Thursday, December 18, 2014

Post Permian Mass Extinction Size Reduction In Glossopteris Plant Lineages

Mass extinctions prune away branches of the tree of life. The late Permian-Triassic mass extinction event affected marine and terrestrial animal life severely, perhaps more than it affected terrestrial plant life. One common observation is that survivor species tend to be smaller bodied representatives of groups. This is known as the Lilliput effect.

A lot of attention has been paid to evolutionary trends in size during and post mass extinction in various animal groups. An interesting paper in Current Science (open access)  documents the Lilliput effect in one of the iconic terrestrial plant groups  of Late Permian -Early Triassic times; the seed fern Glossopteris.

From the paper:

Modern day high-resolution regional palaeoecological studies have proved the myth wrong, which stated that the mass extinction event had little macroecological or evolutionary consequence for terrestrial plants The early Triassic (Panchet Formation) in India witnessed more arid or semi-arid climate in comparison to the Permian. The early Triassic experienced greenhouse conditions with a warmer phase (Figure 6) due to global rise of temperature coupled with episodes of intense volcanism. The reduced size of the lamina is one of the strategies adapted by the plants during the adverse condition in early Triassic when there was indeed a shortage of essential nutrients in the soil, in addition to seasonal dry climate, irregular rainfall and widespread aridity. The leaves possessed cuticles with sunken stomata since the atmosphere during the early Triassic had higher levels of CO2 and lower O2levels (Figure 7). The Glossopteris flora of late Permian was adapted to temperate, cool and moist environments. The phenomenon of dwarfism as evidenced in Glossopteris has been observed only up to th e early Triassic, which is represented by the Panchet Formation. During the middle to late Triassic, typical Dicroidium flora associated with Lepidopteris takes over the preceding Glossopteris flora.

Records of plant fossils substantiate the evidence that numerous physiological, reproductive and behavioural traits enabled the smaller sized plant species to persist in extreme climatic conditions.

I didn't know there was a myth that mass extinctions have little macro-ecological or evolutionary consequences for terrestrial plants. Although, I do get the impression that studies of plant evolution get less attention in the media than animal evolution.

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