Crotalus thalassoporus, Meik & Schaack & Flores-Villela & Streicher, 2018

Meik, Jesse M., Schaack, Sarah, Flores-Villela, Oscar & Streicher, Jeffrey W., 2018, Integrative taxonomy at the nexus of population divergence and speciation in insular speckled rattlesnakes, Journal of Natural History 52 (13 - 16), pp. 989-1016 : 1006-1008

Crotalus thalassoporus sp. nov.

( Figure 5 ; Table 3)

Crotalus mitchelli pyrrhus, Seib 1978 , in part. Crotalus mitchellii, Grismer 2002b , Murphy and Aguirre-Léon 2002, Meik et al. 2012a, in part. Crotalus pyrrhus, Meik et al. 2015 , in part.

Description

A diminutive insular species of speckled rattlesnake with overall pale appearance; background colouration tan to pinkish with a series of 27–40 indistinct blotches; blotches usually only slightly darker than ground colour, pinkish to pale brown, often appearing faintly rust-coloured; dark speckling on body is faint. Tail with 3–5 bands, last two or three distinctly black with pale cream interspaces. The head is similar in colouration to the body, but often with few dark specks, more conspicuous than stippling on trunk; grey postocular stripe indistinct. In colour pattern, C. thalassoporus is similar to C. angelensis , and in both species the anterior scales of the dorsal body blotches are tipped posteriorly with dark brown or black. A single row of nasorostral scales precludes contact between rostral and prenasal scales. Variation in standard phenotypic characters is presented in Table 3.

Diagnosis

The presence of nasorostral scales distinguishes the new species from all congeners except for species of the C. mitchellii complex. From C. mitchellii the new species differs in having typically fewer dorsal scale rows (21.5–22 vs 25), fewer subcaudals (16–22 vs 20–24), fewer temporal scale rows (7 vs 8), fewer supralabials (14 vs 16), fewer interrictals (22–23 vs 28), fewer prefrontals (18–20 vs 30–31), colour pattern (pale tan, pinkish, or beige ground colour with indistinct rust-brown blotches vs variable colour pattern), and smaller adult body size. From mainland populations of C. pyrrhus the new species differs in having typically fewer tail bands (3–4 vs 4–6), fewer dorsal scale rows (21.5–22 vs 25), fewer temporal scale rows (7 vs 8), fewer supralabials (14 vs 16), fewer interrictals (22–23 vs 29), fewer prefrontals (18–20 vs 27–34), colour pattern (pale tan, pinkish, or beige ground colour with indistinct rust-brown blotches vs extremely variable), and smaller adult body size. From C. angelensis , the new species differs in having typically fewer tail bands (3–4 vs 5–8), fewer dorsal body blotches (31–32 vs 40–41), fewer dorsal scale rows (21.5–22 vs 27), fewer subcaudals (16–22 vs 20–25), fewer ventrals (169.5–174 vs 182–188), more supralabials (14 vs 13), fewer interrictals (22–23 vs 29–30), fewer prefrontals (18–20 vs 25–26), and smaller adult body size. From C. polisi , the new species differs in having typically fewer tail bands (3–4 vs 5–6), fewer dorsal body blotches (31– 32 vs 40–42.5), fewer subcaudals in females (16 vs 17), more ventrals in females (174 vs 169), fewer interrictals in males (22 vs 26), fewer prefrontals (18–20 vs 21–27.5), and colour pattern (pale tan, pinkish or beige ground colour with indistinct rust-brown blotches vs slate or charcoal grey ground colour with indistinct blotches).

Holotype

Subadult male, MZFC-26410, field number JMM-648, collected on 19 March 2010 by Jesse M. Meik, Sarah Schaack and Matthew J. Ingrasci. Rostral plate is as high as broad (2.2 × 2.2 mm), separated from the prenasal scales by 3/2 nasorostral scales; internasal scales 2, with an additional tiny scale interpositioned at the anterior suture and in contact with dorsal edge of rostral. Head scalation highly irregular, making some scale designations ambiguous. Distinct canthal scales absent, but approximately 22 knobby scales of variable size and shape in prefrontal area; interocular scales 7; loreal scales 3/3, irregularly shaped; preocular scales 2/2, prefoveal scales 11/8, irregularly shaped, precluding contact between nasal scales and supraocular scales; subocular scales separated from supralabials by two scales at midpoint of eye; supralabial scales 15/15; infralabial scales 17/16; interrictal scales 24; dorsal scale rows at midbody 23; ventrals 169 (exclusive of three preventrals); subcaudal scales 21, undivided (except distal 3, which are divided); rattle fringe scales 10; rattle segments 3, chain incomplete.

Measurements. SVL, 341 mm; tail length, 28 mm; head length (rostral plate to articulation of mandible with quadrate), 18.5 mm; head width (at widest point just anterior to articulation with mandible), 15.7 mm; proximal rattle segment width, 6.7 mm.

Colouration and pattern in preservative. Overall ground colouration dirty cream with faint speckling; head with few faint grey specks; lateral surfaces of head with medium grey suffusion, labial scales with cream spots; ventral surface of head cream, immaculate, ventral surface of trunk cream with diffuse black specks; 37 indistinct body blotches only slightly darker than ground colour, some with pale centres, all primary dorsal blotches wider than long with exception of first four, fusing with faint lateral blotch series over posterior third of body to form crossbands; dark maculations on anterior and posterior margins of blotches give the impression of faint transverse bars along the length of the body; five tail bands, distal three black and two scales long.

Type locality

Piojo Island , Municipality de Ensenada, Baja California, Mexico . Coordinates: N 29.018 W 113.465 ( Figure 5 ).

Type deposition

Holotype at MZFC-UNAM; paratypes at MZFC-UNAM ( MZFC 26411 , MZFC 26412 ) and at UTAARDRC (UTA R-59766, UTA R-59767).

Etymology

The specific name is derived from the Greek word meaning ‘seafarer’, and is a reference to the apparent historical introgression we note between this taxon and the population of speckled rattlesnakes on Smith Island, most likely resulting from oversea dispersal of propagules from Piojo Island (see Discussion).

Figures

Figure 5. Type localities and specimens photographed in situ for new species described herein. Piojo Island in foreground with Angel de la Guarda Island in the distance (upper left); western slope of Cabeza de Caballo Island in foreground with Ventana Island and peninsular mainland in the distance (upper right); paratype of C.thalassoporus (UTA R-59767) basking on a rock outcrop in the intertidal zone (lower left); holotype of C. polisi (MZFC-6248) coiled among boulders near the crest of the island (lower right).