Why does the Australian lungfish not form a mud cocoon during drought?

The Australian lungfish (Neoceratodus) does not form a mud cocoon during drought because, unlike its African and South American counterparts, it is not adapted for estivation in this manner.12

While African and South American lungfishes rely heavily on their lungs for respiration and have evolved the ability to burrow into riverbeds to survive dry periods, the Australian lungfish maintains well-developed gills that handle the bulk of its oxygen uptake and carbon dioxide elimination. Because it remains primarily dependent on aquatic respiration, it does not possess the physiological adaptations required to encase itself in a mucous sheath or enter the state of "dry sleep" used by other species to survive when water levels recede. Instead, the Australian lungfish survives in isolated, oxygen-poor waterholes by supplementing its gill breathing with atmospheric air, surfacing periodically to breathe.123