Eyelashes of the Harvard Museum of Natural History
June 19, 2012
Secretary bird:
Matt pointed out to me something that in retrospect is obvious, though I’d never thought about it before: the eyelashes of birds are not homologous with ours, since mammals’ eyelashes are modified hairs and birds don’t have hair. Instead, their lashes are modified feathers. It would be interesting to see both kinds of eyelash under a microscope and compare.
It certainly looks as though these “feathers” are simple unbranched filaments — much like the earliest protofeathers found on so many of those wacky Chinese raptors. I wonder how closely they resemble the ancestral state?
Sauropod Vertebra Picture of the Week 
June 19, 2012 at 1:54 pm
I would guess they’re some kind of bristle or filoplume, which IIRC are derived from more ‘modern’ feathers. http://3.bp.blogspot.com/-ThS6rZ5nO9c/TnZXC2d-2SI/AAAAAAAAEn4/xkoKn9xKXJQ/s1600/feathers+types+tail+flight+contour+semiplume+down+filoplume+bristle+powder+down.jpg
“It certainly looks as though these “feathers” are simple unbranched filaments — much like the earliest protofeathers found on so many of those wacky Chinese raptors.”
I don’t think any Chinese raptors really exhibit unbranched filaments. Currie & Chen 2001 showed that even Sinosauropteryx seems to have had down-like simple branching, rather than monofilaments, and Foth 2011 showed that even vaned feathers appear filamentous when flattened. It looks like the evidence that any known theropod had simple monofilament “protofeathers” is actually pretty thin (though a more detailed examination of the taphonomy and preserved structure of Yutyrannus and Dilong feathers would be nice).
June 19, 2012 at 3:33 pm
I wonder if these eyelashes are derived from feathers at all, or if they are more similar to the “beards” on turkeys, which are filamentous, but not feathers (see: Sawyer et al. 2003).
Sawyer, R.H., Washington, L.D., Salvatore, B.A., Glenn, T., Knapp, L.K. 2003. Origin of Archosaurian Integumentary Appendages: The Bristles of the Wild Turkey Beard Express Feather-Type Beta-Keratins. J.Exp.Biol(Mol.Dev.Evol). Vol.297B:27-34
June 19, 2012 at 3:33 pm
Ha, finally someone who knows the Foth paper! :)
June 19, 2012 at 3:53 pm
“… finally someone who knows the Foth paper”. Ha – whadda you talking about.. it gets cited all the time!
June 19, 2012 at 4:11 pm
Ha! I keep reading or hearing discussions that ignore it, although it is highly pertinent.
June 19, 2012 at 6:36 pm
Did a quick lit search and it looks like most folks lump them together with similar mono-filamentous facial feathers as “bristles”, a la the rictal bristles of many aerial insectivores (e.g. Brush 2000, Cunningham et al. 2011). Lederer (1972) illustrates the structure of some rictal bristles as having small barbs at the base. Anyway it is suggested that they are modified contour feathers and, to quote Brush (2000):
It is interesting that they eyelash bristles seem especially well developed in ground foraging birds: secretary birds, roadrunners, seriemas ground hornbills, and the like. Though on the last one, I notice that “normal” tree hornbills have them as well. Tempted to make arm wavy hypotheses about protecting the eyes from struggling prey or debris kicked up while hunting.
Incidentally I have always thought Rictal Bristles would be a great name for a band.
Brush, A. H. (2000), Evolving a Protofeather and Feather Diversity. Amer. Zool., 40(4): 631-639 doi:10.1093/icb/40.4.631
Cunningham, S. J., Alley, M. R. and Castro, I. (2011), Facial bristle feather histology and morphology in New Zealand birds: Implications for function. J. Morphol., 272: 118–128. doi: 10.1002/jmor.10908
Lederer, R. J. (1972), The Role of Avian Rictal Bristles. The Wilson Bull., 84(2) 193-197. pdf available here: http://library.unm.edu/sora/Wilson/v084n02/p0193-p0197.pdf
June 20, 2012 at 12:15 pm
The most popular hypothesis used to explain the presence of especially long, thick eyelashes in birds is that they’re used to shield the eyes from the sun. See Martin & Coetzee 2004.
June 26, 2012 at 3:58 am
Squinting is useless without eyelashes to provide diffraction.
But you can’t fool me. Those are obvious fakes. Next you’ll ask what the red integument on the toenails is homologous to, and whether in combination they identify this specimen as a shameless hussy or a drag queen.
June 30, 2012 at 3:10 pm
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