Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog", with hopping adaptations is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona.
ɔːlðˈoʊ ðə fˈɑːsəlz ʌv sˈɛvɹəl ˈoʊldɚ pɹˈoʊɾoʊfɹˈɑːɡz wɪð pɹˈɪmᵻtˌɪv kˌæɹɪktɚɹˈɪstɪks ɑːɹ nˈoʊn, ðɪ ˈoʊldɪst "tɹˈuː fɹˈɑːɡ", wɪð hˈɑːpɪŋ ˌædæptˈeɪʃənz ɪz pɹəzˈælɜːɹəs bˈaɪɾɪs, fɹʌmðɪ ˈɜːli dʒjʊɹɹˈæsɪk keɪˈɛntə fɔːɹmˈeɪʃən ʌv ˌæɹɪzˈoʊnə.