Ancient remains revealed a shocking truth about our earliest kin

Paleontologists have found evidence that cynodonts—early ancestors of mammals—practiced live birth as early as 236 million years ago during the Late Triassic. This finding suggests a shift to viviparity occurred approximately 90 million years earlier than previously estimated for the transition to placental and marsupial reproduction. The conclusion is based on a single fossilized specimen of Chiniquodon theotonicus discovered in the Chañares Formation in Argentina. The study's results were published in the journal Frontiers in Mammal Science. Analyzing Growth Lines to Determine Birth Method Researchers examined the femur and humerus of the adult animal and identified a neonatal line. This microscopic "annual ring" forms in bone tissue at the moment of birth due to a sudden acceleration in growth rate. By analyzing the bone circumference at this specific line, scientists calculated the newborn's mass at approximately 1.5 kg.