Snakes of the genus OxyrhOpus ( Colubridae : Squamata ) in Colombia : taxonomy and geographic variation

Four species of Oxyrhopus occur in Colombia, one (O. leucomelas) of which is Andean and the other three occur in lowlands. No geographic variation was detected in O. occipitalis but there is marked geographic variation in color pattern and scutellation for the widely distributed O. petola. Recognition of subspecies within O. petola is possible but appears to obscure more than it illuminates. The snake previously reported as O. melanogenys or O. aff. melanogenys is diagnosed as a previously unrecognized species.


IntroDuCtIon
The current taxonomy of snakes of the genus Oxyrhopus was established largely by Bailey's accounts and keys to Oxyrhopus published in Peters & Orejas' (1970) catalogue.Either explicitly or implicitly, Bailey reported O. formosus, O. leucomelas, and O. petola (all three subspecies) for Colombia.There have been no subsequent studies published of specimens of Colombian Oxyrhopus although two reports of museum listings (without critical study of the specimens themselves) have appeared (Perez Santos & Moreno, 1988;Sánchez et al., 1995).These two papers reported the same taxa as reported by Bailey but added O. melanogenys as well.These three publications provide only the merest of information about species distributions and nothing about individual (or populational) variation, aspects that are central to the present contribution.Color illustrations (without data other than collection locality) are available Snakes of the genus Oxyrhopus are mostly banded (termed coralsnake mimics by Campbell & Lamar, 1989, 2004) but at least two species (O.melanogenys and O. occipitalis) are red snakes with some head and/or nape dark bands (although some specimens of O. melanogenys have body bands).Oxyrhopus petola may be so completely melanistic that inexperienced persons confuse them with adult Clelia clelia (which does not exhibit preocular-frontal contact).In my survey of Colombian collections, I found O. occipitalis confused with juvenile Clelia clelia and with Pseudoboa neuwiedii and found melanistic O. petola confused with Clelia.), I located 272 specimens of Oxyrhopus with at least locality data.From these specimens, scale counts, measurements, sex, maturity, location of the umbilicus (when neonates), and characters of color patterns were collected by me.Lengths of pale and dark body bands were measured in scale lengths along the vertebral scale row.Aside from males with everted hemipenes, all specimens were sexed by dissection of the base of the tail.When sample size permits, all means are reported as ± 1 standard error of the mean to facilitate simple significance tests.My simple significance tests consist of using twice the S.E. to approximate the 95% confidence intervals of the mean.

Scutellation
Oxyrhopus have smooth scales with a pair of apical pits and exhibit a posterior reduction in scale row number (by two rows).The anal scute is entire.Subcaudals are paired.
Scale row formulae: Aside from the montane species, O. leucomelas, and unusual specimens of other species with only 18 scale rows on the neck, there are 19 scale rows on the nape as well as at midbody (curiously reported as 17 rows by Duellman, 2005, surely a victim of cut and paste) reducing to 17 (occasionally 16) rows anterior to the vent in most Oxyrhopus by means of the loss of scale row 4 or the fusion of 3 + 4 at about ventral scute 113 to 150.Oxyrhopus leuucomelas has 17-17-15 dorsal scale rows.
Number of supralabials and infralabials: Three Colombian Oxyrhopus have long heads whereas O. leucomelas has a shorter head (Fig. 1) and this affects the number of labial scales.Excepting O. leucomelas, supralabials are normally 8 with 4 and 5 entering the orbit (rarely 9, with 5 and 6 entering the orbit, but not bilaterally).Excepting O. leucomelas, there are normally 10 infralabials with 1-6 in contact with the chin shields.

Contact between preoculars and frontal scale:
The preoculars may exhibit sutural contact with the frontal or be separated from the frontal (Fig. 2).This character was used by Bailey to separate species as well as to characterize one subspecies of O. petola as different from the other two subspecies.In order to score individuals, I generated a range of combinations (from each preocular well separated from the frontal to sutural contact with deformation [shape change] of the frontal on each side.Non contact between the preoculars and frontal is seen in combinations 1-2 as well as asymmetrically in combination 3; combinations 4-5 include various degrees of symmetrical contact).Oxyrhopus leucomelas, O. occipitalis, and Middle American populations of O. petola "sebae" are characterized partially by combinations 1 and 2.

