Tall Blonde, Beau & the Beauty of Ossicones

You know you've made fast friends with zookeepers when you get invited to have lunch with a giraffe. My date was with a tall, nobby-kneed male named Beau, and while he smelled surprisingly awful (male giraffes are sometimes known as "stink bulls"...), he was lovely company, and had a surprisingly gentle mouth - unlike so many horses and dogs I've known who seem to like the taste of fingers along with their treats... Beau is a Masai giraffe (Giraffa camelopardalis tippelskirchi) - the tallest of the giraffe subspecies, and distinguished by ragged-edged spots that resemble impossible puzzle pieces.

Giraffes are pretty magical - so wonderfuly ungainly, and all at once lumbering and graceful. Beau was eager to saunter toward the feeding platform to receive our vegetable offerings, but as soon as he spotted the Zoo veterinarian (one of my guides), he side-stepped away in avoidance and assumed a wary, watchful stare with his enormous, thickly-lashed eyes. I imagined that startling a giraffe might easily lead to it's nervous system firing a charge that would betry it's own cumbersome legs... but watching this handsome, stilted giant perform the most fluid nervous pace, I could see that his ambulation - awkward as it was - could be trusted not to fail him under stress.
 

In admiring Beau's great long face, you'll notice how properly lumpy his forehead is, especially over and around his eyes. While periodically holding out handfulls of cubed butternut squash, the keeper explained that male giraffes develop these bumps as they age - a sort of skeletal scar tissue, the result of head-butting and "necking" other male giraffes (in what might be the most ridiculously awkward combat you've ever seen). Males naturally grow larger horns than females, though all of their crashing about wears the tufted fur - that so distinctively tops the apexes of lady giraffe horns - right down to the smooth hide (and yes, this is a reliable method for distinguishing gender). My anatomy interest peaked, I made time for an afternoon visit to Harvard's Museum of Comparative Zoology so I could get a better look at what all of these morphological differences looked like from the inside.

Examining bones and skeletons never fails to thrill me, and exploring comparisons between specimens (of different species, gender, or just age) is extra exciting. From the robust reserach archive of the MCZ I was able to find 2 lovely giraffe skulls - one adult female, and one adult male. Both were collected around the turn of the century and didn't have subspecies classification (Masai, reticulated, etc) listed, but their form revealed everything I was hoping to see regardless. Check out these beauties:
 

Above (clockwise from top left): the adult female skull, full front view; the adult female from 3/4 behind; the adult male skull from straight behind; and the male's forehead over the orbit of the left eye. (photos taken at the Harvard MCZ)

Lifting up each skull revealed the first dramatic gender difference - without a scale, my estimates put the female skull around 8-10lbs, but the male skull was probably about 25lbs (the kind of weight you cradle with both arms, as opposed to just "picking up"). The male skull felt SOLID, and understandably so - from the animation below, check out where the bulk of the bone mass lies: where the female's horns look like they were pinched out as a diminutive sculptural afterthought, the male sports 2 substantial columns of bone that no amount of battering could break off. His third, central horn is also decidedly horn-like, compared to the gentle knoll on the forehead of the female. It certainly isn't uncommon for ruminant ungulates to have sexually dimorphic heads (horns and antlers are much more commonly found in males of many species, and not females) and in this case, all that bone-weight in the male's skull gives it an advantage in the physics of a fight - since males spar by swinging their great heads at each other, a heavier skull would increase the force of a blow, and make for a more triumphant individual.


Beyond weight and shape, the next remarkable difference between these two skulls was in the texture of the bone (the feature that inspired this quest in the first place). In contrast to lovely lady giraffe's uniformly smooth skull surface, the top of the male's skull is built up, gnarled, pitted, and quite rough. This "extra-ossification" (gross build-up of bone formation) in male skulls generates larger, thicker horns than in females, and can lead to the development of a third (as seen in this specimen) and even 4th and 5th horn - the Rothschild subspecies is the only giraffe born with 5 horns, the extras sprouting oddly from behind each ear.

Giraffe horns are quite distinct from typical ungulate horns. Unlike the horns of cattle, goats, and antelope, in which hard keratin sheaths cover boney projections, a giraffe's horns are known as ossicones and are more like boney bumps covered direclty by furred skin (the term ossicones refers to their development as ossified cartilage). Proper horns start to grow from "buds" on the forehead of a baby cow, kid, or lamb, after birth, but giraffe calves are born with tiny ossicones already present. Not yet fully fused to the skull, these cartilaginous nubbins fold back when the baby makes it's passage through the birth canal, eventually standing erect and stitching themselves to the skull as the baby matures. In the female specimen above, the circular demarkation line between the ossicones and the skull is clearly visible (3/4 rear view), but the male's bone has grown so thickly that this line is obscured.

I had time after time watched the progression across the plain of the Giraffe, in their queer, inimitable, vegetative gracefulness, as if it were not a herd of animals but a family of rare, long-stemmed, speckled gigantic flowers slowly advancing.
~ Isak Dinesen, Out of Africa

I have posted many more of my giraffe skull photos from the MCZ into a flickr album. And if you're curious about the slightly comical act of giraffe necking, youtube this & that. Did you know there is a constellation called Camelopardalis? There is. Read a nifty discussion on the history of this celestial feature, and a bit of etymology on the giraffe's species name here. And why is their neck so long anyway? Wouldn't we all like to know! If you'd like to see/read more about the giraffe's only living relative, check out this blog entry I posted last year on the elusive, charismatic okapi. And finally, I can't post on giraffes and not link to something like this (because the internet exists in large part to simply spread cuteness around the universe).

Many thanks to my great friends at the Franklin Park Zoo, for introducing me to Beau, and the Harvard Museum of Comparative Zoology, for allowing me to spend some QT with their exceptional collections.

Comments

[The Daily Toki]

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