Prototype Extinction Criteria and Categories
A species extinction within recent times can be considered resolved only if it meets these Basic Criteria:
1) the species name and status are valid taxonomically.
2) the effective extinction date or EED (the last known date or time-interval in which the species was observed or collected, which provides a minimum date of loss for the taxon) can be positively confirmed as being later than AD 1500 either:
a) because a living specimen has been collected or seen by a reliable source since that date (observation of the species without collected specimens was not classified as acceptable evidence for the study made on fishes); or
b) because fossil remains of the target taxon have been either:
i) radiocarbon-dated, or
ii) found in close association with those of an alien species known to have been introduced post AD 1500.
3) No individuals have been observed reliably in at least the past 50 years.
Additional Sub-Criteria
Some taxa are particularly elusive and so may require a more detailed analysis of absence after the reported EED. For these taxa, it might be appropriate to establish Sub-Criteria to indicate that their absence can be properly attributed to extinction. Such additional criteria may include:
A) significant but unsuccessful attempts have been made to relocate the species after its noted absence (either in a search targeted towards that species or in a sampling exercise that covers well the expected range or habitat of that species);
B) there has been a decline of that particular species, or an environmental threat to it, before the EED.
Have questions about these criteria?
How did we handle subspecies and other entities that are not formal species? Why did we use AD 1500 as a cut-off date? Why wait 50 years before declaring a species' extinction fully resolved? What about species that are functionally extinct, regionally extinct, or extinct in the wild?
Prototype Extinction Categories
Species that meet all of the extinction criteria can be categorized as Resolved Extinctions. Those species for which there is evidence of extinction, but which do not meet all criteria, will be divided into categories of Unresolved Extinctions that indicate which criteria have not been met. This method of categorizing Unresolved Extinctions allows us to clarify gaps in our knowledge of a particular species' status, and highlight important areas where research is needed.Two methods of categorization can be viewed through this link: Categorization Tables. These tables depict two different but compatible systems, one that was developed for organizing evidence for mammal extinctions, the other for freshwater fish extinctions. While categories were named differently, the two systems are nevertheless similar, and comparable categories are shown next to each other. The fish categories represent a more detailed breakdown of information, reflecting the use of more detailed sub-criteria. (This was done in order to account for particular difficulties in finding and identifying fish species -- difficulties that are less applicable to mammals).
The criteria that have not been met for the Unresolved Categories are indicated in bold in the Categorization Tables.