Life in the end-Permian dead zone

Abstract

The fossil record of land plants is an obvious source of information on the dynamics of mass extinctions in the geological past. In conjunction with the end-Permian ecological crisis, approximately 250 million years ago, palynological data from East Greenland reveal some unanticipated patterns. We document the significant time lag between terrestrial ecosystem collapse and selective extinction among characteristic Late Permian plants. Furthermore, ecological crisis resulted in an initial increase in plant diversity, instead of a decrease. Paradoxically, these floral patterns correspond to a "dead zone" in the end-Permian faunal record, characterized by a paucity of marine invertebrate megafossils. The time-delayed, end-Permian plant extinctions resemble modeled "extinction debt" responses of multispecies metapopulations to progressive habitat destruction.

Figure 1

Locality map of Jameson Land and Scoresby Land, East Greenland, showing outcropping Late Permian and Early Triassic strata (modified after ref. 9).

Figure 2

Quantitative distribution pattern of selected spore and pollen types and carbon-isotope (δ¹³C) profile for carbonates (after ref. 11) from the P-Tr transition sequence in Jameson Land, East Greenland (for location, see Fig. 1). The marine macrofaunal “dead zone” embraces the interval between last appearances of the brachiopod Martinia and first appearances of the bivalve Claraia. Although the conodont element H. parvus is the first unquestionable indication of earliest Triassic age, the inception of Claraia may more accurately approximate the P-Tr boundary (11). Small, horizontal lines represent the position of palynological samples. Processed sample material is stored in the collection of the Laboratory of Palaeobotany and Palynology, Utrecht University. The recognized form-genera and other palynological categories typically reflect taxonomic diversity at generic and suprageneric levels; for botanical affinity of the types, see Table 1. Relative abundances are expressed as percentages of the total spore and pollen assemblages. Spore/pollen ratio represents counted number of spores of lycopsids, ferns, and bryophytes, divided by the total number of counted spores and pollen grains; cavate spore tetrads represent four spores. The diagram depicts the principal phases (a–e) of regional vegetation succession indicative of ecosystem collapse and initial recovery. a, decline of cordaite–pteridosperm woodland; b, proliferation of herbaceous lycopsids; c, establishment of diverse gymnosperm shrubland communities; d, renewed lycopsid proliferation; e, extinction of typical Late-Permian Subangaran gymnosperms.