Mammals may have slept through dinosaur extinction

By Karl Gruber 23 October 2014
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Madagascan tenrecs are the first known tropical mammals to hibernate for long stretches without waking

THE DISCOVERY OF A tropical mammal that can hibernate for nine months straight sheds light on how early mammals may have survived the cataclysm that killed off dinosaurs, new research reveals.

Mammals are capable of amazing feats while hibernating, from delaying aging to having sex. But animals that hibernate typically live in temperate regions and go into a torpor in cold, winter conditions, in order to conserve energy. The tenrec is the first known tropical mammal found to hibernate for long stretches without arousal periods.

The common tenrec (Tenrec ecaudatus) is an elusive mammal, weighing up to 2kg, and is found in the forests of Madagascar. One of the world’s largest insect-eating mammals, it is considered a living fossil from the Late Cretaceous, more than 66 million years ago, says Dr Barry Lovegrove, an evolutionary physiologist at the University of KwaZulu-Natal in South Africa, lead author of the report published this week in Proceedings of the Royal Society B.

The findings suggest that prehistoric mammals may have used hibernation as a way to safely slumber through the mass extinction event that wiped out the dinosaurs.

Tropical mammal hibernate “exceptional”

In the study, 15 tenrecs were tagged with radio-transmitters and temperature loggers, which allowed researchers to record how much these animals slept and variations of their body temperature.

After tracking the animals over a two-year period, researchers found some extreme results. “One adult male hibernated for nine months, until we were forced to dig it up because the radio transmitter batteries were dying,” says Barry.

Such long period of hibernation is an exceptional finding in tropical mammals, says Barry. “But what was totally unique about the hibernation was that it was not once interrupted by an arousal which is seen in all temperate hibernators,” he adds. Periods of waking, known as interbout arousals – is a usually pattern seen in mammal and is thought to have evolved to help an organism restore metabolic imbalances.

While body temperature data is an indirect indicator of sleep/wake cycles, measuring metabolism would provide a clearer picture of the tenrecs’ sleep, says Dr Sandy Martin, a developmental biologist from the University of Colorado School of Medicine, in the USA. “It will be important to actually measure metabolic rates during this prolonged hibernation period in tenrecs in future experiments,” she says.

The research also suggests that mammal sleep strategies may be more nuanced than currently thought. ” I think ‘metabolic flexibility’ [the ability to lower metabolism during torpor] is much more widespread in mammals than we had appreciated,” says Sandy. “We have, until very recently, tried to place all mammals – with the exception of hibernators – into two or three boxes, when really there’s a continuum of metabolic flexibility.”

A Madagascan tenrec. (Credit: Barry Lovegrove)

A simple survival strategy: mammal hibernation

Sometime around 65.5 million years ago a meteorite crashed to Earth in Chicxulub, Mexico, causing one of the world’s largest mass extinctions, killing all large land creatures and plants. This period, known as the Cretaceous-Palaeogene (K-Pg) boundary, represents a turning point for many species. While most dinosaurs disappeared, mammals started to bloom.

However, until recently, it was only speculated how mammals survived the asteroid impact and the unhospitable environment that followed.

“To hibernate for nine months, and perhaps even longer, without once needing to arouse, can explain how mammals survived the year-long ecological devastation that occurred across the planet when the meteorite slammed into the Earth,” says Barry.

The new finding also has some potential implications beyond the world of tenrecs.

The lack of interbout arousals may help future studies identify the ‘on’ and ‘off’ metabolic switches found within human physiology, says Barry, which is “extremely useful information for mankind- that can be used to induce hypothermia in medical procedures involving general surgery, traumas, strokes, and asphyxiated neonates. Also, it may provide the information needed to induce a hibernating state in astronauts for the nine-month trip to Mars.”