Morphological Extremes—Two New Snakes of the Genus Atractus from Northwestern South America (Colubridae: Dipsadinae)

2006·2.8 MB·English

by  Charles W Myers

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3532, 13 pp., 7 figures, 1 map, 1 table September 08, 2006
Morphological Extremes—Two New Snakes of the
Genus Atractus from Northwestern South America
(Colubridae: Dipsadinae)
CHARLES W. MYERS1 AND WALTER E. SCHARGEL2
ABSTRACT
TwonewAndeansnakesexhibitextrememorphologyinagenusofSouthAmericandipsadine
colubrids. One, Atractus attenuatus, new species, is a slender, exceptionally attenuated snake
420mmintotallength(adultmaleholotype),with17scalerows,ahighventral+subcaudalcount
(226), and an extremely vague pattern of numerous, closely spaced, indistinct dark crossbars on
abrowngroundcolor.Atractusattenuatuscomesfrom1000melevationinthenorthernendofthe
Cordillera Central (Sabanalarga, Antioquia, Colombia). A geographic neighbor, Atractus
sanguineusPrado,isofsimilarmorphologybutdiffersinhavingdistinct,widelyspacedcrossbars
ona redgroundcolor.
Atanotherextreme,Atractusgigas,newspecies,isaveryrobustsnakethatexceedsameterin
length(adultfemaleholotype1040mmintotallength),withahintofpaletransversedorsalbars
onabrowngroundcolor.ItisthelargestknownAtractus,differingincolorpatternanddetailsof
scutellation from the several other congeners that attain lengths . 700mm. The only known
specimen has an azygous frontonasal scale that is atypical of colubrids (but is not an obvious
aberrancy). Atractus gigas comes from 1900m elevation on the Pacific versant of the Andes
(BosqueProtector R´ıoGuajalito,Pichincha, Ecuador).
RESUMEN
Dos serpientes nuevas Andinas exhiben morfolog´ıa extrema en un ge´nero Suramericano de
colu´bridos dipsadineos. Una de ellas, Atractus attenuatus, especie nueva, es una serpiente
1CuratorEmeritus,DivisionofVertebrateZoology(Herpetology),AmericanMuseumofNaturalHistory.
2DepartmentofBiology,TheUniversityofTexasatArlington,Arlington,TX76019.
CopyrightEAmericanMuseumofNaturalHistory2006 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3532
excepcionalmente delgada, de 420mm en largo total (holotipo macho adulto), con 17 hileras de
escamas dorsales, un alto nu´mero de ventrales + subcaudales (226), y un patro´n muy vago de
barras transversales numerosas y cercanas sobre un color de fondo marro´n. Atractus attenuatus
proviene de 1000m de altitud en el extremo norte de la Cordillera Central (Sabanalarga,
Antioquia,Colombia).Atractussanguineusesunaespeciecercanageogra´ficamentequeposeeuna
morfolog´ıa similar pero difiere en tener barras tranversales bien definidas y espaciadas sobre un
colordefondo rojo.
En el otro extremo, Atractus gigas, especie nueva, es una serpiente muy robusta con un largo
totalde1040mm(holotipohembraadulta),quepresentaindiciosdebarrastransversalespa´lidas
sobreuncolordefondomarro´n.SetratadelAtractusma´sgrandeconocidoydifieredelasotras
especiesenelge´neroqueexcedenunlargototalde700mmenaspectosdelpatro´ndecoloracio´ny
en escamacio´n. El u´nico ejemplar conocido de la nueva especie presenta una escama frontonasal
media,at´ıpicaencolu´bridos(noesunaaberracio´nobvia).Atractusgigasprovienedeunaaltitud
de 1900m en la vertiente del Pac´ıfico de los Andes (Bosque Protector R´ıo Guajalito, Pichincha
Ecuador).
