Systematic Status of the Colubrid Snake, Leptodeira discolor Gunther

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Title: Systematic Status of the Colubrid Snake, Leptodeira discolor Gunther
Author: Duellman, William E., 1930-
Language: English
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UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY

Volume 11, No. 1, pp. 1-9, 4 figs.
July 14, 1958

Systematic Status of the Colubrid Snake,
Leptodeira discolor Günther

WILLIAM E. DUELLMAN

UNIVERSITY OF KANSAS
LAWRENCE
1958

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Robert W. Wilson

Volume 11, No. 1, pp 1-9, 4 figs.
Published July 14, 1958

UNIVERSITY OF KANSAS
Lawrence, Kansas

PRINTED IN
THE STATE PRINTING PLANT
TOPEKA, KANSAS
1958

27-6708

Systematic Status of the Colubrid Snake,
Leptodeira discolor Günther

WILLIAM E. DUELLMAN

At the time of completing my study of the genus _Leptodeira_ (1958) I
had seen no specimens of _Leptodeira discolor_, a species described by
Günther in 1860 and subsequently referred to the genus _Hypsiglena_ by
Cope (1887), Boulenger (1894), and Mocquard (1908), and to the genus
_Pseudoleptodeira_ by Taylor (1938). Günther's description was based on
two syntypes (British Museum of Natural History numbers 1946.1.23.67
and 68) collected in Oaxaca, México, by Auguste Sallé. Information
concerning the scutellation and coloration of the syntypes was provided
by J. C. Battersby; in my revisionary study (_op. cit._) this
information was included in a short discussion of the species, which
was referred to _incerta sedis_ until specimens could be examined and
the relationships of the species determined.

Through the courtesy of John M. Legler of the Museum of Natural History,
University of Kansas, I have been able to study a specimen of
_Leptodeira discolor_ obtained six miles southeast of Tamazulápam,
Oaxaca, México, by J. R. Alcorn on June 22, 1955. Superficial
examination of the external characters of this snake shows a striking
resemblance to _Leptodeira_. The specimen has a vertical pupil, divided
anal, 21 scale rows, and two apical pits. The enlarged posterior
maxillary teeth are without a trace of a groove. Examination of the
hemipenis revealed that the organ was bifurcate and had a forked sulcus;
these penial characteristics are diagnostic of the subfamily
Xenodontinae and not the subfamily Colubrinae that includes the genera
_Hypsiglena_ and _Leptodeira_.

Examination of all available xenodontine genera indicates that this
snake belongs to a heretofore unnamed genus. In recognition of the
mental torment customarily suffered by workers attempting to ascertain
the relationships of the many genera of colubrid snakes, I propose the
generic name

_Tantalophis_, new genus

_Leptodeira_ (in part), Günther, Proc. Zool. Soc. London, pp.
317-318, 1860; Garman, Bull. Essex Inst., vol. 16, p. 23, January
9, 1884; Dunn, Proc. Nat. Acad. Sci., vol. 22, pp. 697-698,
December, 1936; Duellman, Bull. Amer. Mus. Nat. Hist., vol. 114
(1), pp. 95-96, February 24, 1958.

_Hypsiglena_ (in part), Cope, Bull. U. S. Nat. Mus., no. 32, p. 78,
1887; Günther, Biologia Centrali-Americana, Reptilia, pp. 137-138,
pl. 49, fig. A, October, 1894; Boulenger, Catalogue Snakes British
Museum, vol. 2, p. 211, September 23, 1894; Mocquard, _in_ Duméril
and Bocourt, Mission Scientifique Mexique l'Amerique Centrale, vol.
3, p. 871, 1908; Amaral, Mem. Inst. Butantan, vol. 4, p. 183, May,
1930.

_Pseudoleptodeira_ (in part) Taylor, Univ. Kansas Sci. Bull., vol.
25, no. 15, p. 343, June 1, 1938.

