How the giraffe got its long neck
BYSARAH ZIELINSKI 2:30PM, OCTOBER 7, 2015
The neck of a giraffe isn’t all that different from any other mammal’s.
There are seven neck vertebrae, like those of humans, but they are much
bigger. (This is a different strategy than other long-necked creatures in history.
Marine reptiles called plesiosaurs, for instance,had 38 to 42 vertebrae to
lengthen their necks.)
How giraffes evolved their long necks has long been the subject of debate,
dating back to the early days of evolutionary theory. French naturalist
Jean Baptiste Lamarck, for instance, suggested that the giraffe neck
lengthened as the animals stretched to reach leaves high in trees, with a
“nervous fluid” flowing into the neck to make it longer. The giraffe’s offspring would inherit the longer neck, then stretch to reach even higher leaves, and that even longer neck would get passed on.
That’s not how evolution works, though. Animals that had longer necks had some sort of advantage, and they were able to pass on their genes, eventually resulting in super-long necked animals. Just what that advantage might have been is still unknown. Perhaps the feature let giraffes access more food resources high in the treetops. But since female giraffes prefer males with longer necks, sexual selection might also be involved.
But what did that evolution look like? And when did it happen? Insight
into those questions comes from astudypublished October 6 inRoyal
Society Open Science. Melinda Danowitz and colleagues at the New
York Institute of Technology College of Osteopathic Medicine in Old
Westbury analyzed neck vertebrae from 11 species — nine that are
extinct, modern giraffes (of course) andokapi. (Okapi look like a cross
between a zebra and a deer, but they belong to the same family as
giraffes.)
Giraffes, it turns out, are not the first species in their lineage to have
a long neck — they just have the longest one. The species started off
with a shorter neck, 7.5 million years ago, when it first appeared on the
scene,after which the neck became even longer. But the lengthening
beganeven earlier in the giraffe’s lineage, the fossil analysis revealed.
The extinctGiraffasivalensisshares some of the elongation features
found in the modern giraffe. But even it wasn’t the beginning of the
journey. Two other extinct creatures from the giraffe family Giraffidae,
SamotherianandPalaeotragus, also show some of these features, as
does the primitive giraffidCanthumeryx. But what was surprising was
that the neck length appears to predate the giraffe family — an even
earlier species,Prodremotherium, which disappeared some 23 million
years ago, also showed neck elongation.
“Neck length, the most distinguishing and popular attribute ofGiraffa,
is apparently not a defining feature of the family,” the researchers note.
All living giraffes are considered to belong to one species,
G. camelopardis. But a2007 genetic studysuggested that the animal’s
many subspecies may actually be separate species. If that’s true, I’d be curious how the animal’s long neck — and unique bones — have continued to evolve within each of those groups.