A mammoth tusk on Wrangel Island.
Credit: Patrícia Pečnerová
Elephants are well known for the cultural organisation in which a matriarchal group, led by a older female who acts as a repository for group knowledge such as where the water may be found during a drought, etc. This group consists of females with their young but males, when they reach a certain age, generally fend for themselves in smaller groups or as solitary individuals often associated with but not members of a matriarchal group.
This, of course, deprives males of the protection of the group and of the knowledge and wisdom of the matriarch.
Now it seems Eurasian woolly mammoths, Mammuthus primigenius, may have had a similar social structure, suggesting that this may be a structure inherited from a common ancestors. This is a conclusion from the finding that young males are very much over-represented in the remains of mammoths which appear to have met an untimely, accidental death. The fossilised remains of mammoths which died of old age or due to predation are rarely found because they rarely fossilised. To become a fossil, a mammoth needed to be buried or submerged quickly, for instance by falling through ice on a frozen lake or becoming stuck in a bog they blundered into.
The team of researchers discovered this when analysing the DNA of Eurasia mammoths as part of another project, for which the sex of the individual needed to be know. When this disparity emerged, they decided to investigate further.
Researchers who have sexed 98 woolly mammoth specimens collected from various parts of Siberia have discovered that the fossilized remains more often came from males of the species than females. They speculate that this skewed sex ratio -- seven out of every ten specimens examined belonged to males -- exists in the fossil record because inexperienced male mammoths more often travelled alone and got themselves killed by falling into natural traps that made their preservation more likely. The findings are reported in Current Biology on November 2. "Most bones, tusks, and teeth from mammoths and other Ice Age animals haven't survived," said Love Dalen of the Swedish Museum of Natural History. "It is highly likely that the remains that are found in Siberia these days have been preserved because they have been buried, and thus protected from weathering. The new findings imply that male mammoths more often died in a way that meant their remains were buried, perhaps by falling through lake ice in winter or getting stuck in bogs." "We were very surprised because there was no reason to expect a sex bias in the fossil record," added Patrícia Pecnerova, the study's first author, also at the Swedish Museum of Natural History. "Since the ratio of females to males was likely balanced at birth, we had to consider explanations that involved better preservation of male remains."
The suggestion is that, like modern elephants, these young males were more prone to these sorts of accidents because they lack the protection and wisdom of the older matriarchs. Biologically, because one male can impregnate many females, it makes sense in a herbivore to concentrate the effort involve in rearing young on the females of the species, especially where groups are small.
HighlightsThe interesting thing is that this social structure in the elephant family was probably present in the common ancestor of the woolly mammoth and the modern elephants. The Elephantidae diverged into the ancestor of the African elephants (Loxodonta) and the Elephantini in the Early Pleistocene some 2.6 million years ago. The Elephantini again diverged into the Asian elephants (Elephas) and the mammoths (Mammuthus), so the last common ancestor lived in the Early Pleistocene some 2.6 million years ago - only some 200,000 years after the earliest Homo species, H. habilis, had evolved.
- Paleogenomic sexing of 98 mammoth remains shows a significant skew toward males
- This implies a higher rate of preservation of male remains until the present day
- Inexperienced males more often dying in natural traps could explain this pattern
- The excess of male remains may thus be a result of the mammoth’s social structure
Summary
While present-day taxa are valuable proxies for understanding the biology of extinct species, it is also crucial to examine physical remains in order to obtain a more comprehensive view of their behavior, social structure, and life histories [1, 2]. For example, information on demographic parameters such as age distribution and sex ratios in fossil assemblages can be used to accurately infer socioecological patterns (e.g., [3]). Here we use genomic data to determine the sex of 98 woolly mammoth (Mammuthus primigenius) specimens in order to infer social and behavioral patterns in the last 60,000 years of the species’ existence. We report a significant excess of males among the identified samples (69% versus 31%; p < 0.0002). We argue that this male bias among mammoth remains is best explained by males more often being caught in natural traps that favor preservation. We hypothesize that this is a consequence of social structure in proboscideans, which is characterized by matriarchal hierarchy and sex segregation. Without the experience associated with living in a matriarchal family group, or a bachelor group with an experienced bull, young or solitary males may have been more prone to die in natural traps where good preservation is more likely.
Pečnerová, Patrícia; ; Díez-del-Molino, David; Dussex, Nicolas; Feuerborn, Tatiana; von Seth, Johanna; van der Plicht, Johannes; Nikolskiy, Pavel; Tikhonov, Alexei; Vartanyan, Sergey; Dalén, Love
Genome-Based Sexing Provides Clues about Behavior and Social Structure in the Woolly Mammoth Current Biology 27(22), 3510.e3; DOI: 10.1016/j.cub.2017.09.064
Copyright: © 2017 The authors.
Published by Cell Press. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
These cultures, which probably depend on a large brain and a high level of intelligence together with a suite of cultural norms or ethics, had probably evolved in at least this branch of the Elephantidae long before anatomically modern humans had evolved and around the time we were diverging from the Australopithecines.
Something else that was once thought to be unique to humans and which sets us apart from the other animals, culture and group ethics, is probably at least as old as the Homo genus, may well predate us and was well advanced in another species by the time our brains were beginning to expand.
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