The rabbit-like ungulates of ancient Europe were not the leapers we once imagined
In short: Cainotheriidae were small, rabbit-sized artiodactyls that roamed Europe from the Late Eocene to the Middle Miocene. With their long hind legs and large ear structures, scientists long assumed they hopped like hares. However, fossil evidence suggests these creatures moved more like modern ruminants than any modern rabbit.
Cainotheriidae represent a fascinating evolutionary puzzle. These small, extinct artiodactyls, which stood no taller than 15 centimetres at the shoulder, possessed a unique mix of anatomical traits. Their skulls featured large auditory bullae—protective ear structures typically found in small mammals inhabiting open, arid environments—and highly specialized, crescent-shaped teeth similar to those of modern ruminants. Yet, their post-cranial skeletons remained surprisingly primitive, retaining four distinct toes that ended in long, rabbit-like claws.
For decades, researchers drew parallels between cainotheriids and lagomorphs, assuming their elongated hind limbs were an adaptation for jumping. This narrative shifted significantly following the discovery of fossilized trackways in Salinas de Anana, Spain. These lower Miocene traces, attributed to the genus Cainotherium, revealed a gait inconsistent with hopping. Instead, the locomotion of these animals appears to have mirrored that of contemporary small ruminants, challenging the long-standing ecological parallel to rabbits.
The evolutionary history of the group is marked by distinct phases. Early genera like Oxacron and Paroxacron emerged during the Upper Eocene, followed by a radiation of rabbit-sized forms such as Plesiomeryx and Caenomeryx throughout the Oligocene. While earlier studies linked them to Tylopoda, more recent analyses suggest a closer affinity to Ruminantia. The group eventually vanished during the middle Miocene, a decline attributed to the cooling climate of the era. Their extinction marked the end of a lineage that had successfully occupied European landscapes for millions of years, leaving behind a complex record of primitive and specialized features that continue to inform our understanding of artiodactyl evolution.
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- Summary by Intellect · source: Cainotheriidae
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