The Biodiversity Group
Vertebrates the Red List cannot yet speak for · IUCN v2026‑1
What this is
The IUCN Red List is the world's authority on extinction risk, and it has two blind spots. Some species are assessed and come back Data Deficient — IUCN looked, and there was not enough information to say. Others are Not Evaluated — nobody has looked at all. In practice both are treated as though the species were safe.
Every species in the register, one mark each
Hover a mark to name the species; select one to open its record. Darker means a thinner record.
What the record actually says
Data Deficient status on its own predicts very little. Of the species here that IUCN has since reassessed, the group as a whole came out threatened at roughly the ordinary all-species rate. The narrowly restricted subset is different, and that distinction — not the Data Deficient label — is what this register is for.
Held-out test
Between the previous data and v2026‑1, IUCN independently reassessed 108 of these species and gave each a real category. The ranking rules never saw those outcomes, so they work as an answer key. Share reassessed as threatened or extinct:
Composition
By class
By restriction tier
Every row carries the sentence it was judged on. Select a species to read it.
| Species | Class | Tier | Basis | Locality |
|---|
The source is organised geographically, so species cluster by place. Where a single locality carries many of them, one protected area could cover the lot — the cheapest form of conservation available.
Caveat: these localities are extracted at inconsistent grain. Some are a single named river, some an entire ocean basin. Treat the small, specific ones as actionable and the broad ones as an artefact of the source.
Nobody with a specialist's authority. The ranking is produced by a text-classification rule that reads the source's own range statements and sorts them by severity. No taxonomist or conservation biologist has reviewed the individual species. What has been tested is the rule's average behaviour against IUCN's independent reassessments — a statement about the group, not about any one row.
These are not Red List assessments and must not be cited as such. They are a prioritised research agenda: an argument about where to look.
| Evidence of risk | Matthew Richardson, Threatened and Recently Extinct Vertebrates of the World: A Biogeographic Approach, Cambridge University Press, 2023. Vertebrates only — the scope follows the book's. |
|---|---|
| Extinction risk | IUCN Red List v2026‑1, 178,011 taxa, via GBIF's Darwin Core mirror (accessed 2026‑07‑28). |
| Taxonomy | GBIF Backbone, for synonym resolution and for independent verification of assessment status. |
Restriction is the axis because IUCN Criterion B allows a species to qualify as threatened on a small range plus evidence of decline: area of occupancy under 2,000 km² for Vulnerable, 500 for Endangered, 10 for Critically Endangered. A species known only from its type locality sits, on its face, inside the Critically Endangered envelope. Tiers 4 and 5 are the priority stratum.
| Tier | Basis | Species |
|---|
No area of occupancy has been computed. A priority flag argues that Criterion B should be evaluated; it is not a finding that it is met.
The priority rate lands close to the 56% that Borgelt et al. (2022, Communications Biology) predicted for Data Deficient species generally — which suggests that figure belongs to the narrowly restricted subset, and that an unranked list dilutes a real signal with vague-range species.
Two caveats belong with that number whenever it is quoted. The top stratum rests on 19 species, which is thin. And IUCN reassesses where data has appeared, which probably favours species that turned out to be more widespread — a bias running against the finding rather than creating it. Separately, the five tiers were defined before any outcome was seen, but the decision to split them at 4 was made after, which inflates the significance somewhat.
An earlier composite score added points for a species not having been recorded recently and for threats named at its locality. Testing destroyed it: the composite was non-monotonic, and naming a site-level threat turned out inversely associated with being threatened. The reason is legible in hindsight — broad, well-documented regions attract threat prose but hold wide-ranging species, while a genuine type-locality endemic gets one terse line. Those fields survive on each record as description, and are not ranked on.
Proving that IUCN has never assessed a species is much harder than it looks, because the two sources disagree about naming constantly. Deciding it by failing to find a name produced a false-positive rate near 90%. Four distinct failure modes had to be closed:
| Failure | Example |
|---|---|
| Genus reassigned | Amblyopsis rosae is IUCN's Troglichthys rosae (Near Threatened) |
| Genus and family reassigned | Aphanius iberus is IUCN's Apricaphanius iberus |
| Homonym within an order | Sinosuthora przewalskii, an Asian parrotbill, matching Grallaria przewalskii, a South American antpitta |
| Rank change | Cyanoramphus cookii, in fact Least Concern |
Species known only from pre-1500 remains were also removed. The Red List covers extinctions from 1500 AD onward, so those fall outside its remit by policy rather than by neglect — counting them as coverage gaps would be a category error.
Target 4 of the Kunming-Montreal Global Biodiversity Framework commits governments to halting the extinction of known threatened species — a phrase that excludes both categories in this register by definition. Under 3.5% of Mohamed bin Zayed Species Conservation Fund awards have gone to Data Deficient taxa, and under 1% at the People's Trust for Endangered Species. IUCN's own guidance says Data Deficient species should get the same attention as threatened ones, and it is not followed.