Airflow in the secondary bronchi and parabronchi of crocodilians is unidirectional [19,26], a feature once thought to be unique to birds. Unidirectional airflow through the lungs is maintained by aerodynamic valving and is a result of airway geometry in crocodilians [19,26].
However, this hypoxia scenario is not well supported by the fossil record. Many faunas were still synapsid dominated in the immediate aftermath of the P-Tr extinction , and some Triassic synapsids grew to large sizes similar to their archosaurian contemporaries . Archosaurs did not become the main faunal components in terrestrial ecosystems until the Late Triassic , 30 Ma after the P-Tr extinction.
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