Argentina fossils reveal oldest known evidence of pregnancy

Fossil analysis in Argentina has revealed the oldest known evidence of pregnancy in animals. The discovery involves Chiniquodon theotonicus, a type of cynodont—a mammal-like reptile (synapsid) that lived approximately 236 million years ago.

The presence of embryonic tissues suggests that these creatures reproduced through pregnancy rather than egg-laying. This finding shifts the estimated timeline for the emergence of pregnancy in the animal kingdom by roughly 95 million years, indicating it occurred much earlier than previously believed.

While cynodonts shared several evolutionary traits with modern mammals, such as hair, teeth, and milk production, pregnancy was not previously attributed to them. This discovery highlights that the evolutionary shift toward carrying young within the body originated in mammal-like reptiles rather than mammals themselves.