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Title: Morphological Variation in a Population of the Snake, Tantilla gracilis Baird and Girard
Author: Hardy, Laurence M., Cole, Charles J.
Language: English
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and small caps typeface with ALL CAPS.
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Page 625: changed "percent" to "per cent" (92 per cent of the time).
* * * * *
UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY
Volume 17, No. 15, pp. 613-629, 6 figs.
May 14, 1968
Morphological Variation in a Population
of the Snake,
Tantilla gracilis Baird and Girard
BY
LAURENCE M. HARDY AND CHARLES J. COLE
UNIVERSITY OF KANSAS
LAWRENCE
1968
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
Editors: E. Raymond Hall, Chairman, Frank B. Cross, Henry S. Fitch,
J. Knox Jones, Jr.
Volume 17, No. 15, pp. 613-629, 6 figs.
Published May 14, 1968
University of Kansas
Lawrence, Kansas
PRINTED BY
ROBERT R. (BOB) SANDERS, STATE PRINTER
TOPEKA, KANSAS
1968
31-9422
Morphological Variation in a Population of the Snake, Tantilla gracilis
Baird and Girard
By
LAURENCE M. HARDY AND CHARLES J. COLE
INTRODUCTION
Variation of selected taxonomic characteristics of flat-headed snakes
(_Tantilla gracilis_ Baird and Girard) from several midwestern states
was studied by Force (1935), but she did not attempt a comprehensive
evaluation. Taylor (1936) reported on variation in _T. gracilis_ from
various localities in Kansas; Kirn, Burger, and Smith (1949) studied
selected structures of specimens of _T. gracilis_ from throughout its
range. The present study was undertaken to determine the variation in
both currently used and potential taxonomic characteristics of _T.
gracilis_ from one locality.
We are thankful to Charles W. Myers, Gorgas Memorial Laboratory, for
suggestions concerning characteristics examined. We are indebted to Drs.
William G. Degenhardt, University of New Mexico, Herndon G. Dowling, New
York Zoological Society, Charles H. Lowe, University of Arizona, and
Richard G. Zweifel, American Museum of Natural History, for criticizing
the manuscript. Dr. William E. Duellman permitted us to study specimens
in the University of Kansas Museum of Natural History.
Materials and Methods
The specimens examined were donated to the Museum of Natural History,
University of Kansas, by the late Paul Anderson of Independence,
Missouri. All specimens (KU numbers 83435-83680; N = 246) were collected
in the vicinity of Winfield, Cowley County, Kansas, by Charles E. Burt
and students from Southwestern College in the period from 1938 to 1941,
inclusive.
Both authors gathered data on most characteristics and examined each
atypical individual. Hardy determined characters of the maxillae (which
were removed; N = 20), body and total lengths, and the scale formula of
KU 83620.
We examined 22 characteristics of external morphology and 10 of the
maxillae. All paired characteristics (excepting those of the maxillae)
were examined on both sides of each snake and are referred to from the
left side to the right side (for example, "preoculars 1-2" means there
is one preocular on the left side and there are two on the right).
Oviducts and oviducal eggs were observed on specimens designated as
females; hemipenes were examined on specimens designated as males. Total
length was measured by straightening each snake along a 300 mm. scale.
Tail length was measured only on snakes having complete tails, and body
length (snout-vent) was considered as total length minus tail length.
The body length was measured on snakes having incomplete tails.
Supralabials, infralabials, preoculars and postoculars were counted, and
we followed Peters (1960:9) in determining the nature of the temporals.
Occasionally the primary (anterior) temporal is separated from the
postocular by contact of the parietal and a supralabial (Taylor,
1936:338). We followed Peters (1964:219-220) in determining
characteristics of the nasal and we looked for contact of the prefrontal
with particular supralabials (Taylor, 1936:338). We determined which
supralabials are in contact with the eye and whether the mental is in
contact with the anterior pair of chin-shields.
The number of rows of dorsal scales was determined at five locations: a)
around the neck--counts were made from each side diagonally and
posteriorly from the anteriormost dorsal scale in contact with the first
ventral (see below)--counts from the left and right sides are the first
and second counts, respectively, recorded in the scale formula; b) one
head length posterior to head--counts were made either diagonally and
posteriorly or in a zig-zag pattern, beginning at the end of the second
count around the neck--this is the third count recorded in the scale
formula; c) midbody (approximated)--counts were made either diagonally
and posteriorly or in a zig-zag pattern--this is the fourth count in the
scale formula; d) anterior to anus (preanal)--counts were made in a
zig-zag pattern beginning on one side and ending on the other at the
first dorsal scale in contact with the anal plate--this is the fifth
count in the scale formula.