Number of ventral and subcaudal scutes:
These meristic data were collected routinely but are rarely used for species discrimination (but, see Dixon & Soini, 1977;Duellman, 2005;Zaher & Caramaschi, 1992) because of sexual dimorphism and the frequency of specimens with incomplete tails.

Coloration
Ontogenetic changes in color pattern: Oxyrhopus occipitalis exhibits the most dramatic changes.Young specimens have a yellow head and the body is banded black and nearly white whereas in adults, the snout is yellow, the rest of the head is black, and the body and tail red (all red scales with black tips).Partially grown individuals exhibit the adult pattern but with faint retention of the juvenile banded pattern concealed by the red pigment.Ontogenetic variation in O. petola is less marked, consisting of black and yellow-white bands in juveniles versus black and red bands in adults.With an increase in size, the pale bands (beginning posteriorly and extending anteriorly) become orange and lastly red.The other two species do not exhibit comparable ontogenetic variation in patterns.Bailey (1970: 233) mentioned (and this is often repeatedly uncritically in more general accounts of color pattern in O. petola) that large individuals of O. petola digitalis are "often completely melanistic."That is not the case as concerns the 17 O.petola "digitalis" (from Colombia) here examined whereas uncommonly, O. petola "petola" is sufficiently melanistic to obscure completely the banding pattern (ICN 6767, 10971, and 11064) and two specimens of O. "melanogenys" examined in this study are so melanistic that only the orange bands are evident.The other Colombian Oxyrhopus normally (or always) exhibit a banded color pattern with only minor ontogenetic variation.However, in one neonate (ICN 11007) of O. petola that hatched soon after the egg was found beneath a pile of African Palm fronds, the pattern consists of a single vertebral pale stripe from the nape to just anterior to the vent (1 scale wide).Another neonate (MLS 1374) has the first 4 1 / 2 dorsal body bands fused to form a pale longitudinal stripe (1 scale wide), after which, the pattern reverts to dark dorsal bands (64 1 / 2 on body, 30 1 / 2 on tail).Such striped Oxyrhopus are not found in the sample of adults, suggesting that these variants are eliminated by natural selection.
Presence of triads: Triads (a sequence of black-whiteblack-white-black limited by a partial or dorsally complete orange band) occur in one species of Oxyrhopus from Colombia.Using the orange divisions of triads as markers, the more anterior orange divisions on a snake are confined to small patches on the lowest scale rows and do not form complete dorsal bands.As one proceeds posteriorly, the orange blotches become progressively larger and eventually join the blotch on the opposite flank to form a complete band dorsally (Fig. 3).This sort of triad border is markedly different from that seen in O. guibei (Campbell & Lamar, 2004, plate 1212), some O. melanogenys (Campbell & Lamar, 2004, plate 1216), or O. trigeminus (Campbell & Lamar, 2004, plates 1225-26) where the red bands are complete dorsally all along the body.
Number of dark body bands and degree to which these encroach upon venter: Dark body bands vary in number (10 1 / 2 to 72) in Colombian Oxyrhopus.Usually, the last dark body band overlaps the vent.In O. leucomelas, the dark bands completely encircle the body whereas, in the other species, the encroachment of dark bands onto the ventral scutes is limited to the lateral edges of the ventral scutes as well as the subcaudal scutes or is complete across the ventral surfaces under the tail.In the species having triads, dark blotches extend substantially onto the ventral scutes (reaching or nearly reaching the midline) but normally only on the posterior one-half of the snake.

Lengths of dark body bands:
In Oxyrhopus petola, dark body bands exhibit different lengths along the length of the body, being longer anteriorly and shorter posteriorly.This is true as well for the snakes from the Llanos where one sees a high number of body bands (and, as a consequence, a reduction of length variation).The differences between triads in O. "melanogenys" and O. guibei, O. melanogenys, and O. trigeminus suggests that what constitutes a dark body band in O. "melanogenys" includes the orange spots (or band) forming the triad border.If one does so and then measures the length of the dark bands in terms of the number of scale lengths along the vertebral scale row (even when the orange band is complete dorsally), the dark body bands have a more complex arrangement (an alteration of longshort-long with the invasion by orange (producing a triad border) occurring in even-numbered dark body bands.Of the 172 pairs of adjacent dark body bands in O. "melanogenys", only seven pairs were of equal lengths (that is, were the same number of scale lengths long).
Lengths of pale interspaces (excluding the orange bands of the species with triads): Bailey (1970) used the lengths of the pale interspaces on the posterior part of the body as a character useful in detecting geographic variation in O. petola.My collection of these data (for all four species in Colombia, when pale bands are evident) consists of recording these lengths at three points along the length of the body (between dark bands on the neck, at midbody, and anterior to the vent) so as to evaluate differences associated with geography and taxonomy as well as to quantify intrabody variation.
Size and proportions: I recorded snout-vent length and tail length (when the tail was complete) for all specimens examined.From these data, maximum sizes were estimated and relative tail length (as a % of total length) calculated.This proportion is of little value as it reflects the number of pairs of subcaudal scales (Fig. 4) and the two variables are very tightly correlated.

