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Oxybelis microphthalmus BARBOUR & AMARAL, 1926

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Higher TaxaColubridae, Colubrinae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common NamesE: Thrornscrub Vine Snake 
SynonymOxybelis microphthalmus BARBOUR & AMARAL 1926
Dryinus aeneus – WAGLER 1824 (part)
Oxybelis aeneus – DUMÉRIL et al. 1854: 819 (part)
Dryophis acuminata – GÜNTHER 1858: 156 (part)
Oxybelis acuminata – BOULENGER 1896: 192 (part)
Oxybelis aeneus auratus – BOGERT & OLIVER 1945: 381 (part)
Oxybelis aeneus auratus – ZWEIFEL & NORRIS 1955 (part)
Oxybelis aeneus – KEISER 1974: 7 (part)
Oxybelis microphthalmus — JADIN et al. 2020 
DistributionUSA (Arizona),
Mexico (Chiapas, Morelos, Oaxaca, Aguascalientes, Tamaulipas, Campeche, Quéretaro, Jalisco, Sonora, Hidalgo, Guanajuato, Nuevo León, Chihuahua, Nayarit, Puebla, Guerrero, Durango)

auratus: Sonora, Sinaloa, Chihuahua

Type locality: Calabasas Canyon, Arizona, USA (circa 31° 28′ N, 110° 58′ W).  
TypesHolotype: MCZ 22417 
DiagnosisDiagnosis: A vine snake with (1) three upper labials (4–5–6) bordering the orbit; (2) black spots or bars on anterior body, dorsum mostly uniform brown with little black pigment; there are small scattered black spots on the dorsum; (3) venter is finely mottled and it can have a dark lateral stripe on the outer edge of each ventral, and a pale mid-ventral stripe; (4) eye diameter shorter than preocular; (5) second pair of chin shields in contact for most of their length; (6) eight upper labials in most Arizona and Sonora specimens, nine upper labials in other Mexican populations, but all tend to have three labials behind orbit; (7) snout from above is narrow, tapered, and rounded at the tip (snout type A); (8) supraoculars are longer than the prefrontals; (9) lower surface of the head is uniform white or yellow in color (not mottled); (10) last upper labial shorter than primary temporal; and (11) second upper labial does not contact the preocular.
The rostral is visible from above and followed by nine platelike scales on the crown: a pair of internasals, a pair of prefrontals, the frontal and two larger supraoculars, and a pair of parietals. Preoculars extend slightly on to the crown between the prefrontals and supraoculars. In profile the nasal scale is elongate extending from the edge of the rostral, beyond the posterior edge of the internasal to the anterior border of the fused prefrontal–loreal. Eye diameter/internasal ratio in this species averages 0.82 (n = 34, r = 0.58–0.97, SD = 0.10). Preocular scale (Keiser 1974, Jadin et al. 2020).

Variation Geographic variation in the upper labial and ventral counts exists. Arizona (USA) and Sonoran (Mexico) populations tend to have eight upper labials, while Oaxaca and Guerrero (Mexico) populations have nine upper labials. Ventral counts in Arizona and Sonora tend to be at the high end of the range; populations to the south have lower numbers.
In males, total length varies from 1197 to 1337 mm (n = 10, x = 1262.13, SD = 73.17), SVL varies from 713 to 834 mm (n = 10, x = 766.68, SD = 46.37), tail lengths vary from 484 to 538 mm (n=8, x=502.21, SD= 35.99); tail/SVL ratios vary from 0.63 to 0.74 (n = 8, x = 0.68, SD = 0.03). Female total lengths vary from 667 to 1407 mm (n = 14, x = 1238.0, SD = 195.99); tails vary from 250 to 544 mm (n=12, x=475.83, SD= 107.19). Tail/SVL ratios in females vary from 0.60 to 0.72 (x = 0.64, SD = 0.04).
Ventrals in males vary from 184 to 202 (n = 14, x = 192.0, SD = 5.92); ventrals in females vary from 184 to 204 (n = 12, x = 193.58, SD = 5.2). Subcaudals in males vary from 163 to 175 (n=5, x=168.4, SD=4.18); in females, subcaudals vary from 170 to 183 (n = 7, x = 177.2, SD = 4.22) (Jadin et al. 2020).

