Mass extinction, after the end of mass extinction events
In the typical case, a mass extinction event is accompanied by a substantial reduction in biodiversity, very frequently not only on a local, but also on a global scale. The individual ecosystems degrade substantially and only a few species remain, which were originally rare before the mass extinction event but subsequently relatively abundant. For example, the beginning of the Mesozoic was characterized by an enormous expansion of stromatolites, while the beginning of the Tertiary witnessed an enormous increase in Foraminifera of the Guembelitria group (Erwin 1998). Many of these species tend to be characterized by small body dimensions – this phenomenon has been described as the Lilliputian phenomenon. These pioneer species are apparently capable of utilizing the degraded environment effectively but are not capable of surviving in competition with other species under normal conditions. Thus, they are a sort of macro-evolutionary analogy of ecological r-strategists. However, in contrast to r-strategists, they apparently did not adapt evolutionarily to the conditions prevailing after mass extinction, but their adaptation, to be more exact exaptation, occurred accidentally or as preadaptation through the action of different selection pressures.
Over a longer period of time, some of the original species that avoided extinction in locally limited refuges reappear in ecosystems. Of course, some species completely die out and completely disappear from the paleontological record. Some species reappear in the biotope only after a very long time, during which the paleontological record did not contain any traces of them. These species are termed Lazarian species. In contrast to Lazarus of the Bible, we do not know who and why they were called back to life; however, the results of radioactive dating indicate that the personal intervention of Jesus Christ can most certainly be excluded. Cases of “living fossils”, i.e. evolutionarily ancient species or lines that are known in recent fauna and flora and that simultaneously did not occur for long periods of time in the paleontological record, nonetheless indicate that, in some cases species (to be more exact evolutionary lines of subsequent species) can survive tens or even hundreds of million years in geographically or ecologically narrowly defined refuges without leaving any traces in the fossil record.
A less fortunate category of species consists in those that also survived a mass extinction, but then died without any successors after its end, usually at the time when the original biodiversity was renewed (Jablonski 2001). These need not be only individual species, but can even correspond to whole higher taxa which, in addition, could have undergone speciation at the normal rate before the beginning of the mass extinction. This is a quite common and striking phenomenon and has been termed “dead clade walking” by paleontologists, an analogy of the 1995 film Dead Man Walking (Jablonski 2002). Once again, it is not apparent why species or higher taxa that prospered in the period prior to a mass extinction and were capable of even surviving through the mass extinction finally succumbed without successors in the subsequent period. It is quite possible that this mass extinction was survived only by those species that were relatively resistant compared to the other species in the taxon but, for some reason, had a reduced rate of speciation.