Position of the umbilicus:
In neonates (either because they were hatched from clutches found in the field or because the snake retains its umbilicus), the position of the umbilicus was scored in terms of ventral scute count.The umbilicus occupies two or three ventral scutes and is located at scutes 161-162 to 184-186 in the 29 neonates for which the variable was scored (O."melanogenys" and O. petola).Sexual dimorphism (in umbilicus position) was not detected.In O. petola, the umbilicus is located between scutes 164-166 and 184-186, with a weak mode between scutes 169-174.In O. "melanogenys", it is located between scutes 161-162 and 166-168.

reSuLtS
Four species of Oxyrhopus can be recognized among the materials housed in Colombian museums.Geographic variation is very noticeable in one of these within Colombia (O.petola) but not in the other three species.

Oxyrhopus leucomelas (Werner)
Specimens examined: COLOMBIA.( 13 This is the only species of Oxyrhopus in Colombia having complete body bands but also is distinctive for having fewer scale rows (17, reducing to 15).The species was described from the Cañon de Tolima (near Ibagué, Tolima) and the misplaced holotype is certainly a female (based on the tail length/total length proportion).Downs (1961) reported three other specimens (two topotypes as well as another from Moscapan, Huila) that I have not examined but these specimens are males (as reported by Downs or as inferred from the ratio of tail length to total length).I examined thirteen specimens from Colom-bian museums (and when combined with the four specimens reported by Downs, 1961), males have fewer ventrals and more subcaudals than do females (Table 1).This species has either 7 or 8 supralabials with both 3 and 4 or 4 and 5 entering the orbit (as reported by Downs, 1961).The source of variation is a vertical division of the third supralabial to produce two half supralabials.Infralabials are 7-7 or  8-8 (with 1-4 or 1-5 [in one case, 1-3 and 5, UVC  12179] contacting the chin shields).Temporals are 2 + 3 or 2 + 2 (by fusion of two posterior temporals, this difference is seen between individuals and within single individuals [ICN 1371 and UC 553]).Scale row reduction occurs in various ways: in most specimens by means of loss of row 4 but occasionally by loss of row 5.In some cases, the reduction appears to be accomplished by fusion of scale rows 4 and 5. Reduction occurs at ventral scute 109 to 159 based on specimens examined by me.The four specimens examined from the Cordillera Occidental have reductions occurring at ventral scutes 130-159 (mean 142.8) whereas three examined from the Cordillera Central have reductions at ventral scutes 109-147 (mean 129.5) and two from the Cordillera Oriental at ventral scutes 110-122 (mean 118.2).Downs (1961) reported the position of reduction for a specimen from Moscopan, Huila (C.Central) at scutes 124 and 126.Given these limited data, there may be geographic variation in the position of scale row reduction in this species.
Combining my data with those given by Downs (1961), O. leucomelas has 17 1 / 2 to 33 1 / 2 (mean 27.4 ± 1.1) dark body bands and 13 1 / 2 to 21 1 / 2 (mean 15.9 ± 0.6) dark bands on the tail.Dark bands are either of equal length at midline and low on the body or much longer at the midline than low on the body.Dark body bands are 3-5 1 / 2 scale lengths long and pale interspaces are 1 1 / 2 to 2 1 / 2 scale lengths long.Although the sample of females is very small, there may be sexual dimorphism in the number of dark body bands (Table 1).Oxyrhopus leucomelas remains a rare snake in collections, however in three males from the Cordillera Occidental there are 271 / 2 -30 1 / 2 dark body bands whereas in six males from the Cordillera Central there are 17 1 / 2 -33 bands and in three males from the Cordillera Oriental, there are 23 1 / 2 -27 bands, suggesting some geographic variation in number of dark body bands, at least in males.This is the smallest Oxyrhopus found in Colombia.The largest male (UVC 12179) is 722 mm in total length and the largest female (ICN 10025) is 701 mm in total length.Males have longer tails than do females: tail/total length is 25.1-29.1 (mean 27.4 ± 0.4)% in nine males and 20.6-23.0 (mean 21.9)% in three females.
The distribution of the species in Colombia is entirely Andean (Fig. 5), in the cloud forests of all three cordilleras at elevations between 1400 and 2250 m.A record from Norte de Santander (Perez Santos & Moreno, 1988) has not been verified but appears to be the Santa Rita located between the municipalities of Arboledas and Salazar.

