
Mammal ancestors were long assumed to lay eggs, until a growth ring inside the thigh bone of a 236-million-year-old Argentine cynodont put its estimated weight at birth near 1.7 kilograms, 14 percent of the maximum weight it ever reached, and among tMammal ancestors were long assumed to lay eggs, until a growth ring inside the thigh bone of a 236-million-year-old Argentine cynodont put its estimated weight at birth near 1.7 kilograms, 14 percent of the maximum weight it ever reached, and among the livi ScienceBlog.com