We followed the method of Dowling (1951:98-99) in counting ventrals, and
the anal plate was determined as entire, divided, or partly divided.
Subcaudals were counted on only the right side beginning at the first
scale that contacts a corresponding scale from the opposite side; fusion
of particular pairs of subcaudals was determined. The "spine" at the tip
of the tail was not counted. The head scutellation of each specimen was
examined for abnormalities.
We determined the number of fangs and the number of maxillary teeth
anterior to them and recorded the presence or absence of a diastema
between the anterior fang and the maxillary tooth immediately preceding
it. The diastema, if present, is a space distinctly wider than the
spaces separating the prediastemal teeth.
The point of intersection of two perpendicular lines of an ocular grid
determined which tooth-socket occurs directly opposite the distal tip of
the suborbital process (Fig. 5b), but if that point occurs between two
sockets then the number recorded was the number of the tooth immediately
anterior to that point plus one-half.
The anterior and posterior edges of the suborbital process were
determined as parallel or not at any point by aligning them with
parallel lines on an ocular grid (Fig. 5b).
The angle of the posterior edge of the lateral flange was determined as
an acute, obtuse, or right angle by fitting it to a pair of
perpendicular lines of an ocular grid (Fig. 5b).
The number of lateral anterior foramina (Fig. 4b) was determined. If
only two are present, their lengths (anterior to posterior) were
compared by measuring them with an ocular micrometer. Also, if two
lateral anterior foramina are present, the point of intersection of two
perpendicular lines of an ocular grid determined which tooth-socket
occurs directly below the center of the posterior foramen (Fig. 4b).
RESULTS
General Characteristics
From the data given by Force (1935), Taylor (1936), and Kirn _et al._
(1949), and from our own data, we conclude that a typical specimen of
_gracilis_, meaning a specimen having the usual characteristics of the
species, has the following characteristics in combination: supralabials
6-6; infralabials 6-6; preoculars 1-1; postoculars 1-1; temporals 1 + 1
on each side; nasal divided below naris; supralabials 3 + 4 entering
orbit; mental in contact with chin-shields; all five dorsal scale counts
15; and plate divided. (In the present work we use the words usual,
unusual, typical, and atypical with neither quotation marks nor
apology).
Of the 244 specimens on which we could examine each of these
characteristics, only 125 (51.2%) have all of the typical
characteristics in combination. The 119 specimens that do not possess
all of the typical characteristics in combination include 31 (12.7% of
the 244) that lack at least two of the typical characteristics.
Sex
The sample (N = 246) is composed of 107 (43.5%) females and 139 (56.5%)
males.
Measurements
Females have total lengths from 96 to 244 mm. (mean, 173.3; N = 79). One
female (KU 83480) measuring 244 mm. may be the longest specimen known
(Conant, 1958, reports the longest as 9-1/8 inches--approximately 232
mm.). Males have total lengths from 96 to 215 mm. (mean, 162.4; N =
109). Females have tail lengths from 16 to 50 mm. (mean, 34.6; N = 79),
and males have tail lengths from 21 to 53 mm. (mean, 37.8; N = 109).
The ratio of tail length to total length in females is from 0.17 to 0.22
(mean, 0.20; N = 79); in males it is from 0.21 to 0.27 (mean, 0.23; N =
109; Fig. 1). Juveniles (those less than 125 mm. in total length
according to Force, 1935: tables 1 and 2) have proportionally shorter
tails than do adults; the ratio of tail length divided by total length
is 0.17-0.21 (mean, 0.18; N = 14) in females and 0.21-0.23 (mean, 0.22;
N = 16) in males. Adult females (125 mm. or more in total length) have
ratios from 0.18 to 0.22 (mean, 0.20; N = 65) and adult males have
ratios from 0.21 to 0.27 (mean, 0.23; N = 93).
[Illustration: FIG. 1. Ratio of tail length to total length in females
and males of _T. gracilis_.]
Of the 246 specimens examined, 58 have incomplete tails. Of these 58
specimens, six had freshly broken tails, so we assume that 52 (21.1% of
the 246) have incomplete tails resulting from natural causes; the
remaining six specimens could have had their tails broken at or soon
after capture, assuming that none of the snakes was retained in
captivity for an extended period.
Supralabials
The supralabials are either six (usually) or seven on a side (Table 1).
