Scientific name Yungavolucris brevipedalis
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Yungavolucris is a genus of enantiornithine birds. It contains the single species Yungavolucris brevipedalis which lived in the Late Cretaceous (Maastrichtian, c.70.6 - 66 mya). The fossil bones were found in the Lecho Formation at estancia El Brete, Argentina.
Little is known about it because the only remains discovered so far are 6 tarsometatarsi, only one of which is nearly complete. This single foot bone, however, differs from all other birds in being very flat, and also very wide at the lower end. The specimens are small, just over 4 cm long, and if its legs and feet were not excessively shortened in relation to the body, the bird was about the size of a large blackbird in life.
Y. brevipedalis had short, wide, and dorsoplantarly flattened "legs" (actually ankles) with disproportionally broad and splayed "feet" (actually the front part of the feet only) which seem to have pointed markedly outwards (Chiappe 1993). This must have resulted in a somewhat Charlie Chaplin-like waddle if the bird walked on the ground. It was thus probably better adapted to swimming or even perching in trees than for running around in its richly vegetated shoreline habitat that was dotted by - possibly brackish - lakes and/or small rivers (Chiappe 1993).
Y. brevipedalis was an advanced enantiornithine and is sometimes considered to be closely related to Avisaurus. This is quite unlikely however; it certainly lacks the backwards-projecting growth of the trochlea where the middle toe attaches that is typical for Avisauridae. Moreover, as opposed to the undisputed avisaurids which apparently all were fairly large carnivores, it was a much smaller animal and almost certainly did not hunt vertebrates.
Due to the peculiar autapomorphies of the present species' remains, the question of its affinities is hard to decide however. It seems somewhat closer to the avisaurids than Lectavis bretincola, another enantiornithine discovered in the same deposit (Chiappe 1993). On the other hand, given that the Spanish Early Cretaceous (Barremian, 130-125 mya) enantiornithine Concornis lacustris appears closer to the avisaurids than either Yungavolucris or Lectavis (Sanz et al. 1995), a close relationship between the two El Brete taxa and Avisaurus seems highly unlikely.