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Home/Species/ Thornscrub Hook-nosed Snake

Gyalopion quadrangulare

(Günther, 1893)

Thornscrub Hook-nosed Snake

G4Apparently Secure Found in 1 roadless area NatureServe Explorer →
G4Apparently SecureGlobal Rank
Least concernIUCN
LowThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.103585
Element CodeARADB16020
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVertebrate Animal
IUCNLeast concern
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomAnimalia
PhylumCraniata
ClassReptilia
OrderSquamata
FamilyColubridae
GenusGyalopion
Other Common Names
Desert Hooknose Snake (EN)
Concept Reference
Hardy, L. M. 1976. Gyalopion, G. canum, G. quadrangularis. Catalogue of American Amphibians and Reptiles 182.1-182.4.
Taxonomic Comments
The specific name was formerly spelled "quadrangularis." The previous standard English names of Ficimia and Gyalopion were misleading relative to their geographic ranges. All are distributed in Mexico, but Ficimia had the moniker "Mexican," whereas Gyalopion had the name "Plateau," yet is clearly not confined to any plateau. Given that Ficimia has the easternmost distribution, Crother (2017) call it "Eastern" and call Gyalopion "Western."
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-11-11
Change Date1996-10-30
Edition Date2025-11-11
Edition AuthorsHammerson, G. (2005); rev. R. L. Gundy (2025)
Threat ImpactLow
Range Extent20,000-2,500,000 square km (about 8000-1,000,000 square miles)
Number of Occurrences81 - 300
Rank Reasons
This species has a limited range from extreme southwestern Arizona south to Nayarit, México. Little is known about population trends, though it has likely declined slightly and continues to be threatened by agriculture and road mortality.
Range Extent Comments
The range extends from extreme south-central Arizona (Baboquivari, Santa Rita, Patagonia, and Pajarito Mountains area) southward through western México along the Gulf of California to Nayarit at elevations from near sea level to about 1,340 meters (4,400 feet) (Stebbins 2003, Bezy and Cole 2014). Using Global Biodiversity Information Facility (GBIF) (2025) records from 1990-2025, range extent is estimated to be 181,165 km² (RARECAT 2025).
Occurrences Comments
Hardy (1976) mapped roughly 70 collection sites. Applying a 5 km separation distance to GBIF (2025) records, 137 occurrences are estimated (RARECAT 2025).
Threat Impact Comments
No major threats have been identified. Road mortality and agriculture are likely localized threats.
Ecology & Habitat

Habitat

Habitat includes canyon bottoms, outwash plains, creosotebush desert, mesquite grassland foothills (including partly cultivated sections), thorn woodland, and dry tropical and subtropical forest (Stebbins 2003). This snake burrows into loose soil.

Ecology

Rarely seen; a secretive burrowing snake (Stebbins 1985).

Reproduction

Habits of this egg-layer are unknown (Behler and King 1979).
Terrestrial Habitats
Woodland - HardwoodShrubland/chaparralGrassland/herbaceousDesert
Palustrine Habitats
Riparian
Other Nations (1)
United StatesN1
ProvinceRankNative
ArizonaS1Yes
Threat Assessments
ThreatScopeSeverityTiming
2 - Agriculture & aquacultureSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
2.1 - Annual & perennial non-timber cropsSmall (1-10%)Serious or 31-70% pop. declineHigh (continuing)
4 - Transportation & service corridorsRestricted (11-30%)Slight or 1-10% pop. declineHigh (continuing)
4.1 - Roads & railroadsRestricted (11-30%)Slight or 1-10% pop. declineHigh (continuing)

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Roadless Areas (1)
Arizona (1)
AreaForestAcres
TumacacoriCoronado National Forest44,594
References (10)
  1. Behler, J. L., and F. W. King. 1979. The Audubon Society field guide to North American reptiles and amphibians. Alfred A. Knopf, New York. 719 pp.
  2. Bezy, R. L., and C. J. Cole. 2014. Amphibians and reptiles of the Madrean archipelago of Arizona and New Mexico. American Museum Novitates 3810: 1-24. doi: 10.1206/3810.1
  3. Crother, B. I. (editor). 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Sixth edition. Society for the Study of Amphibians and Reptiles Herpetological Circular 37:1-84. Online with updates at: http://www.ssarherps.org/pages/comm_names/Index.php
  4. Crother, B. I. (editor). 2012. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 7th edition. SSAR Herpetological Circular 39:1-92.
  5. Crother, B. I. (editor). 2017. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 8th edition. SSAR Herpetological Circular 43:1-104. [Updates in SSAR North American Species Names Database at: https://ssarherps.org/cndb]
  6. Frost, D. R., and J. T. Collins. 1988. Nomenclatural notes on reptiles of the United States. Herpetological Review 19(4):73-74.
  7. Hardy, L. M. 1976. <i>Gyalopion</i>, <i>G. canum</i>, <i>G. quadrangularis</i>. Catalogue of American Amphibians and Reptiles 182.1-182.4.
  8. Smith, G. R., and J. A. Lemos Espinal. 2025. Diversity, endemism, and conservation status of the herpetofauna of the Sierra Madre Occidental in Mexico with comparison to neighboring biogeographic provinces. Animals 15: 1278. doi: 10.3390/ani15091278
  9. Stebbins, R. C. 1985a. A field guide to western reptiles and amphibians. Second edition. Houghton Mifflin Company, Boston, Massachusetts. xiv + 336 pp.
  10. Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. Third edition. Houghton Mifflin Company, Boston.