Relict (biology)

In biogeography and paleontology, a relict is a population or taxon of organisms that was more widespread or more diverse in the past. A relictual population is a population currently inhabiting a restricted area whose range was far wider during a previous geologic epoch. Similarly, a relictual taxon is a taxon (e.g. species or other lineage) which is the sole surviving representative of a formerly diverse group. A relict (or relic) plant or animal is a taxon that persists as a remnant of what was once a diverse and widespread population. Relictualism occurs when a widespread habitat or range changes and a small area becomes cut off from the whole. A subset of the population is then confined to the available hospitable area, and survives there while the broader population either shrinks or evolves divergently. This phenomenon differs from endemism in that the range of the population was not always restricted to the local region. In other words, the species or group did not necessarily arise in that small area, but rather was stranded, or insularized, by changes over time. The agent of change could be anything from competition from other organisms, continental drift, or climate change such as an ice age. When a relict is representative of taxa found in the fossil record, and yet is still living, such an organism is sometimes referred to as a living fossil. However, a relict need not be currently living. An evolutionary relict is any organism that was characteristic of the flora or fauna of one age and that persisted into a later age, with the later age being characterized by newly evolved flora or fauna significantly different from those that came before. A notable example is the thylacine of Tasmania, a relict marsupial carnivore that survived into modern times on an island whereas the rest of its species on mainland Australia had gone extinct between 3000 and 2000 years ago. Another example is Omma, a genus of beetle with a fossil record extending back over 200 million years to the Late Triassic and found worldwide during the Jurassic and Cretaceous, now confined to a single living species in Australia.