_Type Species._--_Leptodeira discolor_ Günther, Proc. Zool. Soc.
London, pp. 317-318, 1860.

_Diagnosis._--A xenodontine colubrid snake having a bifurcate
hemipenis with a forked sulcus spermaticus, many longitudinal folds
on basal portion, and small spines and calyces on distal part; 12
or 13 maxillary teeth followed by short diastema and two somewhat
enlarged maxillary teeth lacking grooves; small parotid gland;
normal colubrid skull; no hypapophyses on posterior vertebrae;
elliptical pupils; two apical pits; smooth scales; normal colubrid
head shields; divided anal; paired caudals.

The generic name comes from the Greek Tantalos, a mythological
character symbolic of eternal torment, and from the Greek ophis
for snake.

_Tantalophis discolor_ (Günther) New comb.

The synonymy for the species is indicated in the account of the
genus. The description below of the species is based on an adult
male from 6 miles southeast of Tamazulápam, Oaxaca, México
(University of Kansas Museum of Natural History No. 40143).

_Scutellation._--Head shields normal; upper labials 7-7 (third and
fourth entering orbit); lower labials 9-9 (1-4 in contact with
anterior chin-shield, 4 and 5 in contact with posterior
chin-shield); preoculars 1-1 and not in contact with frontal;
postoculars 2-2; temporals 1-2-3, 1-2-3; nasals divided by a
distinct groove below nostril and faint groove above; portion of
rostral visible from above, one-third length of internasals;
internasals pentagonal and one-half as long as prefrontals;
parietal suture approximately as long as frontal; ventrals 178;
anal divided; caudals 80. Scales in 21 rows at midbody and showing
the following reduction:

2 + 3 (130) 8 + 9 (162)
21 --------------- 19 -------------- 17 (178)
2 + 3 (130) 8 + 9 (152)

_Coloration._--Dorsal ground-color light brown and extending onto
edges of ventrals; transverse body blotches numbering 50, each
1-1/2 to 3 scales long and separated by light interspaces 1-1/2 to
2 scales long; blotches brownish black and extending onto second
scale row; lateral intercalary spots forming dark smudges on rows 1
and 2. Top of head black, flecked with tan; nape cream, followed by
dark band six scales long; dark nape stripe from posterior edges of
parietals to first dark body band. Venter cream-tan; throat and
labials cream; posterior margins of all upper labials and of lower
labials 1-3 black-edged (Figure 1).

_Size and Proportions._--Head and body 312 mm. long; tail 118 mm.,
amounting to 37.8 per cent of length of head and body.

_Variation._--Data on the syntypes of _Leptodeira discolor_
furnished by J. C. Battersby give some indication of the variation
in the species. Both are males, and they have 175 and 180 ventrals,
88 and 89 caudals, 1 preocular, 2 postoculars, 1-2-3 temporals, 7
and 8 upper labials, 9 lower labials. They have body lengths of
365 and 402 mm., total lengths of 509 and 555 mm., tail/body ratios
of 38.0 and 39.4. They have 51 and 54 dark blotches on the body.

[Illustration: Fig. 1. Dorsal and lateral views of the head of
_Tantalophis discolor_ (Günther). (KU No. 40143). × 7.]

_Skull._--The skull is typically colubrid and shows no
modifications. The quadrate has both a median and a lateral
depression, forming a strong lateral flange on the anterior edge;
the columellar process is elliptical, and the supra-columellar
crest is robust. The posteroinferior vomerine process extends
directly posteriorly and then angles sharply posterodorsally,
enclosing an elliptical vomerine fenestra. The lateral processes of
the premaxillary are slightly pointed; the median spine is
relatively thin and high. The pterygoids bear 23 and 21 teeth that
decrease in size posteriorly; the transpalatine articulating
process of the pterygoid is rounded, not robust; the lateral crest
is high and moderately robust; the depression in the ventral
surface of the pterygoid is moderate. There are 12 and 13 maxillary
teeth that increase in size posteriorly; these are followed by a
short diastema and two larger, solid teeth. The prediastemal teeth
are slightly curved and slender. The maxillary is laterally
compressed; the posterior knob is not robust; there is one foramen
in the lateral face of the bone (Figure 2). The 10 palatine teeth
are almost uniform in size; the dentary bears 19 teeth that
decrease in size posteriorly.

