Scientists Discover the Real Reason Giraffes Had Long Necks


Intermale competitions of giraffoids, foreground: Discokeryx xiezhi, background: Giraffa camelopardalis. Credit: Wang Yu and Guo Xiaocong

Fossils demonstrate that head-butting fighting contributed to the development of long necks in giraffes.

The study authors offer an alternative theory for the origin of the long necks of modern giraffes: Giraffes needed them for headbutting fights which they used in competition for mates. This theory is supported by an analysis of unique head and neck fossils from a giraffe ancestor, which include a disc-shaped helmet and very complex head-neck joints.

Since Charles Darwin originally proposed the ideas of adaptive evolution and natural selection, the distinctive long neck of the modern giraffe – the tallest land animal and largest ruminant on Earth – has long been considered as an example par excellence of these processes. According to popular belief, food competition led to elongation of the neck, which allowed giraffes to forage for leaves from the treetops in the forests of the African savannah far beyond the reach of other species of ruminants.

High Speed ​​Headbutt Modeling in Discokeryx Xiezhi

High Speed ​​Headbutt Modeling Discokeryx xiezhi using finite element analyses, with (A) and without (B) the complicated joints between the skull and the vertebrae, showing the stable (A) or overflexed (B) head-neck joint. Credit: IVPP

Others, however, have advanced the “neck for sex” theory, which holds that competitively-oriented sexual selection between males may also have played a role in the development of the elongated neck. Shi-Qi Wang and his colleagues say the remains of extinct giraffe species may shed light on these evolutionary mechanisms.

Here, Wang and his team report and describe a new species of Miocene giraffoid, Discokeryx xiezhi. Fossils, dated to around 17 million years ago, indicate that this ancient species of giraffoid had a helmet-like headgear and particularly intricate head and neck joints.

Junggar Basin Fossil Community

The fossil community of the Junggar Basin around 17 million years ago. Discokeryx xiezhi are in the middle. 1 credit

According to the researchers, these particular morphological characteristics show an adaptation to fierce head-butting behavior. In fact, the authors suggest that Discokeryx xiezhi may have possessed the most optimized head and neck adaptation ever identified in vertebrate evolution.

Additionally, tooth enamel isotope data from these fossils suggest that the species also likely filled a specific ecological niche in the ecosystem inaccessible to other contemporary herbivores. Altogether, the scientists suggest that the early evolution of giraffoids is more complex than previously known, where in addition to competition for food, sexual combat likely played an important role in the formation of long necks. and adapted uniquely from the group.

Reference: “Sexual selection favors the evolution and ecological adaptation of giraffoids” by Shi-Qi Wang, Jie Ye, Jin Meng, Chunxiao Li, Loïc Costeur, Bastien Mennecart, Chi Zhang, Ji Zhang, Manuela Aiglstorfer, Yang Wang , Yan Wu , Wen-Yu Wu and Tao Deng, June 3, 2022, Science.
DOI: 10.1126/science.abl8316


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