Wednesday, February 6, 2013

If it looks like a duck, etc., part II

Making a mountain of a mole-duck
While the turtle-jawed goose foraged the forests of Kauai during the day, nighttime on the island brought out an entirely different, and even weirder, character. Snuffling through the underbrush, poking its sensitive bill through the leaf litter, something else was stirring.

Enter Talpanas lippa, the nearly-blind mole-duck. The evolutionary origins of this bizarre bird are still a mystery and, like the turtle-jawed goose with which it existed, the greater age of Kauai had clearly wrought the mole-duck into a super-specialized and unique species. T. lippa was adapted not for a life of browsing or dabbling for water plants; instead, it probed the detritus for worms and insects like the kiwis of New Zealand.
Talpanas lippa, the nearly-blind mole-duck of Kauai. Reconstruction by Julian Hume.
The largest mole-ducks were the size of female mallards, though their physique was much stockier. Its legs were shorter and stronger than those of similarly-sized ducks, and its feet probably lacked webbing, as this was an animal clearly adapted for the terrestrial life. Though a complete skull remains undiscovered, the holotype fossil of this species is its braincase, revealing unique characteristics about the mole-duck beyond its external features.

The true weirdness of the mole-duck lies beyond its stout body. The foramina, holes through which nerves and arteries are connected to other areas around the skull, are unlike those found in any other living species of duck. The optic foramen, connecting the brain to the optic nerves, is extremely reduced, and leads to equally small orbits: T. lippa had beady eyes and extremely poor eyesight. (James et. al, 2009)Now, these adaptations are common among nocturnal insectivores, and they do not pose a problem to the little mole-duck. But every nocturnal hunter needs a way to find its prey; if it didn’t rely on eyesight, just how did it seek out its food?

The mole-duck, rather than using sight to find its prey, used its sense of touch. Kiwis use whisker-like feathers to feel for worms in the soil, but the mole-duck had a much broader, flatter bill. Connected to this bill, however, were huge foramina through which passed the bird’s trigeminal nerves, which are responsible for sensation in the facial region. The mole-duck, it seems, had an extremely sensitive bill, perfect for detecting minute vibrations and movements under the rotting leaves and logs on the forest floors of Kauai. (James et. al, 2009) Platypuses (platypi?) hunt their aquatic prey in a similar fashion: their bills are extremely sensitive, and can be used like a giant, flat hand as they sift through the substrate.

It doesn’t get much weirder than T. lippa. It really doesn’t. Over generations and generations, the awesome powers of evolution turned an ordinary-looking duck to a stumpy, nocturnal, platypus-billed, nearly-blind insect-hunter. It’s a shame that such an interesting and indescribably unique species no longer scuffles through the nighttime Hawaiian forests, where daylight saw the march of heavyset, turtle-jawed, titanic herbivorous waterfowl. The more we discover about the bizarre ducks of Hawaii, the more we learn about the incredible niches which these waterfowl were so diverse to fill.

Cooper, A.; Fleischer, R.C.; James, H.F.; Olson, S.L.; Paxinos, E.E.; Quinn, T.W.; and Sorenson, M.D. 1999. Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA. Proceedings of the Royal Society B 266, 2187-2193.

James, H.F. and Olson, S.L. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands, part I. non-passeriformes. Ornithological Monographs 45, 1-88.

James, H.F.; Olson, S.L.; and Iwaniuk, A.N. 2009. Extraordinary cranial specialization in a new genus of extinct duck (Aves: Anseriformes) from Kauai, Hawaiian Islands. Zootaxa 2296, 47-67.

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