Pterosaur decline (if present) seems unrelated to bird diversity. In fact, at least some bird niches were reclaimed by pterosaurs just before the KT event.
t ɛ ɹ ə s ɔ ɹ WORD_BOUNDARY d ɪ k l aɪ n WORD_BOUNDARY ɪ f WORD_BOUNDARY p ɹ ɛ z ə n t WORD_BOUNDARY s iː m z WORD_BOUNDARY ʌ n ɹ ɪ l eɪ t ɪ d WORD_BOUNDARY t ə WORD_BOUNDARY b ɜː d WORD_BOUNDARY d aɪ v ɜː s ɪ t i WORD_BOUNDARY ɪ n WORD_BOUNDARY f æ k t WORD_BOUNDARY æ t WORD_BOUNDARY l iː s t WORD_BOUNDARY s ʌ m WORD_BOUNDARY b ɜː d WORD_BOUNDARY n ɪ t̠ʃ ɪ z WORD_BOUNDARY w ɜː WORD_BOUNDARY ɹ ɪ k l eɪ m d WORD_BOUNDARY b aɪ WORD_BOUNDARY t ɛ ɹ ə s ɔ ɹ z WORD_BOUNDARY d̠ʒ ʌ s t WORD_BOUNDARY b ɪ f ɔ ɹ WORD_BOUNDARY ð ə WORD_BOUNDARY k eɪ t iː WORD_BOUNDARY ɪ v ɛ n t WORD_BOUNDARY