Oxyrhopus occipitalis (Wagler)
Specimens examined: COLOMBIA.( 23 (1970: 232) mentioned that what he identified as O. formosus was a "complex of forms."He specifically implied that one species occurs in Co-lombia and the Amazon Basin whereas another was found in eastern Brasil and western Peru.Hoge et al. (1973) applied the name O. occipitalis to the former and restricted the name O. formosus to the populations in which adults are banded red and black.The species differences apparent based on Hoge et al. (1973) as well as Jorge da Silva (1993) are minimal and involve only color pattern where O. formosus appears to retain aspects of the juvenile coloration into adulthood whereas O. occipitalis exhibits strong ontogenetic change in color pattern.The distinction may have been premature to judge from character discordancies evident in color photographs available in Martins & Oliveira (1998).However, I use the name O. occipitalis for Colombian populations because they do not exhibit such discordancies and conform to the species concept of Hoge et al. (1973).This is a very distinctive species within Colombia because of its ontogenetic variation in color pattern (juveniles have a yellow head with the body and tail banded black and yellow-white whereas adults have a yellow snout (extending to the suture between the prefrontals and frontal), rest of black head, and red body and tail [scale tips black]).
I have seen only three specimens exhibiting the juvenile pattern of dark body bands, two juveniles (MLS 1228 [male] and 1382 [female]) and one adult male (ICN 10453).Both males have 14 body bands and 9 tail bands; the juvenile female has 19 body bands and 9 tail bands.The most anterior dark bands are longer than those encountered at midbody or on the posterior part of the body (anterior bands 8-16 scale lengths long, others 4 1 / 2 to 8 1 / 2 scale lengths long).Pale interspaces are shorter than the dark bands but have a tendency to be longer more posteriorly (anterior pale interspaces 3-5 scale lengths long, posterior ones 4 1 / 2 to 6 scale lengths long).The banded color pattern of the adult male is a very faint banding.Even less evident banding is seen partially in other specimens (IAvH 3075,3375,4089,and ICN 81).In all of the adult snakes, the yellow snout is characteristic of O. occipitalis and none conforms to the descriptions of O. formosus (with more of the head yellow in adults).
The species is likewise distinctive (among lowland Oxyrhopus) in having a wide separation between the preocular scales and frontal (in 22 of 23 specimens examined).In terms of scutellation, males have fewer ventrals and more subcaudals than do females (Table 1).Ten specimens were examined for other scutellation features: all have 8-8 supralabials with 4 and 5 contacting the orbit, 9-9 infralabials with 1-5 contacting the chin shields) and 2 + 3 temporal scales (aside from ICN 8150 who has 2 + 2 temporals on one side and 2 + 3 on the other).Scale reduction involves the loss of scale row 4 at ventral scutes 123 to 144.For three specimens from the Middle Magdalena forests, reduction occurs at scutes 128-139 (mean 134.5) whereas for six from Amazonia, it occurs at scutes 123-144 (mean 131.9).
The largest male examined (MLS 1377) is 817 mm in total length and the largest female (ICN 10745) is 1108 mm in total length.Males have longer tails than do females: tail/total length is 22.7-25.3(mean 24.4 ± 0.4)% in six males and 18.6-21.3(mean 19.8 ± 0.2)% in 14 females.
In Colombia, O. occipitalis is distributed across the forested lowlands of Amazonia as well as in the forests termed the Middle Magdalena and within the Maracaibo Basin (Fig. 6).Given that I have seen only 23 specimens from Colombia, when these are divided among these three regions (and by sex), it is difficult to detect any geographic difference in scutellation; for the present, it appears that no geographic variation occurs among the distributional disjuncts separated by the Andean cordilleras.
Of these 23 individuals, only one (ICN 81, from Depto.Santander in the Middle Magdalena) was used explicitly in a publication (cited by both Perez Santos &Moreno, 1988, andby Sánchez et al. 1995).In each case, the authors incorrectly identified the specimen as O. melanogenys, a species not found outside of the Amazon Basin.This species was reported as well, using the combination Pseudoboa bitorquata by Niceforo María (1942: 96)  What was reported as Clelia bicolor from northeastern Peru by Dixon & Soini (1977, 1986)   Chocó, (4) those from the formerly dry tropical forests of the upper Río Cauca, Caribbean lowlands, and upper Magdalena Basin, (5) those from the formerly dry tropical forests of the Maracaibo Basin, and (6) those from the wet lowland forests of the Middle Magdalena valley (this unit extends westward along the Andean foothills of northern Antioquia and southern Córdoba).Niceforo María (1942: 96) cited many locality records (as Pseudoboa petola and, possibly P. rhombifer), of which I've seen MLS material of seven.