When seven supralabials are present on either one or both sides, the
addition results from one of the following conditions: a) 5 is divided
to form 5 and 6 (N = 6); b) 2 and 3 form 2, 3, and 4 (N = 1); c) 5 and 6
form 5, 6, and 7 (N = 12); d) 4, 5, and 6 form 4, 5, 6, and 7 (N = 1);
e) 1 and 2 form 1, 2, and 3 (N = 1); f) 1, 2, and 3 form 1, 2, 3, and 4
(N = 1); g) 2 is fused with the nasal, and 3 and 4 are reduced to
granules (N = 1); h) type of addition unknown (N = 5).
TABLE 1. Variation in Number of Supralabials (N = 245) and
Infralabials (N = 246) of Tantilla gracilis.
------------+----------+-----------+------------+---------+----------
Number |Number |Per cent |Number |Number |Per cent
of |of |of |of |of |of
Supralabials|specimens |occurrence |infralabials|specimens|occurrence
------------+----------+-----------+------------+---------+----------
6-6 | 221 | 90.2 | 5-5 | 5 | 2.0
6-7 | 10 | 4.1 | 5-6 | 4 | 1.6
7-6 | 10 | 4.1 | 6-5 | 5 | 2.0
7-7 | 4 | 1.6 | 6-6 | 229 | 93.1
| | | 6-7 | 1 | 0.4
| | | 7-6 | 2 | 0.8
------------+----------+-----------+------------+---------+----------
In three of the four specimens with 7-7 supralabials, the type of
addition is the same on each side, whereas the other specimen has a
different type of addition on each side. Of the 23 examples for which
the type of addition is known, 19 (82.6%) have the increase in number on
the posterior half of the series.
In one specimen the third supralabial on the right is diagonally divided
and the resulting upper part does not contact the edge of the lip; hence
the specimen has 6-6 supralabials.
Infralabials
The infralabials are five, six (usually), or seven on a side (Table 1).
When five infralabials are present on either one or both sides, the
reduction results from one of the following conditions: a) 2 and 3 are
fused (N = 3); b) 1, 2, and 3 form 1 and 2 (N = 6); c) 2, 3, and 4 form
2 and 3 (N = 3); d) 5 is separated from the edge of the lip by a
projection from an adjacent infralabial (N = 1); e) 1, 2, 3, and 4 form
1, 2, and 3 (N = 2); f) type of reduction unknown (N = 4).
Of the specimens with 5-5 infralabials, two have the same type of
reduction on each side, one has a different type of reduction on each
side, and the type of reduction is unknown for the other two specimens.
When seven infralabials are present on either one or both sides, the
addition can result from infralabials 2 and 3 forming 2, 3, and 4 (N =
2); the type of addition is unknown in one specimen.
In one specimen the second infralabial on the right side is reduced to a
small wedge-shaped granule and in another specimen several infralabials
on both sides are irregularly divided horizontally, although both
specimens have six infralabials on the sides having the abnormalities.
Preoculars
Of the 245 specimens examined, 242 (98.8%) have one preocular on each
side. Both preoculars are absent from two specimens, and one specimen
has 1-0. In each case when a preocular is lacking, the "preocular" and
prefrontal are fused. One specimen having 1-1 preoculars has both of
them reduced to small vertical slivers.
Postoculars
Of the 245 specimens examined, 242 (98.8%) have one postocular on each
side. Postoculars are 2-1 in two specimens and 1-2 in one. In one
specimen the lower of the two postoculars on each side is very small,
being approximately 1/6 the diameter of the upper one (measured with an
ocular micrometer).
Temporals
Of the 245 specimens examined, 235 (95.9%) have 1 + 1 temporals on each
side. Four specimens exhibit addition of temporals: one specimen has two
secondary temporals on the left, and one has a tertiary temporal on the
left. Two specimens have partly healed head injuries that probably
caused atypical temporal conditions: one specimen has two primary
temporals on the left, and one has two secondary temporals on the left
and two upper and one lower secondary temporal on the right.
Six specimens exhibit reduction of temporals: one lacks a primary
temporal on the left ("temporal" is fused with sixth supralabial), two
lack secondary temporals on the right, and three lack secondary
temporals on the left. The right secondary "temporal" of one specimen is
separated from the supralabials by a posterior extension of the primary
temporal.
Of the 246 specimens examined, 200 (81.3%) have both primary temporals
in contact with their adjacent postoculars. Thirteen specimens (5.3%)
have only the left primary temporal in contact with the postocular and
eight (3.3%) have only the right primary temporal in contact with the
postocular. Twenty-five specimens (10.2%) have both primary temporals
separated from the postoculars. Separation of the primary temporal from
the postocular, whenever it occurs, results from contact of mutual
extensions from the adjacent parietal and supralabial (usually the
fifth).
