Fossil amphibian offers insights into the interplay between monsoons and amphibian evolution in palaeoequatorial Late Triassic systems

The severe greenhouse climate and seasonality of the early to mid-Late Triassic are thought to have limited terrestrial diversity at lower latitudes, but direct adaptations to these harsh conditions remain limited in vertebrates at the palaeoequator. Here, we present <i>Ninumbeehan dookoodukah</i> gen. et sp. nov., an early amphibian with specialized adaptations for seasonal estivation from the upper Jelm Formation of the Late Triassic of Wyoming, USA. <i>Ninumbeehan</i> are found in an association of vertebrate estivation burrows across a locally dense horizon, offering insights into the evolution and ecology of vertebrates amid the challenging conditions of low-latitude Late Triassic ecosystems. Estivation chambers were excavated within point bar deposits of an ephemeral river system, recording the cyclical signature of Triassic megamonsoons and documenting a vertebrate response to annual climate extremes across tens to hundreds of seasons. Phylogenetic analysis recovers <i>Ninumbeehan</i> within a group of temnospondyls characterized by fossorial adaptation, underscoring the widespread adoption of burrowing and estivation in total group Lissamphibia. <i>Ninumbeehan</i> hints at the pivotal role seasonal dynamics played in shaping amphibian evolution.