This species currently enjoys instability of names.Savage (2002) used the combination Oxyrhopus petolarius for the same species identified as Oxyrhopus petola by most authors, including Duellman (2005).The last author applied the name O. petolarius to what he called another sympatric species, distinguished solely by its higher subcaudal scale count.
However, using the number (and their lengths) of dark dorsal body bands does lend some credence to Bailey's proposal.Using only the number of dark body bands, sexual dimorphism is not evident for any population (Table 1) but four geographic units are readily discriminating using this metric (unit 1, unit 2, unit 3, and units 4-6).The greatest mean number of bands (Table 1) is seen in unit 1 (O.petola "petola") and significantly fewer in units 4-6 (O.petola "sebae").The wettest portions of the country (units 2 and 3) harbor snakes having significantly fewer bands (and each unit differs significantly from the other).Snakes of units 2 and 3 correspond to O. petola "digitalis".
Combining all the ecogeographic units that Bailey ascribed (or would have) to O. petola" sebae" (within Colombia) covers a range of 16 1 / 2 to 38 1 / 2 dark body bands.Colombian snakes assigned to this subspecies occupy both dry and wet lowland tropical forests as well as being fragmented into three geographic units partially divided or isolated by montane barriers (upper Río Cauca valley, Maracaibo Basin, and coastal lowlands plus Middle Magdalena).Considering the three geographic units, only six specimens are available for the southwestern Maracaibo Basin and adjacent Cesar of Colombia (17 1 / 2 -28 1 / 2 body bands, mean 24.7).Twenty-one are available for the Alto Río Cauca (19 1 / 2 -36 body bands, mean 25.3 ± 1.0).Fiftyeight are available the Caribbean coast and Magdalena valley (16 1 / 2 -38 1 / 2 body bands, mean 26.1 ± 0.6).However, between these three ecogeographic units, the differences are not significant.
Bailey (1970) used a combination of number of dark body bands and the lengths of the pale interspaces posteriorly in his definition of O. petola "sebae".These two characters are inversely related (Fig. 8) and not independent.There is no surprise that as one increases the number of dark body bands, one must decrease the lengths of the pale interspaces.Oxyrhopus petola "petola" is distinctive by either measurement but the distinctions among O. petola "digitalis" and O. petola "sebae" are solely the number of dark dorsal body bands.
In terms of scutellation, O. petola has 8-8 supralabials (4 and 5 contacting orbit) in all populations although two specimens from the Chocó (ICN 11283-84) each have 8-9 supralabials (the supralabial # 3 is divided vertically so as to increase the number of supralabials to 9 on one side of the head with 5 and 6 contacting the orbit on that side of the head).Infralabials are normally 10-10 with 1-6 contacting chin shields (1-5 in 10 % of the specimens).One specimen (ICN 8474) has 9-10 infralabials, two (ICN 2997, 10560)  For all populations here assigned to O. petola, males have significantly more subcaudal scutes than do females but the number of ventral scutes does not differ significantly contrasting sexes (Table 1).Given that the color pattern differences used by Bailey (1970) to distinguish subspecies are inversely correlated, I attempted to quantify geographic variation in O. petola using the number of ventral and subcaudal scales.
East of the Andes, snakes from the forested Amazonas have more scutes than do those from the more open Llanos.Differences in subcaudal counts (Table 1) are significantly different for each sex contrasting the open Llanos snakes (assigned to O. petola petola by Bailey, 1970) with those from the forested Amazon (assigned to O. petola digitalis by Bailey, 1970) and this difference is accentuated in the Iquitos region (Dixon & Soini, 1977, 1986), extending the meristic cline farther south.The only discordant data point is Duellman's (2005) report of a male from central Peru having only 86 pair of subcaudals (however, given its tail length, the subcaudal count datum is suspect; Fig. 4).In addition, using only the difference (males >females or males < females), the ventral scute means for Amazonian specimens are greater in males than females whereas for the Llanos, they are greater for females than males, but the differences are not significant.
West of the Andes in Colombia, the situation is more complex although snakes from the Chocó (also assigned to O. petola digitalis by Bailey, 1970) also have high scute counts (Table 1).Chocoan males have significantly fewer ventral and subcaudal scutes than do those from Amazonas whereas the values for females are not statistically different.
