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Crotalus ornatus HALLOWELL, 1854

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Higher TaxaViperidae, Crotalinae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common NamesE: Ornate Black- tailed Rattlesnake, Black-tailed Rattlesnake 
SynonymCrotalus ornatus HALLOWELL 1854: 192
Crotalus ornatus — ANDERSON & GREENBAUM 2012
Crotalus ornatus — WALLACH et al. 2014: 193
Crotalus ornatus — PRICE 2022 
DistributionUSA (Texas, New Mexico), Mexico (Chihuahua, Nuevo León)

Type locality: near Pecos River, N. W. Texas.  
TypesHolotype: USNM 486, adult female; Fig. 10) collected by A. Heermann. The specimen was collected during the survey of a railroad route to the Pacific, led by Lieutenant Parke, US Topographical Engineer (collection date unknown). 
DiagnosisDiagnosis: Crotalus ornatus (Fig. 11) can be distinguished from most congeners by having (1) a medium-sized SVL (adults 70– 100 cm, rarely to 130 cm SVL); (2) two large, triangular internasal scales; (3) two large prefrontals; (4) two large frontal scales; (5) 6– 10 prefoveals; (6) 2–4 loreals; (7) two preocu- lars; (8) five postoculars; (9) 2–7 intersuprao- culars; (10) 16–18 supralabials; (11) 14–21 infralabials; (12) 23–29 dorsal scale rows at midbody; (13) 164–205 ventrals; (14) 16–30 subcaudals (16–26 in females and 21–30 in males); (15) internasal–prefrontal region and supraoculars black or dark brown; (16) dark pigmentation of dorsal pattern extends from nape to occipital and parietal regions; (17) 22– 33 (mean 5 29) rhomboid dorsal body blotches that often coalesce with lateral blotches at midbody to form bands or chevrons (dorsal blotches of some specimens may become diffuse posteriorly, represented by barely distinct or absent bands anterior to vent); (18) light medial spots longer than wide on anterior portion of body, becoming broader at midbody and separating dorsal blotches; (19) medial spots often become indistinguishable from ground color on posterior one-quarter of body; (20) two white or light grey, irregular paraver- tebral spots present within each dorsal blotch, usually separated by 1–6 dorsal scale rows on anterior portion of body, but darken slightly and grow to extend across midline of dorsum to fill interior of dorsal blotches on posterior half of body; (21) tail black or dark brown with faint crossbands sometimes visible; (22) proximal rattle segment black or dark brown (Tables 6–7; from ANDERSON & GREENBAUM 2012).

Comparisons.—Crotalus ornatus is unique among C. molossus lineages in having 4–11 prefoveals; 2–7 loreals; a ground color of gray, olive-green, olive-brown, or tan; 22–33 rhom- bic dorsal blotches, each separated by a light gray, white, or pale yellow medial spot; and anterior 6–10 dorsal blotches connected by 1–3 scale rows, often resembling paravertebral stripes or a thick dorsal stripe surrounding light medial spots. Crotalus ornatus most closely resembles C. molossus sensu stricto, but can be distinguished from the latter taxon by its lower average scale counts (P = 0.001) for prefoveals (8 vs. 10) and loreals (3 vs. 4), fewer dorsal blotches (29 vs. 32), and a dorsal blotch pattern where the first 6–10 dorsal blotches are almost always connected (dorsal blotches are almost always separated by a light medial spot in C. molossus sensu stricto). Crotalus ornatus can be distinguished from C. m. nigrescens and C. m. oaxacus by having a higher number of dorsal scale rows at mid- body (27 vs. 25); a higher number of ventrals (up to 205 in females vs. 187 in C. m. nigrescens and fewer in C. m. oaxacus; Klauber, 1972); dark pigmentation on the head restricted to the internasal–prefrontal area, with thin (1 scale row wide), sometimes ornate lines on the occipital and parietal regions (extensive pig- mentation often covers most of the head of the latter two lineages); and light medial and paravertebral spots in the dorsal pattern (usually absent in the latter two taxa). In C. m. oaxacus, it is common for adults to retain black and white tail rings that are typical in juveniles of the C. molossus group (Campbell and Lamar, 1989, 2004), but this character does not persist to adulthood in C. ornatus.
Crotalus ornatus is most easily distin- guished from C. estebanensis by geographic distribution; the former is widespread throughout most of the Chihuahuan Desert, whereas the latter is an insular endemic in the Gulf of California. Morphologically, C. orna- tus differs from C. estebanensis in having relatively dark dorsal blotches that boldly contrast with the ground color (dorsal blotch- es are paler and the pattern is moderately contrasting with the ground color in C. estebanensis), and dark pigmentation on the head in the internasal-prefrontal area (absent in C. estebanensis; Grismer, 1999; Campbell and Lamar, 2004). Klauber (1949) noted longitudinal and transverse compression of the rattle of C. estebanensis, which is a unique character among members of the C. molossus group, including C. ornatus.
Crotalus ornatus differs from C. totonacus in being smaller (rarely to 130 cm vs. commonly exceeding 150 cm); in having a larger number of intersupraoculars (5 vs. 1 or 2), prefoveals (8 vs. 3 or 4), supralabials (17 vs.14), and infralabials (17 vs. 15); in having an anterior dorsal pattern of interconnected but usually distinct dorsal blotches (paravertebral stripes [usually without distinct blotches] on the neck transition into an intricate pattern on the head in C. totonacus); and by the lack of a vertebral ridge (relatively well-developed in C. totonacus; Campbell and Lamar, 2004, Anderson & Greenbaum 2012). 
CommentSynonymy: Crotalus ornatus was revalidated from the synonymy of C. molossus by Anderson & Greenbaum 2012, hence C. ornatus has been subsumed under C. molossus in the older literature.

