Atractus gigas, MYERS & SCHARGEL, 2006

MYERS, CHARLES W & SCHARGEL, WALTER E, 2006, Morphological Extremes-Two New Snakes of the Genus Atractus from Northwestern South America (Colubridae: Dipsadinae), American Museum Novitates 3532 (1), pp. 1-16 : 8-12

Atractus gigas , new species

Figures 5–7 , Map 1

HOLOTYPE: Fundación Herpetológica ‘‘ Gustavo Orcés’ ’ ( FHGO) no. 194, an adult female, from Bosque Protector Río Guajalito , antigua Hacienda Las Palmeras, old highway between Quito and Santo Domingo, 1900 m, Pichincha, Ecuador (00 ° 14 9 S, 78 ° 49 9 W). Collected by Vlastimil Zak in January 1990.

ETYMOLOGY: The species name gigas (a giant) is a Latin noun of Greek origin. (The gigantes or giants, born of Mother Earth, were enormous beings who had thick serpents for legs. They fought a losing battle with the gods and man.)

DIAGNOSIS: Atractus gigas is distinguished from all species of Atractus by its unparalleled large size (. 1 m) and robust body (fig. 5). It differs from adult specimens of other large species ($ 700 mm) in having pale dorsal crossbars (indistinct in the only known specimen) rather than a false coral snake pattern ( A. obesus ) or definite dark markings on a brown ground color ( A. depressiocellus , A. major , A. torquatus ). See Comparisons for further comments.

Although the juvenile color pattern of Atractus gigas is unknown, young specimens conceivably might be confused with a few much smaller species of Atractus from the Pacific versant of Ecuador. Atractus dunni has fewer ventrals (125–136 in males, 138–150 in females) than A. gigas (170 in one female) and small dark spots dorsally ( Cisneros-Heredia, 2005). Atractus multicinctus differs from A. gigas in having 5 or 6 maxillary teeth (8 in gigas ) and a mostly white venter (mostly grayish brown in gigas ). Atractus paucidens also differs from A. gigas in having 5 or 6 maxillary teeth, and it has 4 infralabials in contact with the genials (3 in gigas ). Atractus multicinctus and A. paucidens are rather slender snakes, whereas A. gigas juveniles are expected to have relatively stout bodies.

DESCRIPTION OF HOLOTYPE

The holotype is a sexually mature female, with active ovaries and enlarged convoluted oviducts with developing ova. The specimen is in a fair state of preservation, although contorted and impossible to measure precisely. The digestive tract has been removed and the other internal organs somewhat disrupted. See table 1 for detailed measurements.

PROPORTIONS AND SCUTELLATION: Total length approximately 1040 mm, tail length 124 mm (11.9% of total). A very robust snake, with head barely wider than neck, and middle body slightly wider than head; body about as wide as high, either rounded or slightly angular ventrolaterally; 7 greatest head width

7 Contortion makes it impossible to determine with confidence the nature of the ventrolateral edge, which seems to be slightly angular on part of the anterior body.

about same as head length from snout to end of parietals and 73% of length from snout to end of mandible; head width (and also greatest body width) roughly 3% of SVL. Dorsal scales smooth, lacking apical pits, in 17-17-17 rows. Ventrals 170 (not counting a half-ventral anterior to anal plate); anal plate undivided; subcaudals in 35 pairs.

Snout rounded in dorsal and lateral view; rostral wider than high, visible from above; internasals small, wider than long, more than half (56%) the length of prefrontal suture; an azygous frontonasal scale situated between internasal and prefrontal sutures (figs. 6, 7A), diamond-shaped (1.9 mm long, 2.0 mm wide) with rounded points; prefrontals large, little longer than wide (greatest prefrontal width 93% of greatest length); prefrontal suture 67% length of frontal plate; supraoculars large, anteriorly narrowed, longer than wide; frontal barely wider than long (length 99% of anterior width), roughly pentagonal in shape; interparietal suture longer than prefrontal suture, 96% of frontal length.

