1. Species is valid taxonomically. 

2. Date of last existence (EED) proven to postdate AD 1500 according to one or more of the following: 

(i) specimens collected after AD 1500 

(ii) observation of the species by a reliable source after AD 1500 

(iii) fossil remains radiometrically postdate AD 1500, or are associated with other datable remains. 

1. Species is valid taxonomically. 

2. Date of last existence (EED) proven to postdate AD 1500 because specimens have been collected after this date (observation of the species without collected samples is not acceptable evidence). 

3. EED attributed to more than 50 years ago because specimens were not collected during the last 50 years.

4. Absence of the species after its EED can be attributed to an extinction, rather than the species simply being overlooked, because of evidence of both of the following: 

(i) appropriate sampling either in a search targeted toward that species or in a sampling exercise that covers the expected range or habitat of that species, 

(ii) a decline of that particular species, or presence of an environmental threat to it, before the EED.

(Criterion #4 was not applied to mammals).

Extinction not fully resolved because of one or both of the following: 

1. Species may be invalid taxonomically. 

2. Evidence to confirm the EED as after AD 1500 but more than 50 years ago (see Category I, points 2 and 3) is ambiguous.

1. EED proven to postdate AD 1500 because specimens have been collected after this date. 

2. EED attributed to more than 50 years ago because specimens were not collected during the last 50 years. 

3. But the extinction remains unresolved because of ambiguity in one of the following: 

(i) the taxonomy of the species, 

(ii) the evidence that attributes the absence of the species after the EED to its extinction.

1. EED proven to postdate AD 1500 according to one or more of the following: 

(i) specimens collected after AD 1500 

(ii) observation of the species by a reliable source after AD 1500 

(iii) fossil remains radiometrically postdate AD 1500, or are associated with other datable remains. 

3. But extinction remains unresolved because the species is not yet taxonomically named and described (for fishes, these species are included with species which are taxonomically invalid).

1. Absence of the species after the EED can be attributed to an extinction, rather than the species having been overlooked, because of evidence of one or both of the following: 

(i) appropriate sampling either in a search targeted toward that species or in a sampling exercise that covers the expected range or habitat of that species, 

(ii) a decline of that particular species, or presence of an environmental threat to it, before the EED.

(Criterion #1 was not applied to mammals). 

1. Species is taxonomically valid.

2. The species' absence after the EED may be attributed to its extinction because of evidence of a decline of the species, or presence of an environmental threat to it, before the EED. 

3. But the species' absence after the EED cannot be fully substantiated as an extinction because of insufficient evidence of representative sampling through the species' range and habitat after the EED.

1. Species is taxonomically valid. 

2. The species' absence after the EED may be atrributed to its extinction because representative sampling through the species' range and habitat after the EED failed to produce specimens. 

3. But the species' absence after the EED cannot be fully substantiated as an extinction because of insufficient evidence of a decline of the species, or of an environmental threat to it, before the EED.

1. Species is taxonomically valid. 

2. EED proven to postdate AD 1500 according to one or more of the following: 

(i) specimens collected after AD 1500 

(ii) observation of the species by a reliable source after AD 1500 

(iii) fossil remains radiometrically postdate AD 1500, or are associated with other datable remains. 

1. Species is taxonomically valid. 

2. EED proven to postdate AD 1500 because specimens have been collected after this date (observation of the species without collected samples is not acceptable evidence). 

3. The extinction is not fully resolved because the EED falls within the last 50 years; but the EED is substantiated because specimens have not been collected following the EED. 

4. Absence of the species after the EED can be attributed to an extinction, rather than the species simply being overlooked, because of evidence of both of the following: 

(i) appropriate sampling either in a search targeted towards that species or in a sampling exercise that covers well the expected range or habitat of that species, 

(ii) a decline of that particular species, or of an environmental threat to it, before the EED. (Criterion #4 was not applied to mammals.)

1. EED proven to postdate AD 1500 because specimens have been collected after this date. 

2. The extinction is not fully resolved because the EED falls within the last 50 years; but the EED is substantiated because specimens have not been collected following the EED. 

3. The extinction remains unresolved also because of ambiguity in one of the following: 

(i) the taxonomy of the species, 

(ii) the evidence that attributes absence of the species after the EED to its extinction.

1. Absence of the species after the EED can be attributed to an extinction, rather than the species having been overlooked, because of evidence of one or both of the following: 

(i) appropriate sampling either in a search targeted towards that species or in a sampling exercise that covers the expected range of that species, 

(ii) a decline of that particular species, or presence of an environmental threat to it, before the EED.  

1. Species is taxonomically valid. 

2. The species' absence after the EED may be attributed to its extinction because of evidence of a decline of the species, or of an environmental threat to it, before the EED. 

3. But the species' absence after the EED cannot be fully substantiated as an extinction because of insufficient evidence of representative sampling through the species' range and habitat after the EED.

1. Species is taxonomically valid. 

2. The species' absence after the EED may represent its extinction because representative sampling through the species' range and habitat after the EED failed to produce specimens. 

3. But the species' absence after the EED cannot be fully substantiated as an extinction because of insufficient evidence of a decline of the species, or of an environmental threat to it, before the EED.

1a. EED at least 50 years ago = Go to 2 

1b. EED less than 50 years ago, but supported by evidence of: living specimen seen or collected; fossil remains dateable by radio-carbon techniques or by associated remains of species known to have been introduced post AD 1500 = Category IV

1a. EED at least 50 years ago = Go to 2  

1b. EED less than 50 years ago = Go to 7

2b. Species taxonomically valid and fully described/named = Go to 6

2b. Species taxonomically valid and fully described/named = Go to 4

3b. Species not taxonomically named and described = Go to 5

1) appropriate but unsuccessful sampling after the EED; and/or, 

2) population decline/environmental threat before the EED = Category B1 

1) appropriate but unsuccessful sampling after the EED; nor 

2) population decline/environmental threat before the EED = Go to 12

4b. Species not taxonomically valid and EED without sufficient evidence to be allocated after 1500 and prior to 50 years ago = Category II

1) appropriate but unsuccessful sampling after the EED; and 

2) population decline/environmental threat before the EED = Category A 

5b. Species not taxonomically named and described and EED without sufficient evidence to be allocated to after 1500 and prior to 50 years ago = Category III

1) appropriate but unsuccessful sampling after the EED; or 

2) population decline/environmental threat before the EED = Go to 6 

1) appropriate but unsuccessful sampling after the EED; and 

2) population decline/environmental threat before the EED = Go to 12

6b. Species taxonomically valid and fully described/named, but EED without sufficient evidence to be allocated after 1500 and prior to 50 years ago = Category II

6b. EED lacking evidence of population decline/environmental threat before the EED, but supported by evidence of appropriate but unsuccessful sampling after the EED = Category B3

7b. Species taxonomically valid and fully described/named = Go to 9  

1) appropriate but unsuccessful sampling after the EED; and/or, 

2) population decline/environmental threat before the EED = Category D1 

1) appropriate but unsuccessful sampling after the EED; nor 

2) population decline/environmental threat before the EED = Go to 12 

1) appropriate but unsuccessful sampling after the EED; and 

2) population decline/environmental threat before the EED = Category C 

1) appropriate but unsuccessful sampling after the EED; or 

2) population decline/environmental threat before the EED = Go to 11 

1) appropriate but unsuccessful sampling after the EED; and 

2) population decline/environmental threat before the EED = Go to 12 

11b. EED lacking evidence of population decline/environmental threat before the EED, but supported by evidence of appropriate but unsuccessful sampling after the EED = Category D3