问答题 Birds evolved during the great reptilian radiation of the Mesozoic era, Amniotic eggs and scales on the legs are just two of the reptilian features we see in birds.But modem birds look quite different from modem reptiles because of their feathers and other distinctive flight equipment.

【正确答案】ancestor of birds

【答案解析】文章最后一段第二句提到，鸟类的祖先被大数研究者视为是一种有羽毛的兽脚亚目恐龙。因此，填入ancestor of birds。