Saddled Leaf-nosed Snake – Tucson Herpetological Society

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Saddled Leaf-nosed Snake (Phyllorhynchus browni)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2117″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Saddled Leaf-nosed Snake. Photo by Larry Jones[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2437″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Saddled Leaf-nosed Snake, Avra Valley © 2007 Manny Rubio / ASDM Sonoran Desert Digital Library[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2436″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Saddled Leaf-nosed Snake, Sonora, MX. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2438″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Saddled Leaf-nosed Snake. Note enlarged, leaf-like rostral scale. Photo by Young Cage[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2439″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Saddled Leaf-nosed Snake (the “Maricopa” form), vicinity of Ajo. Photo by James Atkinson[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Saddled Leaf-nosed Snake (Phyllorhynchus browni) is a small (< 510 mm total length [TL]) but stout, burrowing snake with a distinctive enlarged, triangular rostral scale that is folded over the snout and has its edges raised up. The background dorsal color is pinkish-tan to light gray or cream. Ten to 18 relatively large and regularly-shaped brown to slate-gray dorsal blotches or saddles are on the body, with 2-4 on the tail. These blotches do not reach the ventrals. Some individuals have smaller, lateral dark blotches, but most do not. The dark dorsal blotches usually have dark edges. Lighter areas between the blotches have diffuse dark speckling. A dark band crosses over the top of the head and through the eyes, angling back to the corners of the mouth. The ventral surface is immaculate white (Bogert and Oliver 1945, Hardy and McDiarmid 1969, Ernst and Ernst 2003).

The dorsal scales are arranged in 19 (rarely 20) smooth scale rows at mid-body. The subcaudals are divided, but the anal plate is undivided. Loreal scales usually number 1-2 on each side, and if more than one occurs on a side, they typically differ in size. The pupil is vertically elliptical. Four subspecies have been described, however, none are currently recognized (McDiarmid and McCleary 1993, Crother 2012). Two of those occur in Arizona, including the Pima Leaf-nosed Snake (formerly Phyllorhynchus browni browni) and the Maricopa Leaf-nosed Snake (formerly P. b. lucidus). The former has dark dorsal blotches broader than the intervening light spaces. The latter has dark blotches not as broad to only slightly broader than the intervening light spaces. Male Pima Leaf-nosed Snake also have 166 or fewer ventral scales, whereas male Maricopa Leaf-nosed Snakes have 168 or more (Ernst and Ernst 2003). Rosen et al. (1996) found two distinctive pattern classes in the Organ Pipe Cactus National Monument region that correspond to these former subspecies. In this region, the two are geographically disjunct (P. b. lucidus occurs to the south of P. b. browni), and the authors argue that taxonomic recognition should be maintained for these forms.

This species is most likely to be confused with the Spotted Leaf-nosed Snake (Phyllorhynchus decurtatus), which is of similar size and body configuration, and with which it shares the distinctive enlarged rostral scale. Descriptively their suite of characters overlap (e.g., number of dorsal blotches, number of loreal scales, presence of lateral dark blotches) but the two are distinguishable based on dorsal pattern. The dorsal blotches in the Saddled Leaf-nosed Snake are larger and more regular in shape, in addition to almost always being fewer in number. The Spotted Leaf-nosed Snake has numerous small, dark lateral blotches, which are usually absent in the Saddled Leaf-nosed Snake. The morphology of the hemipenis also differs between the two Phyllorhynchus species (Cadle 2011).

The Saddled Leaf-nosed Snake is a species of bajadas and valleys that in Arizona occurs from Organ Pipe Cactus National Monument east to Tucson and north to near Gila Bend. Its distribution also runs north from Tucson to Florence, Superior, Stewart Mountain Dam, and near Cave Creek. It also occurs in the lower San Pedro River Valley northward from Mammoth to at least Aravaipa Canyon, and Weber (2016) found it at the base of the Mescal Mountains on Highway 77 in Gila County. Brennan and Holycross (2006) show the distribution extending westward almost to Yuma County, but there are no museum specimens or other records of which we are aware from west of Organ Pipe Cactus National Monument, or very far west of Highway 85. James Atkinson, biologist at Cabeza Prieta National Wildlife Refuge, is not aware of any records from the Refuge (pers. comm., 2015). In the Circle, this is a species primarily of rich Sonoran desertscrub; however, it ranges upslope into semi-desert grassland in the Altar and Santa Cruz valleys, and a record from Ruby Road in Santa Cruz County is likely from an area with scattered oaks in semi-desert grassland. In Sonora and Sinaloa, it is also known from foothills and coastal thornscrub and tropical deciduous forest. There are no records from the Sonora portion of the Circle, but it likely occurs in the deserts east of Sonoyta, and potentially in the Río Bambuto Valley south of Nogales. Elevational range in the Circle is about 400-1150 m. It occurs to near sea level in Sonora. Throughout its range, the Saddled Leaf-nosed Snake occurs from south central Arizona south through western portions of Sonora, and east of the Sierra Madre Occidental in Sinaloa.