INTRODUCTION DIAGNOSIS: Atractus attenuatus is distin-
guished by its exceptionally slender, drawn-
With more than 100 recognized species,
out habitus, combined with 17 scale rows,
Atractusisbyfarthelargestgenusofcolubrid
ahighventral+subcaudalcount(226),andan
snakes in the New World. The genus is
extremely vague pattern of numerous, closely
confined almost entirely to the South
spaced,indistinctcrossbars.Themostrelevant
American mainland, extending northward
comparisoniswithAtractussanguineus,which
only to Central Panama. There are some
has fewer, more widely spaced crossbars that
widely distributed species, especially in low-
are distinctly darker than the ground color
landseastoftheAndes,butgeographicranges
and that are connected by a vertebral dark
elsewhere tend to be small, with many taxa
line. In life, the dorsal ground color of A.
being known only from their type localities.
attenuatus is probably brown, whereas A.
As an aside to other ongoing work on
sanguineus is red. See Comparisons.
Atractus, we describe herein two additional
species of presumably limited distribution.
The new snakes represent morphological
DESCRIPTIONOF HOLOTYPE
extremes within the genus, the first being
notable for its elongated slenderness, the The specimen is a male judged to be adult
second for its stocky hugeness. becausethehemipenialspinesaremineralized.
It is fairly well preserved, undissected except
forthetail,andthestratumcorneumislargely
Atractus attenuatus, new species
intact. See table 1 for detailed measurements.
Figures 1–3, Map 1
PROPORTIONS AND SCUTELLATION: Total
HOLOTYPE: AMNH R-19998, an adult length 420 mm, tail length 66 mm (15.7% of
male obtained by Hermano Nice´foro Mar´ıa total). Elongated and slenderly proportioned
on May 16, 1921, at Sabanalarga, on Cauca (fig. 1). Body slightly wider than high, round-
River, [6u519N, 75u499W, Department of ed ventrolaterally; greatest head width 70.1%
Antioquia], Colombia. The type locality, of head length from snout to end of parietals
Sabanalarga (Nice´foro Mar´ıa, 1942: 87, and 57.3% of length from snout to end of
map), lies on the east bank of the R´ıo Cauca mandible;headwidthandgreatestbodywidth
at an elevation of about 1000 m (Paynter, each 1.7% of SVL. Dorsal scales smooth,
1997: 372), in the northern end of the lacking apical pits, in 17-17-17 rows. Ventrals
Cordillera Central. 178, anal plate undivided, subcaudals in 48
ETYMOLOGY: The species name attenuatus pairs.
is the passive past participle of the Latin verb Head (fig. 2) barely wider than neck; snout
attenuo (to stretch or make thin), and also (as bluntly rounded in dorsal view, rounded in
used here) a derived adjective meaning profile; rostral wider than high, visible from
stretched out and slender. above; internasals small, as wide as long, less
2006 MYERSAND SCHARGEL: NEWSNAKES 3
TABLE1 length slightly smaller (93%) than distance to
Measurementsa(in mm)ofHolotypes of Atractus lip;eyenotprotuberanttoedgeoflipandnot
attenuatusandAtractus gigas visible from below. Nasal divided above and
below naris, its greatest length 90% of loreal
A.attenuatus A.gigas length; loreal long, 2 times longer than great-
adult= adultR est height, well separated from internasal,
entering eye; no preoculars; supralabials 7,
Totallength 420 1040
Taillength 66 124 3rdand4theachaswideashighandtouching
Tail/totallength3100 15.7 11.9 eye; 6th supralabial on right side separated
Headlength,snouttoendsof 9.9 27.5 from lip by an aberrant anteroventral pro-
parietals jection of 7th labial; postoculars 2, subequal;
Headlength,snouttoendof 12.2 37.5 temporals 1 + 2, the upper one in row 2
mandible elongated, reaching past end of parietal.
