According to new research from the University of Zürich, the cave bear (Ursus spelaeus) — one of the biggest bear species in history — had an unusually small brain relative to its body size.
Reconstruction of the cave bear (Ursus spelaeus). Image credit: Sergio de la Larosa / CC BY-SA 3.0.
The cave bear was a massive omnivore that lived in Europe during the Pleistocene epoch and became extinct approximately 25,000 years ago.
Despite their name, cave bears didn’t actually live in caves but only used them for hibernation. Nevertheless, the occasional death of animals in various caves in Europe over several tens of thousands of years eventually led to enormous accumulations of bones and teeth.
The animal weighed between 500 and 1,100 pounds (225-500 kg), was 8.9-11.5 feet (2.7-3.5 m) long and up to 5.6 feet (1.7 m) at the shoulder.
The massive grinding molars and nitrogen-isotope data from its bones indicate that the cave bear was primarily herbivorous, with foliage its main dietary staple. Cave bears and people likely encountered one another occasionally.
Most paleontologists think that the cave bears fell victim to the profound environmental changes following the glaciers’ withdrawal from Europe rather than human hunting.
Collecting data on relative brain size for present-day and extinct bears, University of Zürich paleontologist Kristof Veitschegger found that the cave bear had an unusually small brain relative to its body size.
“Zoologists use a measure known as the encephalization quotient (EQ) to express this ratio,” Veitschegger explained.
“I collected and investigated a dataset of 412 brain and body size estimates based on the skulls of 10 extant and extinct bear species,” he said.
“EQ of cave bears is significantly lower than that of most other species. Cave bears exhibit an EQ of 0.60, which is considerably lower than the one of brown bears (0.83) or the one of Malayan sun bears (1.31).”
Veitschegger interprets this as evidence that the increase in body size during the evolution of the cave bear did not correlate with change in brain size. However, the proportionately small brain may also reflect a less energy-rich diet — as other bears consume more animal protein — and a highly seasonal environment that probably required longer periods of hibernation.
Cave bears gave birth to numerous cubs after long gestation periods, according to the researcher.
“Based on relative brain size, I hypothesize that cave bears had a small birth and weaning weight but produced many cubs and had a prolonged gestation time,” he said.
His examination of the microscopic structure of their leg bones indicates that cave bears grew more rapidly but attained sexual maturity later in life than other bear species.
“Longevity estimates based on cementum analysis of 95 cave bear teeth from 21 localities provided a minimum age of 29 years for cave bears,” Veitschegger said.
He reported his results August 25, 2017 at the 77th Annual Meeting of the Society of Vertebrate Paleontology in Alberta, Canada.
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Kristof Veitschegger. 2017. Life History Evolution in Cave Bears – Elucidating the Biology of an Extinct Megafaunal Element. SVP 77th Annual Meeting