Nasal
Of the 243 specimens examined, 237 (97.5%) have the nasal divided below
the naris on both sides. Three specimens have the nasal completely
divided (above and below the naris) on only the left side; one specimen
has a completely divided nasal on only the right side. A groove, but not
a complete division of the nasal, is present above the left naris of one
specimen. One specimen lacks the typical division below the naris on
both sides, but a complete suture is present posterior to the naris and
the resulting postnasal scales are, according to position, loreals.
Contact of prefrontal with supralabials
Of the 243 specimens examined, 147 (60.5%) have the prefrontal separated
from the labials on each side. Of the remaining 96 specimens, 53 (21.8%
of the 243) have the prefrontals in contact with the second labial on
each side; five other variations of this characteristic were observed
(Table 2).
TABLE 2. Variation in Contact of the Prefrontals and the Labials in 243
Specimens of Tantilla gracilis.
----------------------------------------------------+---------+----------
|Number |Per cent
CHARACTERISTIC |of |of
|specimens|occurrence
----------------------------------------------------+---------+----------
No contact | 147 | 60.5
Contact of prefrontal with second labial on right | 26 | 10.7
Contact of prefrontal with second labial on left | 10 | 4.1
Contact of prefrontal with each second labial | 53 | 21.8
Contact of prefrontals with labial two on left and | |
labial three on right | 1 | 0.4
Contact of prefrontals with labial three on left and| |
labial two on right | 3 | 1.2
Contact of prefrontals with labial two on left and | |
labials two and three on right | 3 | 1.2
----------------------------------------------------+---------+----------
The specimen having the prefrontal in contact with labial 2 on the left
and labial 3 on the right has seven supralabials on the right, the extra
labial being added anterior to the eye. In two of the three specimens
with the prefrontals in contact with labial 3 on the left and labial 2
on the right, the preoculars and prefrontals are fused on each side; the
third specimen has each preocular reduced to a small vertical sliver. Of
the three specimens having the prefrontals in contact with labial 2 on
the left and labials 2 and 3 on the right, two are typical with respect
to other characteristics that might result in this atypical condition,
but one has the prefrontals and preoculars fused.
Supralabials entering orbit
Of the 246 specimens examined, 233 (94.7%) have the third and fourth
supralabials entering each eye (Table 3). All snakes that have the
fourth and fifth labials entering the orbit on either side also have
seven supralabials on the same side. One specimen having only the fourth
labial entering the eye on the right side also has six supralabials on
that side, but the third supralabial is split diagonally and the part
contacting the eye does not contact the lip and hence is not a
supralabial. The remaining three atypical conditions (4/3 + 4; 3 + 4/3 +
4 + 5; 3 + 4 + 5/3 + 4) occur only one time each and on snakes having
6-6 supralabials.
Contact of mental with chin-shields
Of the 246 specimens examined, 190 (77.2%) have the mental in contact
with both anterior chin-shields. The mental is in contact with only the
left anterior chin-shield in 15 specimens, only the right anterior
chin-shield in 2 specimens, and the mental does not contact either
anterior chin-shield in 39 specimens. Separation of the mental and an
anterior chin-shield always results from the posterior elongation of a
first infralabial.
TABLE 3. Variation in Number of Supralabials Entering the Eye in 246
Specimens of Tantilla gracilis.
----------------------+-----------+------------
SUPRALABIALS | Number of | Per cent of
----------------------+ specimens | occurrence
Left | Right | |
----------+-----------+-----------+------------
3 + 4 | 3 + 4 | 233 | 94.7
4 + 5 | 3 + 4 | 4 | 1.6
4 | 3 + 4 | 1 | 0.4
3 + 4 | 4 + 5 | 5 | 2.0
3 + 4 | 4 | 1 | 0.4
3 + 4 | 3 + 4 + 5 | 1 | 0.4
3 + 4 + 5 | 3 + 4 | 1 | 0.4
----------+-----------+-----------+------------
Dorsal scale rows
Of the 245 specimens examined for this characteristic, 228 (92.7%) have
scale counts of 15-15-15-15-15. The number of scale rows around the neck
and one head length behind the head are 15 except in a single specimen
that has 14 scale rows at these three places. The number of scale rows
around midbody is 15 in 244 of 246 specimens (99.2%); two specimens have
14 scale rows around midbody. The number of preanal scale rows is more
variable; counts of 14 through 17 were recorded. Fourteen specimens have
14 preanal scale rows (5.7%), 229 have 15 preanal rows (93.1%), two have
16 preanal rows (0.8%), and one has 17 preanal rows (0.4%). Known causes
for atypical numbers of preanal scale rows are listed in Table 4. A
preanal count at one head length anterior to the anus would have omitted
most of the above variation in numbers of preanal scale rows.
