Analysis of woolly mammoth tusks reveals surging testosterone levels in males.
Researchers say traces of sex hormones extracted from the animal’s tusk provide the first direct evidence adult males experienced musth.
This is a testosterone-driven episode of heightened aggression against rival males, associated with mating season.
According to scientists, in male elephants, elevated testosterone during musth was previously recognised from blood and urine tests.
Tusks hold particular promise for reconstructing aspects of mammoth life history because they preserve a record of growth in layers of dentin that form throughout an individual's life— Professor Daniel Fisher
Research suggests musth battles in extinct relatives of modern elephants have been inferred from skeletal injuries, broken tusk tips and other indirect lines of evidence.
But the new study is the first to show that testosterone levels are recorded in the growth layers of mammoth and elephant tusks.
Lead author Michael Cherney, a research affiliate at the University of Michigan Museum of Palaeontology, said: “Temporal patterns of testosterone preserved in fossil tusks show that, like modern elephants, mature bull mammoths experienced musth.”
The researchers report annually recurring testosterone surges – up to 10 times higher than baseline levels – within a permafrost-preserved woolly mammoth tusk from Siberia.
The adult male mammoth lived more than 33,000 years ago.
According to the findings, the testosterone surges seen in the mammoth tusk are consistent with musth-related testosterone peaks the researchers observed in an African bull elephant tusk.
The word “musth” comes from the Hindi and Urdu word for intoxicated.
Both modern and ancient tusks hold traces of testosterone and other steroid hormones, the study suggests.
These chemical compounds are incorporated into dentin, the mineralised tissue that makes up the interior portion of all teeth (tusks are elongated upper incisor teeth).
Hormones help regulate physiology and behaviour, and testosterone – a steroid hormone – is the main sex hormone in male vertebrates.
It circulates in the bloodstream and accumulates in various tissues.
Scientists have previously analysed steroid hormones present in human and animal hair, nails, bones and teeth, in both modern and ancient contexts.
However, the significance and value of such hormone records have been the subject of ongoing scrutiny and debate.
The researchers say their findings should help change that by demonstrating that steroid records in teeth can provide meaningful biological information that sometimes persists for thousands of years.
Study co-author Daniel Fisher, a curator at the University of Michigan Museum of Palaeontology and professor in the Department of Earth and Environmental Sciences, said: “Tusks hold particular promise for reconstructing aspects of mammoth life history because they preserve a record of growth in layers of dentin that form throughout an individual’s life.
“Because musth is associated with dramatically elevated testosterone in modern elephants, it provides a starting point for assessing the feasibility of using hormones preserved in tusk growth records to investigate temporal changes in endocrine physiology.”
For the study, researchers sampled tusks from one adult African bull elephant, aged 30 to 40 years old – and two adult woolly mammoths – a male (who lived to be about 55 years old) and a female – from Siberia.
The researchers used CT scans to identify annual growth increments within the tusks.
A tiny drill bit was used to grind half-millimetre-wide samples representing approximately monthly intervals of dentin growth.
The powder produced during this process was collected and chemically analysed.
New research methods were needed to extract steroids from tusk dentin.
The findings are published in the Nature journal.
