not have their radius or ulna counterpart, which is standard equipment in all tetrapods with limbs. Not sure why this went unnoticed by the experts.

On a side note,
the foot was not reconstructed because the bones were very faint and intermixed with tail bones (Fig. 1). Dr. Padian reported that nothing below the waist was known. That is incorrect. He must have been shown only one plate or counter plate.

With the recent reconstruction of a sister taxon,
Omnivoropteryx, which has an odd (autapomorphic) long pedal digit 4, a second attempt was made to trace and reconstruct the foot of Yi qi (Fig. 1). If the tracing is correct, then the reconstruction of the Yi pes greatly resembles that of it sister, Omnivoropteryx, as one would expect. However, digits 3 and 4 are similar in length. In some other scansoriopterygids, digit 4 is shorter to much shorter.

This tracing
is just about at the limit of DGS capabilities without a higher resolution dataset. Fortunately a sister taxon provides a blueprint to model this foot against. And yes, the caudal vertebrae are confusing as they mix in with the pedal elements. And yes, some of the bones are only represented by faint impressions distally and proximally with the rest filled in using a-z bracketing.

Figure 1. The foot (pes) of the scansoriopterygid bird, Yi qi, both in situ and reconstructed. The amber bones are causals.

Figure 1. The foot (pes) of the scansoriopterygid bird, Yi qi, both in situ and reconstructed. The amber bones are causals.

Back to the ‘styliform element’
Dr. Padian (2015) reports, “Their (Xu et. al) find opens two cans of worms: about interpreting unique structures in fossils and about what it means to fly. The styliform element, which may be a hypertrophied wrist bone or a neomorphic calcified structure, is longer than any of the animal’s fingers and is curved at both ends. It is probably not a true finger. How the structure is attached to the wrist is not clear, because its proximal end seems quite  squared off; this means that we also do not know if or how it could move.  What could this element be except a support for some kind of aerofoil? The authors infer this on the basis of its position and the presence of membranous tissue in the wrist area.”

Note that 
Dr. Padian does not consider the possibility that the ‘styliform element’ is either a displaced radius or ulna, despite matching lengths and morphologies. This lack of recognition is rare, but not unknown. For instance, in 2000 I did not recognize the stem of the displaced prepubis in Cosesaurus.

Padian also notes: “Furthermore, in flapping animals the outboard skeletal elements (wrist, hand and so on) are primarily responsible for thrust, the essential component of powered flight, but these are not particularly long in Yi qi. So, at present we can shelve the possibility that this dinosaur flapped.” This appears to be an oversight statement. Not only does Yi qi have an elongate hand, the point is: it doesn’t matter how large or feathered a forelimb is. Even flightless birds, including most baby birds, flap. However tetrapods that flap for locomotion all have locked down and elongate coracoids. Perhaps Padian meant ‘flying.” If so, he is likely correct. Scansoripterygids have been discovered with tail feathers, but not bird-like wing feathers. This may have been the first clade of flightless birds. As we learned yesterday, the dromaeosaurid, Balaur was not a basal flightless bird. If you want to see what basal flightless birds actually look like, check out the scansoriopterygids.

Padian K. 2015. Paleontology: Dinosaur up in the air. Nature (2015) doi:10.1038/nature14392
Xu X, Zheng X-T, Sullivan C, Wang X-L, Xing l, Wang Y, Zhang X-M, O’Connor JK, Zhang F-C and Pan Y-H 2015.
 A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings.Nature (advance online publication)


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