TABLE 4. Atypical Numbers of Preanal Scale Rows in Specimens of Tantilla
gracilis.
-------+---------+--------------------------------------------+----------
Preanal|Number | |Per cent
scales |of | CAUSE |of
|specimens| |occurrence
-------+---------+--------------------------------------------+----------
| |Scale rows seven and eight on left fuse |
14 | 10 |within the last five ventrals | 4.1
| | |
| |Scale row two on the right is lost adjacent |
14 | 1 |to the penultimate ventral | 0.4
| | |
| |Scale row eight on the left divides adjacent|
16 | 1 |to the last ventral | 0.4
| | |
| |A scale row is added on the right adjacent |
16 | 1 |to and anterior to the anal plate | 0.4
| | |
| |A scale row is added on each side adjacent |
17 | 1 |to and anterior to the anal plate | 0.4
-------+---------+--------------------------------------------+----------
The complete dorsal scale formula for KU 83620, a male, is as follows:
6 + 7(2) + 7(4) 6 + 7(11)
15 --------- 13 --------- 14 --------- 15 ---------- 13 --------------,
6 + 7(2) +7(5) 6 + 7(11) 6 = 6 + 7(17)
14 ------------- 13---------,
6 + 7(18) +7(25)
+ 7(26) 6 + 7(38) +7(39)
14 ---------- 15 ---------- 14 ------------ 13---------- 14----------,
6 + 7(36) +7(42)
15 --------- 14 ---------,
-6(45) +7(53)
7 + 8(67) + 7(69)
15 ------------ 14 ----------- 15 ----------- 14 ---------- 15----------,
6 + 7(90) +7(93) 6 + 7(99)
14 ------------ 15(122).
+ 7(100)
Specimen 83620 is the only one for which we have determined the complete
dorsal scale formula. Obviously the formula is complex, and possibly the
specimen is atypical in this regard. Nevertheless, addition and
reduction of scale rows is apparent on other specimens and can be easily
observed by examining specimens under a dissection microscope.
Anal plate
Of the 246 specimens examined, 232 (94.3%) have the anal plate divided.
Of the 14 specimens having undivided anal plates, four have an
incomplete groove anteriorly in the plate.
Ventrals
[Illustration: FIG. 2. Number of ventrals in females and males of _T.
gracilis_.]
Females have from 122 to 137 (mean, 130.8 ± 0.26; N = 107) ventrals;
males have from 117 to 131 (mean, 122.3 ± 0.21; N = 139; Fig. 2). Of the
246 specimens examined, 29 (11.8%; 11 females and 18 males) have an
added half-ventral immediately anterior to the anal plate. Of these
specimens, 27 have the added half-ventral on the left side and two have
it on the right. Five specimens have the last ventral divided similar to
the normal division of the anal plate. One specimen has the last ventral
incompletely divided transversely. Excluding the last ventral, seven
specimens have divided ventrals (half-ventrals). Four of these specimens
have added half-ventrals on the right side (two specimens with one
half-ventral each, one specimen with two half-ventrals, and one specimen
with three half-ventrals), and four have added half-ventrals on the left
side (one half-ventral on each specimen).
Subcaudals
Females have from 37 to 47 (mean, 42.0 ± 0.20; N = 79) subcaudals; males
have from 43 to 55 (mean, 48.4 ± 0.23; N = 109; Fig. 3). Of the 187
specimens examined, 13 (7.0%) have the last pair of subcaudals fused.
One specimen has left subcaudal 28 fused with both adjacent subcaudals
(also fused) on the right. While reading proof we found two omissions in
Fig. 3; there should be illustrated two males with 43 subcaudals and
three males with 44 subcaudals.
[Illustration: FIG. 3. Number of subcaudals in females and males of _T.
gracilis_.]
Ventrals minus subcaudals
The value for number of ventrals minus the number of subcaudals varies
from 80 to 96 (mean, 88.8 ± 0.39) for 79 females, and from 67 to 83
(mean, 73.8 ± 0.28) for 109 males.
Additional scale characteristics
Of the 246 specimens examined, four (1.6%) have the rostral in contact
with the left prefrontal, and hence the internasals are separated from
one another. One snake has approximately one-fourth (anteriorly) of the
suture between the parietals fused. One specimen has the posterior edge
of the frontal fused with the left parietal. One specimen has the
parietal shield on the right side abbreviated posteriorly. One specimen
has both prefrontals fused with the frontal, although an incomplete
suture is present.