Head,greatestwidth 7.0 27.4
Infralabials 7, first pair in contact behind
Body,greatestwidth 7 ca.29
mental, first three in contact with genials;
Body,greatestheight 6 ca.28
single pair of large genials, 2.5 times longer
Eyetosnouttip(sagittal) 3.7 10.0
Eyelength 1.3 3.6 than wide; three large median gulars or
Loweredgeofeyetolip 1.4 4.3 preventrals between genials and 1st ventral.
Nasallength 1.8 4.2 Headplatetuberclestiny,inconspicuous,most
Loreallength 2.0 6.3 concentratedonrostralplate,otherwisesparse.
Loreal,maximumheight 1.0 1.9 COLOR PATTERN: The specimen in preser-
Internasal,greatestlength 1.1 2.8 vative (fig. 1) is medium brown dorsally,
Internasal,greatestwidth 1.1 3.5
somewhatlighteronthelowertwoscalerows,
Internasalsuturelength 0.9 1.0
with an extremely vague pattern of narrow
Prefrontal,greatestlength 3.0 7.0
dorsal crossbars.3 The indefinite crossbars are
Prefrontal,greatestwidth 2.4 6.5
Prefrontalsuturelength 2.5 5.0 narrow (about 2–3 scales wide) and closely
Frontallength 3.0 7.5 spaced (about 1 scale apart), and extend to
Frontalwidth(anterior) 3.0 7.6 about the 4th or 5th scale row on each side.
Supraocularlength 1.5 4.8 Although impossible to count accurately,
Supraocular,greatestwidth 1.4 3.9 there are an estimated 95 dorsal crossbands
Parietal,greatestlength 5.0 14.5 on the body; there are an indefinite two or
Interparietalsuturelength 2.6 7.2
three such markings on the base of the tail,
Geniallength 3.8 9.7
which otherwise is patternless.
Genialwidth 1.5 4.7
Top of head brown like body, vaguely
aMeasurements , 12mm were made with ocular mottled, becoming paler yellowish brown on
micrometer in a dissecting microscope (Wild M7S), with lower three-fourths of supralabials and be-
the main objective displaced coaxially to the left beam
neath head and neck. The venter becomes
path, to eliminate problems of parallax. Other measure-
increasingly and irregularly blotched with
mentsweretakenwithadialcaliperorbystretchingthe
light brown posteriorly; subcaudal surfaces
specimensalongametricruler.
nearly uniform light brown.
MAXILLO-PALATO-PTERYGOID ARCH: Some
than half (44%) the length of prefrontal
teeth on each side are broken; the left maxilla
suture; prefrontals large, longer than wide
itself is broken, as is the right ectopterygoid.
(greatest prefrontal width 80% of greatest
Description is of right side in situ. Maxilla
length); prefrontal suture asymmetrical, no-
rather robust, weakly arched, extending ante-
ticeably dextral to the internasal suture; pre-
riorly to first supralabial, with 10 recurved
frontal suture 83% length of frontal plate;
supraoculars large, nearly as broad as long; 3Thecrossbarredpatternisbestvisualizedbythenaked
frontal as long as broad, roughly pentagonal eye,withthespecimenimmersedinalcohol.Theindefinite
in shape; interparietal suture slightly longer markingsvirtuallydisappearwhenthespecimenisviewed
than prefrontal suture, 87% of frontal length. under a dissecting microscope. The vagueness of this
pattern does not seem to be the result of fading in
Eye moderate, contained 1.4 times in loreal
preservative, and the pattern was probably indistinct in
length,2.8times in snoutlength(sagittal);eye life.
4 AMERICAN MUSEUMNOVITATES NO. 3532
Fig.1. Atractusattenuatus,newspecies.Dorsalandventralviewsoftheadultmaleholotype(AMNHR-
19998),shown 1.5times lifesize.
