Analysis of the neck bones of an extinct member of the giraffe family reveal how today’s giraffe got its exceptionally long neck.
It has long been thought that the giraffe’s neck was a result of evolution, but fossil evidence had been lacking.
In a paper published in Royal Society Open Science, scientists describe the neck of a “transitional” or “intermediate” species that existed about 7 million years ago.
The vertebrae were compared with neck bones from the only two living members of the Giraffidae family – the giraffe (Giraffa camelopardalis) and okapi (Okapia johnstoni), a short-necked mammal that lives in central Africa.
Like all mammals, members of the giraffe family have seven bones in their neck.
While today’s giraffe’s neck is about two metres long, the neck of Samotherium major was about half that length, while the okapi neck is just 60 centimetres long.
Co-author Ms Melinda Danowitz revealed the ancient giraffid’s neck was not only intermediate in length, but also in many morphological and proportional features.
“We can finally see the transitional stages in the elongation of the giraffe neck,” she said.
Construction of neck from four individuals
Senior author Professor Nikos Solounais, also from the American Museum of Natural History, said the neck was reconstructed from no more than four individuals that were all excavated from Samos in Greece.
“The bones might not be one individual, but considering the rarity of well-preserved fossil necks, it is likely they came from very few individuals, and that several of the bones came from the same individual,” he said.
Today’s study builds on earlier published work by the team that showed Samotherium underwent the first stage of neck elongation, which involved elongation of the cranial, or front end, of each neck bone.
However the second stage involving elongation of the back end of each neck bone, or the caudal, was not evident.
Ms Danowitz said the Samotherium neck had other characteristics that were also intermediate between the giraffe and okapi.
She said in the okapi the sixth neck bone included a completed ridge on the bone surface known as the ventral ridge.
This ridge was absent in the giraffe, but in Samotherium, this ridge was present on only half the bone.
On the same sixth bone, the ventral lamina, a bony protrusion for muscle attachments, was also transitional.
“In the okapi, the ventral lamina is a large, complete square-shaped plate, and in the giraffe, it is completely excavated, making a crescent,” Ms Danowitz said.
“In Samotherium, it has a shape intermediate between the two, where the ventral lamina is present but has a large notch.”
While Samotherium was not the direct ancestor of the giraffe, it was likely closely related, based on neck features as well as other skeletal features, Professor Solounais said.
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