They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature.
ðeɪ nˈiːdᵻd tə dɪvˈɛləp nˈuː mˈɛθədz tə ɹˈɛɡjʊlˌeɪt ðɛɹ bˈɑːdi hˈiːt tə kˈoʊp wɪð flˌʌktʃuːˈeɪʃənz ɪn ˈæmbiənt tˈɛmpɹɪtʃɚ.