Natural history: On 28 October 2006, a clutch of eight near-term eggs was found beneath a pile of fronds of African Palm in a palm plantation belonging to Palmeras de Meta.During the next hour, possibly responding to warm hands, six eggs hatched resulting in seven neonates (two were obviously within a single egg shell).The other two eggs hatched two days later.These are now ICN 11003-11011.Our collecting at Palmeras de Meta in late October 2006 found O. petola to be relatively common and we secured several other neonates as well as a single, completely melanistic female (ICN 10971) containing nearly mature ova (11 ova, 9-10 mm wide and 20-21 mm long).Collecting at the same site in March 2006, did not yield in any O. petola, suggesting that activity and reproduction are markedly seasonal.
Subspecies: Bailey (1970) recognized three: O. p. sebae, from Mexico to the Caribbean coast and interandean valleys of Colombia, O. p. digitalis, disjunct in the Pacific lowlands of Colombia and in the Amazon Basin, and O. petola petola for open habitats of the Colombian-Venezuellan Llanos and east to the Atlantic.Bailey's proposal suffers from variation discordant with his proposal.The degree of preocular-frontal contact does not map well with O. p. "sebae", at least for Colombian populations.Significant differences in number of dorsal body blotches and in number of subcaudal scutes support separation of the Chocoan and Amazonian populations assigned by Bailey (1970) to O. p. digitalis.In spite of some significant differences contrasting populations, I decline to use subspecies for O. petola because I think use of subspecies names implies more than we know.One can investigate geographic variation using characters without obscuring that variation under subspecific names.
Contrasting the two phenetically different units east of the Andes, the Llanos population is very different from that of the forested Amazon.Nonetheless, one male specimen (ICN 368), from a geographically intermediate point, is very nicely intermediate in dorsal dark body blotch count (25 1 / 2 ), with longer posterior pale interspaces (2 scales long), and a high ventral scute count (207), providing evidence of gene flow between the two units.A second geographic unit exhibits comparable intermediacy in extreme eastern Colombia (Vichada: adjacent to the Amazonian forests of southern Venezuela).Two males (ICN 2583 and UVC 5377) have 23 1 / 2 and 24 1 / 2 dark dorsal body bands separated posteriorly by pale interspaces 1 3 / 4 to 2 1 / 2 scales long.A female (MUJ 784) has only 18 1 / 2 dark dorsal body blotches separated by pale interspaces 2-2 1 / 2 scales long.The presence of such snakes in eastern Vichada implies the existence of the digitalis phenum in Amazonian Venezuela.
The triad boundary markings and the nape band are orange in life in the few living specimens I have seen (or for which color notes are available to me).However, Dixon & Soini (1977, 1986) reported these markings as yellow, orange, or red and Martins & Oliveira (1998) as yellow.The specimens illustrated in color by Campbell & Lamar (1989, 2004) have orange bands or spots.
The first dark dorsal band is long (9-18 scale lengths, N = 29, mean 13.2 ± 0.5).The narrow white bands vary in lengths from 1 / 3 to 2 1 / 2 scale lengths along the length of the body with a modal value of 1 / 2 scale lengths for most specimens.Some snakes have greater modes (1 1 / 2 , ICN 6135 and MLS 2004).
Oxyrhopus vanidicus is smaller than O. occipitalis and O. petola but larger than O. leucomelas.The largest male O. vanidicus examined is MLS 1353 (861 mm total length) and the largest female (ICN 1886) is 927 mm.Tail length is sexually dimorphic and males have longer tails (tail/total length 20.5-28.2,mean = 23.6 ± 0.3%) than do females (19.4-24.8,mean 22.0 ± 0.6%).This is the only species of Oxyrhopus found in Colombia exhibiting a color pattern involving triads.Occasional specimens can be described as melanistic, i.e., the narrow white bands defining limits of the dark bands are not visible, although the orange spots/bands are evident on an otherwise black snake (ICN 10789 and MLS 1353).In Oxyrhopus vanidicus, the central dark band of a triad normally (29 of 32 adults and in all 10 neonates) coincides with the vent.However, in one specimen (ICN 272), the vent corresponds to a triad border and in another (IAvH 3076), the vent occurs within a quintet of dark bands.In MLS 2745, the vent corresponds to the third dark band of a triad.The number of triads varies individually.For 32 adults, there are 1.5-7.5 (mean = 4.8 ± 0. 9) body triads and 1.5-5.5 (mean = 2.8 ± 0.2) tail triads.In 19 adult males, there are 1.5-7.5 body bands (mean 4.8 ± 0.3) and 1.5-5.5 tail triads (3.1 ± 0.3) whereas 13 females have the same number of body triads (1.5-7.5, mean 4.8 ± 0.4) but fewer tail triads (1.5-4.0,mean 2.3 ± 0.2).In 10 neonates, there are as few as one triad overlying the vent to as many as 8.5 (body) and 4.5 (tail) triads.In one neonate (MLS 2742), there is a quintet rather than a triad between the first two body triads.Quintets were found in three adults (IAvH 3076, overlying vent; ICN 247, before the first body triad; and MLS 1351, following the first three body triads).ICN 6135 has a quartet following the first body triad and MLS 1226 has a sextet anterior to the first body triad.