Maxillary characteristics (_Figs. 4 and 5_)
Maxillary teeth anterior to fangs 10-14 (mean, 12.1; N = 20);
tooth-socket number 6.5-8.5 (mean, 7.2; N = 20) directly opposite distal
tip of suborbital process; lateral anterior foramina 1-3 (mean, 1.8; N =
20); tooth number 6-9 (mean, 6.9; N = 12) directly below center of
posterior foramen (if only two foramina present). Three specimens lack a
diastema and 17 specimens have a diastema. The anterior and posterior
edges of the suborbital process are parallel in two specimens and not
parallel in 14; the process is broken in four specimens. The lengths
(anterior to posterior) of the lateral anterior foramina (if only two
are present) are approximately equal in six specimens, and in six the
anteriormost one is the longest; six specimens have one foramen and two
specimens have three foramina. All specimens examined have two fangs,
with the posterior edge of the lateral flange forming an obtuse angle.
[Illustration: FIG. 4. Lateral view of right maxilla of _T. gracilis_
(KU 83484), × 39. Actual length of bone is 2.44 mm. A. Detail of bone.
B. Outline sketch of bone to illustrate characteristics examined.
Lateral anterior foramina (LF); fangs (F); "prediastemal" maxillary
teeth (MT); lateral flange (PLF); perpendicular lines, A-B and C-D, are
used to determine which tooth-socket occurs directly below the center of
the posterior foramen (the specimen illustrated is atypical because
there are three foramina present).]
Discussion and Conclusions
Generic characteristics of _Tantilla_ are as follows: size small, body
slender, head not noticeably distinct from body; preoculars one;
postoculars one or two; nasals two; loreal absent; smooth dorsal scales
in 15 rows; anal plate usually divided but sometimes single; subcaudals
paired; usually two enlarged, posterior, grooved fangs on the maxilla
separated by a small diastema from the other maxillary teeth (Baird and
Girard, 1853:131; Cope, 1900:1110; Dunn, 1928:24; Blanchard, 1938:369;
Schmidt and Davis, 1941:268; Wright and Wright, 1957:722; Conant,
1958:180). Of these characteristics, only the following were invariable
in our sample: size small, body slender, head not noticeably distinct
from body; postoculars one or two; smooth dorsal scales; posterior
grooved fangs on maxilla. The dorsal scales, anal, and subcaudals were
"correct" 92 per cent of the time; the preoculars and nasals were
"correct" 97 per cent of the time.
[Illustration: FIG. 5. Ventral view of right maxilla of _T. gracilis_
(KU 83484), × 39. Actual length of bone is 2.44 mm. A. Detail of bone.
B. Outline sketch of bone to illustrate characteristics examined.
Lateral flange (PLF) forms an obtuse angle (ADC) with main axis of bone
(AB); a reference line (2), perpendicular to the main axis of the bone,
is used to locate the tooth-socket directly opposite the tip of the
suborbital process (SOP); the anterior and posterior edges of the
suborbital process are not parallel at any point (reference lines 1 and
3).]
_Tantilla_ reportedly has two nasals (Baird and Girard, 1853:131; Cope,
1900:1110; Wright and Wright, 1957:722). _Tantilla gracilis_ usually has
a single nasal that is divided below the naris; variation in this
characteristic is discussed above.
In addition to the generic characteristics, specific characteristics for
_T. gracilis_ are as follows: supralabials 5-8 (usually 6); supralabials
3 and 4 entering orbit; infralabials 5-7 (usually 6); temporals 1 + 1;
ventrals 115-138 in females, 106-132 in males; subcaudals 33-53 in
females, 40-57 in males; tail length 13-27 per cent total length in
females, 15-30 per cent in males (Baird and Girard, 1853:132; Cope,
1900:1111-12; Force, 1935:653-54; Taylor, 1936:337-38; Blanchard,
1938:371-72; Kirn, Burger, and Smith, 1949:240-49). Excepting the number
of temporals and the supralabials entering the orbit, the
characteristics of the specimens in our sample are within the ranges of
variation mentioned above. Of the 10 maxillary characteristics studied,
no variation was observed in number of fangs or angle of lateral flange.
Because our data have some bearing on the problem of geographic
variation in _T. gracilis_ and the recognition of subspecies, we comment
briefly on the status of subspecies in _T. gracilis_. Kirn, Burger and
Smith (1949) proposed the recognition of two subspecies of _Tantilla
gracilis_ (_T. g. gracilis_ Baird and Girard and _T. g. hallowelli_
Cope). These subspecies were diagnosed on the basis of differences in
ventrals, subcaudals, and the ratio of tail length to total length;
sexual dimorphism in each characteristic was considered. We do not
recognize these subspecies for the reasons given below.