[Illustration: Fig. 2. Lateral view of the left maxillary of
_Tantalophis discolor_ (Günther). (KU No. 40143). × 17.]

A thin and otherwise small parotid gland or "venom sac" extends
posteriorly from beneath the eye to about the angle of the jaw; a
minute duct connects with the anteromedian surface and extends to
the fleshy part of the mouth at the posterior end of the maxillary
(Figure 3).

[Illustration: Fig. 3. Lateral view of the head of _Tantalophis
discolor_ (Günther), showing the position and relative size of the
parotid gland. (KU No. 40143). × 3.]

_Hemipenis._--In _situ_ the hemipenis extends to the posterior edge
of the thirteenth caudal. The unforked part of the organ is
bedecked with numerous heavy longitudinal folds alternating with
thinner folds. The basal parts of the two heads are covered with
moderate sized spines, those closest to the base and the sulcus
being the smallest. The distal parts of the heads are covered with
calyces. The sulcus bifurcates on the unforked part of the organ at
a point about two-thirds of the distance from the base to the
division of the organ. The sulcus is a deep groove between heavy
folds proximally and is a shallower furrow distally (Figure 4).

[Illustration: Fig. 4. Hemipenis of _Tantalophis discolor_
(Günther). The organ was cut on the ventral surface and opened.
(KU No. 40143). × 4.]

_Relationships._--Using Dunn's (1928) arrangement of the American
colubrid snakes as a guide permits the taxonomist to group _Tantalophis_
with several genera, some of which occur in South America and others in
the West Indies. Although the significance of such generic characters as
scale pits and nature of the hemipenis is not clear, these characters
must, of necessity, be utilized in attempting to ascertain the
relationships of _Tantalophis_ to other colubrid snakes. Assuming that
the primary divisions of the American colubrids into subfamilies based
on the nature of the sulcus spermaticus and the presence or absence of
hypapophyses on the posterior vertebrae have some reality, _Tantalophis_
must be placed in the subfamily Xenodontinae comprising genera chiefly
South American in their distribution, but with several genera in Middle
America and a few in North America and the West Indies. In order to
limit the number of genera to be compared with _Tantalophis_, only those
xenodontines having apical pits and bifurcate hemipenis are considered.
These include _Cyclagras_, _Drepanoides_, _Hypsirhynchus_, _Ialtris_,
_Leimadophis_, _Pseudablabes_, _Siphlophis_, _Tachymenis_, _Tomodon_,
and _Trypanurgos_. Aside from differences in scutellation,
_Leimadophis_, _Siphlophis_, and _Trypanurgos_ have the heads of the
hemipenes terminating in a disc, and _Ialtris_ has a plicate hemipenis.
_Tomodon_ has basal spines on the hemipenis. The hemipenes of the other
genera have proximal folds, distal spines, and distal calyces, not
greatly unlike the condition found in _Tantalophis_. Of these,
_Cyclagras_, _Hypsirhynchus_, and _Pseudablabes_ have round pupils and
certain differences in scutellation. _Drepanoides_ and _Tachymenis_ have
elliptical pupils like those of _Tantalophis_, but _Tachymenis_ has only
one apical pit, and _Drepanoides_ has one apical pit or none. In the
above characters no especially close relationship between _Tantalophis_
and any one of these genera is apparent.

