A species extinction within
recent times can be considered resolved only if it meets these Basic
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);
b) because fossil remains
of the target taxon have been either:
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.
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
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
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