The data of Kirn _et al._ (1949) appear to be presented inaccurately in
part. Both of us independently recalculated the mean given for each
characteristic for each subspecies, using the data in figures 2-4 of
Kirn _et al._ (1949:242, 244-245). Of their 12 means presented (table 1,
p. 247) only two agree with our recalculated means, although the means
calculated by each of us independently are in complete agreement (Table
5). Also, we independently calculated the percentages of specimens of
each "subspecies" that are included in the ranges of variation given in
their diagnoses (Table 5); again, our independent calculations are in
complete agreement. In our opinion the differences between the
populations for the characteristics analyzed do not warrant recognition
of subspecies (Fig. 6).
TABLE 5. Means of "Diagnostic" Characteristics of T. g. gracilis Baird
and Girard and T. g. hallowelli Cope.
=============================================================================
| _T. g. gracilis_ | _T. g. hallowelli_
-----------------+-----------------------------+-----------------------------
| | |Per cent | | |Per cent
CHARACTERISTICS | | Mean |specimens | | Mean |specimens
| Mean | (Kirn, |of Kirn, | Mean | (Kirn, |of Kirn,
|(Kirn, |_et al._)|_et al._ | (Kirn, |_et al._)|_et al._
|_et al._|recalcu- |included |_et al._ |recalcu- |included
| 1949) | lated |their |in 1949) | lated |in their
| | by us |diagnosis | | by us |diagnosis
-----------------+--------+---------+----------+---------+---------+---------
Ventrals--females|125.67 | 125.71 | 69.4 | 130.07 | 130.07 | 79.6
Ventrals--males |115.97 | 116.61 | 70.0 | 121.22 | 120.87 | 69.7
| | | | | |
Caudals--females | 40.99 | 40.82 | 62.8 | 46.79 | 43.82 | 77.4
Caudals--males | 47.75 | 48.29 | 78.3 | 51.67 | 50.29 | 51.0
| | | | | |
Tail L./total L. | | | | | |
females | .1976| .1976| 69.0 | .2084| .2076| 74.2
Tail L./total L. | | | | | |
males | .2336| .2362| 56.1 | .2477| .2423| 79.6
-----------------------------------------------------------------------------
The data presented by Kirn _et al._ do not demonstrate intergradation
between two populations. Moreover, the diagnostic ranges of the number
of subcaudals in males of _hallowelli_ and the ratio of tail length to
total length in males of _gracilis_ do not include the recalculated
means for those characteristics. Furthermore, the means for the
following characteristics are dangerously close to being excluded from
their respective "diagnostic" ranges: in _hallowelli_, the number of
ventrals in males; in _gracilis_, the number of subcaudals in females,
and the ratio of tail length to total length in females. It is
incongruous that Kirn _et al._ state (p. 243) that "the coefficient of
geographic divergence is .6 per degree latitude" for ventrals, and on
the same page they state that "The average number of ventrals gradually
increases toward the north in _Tantilla gracilis_ except in southern
Oklahoma and central Arkansas (the area of intergradation between _T. g.
gracilis_ and _T. g. hallowelli_) where the change seems to be more
abrupt." The data presented in Kirn _et al._ (1949) do not demonstrate
an abrupt change.
The present sample of _T. gracilis_ from Kansas is clearly within the
geographic range of _T. g. hallowelli_ as mapped by Kirn _et al._
(1949:241). However, for the sample from Kansas, the mean number of
subcaudals of males is well within the diagnostic range for _T. g.
gracilis_ (Table 6), the mean number of subcaudals of females is closer
to the mean of _gracilis_ than it is to the mean of _hallowelli_ (Table
5), and the mean of the ratio of tail length to total length of both
sexes is within or very close to the diagnostic range for _gracilis_
(Table 6).
[Illustration: FIG. 6. Frequency polygons presenting ratios of tail
length to total length for males of _T. g. gracilis_ and _T. g.
hallowelli_ from Kirn, _et al._ (1949). The dotted vertical lines
represent the means given by Kirn, _et al._ (1949) for _gracilis_ (left)
and _hallowelli_ (right); the solid vertical lines represent the
recalculated means for _gracilis_ and _hallowelli_, respectively, using
the data of Kirn, _et al._ The hatched bars represent the range included
by Kirn, _et al._ (1949) in their diagnoses of _gracilis_ (left) and
_hallowelli_ (right).]