Eye moderate, contained 1.8 times in loreal length, 2.8 times in snout length (sagittal); eye length shorter (84%) than distance to lip; eye not protuberant; lips flared, eyes concealed in ventral view. Nasal weakly divided above and below naris, its greatest length 63% of loreal length; loreal long (6.3 mm), 3.3 times longer than greatest height, entering eye, loreals well separated from internasals. No preoculars. Supralabials 7 on right side with 3rd and 4th touching eye, 8 on left with 4th and 5th touching eye; supralabials entering eye are noticeably higher than their basal width. Postoculars 2 on right side, 3 on left, subequal; temporals 1 + 2, the upper one in row 2 elongated, extending almost to the end of parietals.

Infralabials 7, first pair in contact behind mental, first three on each side in contact with a genial; single pair of large genials, 2.1 times longer than wide; three large medial gulars (preventrals) between genials and first ventral (fig. 7B). Head plate tubercles not detected, probably due to loss of stratum corneum.

COLOR PATTERN: In preservative (alcohol after formalin), the dorsal ground color is cinnamon-brown, turning gray on the lower two scale rows; the dorsal scales bear sparse gray specks that become denser on the bases of the scales—this pigmentation increasing ventrad to form an ill-defined gray stripe along the lower sides. There are about 30 faint, poorly defined, pale transverse bars along the body (barely evident in fig. 5); about 8 on the tail. The bars are pale amber color, one dorsal scale wide, and extend down to scale row 4 or 5. The bars are separated from each other by four to five dorsal scales. The color of the top of the head is similar to the dorsal color of the body, but with dark brown suffusions anteriorly and increasing toward the snout. Supralabials are grayish brown with cream specks toward the lips. Infralabials, mental, genials, and gulars are grayish brown with cream specks. Ventrals and subcaudals have an irregularly mottled pattern of grayish brown and cream.

MAXILLO- PALATO- PTERYGOID ARCH: Examined in situ on right side. Maxilla arched, extending anteriorly to middle of first supralabial, with a total of eight large to small recurved teeth, differentiated as follows: Teeth 1–5 large, subequal, tooth 6 noticeably smaller (medium-sized). Teeth 2–6 separated by increasingly wider gaps, followed by a somewhat wider diastema and two well separated small teeth (7–8), the ultimate of which is smaller than the penultimate.

First tooth rises from socket at anteroventral end of maxilla (not springing from anterior tip). All teeth firmly ankylosed, resistant to being dislodged (there are no empty sockets). All teeth angular in cross section, with a sharp longitudinal ridge on the labial side, this ridge gradually shifting from an anterior position on the first few teeth to a lateral position posteriorly.

Maxilla extending posteriorly past small teeth as a short toothless process. A large expanded flange on maxilla extending mediad and ventrad adjacent to the two small posterior teeth. Ectopterygoid strongly forked, with nearly equal-length stout branches cupping flange of maxilla. Palatine with an elongated shallow, nonprojecting maxillary process.

DISTRIBUTION AND HABITAT: Atractus gigas is known only from the type locality (Bosque Protector Río Guajalito) on the Pacific slope of the Ecuadorian Andes (map 1). The much smaller Atractus dunni (, 350 mm SVL) also occurs in this forest ( Cisneros-Heredia, 2005).

The Bosque Protector Río Guajalito (BPRG) was established as a private natural reserve in 1978 by its owner, Mr. Vlatismil Zak (who also collected the holotype of A. gigas ), and acquired legal status as a protected forest (Bosque Protector) in 1993 ( Freile and Hoeneisen, 2005). The vegetation in the neighboring Reserva Florística Río Guajalito—a smaller reserve adjacent to the BPRG—has been relatively well studied (see articles in Nieder and Barthlott, 2001). At the elevation (1900 m) where A. gigas was found, the vegetation has been classified as submontane rain forest ( Mutke, 2001). This is the typical vegetation at similar elevations throughout the Pacific versant of the Ecuadorian Andes ( Neill, 1999).

