What’s up with that two meter long neck? In addition to the elongated cervical vertebrae, the giraffe’s trademark has another secret, a study makes clear: the seven cervical vertebrae that are common in mammals are supplemented by a converted thoracic vertebra, the scientists have now been able to confirm through analyzes and simulations. As they further report, interestingly, the bison developed in the opposite direction: a cervical vertebra was converted into a thoracic vertebra.
No other animal is so “snooty”: Giraffes can reach heights of up to six meters. This enabled these bizarre cloven-hoofed to tap the leaves of the treetops as a source of food in their African habitats. According to the principle of evolution, the ancestors of the giraffes apparently grew longer and longer in the course of their evolution. But how? This question has long fascinated anatomists and evolutionary biologists. One thing is clear: there was no increase in cervical vertebrae in the giraffes either. Despite its enormous length, the neck is only formed by seven cervical vertebrae – like ours. This is a rule in mammals – with only a few exceptions.
Specially extended
The cervical vertebrae of the giraffes are, however, strongly stretched in order to jointly ensure an elongation of the bony support structure. “But already in an anatomical work from the beginning of the previous century the hypothesis was put forward that the striking shape of the first thoracic vertebra also contributes to the lengthening of the neck in giraffes,” says John Nyakatura from the Humboldt University in Berlin. He and his colleagues have now devoted a study to this hypothesis. The researchers initially scanned and examined hundreds of vertebrae and skeletons from various scientific collections. Next to the giraffes
Böhmer (Ludwig-Maximilians University), Müller (Humboldt University), Nyakatura (Humboldt University)
they included many other related cloven-hoofed animals – cattle, sheep, antelopes and deer, as well as representatives of the camels. From the data, the researchers developed a digital library of virtual bone models.
They then subjected the structures to a three-dimensional statistical shape analysis. The peculiarity of the first thoracic vertebra of the giraffes became clear: Although this bone has ribs and is therefore part of the thoracic spine, its shape resembles a cervical vertebra, the studies showed. The giraffe is unique in this respect: even ungulates, which also have long necks, such as the giraffe gazelles or the vicuñas, do not have thoracic vertebrae with these special characteristics.
An additional element
As part of their study, the scientists also examined the functional significance of this special feature. To do this, they used software that is also used in animation films. It made it possible to simulate the movements between the vertebrae. In this way, the researchers were able to virtually record the freedom of movement until the bones meet or the joints reach their limits. In this context, it became apparent that the special features of the giraffes’ first thoracic vertebra enable special freedom of movement. Functionally, the cervical spine of the famous long necks consists of eight elements. “With the modern technical possibilities we were able to prove the old hypothesis”, summarizes Nyakatura.
As the researchers finally report, their investigations also uncovered an interesting peculiarity of the cervical spine in another articulated ungulate: While the giraffes converted a thoracic vertebra into a cervical vertebra, the bison did the opposite: in these short-necked colossi, the seventh cervical vertebra in the course of the Evolution has assumed the shape of a thoracic vertebra, the analyzes make clear. As the researchers explain, this is probably an adaptation to the heavy loads in the context of the rival fights between the bulls: The more robust transition from the neck to the torso provides increased stability when the heavyweights thunder their heads at one another.
Video: Okapi and giraffe: comparison of the thoracic vertebrae (Credit: Humboldt-Universität zu Berlin)
Source: Humboldt University of Berlin, specialist article: Evolution, doi: 10.1111 / evo.14171