Ecological success Early Triassic isoetaleans
The extinction of arborescent competitors, during the end-Permian crisis, paved the way for the remarkable expansion of isoetalean lycopsids during Early Triassic times. Dense populations of the most dominant genus, Pleuromeia (see figure), are recorded worldwide, occupying habitats ranging from semi-arid to tidal. Comparisons between fossil and extant representatives suggests the existence of common physiological properties that could explain the resilience of the Isoetales during the biotic crisis and their success during Early Triassic repopulation. In relation to conceptual models linking patterns of mass extinction, survival and recovery, the Isoetales can be classified as crisis progenitors. Principal considerations are: (1) the Isoetales are likely to be adapted to local conditions, similar to the imposed stress at the time of biotic crisis, (2) in pre-crisis communities, they play a very subordinate role that may even be below the detection level of regional palynological records, (3) during the crisis, on the other hand, they may suddenly emerge in fossil assemblages, albeit in low frequencies, and (4) they are amongst the first surviving plant taxa to diversify after the mass extinction event.
Looy C.V., Van Konijnenburg-Van Cittert J.H.A., and Visscher H., 2000. On the ecological success of isoetalean lycopsids after the end-Permian biotic crisis. LPP Contributions Series 13: 63-70.