The long neck of the giraffe: New insights to an icon of evolutionary biology
Analysis of digitized collection specimens supports an old hypothesis.
For a long time, the long neck of giraffes has fascinated evolutionary biologists and anatomists. Despite its enormous length of approximately 2 meters it is made up of only 7 vertebrae, just like in us humans, in tiny shrews and almost all other mammals. New methods help researchers of the Humboldt-Universität zu Berlin (HU) and the Ludwig-Maximilians-Universität München (LMU) in Germany to find support for a more than 100 years old hypothesis: an aberrant shape of the first thoracic vertebra is functionally elongating the neck of giraffes. This demonstrates the giraffe’s unique evolutionary path.
Insights from natural history collections
The researchers scanned and analysed hundreds of vertebrae and skeletal material from diverse natural history collections. “Already a classic anatomical paper from the beginning of the last century proposed that the conspicuous shape of the first thoracic vertebra contributes to the elongation of the giraffe’s neck. With today’s technical tools we were now able to quantitatively show this to be true”, John Nyakatura, a professor for comparative zoology at HU, reports. The work was conducted in his team. Besides the giraffes, many other ruminants (e.g., cows, sheep, antelopes, and deer), but also camels like dromedaries and llamas were included in the study. A digital library of virtual bone models ensued, which – just like the article – is published “open access” (find the links below).
3D bone models were used to simulate movements
Marilena Müller (HU) performed a comparative 3D analysis of bone shape. The shape of the first thoracic vertebrae indeed had a differing shape and contrasted even other long-necked evolutionary relatives such as the gerenuk and the vicugna. Despite the presence of ribs and thus clearly maintaining the identity of a thoracic vertebra, its shape resembles a cervical vertebra. In terms of the anatomy of the first thoracic vertebra, giraffes are unique.
Taking this result as a starting point, Luisa Merten (HU) addressed the functional significance of this anatomical speciality. She used software, which was developed for the creation of 3D animation movies such as Shrek. The software allowed the simulation of the movement between the vertebrae. In these virtual experiments it was possible to quantify the possible mobility within the limitations of the joints. It was demonstrated that the giraffe had the largest mobility which contributes to the elongation of the neck.
Revealing evolutionary trends within even-toed ungulates
The researchers further showed, for instance, that the seventh cervical vertebrae of the European bison took on the shape of a thoracic vertebra during evolution. This appears to be an adaptation for extra robust transition from neck to trunk in this species, where the bulls engage in intense wrestling matches with their horns during the rutting season. Also, the shapes of the seventh cervical in long-necked species resemble each other in striking fashion. The typical shape was acquired independently in several lineages. “The ‘old’ natural history collections are indispensable for the understanding of step-wise evolutionary changes and help us to evaluate and integrate new results from molecular systematics”, Dr. Christine Böhmer from LMU explains. She has modelled the evolution of the anatomical structures analysed in the study over the last 65 million years.
Prof. Dr. John Nyakatura
Humboldt-Universität zu Berlin, Institut for Biology, Comparative Zoology, Tel.: +49 030 2093-98230, E-Mail: email@example.com
Dr. Christine Böhmer, Ludwig-Maximilians-Universität München, Department für Geo- und Umweltwissenschaften und GeoBio-Center, E-Mail: firstname.lastname@example.org
Link to article: https://doi.org/10.1111/evo.14171