Early mammals weren't all loners—some may have lived in pairs alongside the dinosaurs
About 200 million years ago, furry, little egg-laying creatures evolved the ability to feed their offspring with a secretion from special glands: milk. Their evolutionary journey continued, and by about 160 million years ago, the first mammals with a real placenta had come into being. Instead of laying eggs, they gave birth to live young that had been connected directly to their mother via a…
About 200 million years ago, early mammals appeared, evolving the ability to provide milk to their offspring. By 160 million years ago, the first mammals with a true placenta emerged, giving birth to live young. These early mammals resembled modern shrews, being small with long bodies, nocturnal eyes, and small teeth for insect consumption.
However, they were not shrews but the ancestors of all placental mammals, including shrews, bats, elephants, and humans. While scientists knew about their physical characteristics, their social behavior remained unknown due to the inability to fossilize such behaviors. Researchers previously assumed that these early mammals, like modern shrews, were solitary.
Yet, a 10-year study reviewed over 15,000 scientific publications and estimated that the first placental ancestors lived in stable female-male pairs and formed groups. This challenges the belief that mammalian sociality evolved much later, suggesting that the roots of mammalian sociality extend deeper into evolutionary history.
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