Coloration and pattern The crown of the head and upper face are brown to tan (Fig. 10). The upper labials and ventral surface of the head are a uniform cream. The transition in color is separated by a preocular dark brown stripe extending from the nasal scale, under the eye, and onto the anterior body. This stripe may continue as a series of spots onto the body. The first two scale rows on the anterior body are the same yellow color as the ventral surface, and form a ventrolateral stripe. At midbody, the first four dorsal scale rows and the lower half of the fifth scale row are mottled heavily with dark pigment; the upper half or row five and rows 6–8 lack the dense mottling, giving the overall impression of a series of lateral stripes. On the ventral surface is an indistinct mid-ventral stripe.
In alcohol (UAZ 39545), the coloration has often faded but the elements of the pattern and the colors are still detectable (Jadin et al. 2020).

Comparison A vine snake with eight (Arizona and Sonora) or nine (remainder of distribution in Mexico) upper labials with three behind the orbit, an eye diameter that is about 0.8 of the internasal (no other species of Oxybelis has an eye diameter this small). It also has two or three upper labials in contact with the primary temporal and the second pair of chin shields are in contact for most of their length. Oxybelis aeneus and those from northern South America have the second pair of chin shields separated for most of their length. Oxybelis koehleri and those from Panama usually have two upper labials behind the orbit (Jadin et al. 2020). 
CommentHabitat: fully arboreal (Harrington et al. 2018, by implication).

Synonymy: After Jadin et al. 2020 who revalidated Oxybelis microphthalmus from the synonymy of O. aeneus. 
EtymologyThe generic name Oxybelis is derived from the Greek words oxy, meaning "pointed" and belas, meaning "dart," in reference to the elongated head. The specific epithet is the Latin word aeneus, meaning "bronze, or copper" in reference to the body color of the holotype (LEMOS-ESPINAL & DIXON 2013). 
  • Barbour, T.; Amaral, A. D. 1926. A new North American snake. Proceedings of the New England Zoological Club 9: 79-81
  • Bogert, Charles M.; Oliver, James A. 1945. A preliminary analysis of the herpetofauna of Sonora. Bull. Amer. Mus. Nat. Hist. 83 (6): 297-426
  • Boulenger, G.A. 1896. Catalogue of the snakes in the British Museum, Vol. 3. London (Taylor & Francis), xiv + 727 pp. - get paper here
  • Günther, A. 1858. Catalogue of Colubrine snakes of the British Museum. London, I - XVI, 1 - 281
  • Jadin, R.C., Blair, C., Orlofske, S.A. et al. 2020. Not withering on the evolutionary vine: systematic revision of the Brown Vine Snake (Reptilia: Squamata: Oxybelis) from its northern distribution. Org Divers Evol (2020) - get paper here
  • Keiser, E. D., Jr. 1974. A systematic study of the neotropical vine snake Oxybelis aeneus (Wagler). Bull. Texas Mem. Mus. 22: 1-51.
  • Wagler, J. 1824. Serpentum Brasiliensium species novae, ou histoire naturelle des espèces nouvelles de serpens. In: Jean de Spix, Animalia nova sive species novae. [NAtrix bahiensis: 27,. Monaco, Typis Franc. Seraph. Hübschmanni, vii + 75 pp.
  • Zweifel,R.G. and Norris,K.S. 1955. Contributions to the herpetology of Sonora, Mexico:Descriptions of new subspecies of snakes (Micruroides euryxanthus and Lampropeltis getulus) and miscellaneous collecting notes. American Midland Naturalist 54: 230-249 - get paper here
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