It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed.
ɪt wʌzðə dɪvˈɛləpmənt ʌvðɪ ˌæmnɪˈɑːɾɪk ˈɛɡ, wˌɪtʃ pɹɪvˈɛnts ðə dɪvˈɛləpɪŋ ˈɛmbɹɪˌoʊ fɹʌm dɹˈaɪɪŋ ˈaʊt, ðæt ɛnˈeɪbəld ðə ɹˈɛptaɪlz tə ɹᵻpɹədˈuːs ˌɔn lˈænd ænd wˌɪtʃ lˈɛd tə ðɛɹ dˈɑːmɪnəns ɪnðə pˈiəɹɪəd ðæt fˈɑːloʊd.