2006 MYERSAND SCHARGEL: NEWSNAKES 5
alternate teeth represented only by sockets;
teeth rounded in cross section (lacking an
angular edge on labial side). A gap between
the small teeth (9–10), these posterior two
teeth broken but apparently much smaller
than those anteriorly. Maxilla extending pos-
teriorly past small teeth as a short toothless
process. An expanded curved flange on
maxilla extending mediad and ventrad; ante-
rior edge of flange adjacent to ultimate small
Fig. 2. Atractus attenuatus, new species. Head
tooth, with most of flange lying posterior to
ofholotype (AMNH R-19998),35.
the small teeth. Ectopterygoid (broken; de-
teeth, large anteriorly, decreasing in size scribed from left side) weakly and shallowly
posteriorly. Anterior 8 teeth closely to mod- bifurcated, the ventromedial branch being
erately spaced, not firmly ankylosed, with more robust; ectopterygoid fork braced
Fig.3. EvertedhemipenisofAtractusattenuatus,newspecies,insulcateandasulcateviews.Leftorgan
of holotype (AMNH R-19998), 38.9. (Laboratory preparation from hemipenis preserved in retracted
condition;fully evertedbutnotnecessarily completelyexpanded.)
6 AMERICAN MUSEUMNOVITATES NO. 3532
against posterior half of flange on maxilla. Cauca drainage, about 1000 m elevation, on
Palatine lacking a maxillary process. the western side of the northern end of the
HEMIPENIS: Before removal, the left re- Cordillera Central (map 1).
tracted hemipenis of the holotype bifurcated
at the level of the middle of subcaudal 8 and COMPARISONS
terminatedattheendofsubcaudal9,withthe
two slips of retractor muscle merging at the Very few Atractus have such a strikingly
middle of subcaudal 11 and the muscle slender habitus, the main exception we are
originating at the end of subcaudal 30. aware of being Atractus sanguineus Prado
Although the lobes of this bifurcated hemi- (1944, 1946). This species also is known only
penis were equal in length and width, the from its holotype (a male 424 mm in total
dorsal lobe was noticeably higher than the length), whose size and scutellation are com-
ventral lobe, with a more massive appearance parable to A. attenuatus.4 Each has a high
(the size differential was not noticeable after ventral + subcaudal count (222 in sanguineus,
eversion); the lobes appear equal in the right 226 in attenuatus), and sanguineus appears to
hemipenis as examined in situ. besimilarlyattenuatedbasedonaphotograph
The left hemipenis was removed and the published first with the original description
retractor muscle was severed across the in- (Prado, 1944) and later reprinted (Prado,
sertion slips close to the lobes. The organ was 1946). The second printing was of better
immersed for 3.5 hours in a 2% solution of quality and is reproduced here as figure 4.
potassium hydroxide (KOH), after which it It is evident from comparisons of photo-
wasmovedto3%KOHforanother3 hoursto graphs(figs. 1,4)thatthedorsalcrossbarsare
hasten the softening process. It was then fewer, more widely spaced, and more pro-
evertedwithforceps;thetipsofthelobeswere nouncedinA.sanguineus,whichalsohasthese
pushed out using the round head of an insect markings interconnected by a vertebral dark
pin. Finally, the organ was inflated with line that is lacking in A. attenuatus. Atractus
carmine-dyed petroleum jelly for study and attenuatus has a ground color of medium
illustration. brown in preservative and presumably was
similarly colored in life,5 whereas the lighter
The manually everted left hemipenis (fig. 3)
ground color of the preserved specimen of A.
is 12.9 mm long, with lobes comprising about
sanguineus was described by Prado (1944,
30% of its length. The sulcus spermaticus
1946) as vermelho-sanguinea (blood-red).
divides about 8 mm (62%) above the base,
Daniel (1949: 317) later also commented on
with the branches extending in centrifugal
the red color of the sanguineus holotype.
orientation to the tips of the lobes. The organ
Atractus attenuatus and A. sanguineus are
is noncapitate.
geographic neighbors in northern Colombia.
