The mammals’ adventure began around 220 million years ago. Characteristic traits contributed to their evolutionary success: teeth became specialised, most mammals gestated, produced milk and established relationships between mother and offspring. Various groups of mammals existed in the Mesozoic era, even though they did not seem to be very different from each other. Only three of these groups lasted through the Tertiary era to the present day: monotremes, marsupials and our group, the placentals.
The oversized antlers of the megaloceros show the importance of sexual selection. Bone is costly to produce for an organism but plays an important role in male rivalry and in attracting females.
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