Early bears were omnivores that ate anything and everything they could find

Scientists have just tested the jaw of Europe’s earliest bear to see what was on the menu. The answer? Early bears ate a little bit of everything – they were omnivores.

Ursus minimus lived 4.9 to 1.8 million years ago and ate a mixed diet rather than specializing on insects. It is thought to be the first known member of the genus Ursus, which later gave rise to brown and polar bears.

The work was led by Anneke van Heteren from the Bavarian State Collection of Zoology (BSC) in Munich. She centered the analysis on chewing mechanics because feeding leaves reliable signals in bone.

Ursus minimus food choices

Jawbones carry the marks of how an animal bit and chewed throughout its life.

Scientists study the height of the upper jaw hinge and where the main chewing muscles connect to understand what kinds of foods the animal could process.

Different foods require different jaw-opening angles and leverage. Those mechanical demands leave measurable patterns that can be compared across species.

This is not trivia about a single fossil. It clarifies how flexible feeding strategies can set the stage for the later rise of specialists.

3D test rewrites bear diet

Software called MorphoJ extracted shape information through a procedure called Procrustes superimposition and allowed researchers to compare shapes independent of size, position, and orientation.

In the new analysis, the single known mandible of Ursus minimus was compared with 108 jaws from living and fossil bears with known diets. The fossil clustered with omnivorous species rather than with insect specialists.

“The present study reveals that the mandibular morphology of Ursus minimus aligns more closely with omnivorous species than with insectivorous bears,” wrote van Heteren.

That result replaces the older picture of a bug-focused feeder with a more balanced eater.

The bone is deeper and the coronoid higher than in many modern generalists. Those traits fit a jaw able to process tougher plant foods, including hard mast such as nuts and seeds.

Chewing muscles leave clear marks

An omnivore typically balances slicing and grinding. Its jaw tends to be intermediate rather than extreme in any one direction.

The researchers measured the space between two key points on the jaw to see how much power the main closing muscle could generate.

They also looked at where one of the major chewing muscles attached, since that muscle helps move the jaw not just up and down but also forward and side to side.

Ursus minimus and climate shifts

The Pliocene epoch was a time of shifting climates, with alternating wet and dry phases across Europe. These changes reshaped plant communities and affected the availability of nuts, fruits, and small animals.

For early bears like Ursus minimus, being able to switch foods likely offered an advantage.

Adaptability meant survival during unstable periods, which may explain why this ancestor gave rise to such a wide range of later bear lineages.

Common ancestor ate varied foods

Early bear work links the first ursine line to plant-focused omnivory. That background makes an omnivorous ancestor for modern Ursus species a sensible starting point.

Later branches went in different directions. Independent isotopic evidence shows cave bears were strongly herbivorous.

The new jaw analysis argues the common bear ancestor was a flexible feeder rather than an insect hunter. That helps explain how one branch could specialize on vertebrate prey while another leaned on plants.

Ursus minimus also shows a more robust lower jaw than many living generalists. That robustness hints at harder items in its menu without pointing to strict plant eating or strict meat eating.

Brown bears kept ancient diets

A global review details how brown bear diets change with geography and season. Flexibility is one reason brown bears occupy forests, mountains, and coastlines across three continents.

A nutritional analysis quantifies how brown bears mix protein, carbohydrates, and fats throughout the year. The new fossil result pushes that kind of flexibility far back in time.

This connection between past and present matters for conservation. Animals that can switch foods ride out environmental swings more easily than narrow specialists.

It also matters for how we tell the bear story. Modern variety – from berry eating to salmon runs – makes sense if the starting point was a generalist.

Only one good lower jaw of U. minimus has the necessary features for this kind of landmark based analysis. More fossils from the same time window would help measure natural variation within the species.

Teeth can add wear patterns and enamel details that record food textures. New finds from Europe and Asia could also pin down routes and timing for the spread of the earliest Ursus lines.

The study is published in Boreas.

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