TABLE 6. Comparison of the Means of Some Characteristics of the Sample
of _Tantilla gracilis_ from Kansas (Our Data) with Some of the
Diagnostic Characteristics (Kirn _et al._, 1949:240) of _Tantilla
gracilis gracilis_.
============================================================
|Diagnostic range for | Mean of the sample
CHARACTERISTIC | _T. g. gracilis_ |("_T. g. hallowelli_")
| | from Kansas
---------------+---------------------+----------------------
No. of | |
subcaudals | 40-50 | 48.4 (N = 109)
males | |
| |
Tail L./ | |
Total L. | .160-.200 | .20 (N = 79)
females | |
| |
Tail L./ | |
Total L. | .200-.235 | .23 (N = 109)
males | |
---------------+---------------------+----------------------
Smith and Sanders (1952:218) pointed out an error in the range of
subcaudals in female _T. g. gracilis_ as stated in table 1 (p. 247) of
Kirn _et al._ We add some additional corrections that should be made on
the same page. In table two, column two ("Sex"), the words "male" and
"female" are reversed for each characteristic. Also, in table two,
column four ("Means from data of Force"), the means for caudals should
be corrected from 33.61 to 43.61 in females and from 39.99 to 50.32 in
males, as based on our recalculations from Force's data; we did not
recalculate the means of Force's data for the other characteristics.
The discussion above demonstrates that the number of subcaudals and the
ratio of tail length to total length are weak characteristics for
diagnosing _T. g. gracilis_ and _T. g. hallowelli_. The only remaining
diagnostic characteristic given by Kirn _et al._ (1949) is the number of
ventrals. Nevertheless, a step-cline in the number of ventrals, if one
exists, is yet to be demonstrated. Therefore, we completely agree with
Dowling (1957:32), who stated that "... the overlap in each character is
so great that any subspecific differences appear to be as yet undefined.
It is here suggested that _T. gracilis_ be retained as binomial...."
LITERATURE CITED
BAIRD, S. F. and GIRARD, C.
1853. Catalogue of North American Reptiles in the museum of the
Smithsonian Institution. Part I.--Serpents. Smithsonian Misc.
Colls., 2:1-172.
BLANCHARD, F. N.
1938. Snakes of the genus _Tantilla_ in the United States. Zool.
Ser. Field Mus. Nat. Hist., 20(28):369-376.
CONANT, R.
1958. A field guide to reptiles and amphibians. Houghton Mifflin
Co., Boston, 366 pp.
COPE, E. D.
1900. The crocodilians, lizards, and snakes of North America. U. S.
Nat. Mus. Rept. (1898), 153-1270.
DOWLING, H. G.
1951. A proposed standard system of counting ventrals in snakes.
British J. Herpetology, 1(5):97-99.
1957. A review of the amphibians and reptiles of Arkansas. Occas.
Paps. Univ. Arkansas Mus., No. 3:1-51.
DUNN, E. R.
1928. A tentative key and arrangement of the American genera of
Colubridae. Bull. Antivenin Inst. Amer., 2 (147):18-24.
FORCE, E. R.
1935. A local study of the opisthoglyph snake _Tantilla gracilis_
Baird and Girard. Papers Michigan Acad. Sci., Arts and
Letters, 20:645-659.
KIRN, A. J., BURGER, W. L., and SMITH, H. M.
1949. The subspecies of _Tantilla gracilis_. Amer. Midl. Nat.,
42(1):238-251.
PETERS, J. A.
1960. The snakes of the subfamily Dipsadinae. Misc. Pubis. Mus.
Zool., Univ. Michigan, No. 114:1-224.
1964. Dictionary of herpetology. Hafner Publ. Co., New York, 392 pp.
SCHMIDT, K. P. and DAVIS, D. D.
1941. Field book of snakes. G. P. Putnam's Sons, New York, 365 pp.
SMITH, H. M. and SANDERS, O.
1952. Distributional data on Texan amphibians and reptiles. Texas J.
Sci., 4(2):204-219.
TAYLOR, E. H.
1936. Notes and comments on certain American and Mexican snakes of
the genus _Tantilla_, with descriptions of new species. Trans.
Kansas Acad. Sci., 39:335-348.
WRIGHT, A. H. and WRIGHT, A. A.
1957. Handbook of snakes. Comstock Publ. Assoc, Cornell, Vol. II,
pp. 565-1105.
_Department of Biology, The University of New Mexico, Albuquerque,
87106, and Department of Zoology, The University of Arizona, Tucson,
85721._
_Transmitted July 11, 1967._
* * * * *
Transcriber's Notes
The following corrections were made to the text:
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