Thamnophis exsul ROSSMAN, 1969
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Thamnophis exsul
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| Higher Taxa | Colubridae (Natricinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes) |
| Subspecies | |
| Common Names | E: Montane Garter Snake G: Zwerg-Strumpfbandnatter S: Jarretera Mexicana Exilada |
| Synonym | Thamnophis exsul ROSSMAN 1969 Thamnophis exsul — ROSSMAN et al. 1989 Thamnophis exsul — LINER 1992 Thamnophis exsul — LINER 1994 Thamnophis exsul — WALLACH et al. 2014: 722 |
| Distribution | Mexico (Tamaulipas, Nuevo León, Coahuila) Type locality: relatively dry pine forest, 11 mi. E, 3.5 mi S San Antonio de las Alazanas, Coahuila, ca. 9,100 feet elevation. |
| Reproduction | ovoviviparous |
| Types | Holotype: USNM 166423, adult female |
| Diagnosis | Definition and Diagnosis: Thamnophis exsul is the smallest known species in the genus, having a maximum recorded length of 360 mm; 17 dorsal scale rows in 90% of known specimens, usually (80%) with no posterior reduction to 15 rows; 7 supralabials (90%) on at least one side; 8 infralabials (90%) on at least one side; females with 142-150 ventrals (x̅ = 145), males with 152-156 (x̅ = 154); females with 52-56 subcaudals (x̅ = 53), males with 63-65 (x̅ = 64); tail length 18.9-20.0% (x̅ = 19.4) of TL in females, 21.8-22.2% (x̅ = 22.0) in males; 19-21 (x̅ = 20.3) maxillary teeth, the last 2 or 3 slightly enlarged; dorsum almost uniform putty brown with 3 indistinct light stripes, or having 3 or 4 alternating rows of spots or blotches with the light stripes partially or completely suppressed. Specimens from Nuevo León show a marked ontogenetic pattern variation. Juveniles are prominently spotted in 3 or 4 rows. A vertebral stripe is absent or faint and sometimes interrupted at intervals by the dorsal spotting. The nuchal blotch may be divided by the faint vertebral stripe, color may be continuous with the dark dorsal head coloration or separated by a very thin lighter zone immediately posterior to the parietals. The subadult spotted condition is not as prominent as in juveniles and is barely evident, if at all, in larger adults. The single everted hemipenis available is single with the distal half greatly expanded. The sulcus spermaticus is simple, terminating apically between raised lips. The apical surface of the expanded portion is nude, the remainder spinose; spines are very small distally, larger proximally. An enlarged basal hook is slightly distant from the other spines. (Liner 1992) Detailed description: Rossman 1996: 181 |
| Comment | Smallest member of the genus with a maximal total length of 46 cm. Not listed by Liner 2007. |
| Etymology | Named after the Latin “exsul” meaning "banished person", in reference to its geographic isolation from its closest relatives. |
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