At Organ Pipe Cactus National Monument, the Saddled Leaf-nosed Snake was the 9^th most encountered snake on Highway 85 during 1987-1994 (Rosen et al. 1996). In 1949, between Ajo and the Mexican border, the Saddled Leaf-nosed Snake was the second-most encountered snake on Highway 85, only exceeded in number by the Spotted Leaf-nosed Snake (Hensley 1950). Rosen et al. (1996) surmised that this and other changes in numbers of snakes encountered were real and might be the result of increasing vegetation cover from 1949 to 1987-1994.

Jones et al. (2011) did not find the Saddled Leaf-nosed Snake on either the Sun Valley Parkway or the Maricopa Road (Hwy 238) in Maricopa County. It was not found at the Rocking K Ranch adjacent to Saguaro National Park East (Murray 1995). Lazaroff et al. (2006) reported a single Saddled Leaf-nosed Snake from the Sabino Canyon Recreation Area, but said there are numerous records from Sabino Canyon Road, just south of the Recreation Area. Surprisingly, Averill-Murray and Averill-Murray (2006) did not find the species at Ironwood Forest National Monument, but considered it as potentially occurring there. Old records exist for various locations in the Tucson basin, but the species has been extirpated from urban and agricultural areas.

Collection dates for the species and in the Circle run from 20 March to 21 November, however, most are found from June through August. On Highway 85 in Organ Pipe Cactus National Monument, most of the records were during May-July. Rosen et al. (1996) state that in the Arizona Upland subdivision of Sonoran desertscrub in Pima County, Phylloryhnchus activity is rarely observed until about 20 May, and it essentially ends after 30 August. This burrowing species is almost exclusively a nocturnal snake. When annoyed it may flatten its throat and hiss (Stebbins 1954), and some try to bite (Ernst and Ernst 2003).

Based on specimens from Arizona, Goldberg (1996) found males in spermiogenesis from April through September collections. Females with enlarged follicles or oviductal eggs were found in June and July, although only 34% of mature females were reproductively active. Rosen et al. (1996) report clutch sizes of 2, 3, and 4. Stebbins (1954) found a female near Álamos, Sonora that contained five eggs about ready to be laid. The smallest mature males and females reported were 229 mm SVL and 293 mm SVL, respectively (Goldberg 1996).

Gardner and Mendelson III, Jr. (2003) examined digestive tract contents of 242 specimens of the Saddled Leaf-nosed Snake. Eighty-two of those specimens contained from one to 10 squamate eggs and/or the presumed contents of those eggs, including portions of an unidentified embryonic lizard. No specimens collected in April (n=15) had prey items in their stomachs. Based on their findings, Gardner and Mendelson III, Jr. (2003) suggested that Saddled Leaf-nosed Snakes may occasionally slash squamate eggs open, possibly with their enlarged rear maxillary teeth, and only consume the contents, or they may regurgitate some egg shells. Rosen et al. (1996) found only lizard eggs in dissected specimens from Organ Pipe Cactus National Monument and vicinity. Stebbins (1954) reported what appeared to be a lizard egg in the stomach of a specimen from near Álamos, Sonora. The enlarged rostral scale may aid in excavating lizard and snake eggs out of soil and sand.

The Saddled Leaf-nosed Snake is a species of least concern on the IUCN’s 2014 Red list. With a valid Arizona hunting license, four can be collected per year or held in possession, alive or dead. However, collection is illegal without specific authorization in protected areas, such as Organ Pipe Cactus National Monument and Saguaro National Park. Rosen et al. (1996) thought the species had declined at Organ Pipe Cactus National Monument and vicinity from 1949 to 1987-1994 (see discussion above). In the same report, road mortality was found to be substantial. Sixty-two of 107 Saddled Leaf-nosed Snakes found on Highway 85 from Ajo to the international boundary during 1988-1994 were dead. The species is also eliminated in areas of urban development and agriculture.

Saddled Leaf-nosed Snake (Phyllorhynchus browni)

Description

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