FIgure 2 :
FIgure 2: Dorsal views of heads of snakes of the genus Oxyrhopus illustrating combinations of contact (or lack thereof ) between preocular and frontal scales.(A) Scores of 1 (left side) and 2 (right side); (B) Scores of 4 (left side) and 6 (right side); (C) Score of 8. Snakes with scores of 2 and 4 or 2 and 8 were classed as score 3. Snakes with scores of 4 and 8 were classed as score 5.Those with scores of 6 and 8 were classed as score 7.

FIgure 3 :
FIgure 3: Lateral views of schematics of the color pattern in Oxyrhopus "melanogenys" focused upon the triad boundaries.From top to bottom, these are the first through fifth triad borders in ICN 260.Orange pigment is stippled.

FIgure 4 :
FIgure 4: Relationship between tail length (as % of total length) and mean number of pairs of subcaudal scales in Oxyrhopus petola.Solid symbols (males) and open symbols (females).Populations are identified by letters: d = O. petola digitalis, p = O. petola petola.Letters in capitals refer to subdivisions of trans-Andean populations: A = Upper Río Cauca valley, C = Caribbean coast, Ch = Chocó, I = Magdalena valley, M = Maracaibo Basin.
from four localities/municipalities in Colombia.For three of these, I believe I have seen the specimens.Ayerbe González et al. (2007) reported O. formosus from two localities in western Colombia (Córdoba and Valle del Cauca).I located the specimen from Alto de Quimarí, Córdoba, 500 m (MHNUC 87) and it is a banded Atractus of what Passos et al. (MS) termed the multicinctus group.

tAbLe 1 :
Variation in ventral scute and subcaudal scute counts and dark body blotches 1 in Oxyrhopus from Colombia.First line reports range of the variable and sample size; second line reports the mean ± 1 Standard Error of Mean.
FIgure 9: Distribution of Oxyrhopus vanidicus in Colombia.Lynch, J.D.: Colombian OxyrhOpus placed greater confidence on a hemipenial character (absent in O. trigeminus) to group O. formosus, O. guibei, O. melanogenys, O. petola, and what is here named O.vanidicus; they viewed the presence of triads as homoplastic.However, there is no reason to prefer one of these putative incompatible synapomorphies over the other except that what is taken as a triad in O. vanidicus may not be homologous with the triads seen in O. guibei, O. melanogenys, and O. trigeminus (see text).