Macroevolution of corals across the Triassic–Jurassic transition: morphological disparity, diversity response, and recovery patterns
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Abstract:
The mass extinction event at the Triassic–Jurassic boundary (~201 million years ago) profoundly impacted marine ecosystems. Current research indicates that massive volcanic eruptions of the Central Atlantic Magmatic Province (CAMP) served as the primary trigger for this event. The resulting environmental stresses—including perturbations to the carbon cycle, drastic sea-level fluctuations, and ocean acidification—led to a dramatic decline in marine benthic biodiversity. Among the most severely affected groups were reef-building organisms such as scleractinian corals, reef-dwelling sponges, and bivalves. During this extinction event, corals exhibited distinct phased extinction patterns, with a generic extinction rate of 56.41% and two extinction peaks occurring in the late Rhaetian and late Pliensbachian stages. Environmental analyses indicate that reduced seawater carbonate ion (CO?2?) concentrations and declining aragonite saturation (Ωarag) were critical limiting factors for coral survival. These changes directly inhibited the calcification capacity of reef-building corals and disrupted their symbiotic relationships with zooxanthellae, ultimately leading to the preferential extinction of highly integrated corals (i.e., complex taxa dependent on symbiosis). Concurrently, associated reef-dwelling sponges experienced one of the most severe extinction events in the Phanerozoic. Post-extinction coral recovery displayed clear phasic characteristics. During the early Hettangian, more resilient solitary corals with low levels of morphological integration initiated the recovery process, driving the initial rebound of coral diversity. In contrast, the full recovery of highly integrated reef-building corals was delayed until the Sinemurian. Spatially, corals exhibited a notable high-latitude refuge effect: reef-building corals were predominantly distributed in high-latitude regions (＞30°) and began migrating toward mid- to low-latitudes (25°–35°) areas only in the late Pliensbachian, without crossing into equatorial zones. It was not until environmental conditions stabilized during the Bajocian that reef-building corals re-established flourishing communities in equatorial regions, marking the complete restoration of structural complexity in coral-reef ecosystems.