Interestingly, the greatest number of endemic and restricted-range species of plants in Ecuador occurs at similar mid-elevations in the Andes (900–3000 m; Borchsenius, 1997). The following description of the area is based on information provided by Mutke (2001), who studied the Reserva Florística Río Guajalito. The primary forests of this site have trees attaining heights greater than 40 m, with the largest crown area of the forest having a canopy height of 20– 25 m. The upper canopy is especially dominated by Croton sp. ; the greatest percentage of individual trees reach heights of 5– 11 m. The typical soils in the area are andosols on volcanic material (the BPRG lies about 30 km northwest, descending from Atacazo, a Pleistocene volcano). The annual mean precipitation is about 2700 mm, and the annual mean temperature is about 16.4 ° C at a nearby climatic station in Chiriboga.

COMPARISONS

We know of no other Atractus exceeding 1 m in length, although several species attain total lengths of about 700 mm or greater. These can be most quickly distinguished from Atractus gigas as follows.

Atractus depressiocellus Myers is known from its holotype (750 mm in total length) collected below 1000 m elevation in eastcentral Panama. The specimen has irregular black dorsal crossbars on a light brown ground color. It also differs from A. gigas in having a very small eye set in a pronounced depression, with very tall supralabials entering the eye. See Myers (2003: 20–22, figs. 1C, 2C, 3E).

Atractus obesus Marx (758–762 mm in total length) is known from the type and paratype from high elevation (2640–2700 m) in the Cordillera Occidental of western Colombia. It is the only other named giant Andean Atractus , and it is immediately distinguished from other large species by encircling black and pale rings in a false coral snake pattern ( Marx, 1960: fig. 71).

Atractus major Boulenger and Atractus torquatus (Duméril, Bibron, and Duméril) are fairly wide-ranging Amazonian species attaining lengths in excess of 700 mm. They normally have color patterns of variably shaped dorsal dark markings distinctly different from the vague pattern of the trans- Andean A. gigas . See, for example, descriptions and photographs in Hoogmoed (1980 [ A. torquatus ]), Martins and Oliveira (1993 [ A. major , A. torquatus ]), and Savage (1960: 47–52 [ A. major ]).

We have at present no suggestions as to the nearest relationships of Atractus gigas . The barely discernible pale transverse lines on the dorsum conceivably might represent pale edging of dark markings (e.g., as in some A. major ) that have been lost either phylogenetically or ontogenetically. Juvenile specimens might provide insight when available.

REMARKS

To our knowledge the azygous frontonasal scale on the holotype of Atractus gigas is unique in the genus (figs. 6, 7A). Median scales on the upper anterior part of the snout are quite rare in colubrids ( Heterodon and Hydrops come to mind as exceptions). The scale is symmetrical in its diamond shape, and the bordering internasals and prefrontals are of regular appearance, suggesting that the frontonasal is not a developmental aberrancy.

The upper anterior part of the snout seems to be an area of some plasticity in Atractus , as shown by two additional examples. (1) The median suture between the prefrontal plates either lies in a straight line with the internasal suture or else is asymmetrical and noticeably dextral to the internasal suture ( Myers, 2003: 9). The straight-line condition of the prefrontal suture probably is the most common configuration among colubrids, although both sinistral and especially dextral asymmetries occur widely. The straight-line and dextral conditions may be species specific in Atractus , although the character has yet to be coded broadly or checked for intraspecific variation in large samples. (2) The internasals appear to be either exceptionally tiny or else fused with the prefrontals in Atractus depressiocellus (rostral abrasion in the unique specimen precluded precise interpretation; Myers, 2003: 20–22, fig. 3E).

Figures

Fig. 5. Atractus gigas, new species. Views of the adult female holotype (FHGO 194), shown much smaller than life (X0.48).

Fig. 6. Atractus gigas, new species. Head of holotype (FHGO 194) in dorsolateral view, nearly twice life size (line 5 10 mm). Arrow points to diamond-shaped frontonasal scale between internasal and prefrontal sutures (see also fig. 7).

Fig. 7. Atractus gigas, new species. Head of holotype (FHGO 194). A. Dorsal view, X1.7. Arrow points to diamond-shaped frontonasal scale between internasal and prefrontal sutures. B. Ventral view, X1.2. Scale divisions 5 mm.