If the characteristics usually employed in distinguishing and relating
genera are ignored and other more subjective criteria are used, the
relationships of _Tantalophis_ still remain obscure. Of the xenodontine
genera _Tantalophis_ approaches _Leimadophis_ in general physiognomy;
perhaps it represents an early divergent stock of _Leimadophis_ that has
undergone radical changes in the hemipenis and other characters. On the
other hand, if the nature of the hemipenis is of no importance in
defining supergeneric groups of colubrid snakes, _Tantalophis_ may have
its relationships with _Leptodeira_ and _Hypsiglena_. Although
herpetologists have been working intensively on American colubrids for
many decades, the relationships of the majority of the groups are not
well understood. Until the hemipenes and skulls of all of the forms have
been studied and compared, and the evolutionary significance has been
determined for the characters of the hemipenes, dentition, and apical
pits, our knowledge of the relationships of these snakes will be
incomplete.

_Remarks._--The individual on which this paper is based is the only
specimen of the species with definite locality data. It is from a
locality six miles southeast of Tamazulápam in northwestern Oaxaca. This
town lies at an elevation of about 6500 feet in the upper reaches of the
Balsas Basin, an arid interior valley that expands in its upper end to
form a broad basin of rolling and dissected terrain ranging from about
4000 to 6800 feet in elevation. The countryside around Tamazulápam is
arid and supports plants of the genera _Prosopis_, _Acacia_, _Ipomoea_,
and _Cassia_, and also columnar cacti. Oaks and pines grow on the
limestone hills rising above the rolling valley. _Tantalophis_ may be
endemic to the Balsas Basin, as are many other species of reptiles.
However, if the snake has its relatives to the south in lower Central
America and South America, such a distribution seems unlikely, even for
an apparent relict.

_Acknowledgments._--For permission to study and report on this specimen
I am indebted to Dr. E. Raymond Hall and Mr. John M. Legler. I am
grateful to Dr. Laurence C. Stuart for many helpful suggestions and to
Dr. Norman E. Hartweg for placing at my disposal the facilities of the
Museum of Zoology at the University of Michigan.

LITERATURE CITED

AMARAL, A. DO

1930 Estudos sobre ophidios neotropicos XVIII--Lista remissiva dos
ophidios da região neotropica. Mem. Inst. Butantan, 4:129-275.

BOULENGER, G. A.

1894 Catalogue of the snakes in the British Museum (Natural
History). London, 2:xi + 382, pls. 1-20, figs. 1-25.

COPE, E. D.

1887 Catalogue of the batrachians and reptiles of Central America
and Mexico. Bull. U. S. Nat. Mus., 32:1-98.

DUELLMAN, W. E.

1958 A monographic study of the colubrid snake genus _Leptodeira_.
Bull. Amer. Mus. Nat. Hist., 114:1-152, pls. 1-31, figs. 1-25,
maps 1-25.

DUMÉRIL, A. M., and BOCOURT, F.

1870-1909 Études sur les reptiles. Mission scientifique au Mexique
et dans l'Amerique Centrale, Recherches zoologiques. Paris,
Pt. 3, 1:xiv + 1012, pls. 1-77.

DUNN, E. R.

1928 A tentative key and arrangement of the American genera of
Colubridae. Bull. Antivenin Inst. Amer., 2 (1):18-24.

1936 Notes on North American _Leptodeira_. Proc. Nat. Acad. Sci.,
22 (12):689-698.

GARMAN, S.

1884 The North American reptiles and batrachians. Bull. Essex
Inst., 16:1-46, 3 figs.

GÜNTHER, A. C. L. G.

1860 On new reptiles and fishes from Mexico. Proc. Zool. Soc.
London, pp. 316-319.

1885-1902 Biologia Centrali-Americana. Reptilia and Batrachia.
London, pp. xx + 1-326, pls. 1-76.

TAYLOR, E. H.

1938 Notes on Mexican snakes of the genus _Leptodeira_, with a
proposal of a new snake genus, _Pseudoleptodeira_. Univ.
Kansas Sci. Bull., 25:315-355, pls. 30-34, figs. 1-7.

_Transmitted March 11, 1958. Contribution No. 11 from the Department of
Biology, Wayne State University, Detroit 2, Michigan._

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