How the giraffe got its long neck
BY SARAH 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.)
The giraffe’s journey to long-necked
How giraffes evolved their long necks has long been the subject of debate,
wonder began more than 20 million
dating back to the early days of evolutionary theory. French naturalist
years ago, a new study finds.
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 a study published October 6 in Royal
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) and okapi. (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
began even earlier in the giraffe’s lineage, the fossil analysis revealed.
The extinct Giraffa sivalensis shares 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,
Samotherian and Palaeotragus, also show some of these features, as
does the primitive giraffid Canthumeryx. 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
Giraffes have the longest necks of this
years ago, also showed neck elongation.
bunch, but ancestral species going
“Neck length, the most distinguishing and popular attribute of Giraffa,
back as far as 25 million years ago
is apparently not a defining feature of the family,” the researchers note.
show signs of neck elongation.
All living giraffes are considered to belong to one species,
G. camelopardis. But a 2007 genetic study suggested 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.
https://www.sciencenews.org/blog/wild-things/how-giraffe-got-its-long-neck