Similar species: C. molossus. 
EtymologyThe Latin ornata, -us, = decorated" or "ornamented," refers to the ornate coloration. 
  • Anderson, Christopher G. and Eli Greenbaum 2012. Phylogeography of Northern Populations of the Black-Tailed Rattlesnake (Crotalus molossus Baird And Girard, 1853), With the Revalidation of C. ornatus Hallowell, 1854. Herpetological Monographs 26 (1): 19-57. - get paper here
  • Davis DR, LaDuc TJ 2018. Amphibians and reptiles of C. E. Miller Ranch and the Sierra Vieja, Chihuahuan Desert, Texas, USA. ZooKeys 735: 97-130 - get paper here
  • EMERSON, JAMES D.; DOMINIC L. DESANTIS, VICENTE MATA-SILVA, AMY E. WAGLER & JERRY D. JOHNSON. 2022. Movement, Home Range Size, and Habitat Use of Eastern Black-Tailed Rattlesnakes (Crotalus ornatus) in the Northern Chihuahuan Desert. Herpetologica 78(2): 110–118. - get paper here
  • García-Padilla, Elí, Gerson Josué Herrera-Enríquez, Manuel Nevárez de los Reyes, David Lazcano, Vicente Mata-Silva, Jerry D. Johnson and Larry David Wilson. 2016. Crotalus ornatus Hallowell, 1854. Mexico, Nuevo León. Mesoamerican Herpetology 3 (3): 778 - get paper here
  • Hallowell,E. 1854. Notices of new reptiles from Texas. Proc. Acad. Nat. Sci. Philad. 1854: 192-193 - get paper here
  • Heimes, P. 2016. Snakes of Mexico. Chimaira, Frankfurt, 572 pp
  • Hernandez T, Herr MW, Stevens S, Cork K, Medina-Nava C, Vialpando CJ, Warfel T, Fields N, Brodie C, Graham SP 2019. New distribution records for amphibians and reptiles in eastern Chihuahua, Mexico. Check List 15(1): 79-86 - get paper here
  • Lazcano D, Nevárez-de los Reyes M, García-Padilla E, Johnson JD, Mata-Silva V, DeSantis DL, Wilson LD. 2019. The herpetofauna of Coahuila, Mexico: composition, distribution, and conservation status. Amphibian & Reptile Conservation 13(2) [General Section]: 31–94 (e189) - get paper here
  • Muñoz-Mora, V. H., Suárez-Atilano, M., Maltagliati, F., Ramírez-Corona, F., Carbajal-Saucedo, A., Percino-Daniel, R., ... & Sunny, A. 2022. A tale about vipers’ tails: phylogeography of black-tailed rattlesnakes. Herpetozoa, 35, 141-153 - get paper here
  • Nevárez de Los Reyes, Manuel, David Lazcano and Javier Banda-Leal. 2016. Geographic Distribution: Crotalus ornatus (Eastern Black-tailed Rattlesnake). Herpetological Review 47 (2): 261 - get paper here
  • Nevárez-de-los-Reyes, Manuel, David Lazcano, Elí García-Padilla, Vicente Mata-Silva, Jerry D. Johnson and Larry David Wilson. 2016. The Herpetofauna of Nuevo León, Mexico: Composition, Distribution, and Conservation. Mesoamerican Herpetology 3 (3): 558–638 - get paper here
  • Price, Michael S. 2022. Reptiles of the Trans-Pecos Texas. ECO Natural History Series, ECO Publishing, Rodeo, New Mexico, 210 pp., ISBN: 978-1938- 85041-7. [review in HR 54 (1): 152]
  • Spinner, L. 2017. Die Klapperschlangen der USA in Natur und Terrarium. Reptilia (Münster) 22 (124): 18-33 - get paper here
  • Wallach, Van; Kenneth L. Williams , Jeff Boundy 2014. Snakes of the World: A Catalogue of Living and Extinct Species. [type catalogue] Taylor and Francis, CRC Press, 1237 pp.
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