Thehemipeniallobesarecompletelycovered
Theirtypelocalitiesareonly46 kmapart,but
by papillate calyces, which extend proximally
atdifferentelevationsandonoppositesidesof
between the sulcus branches to the fork. Two
the northern end of the Cordillera Central.
rowsofsmallspinesbelowthesulcusbranches
Atractus sanguineus came from Yarumal
extend chevronlike to the sides of the organ;
(2300 m fide Paynter, 1997: 471) on the
these rows do not retain their integrity on the
eastern side of the Central Andes, whereas
asulcateside,whichbearssmallspinesimmedi-
A. attenuatus is from Sabanalarga, at a lower
ately below the lobes. The midsection of the
elevation (1000 m) on the western side.
hemipenis is encircled by numerous medium-
sized spines, which decreaseinsizeproximally; 4Pradonoted3infralabiasemcontactocomamental,but,
no large spines. Except for being nude at the fromhis various descriptionsof Atractusspp., it isclear
base, the proximal 30% of the organ is that he used the term ‘‘mental’’ for the paired genials.
Atractusnormallyhasoneachside3or4infralabialsin
spinulate.Anudepocketispresentonthebasal
contactwiththesinglepairofgenials,withthe1stpairof
side (dextral to sulcus spermaticus), extending
infralabialsusuallyincontactbehindtheazygousmental
distadnearlytotheedgeofthespines. plate(e.g.,fig.7B).
DISTRIBUTION: Atractus attenuatus is 5Mediumbrownpigmentationusuallychangesrelatively
known only from its type locality in the R´ıo littleinpreservativeunlessfadedinlight.
2006 MYERSAND SCHARGEL: NEWSNAKES 7
Map1. TypelocalitiesofthenewspeciesinthenorthernAndes.Atractusattenuatusinthenorthernend
oftheCordilleraCentral, R´ıoCaucadrainage,Colombia.Atractus gigasonthePacificversant ofwestern
Ecuador.ThesymbolovertheAtractusattenuatuslocalitynearlyoverlapsthetypelocalityofA.sanguineus
Prado,46kmnortheastward, at ahigher elevation onthe opposite side ofthe Cordillera Central.
8 AMERICAN MUSEUMNOVITATES NO. 3532
Moreno interpreted as Sabanalarga at an
elevation below 100 m in the Department of
Atla´ntico, on the north coast of Colombia.
However, the specimen and locality were
provided by Brother Nice´foro Mar´ıa, who
mapped his locality as being the Sabanalarga
that is situated much higher in the Cauca
Valley (Nice´foro Mar´ıa, 1942: 87); Paynter
(1997: 372) provided an elevation of 1000 m.
Nice´foro Mar´ıa had sent to the American
Museum unidentified specimensthat were not
included in his 1942 report, which recorded
only Mastigodryas pleei (as Dryadophis) and
Bothrops atrox from Sabanalarga.
Atractus gigas, new species
Figures 5–7, Map 1
HOLOTYPE: Fundacio´n Herpetolo´gica ‘‘Gu-
stavo Orce´s’’(FHGO)no. 194,an adultfemale,
from Bosque Protector R´ıo Guajalito, antigua
Hacienda Las Palmeras, old highway between
Quito and Santo Domingo, 1900 m, Pichincha,
Ecuador (00u149S, 78u499W). Collected by
VlastimilZakinJanuary1990.
ETYMOLOGY: The species name gigas (a
giant) is a Latin noun of Greek origin. (The
gigantesorgiants,bornofMotherEarth,were
Fig. 4. Atractus sanguineus Prado. The holo- enormous beings who had thick serpents for
type,reproducedfromPrado(1946),bypermission legs.Theyfoughtalosingbattlewiththegods
of InstitutoButantan. and man.)
