Hoopoe-billed Akialoa (Hemignathus upupirostris)  

The Hoppoe-billed Akialoa, so named for the structure of its beak, is known only on the basis of well-preserved subfossil remains that were found on the islands of Kaua’i and O’ahu, and which can apparently be assigned to one and the same species.  

The morphology of the beak shows that the bird had a quite short tongue, in contrast to the other historically known akialoa forms, which all had their tongues about as long as their beaks., thus the Hoopoe-billed Akialoa is thought to have had a somewhat distinct, possibly in some way specialized feeding behavior. [1][2]  

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Subfossil remains of this, or a closely related form, are now known from other islands of the Hawaiian chain as well.  

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References:  

[1] S. L. Olson; H. F. James: Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part II. Passeriformes. Ornithological Monographs 45: 1-91. 1991 
[2] H. D. Pratt: The Hawaiian Honeycreepers: Drepanidinae. Oxford Univ. Pr. 2005  

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edited: 21.09.2017