DIAGNOSIS: Atractus gigas is distinguished
REMARKS fromallspeciesofAtractusbyitsunparalleled
large size (. 1 m) and robust body (fig. 5). It
The holotype of Atractus attenuatus differs from adult specimens of other large
(AMNH R-19998) inexplicably was cata- species ($ 700 mm) in having pale dorsal
logued originally as ‘‘Atractus major’’, a rea- crossbars (indistinct in the only known spec-
sonably well-known Amazonian snake. It imen) rather than a false coral snake pattern
remained under that suspect identification (A. obesus) or definite dark markings on
for decades, until curatorial attention was a brown ground color (A. depressiocellus, A.
given to the AMNH Atractus collection. major, A. torquatus). See Comparisons for
Pe´rez-SantosandMoreno(1988:86)commen- further comments.
ted on the specimen as A. major without Although the juvenile color pattern of
indicatingthattheyhadnotexaminedit.6The Atractus gigas is unknown, young specimens
catalogued locality was ‘‘Sabanalarga, on conceivably might be confused with a few
Cauca River’’, which Pe´rez-Santos and much smaller species of Atractus from the
PacificversantofEcuador.Atractusdunnihas
6Pe´rez-Santos’visitstotheAmericanMuseumwerespent fewer ventrals (125–136 in males, 138–150 in
incopyinggeographicrecords;heunfortunatelynevergot females)thanA.gigas(170inonefemale)and
time to examine specimens and confirm names. It is
small dark spots dorsally (Cisneros-Heredia,
aregrettablefactoflifethatallmajormuseumcollections
2005). Atractus multicinctus differs from A.
havemanyspecimensbearingidentificationsthatareout
ofdateorobviouslywrongtobeginwith. gigas in having 5 or 6 maxillary teeth (8 in
2006 MYERSAND SCHARGEL: NEWSNAKES 9
Fig. 5. Atractus gigas, new species. Views of the adult female holotype (FHGO 194), shown much
smallerthanlife(30.48).
10 AMERICAN MUSEUMNOVITATES NO. 3532
Fig. 6. Atractus gigas, new species. Head of
holotype (FHGO 194) in dorsolateral view, nearly
twice life size (line 5 10mm). Arrow points to
diamond-shaped frontonasal scale between inter-
nasal andprefrontal sutures (see also fig.7).
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
Fig. 7. Atractus gigas, new species. Head of
expected to have relatively stout bodies.
holotype(FHGO194).A.Dorsalview,31.7.Arrow
pointstodiamond-shapedfrontonasalscalebetween
DESCRIPTIONOF HOLOTYPE internasal and prefrontal sutures. B. Ventral view,
31.2.Scaledivisions5mm.
The holotype is a sexually mature female,
with active ovaries and enlarged convoluted about same as head length from snout to end
oviductswithdevelopingova.Thespecimenis of parietals and 73% of length from snout to
in a fair state of preservation, although endofmandible;headwidth(andalsogreatest
contortedandimpossibletomeasureprecisely. bodywidth)roughly3%ofSVL.Dorsalscales
The digestive tract has been removed and the smooth, lacking apical pits, in 17-17-17 rows.
otherinternalorganssomewhatdisrupted.See Ventrals 170 (not counting a half-ventral
table 1 for detailed measurements. anterior to anal plate); anal plate undivided;
PROPORTIONS AND SCUTELLATION: Total subcaudals in 35 pairs.
length approximately 1040 mm, tail length Snout rounded in dorsal and lateral view;
124 mm(11.9%oftotal).Averyrobustsnake, rostral wider than high, visible from above;
with head barely wider than neck, and middle internasals small, wider than long, more than
body slightly wider than head; body about as half (56%) the length of prefrontal suture; an
wide as high, either rounded or slightly azygous frontonasal scale situated between
angular ventrolaterally;7 greatest head width internasal and prefrontal sutures (figs. 6, 7A),
diamond-shaped (1.9 mm long, 2.0 mm wide)
7Contortion makes it impossible to determine with
with rounded points; prefrontals large, little
confidence the nature of the ventrolateral edge, which
seemstobeslightlyangularonpartoftheanteriorbody. longer than wide (greatest prefrontal width