Biology Reference
In-Depth Information
diastema from two enlarged, slightly curved posterior teeth that are almost three
times the length of the anterior teeth and are angled 30° to the maxilla (McAlister,
1963). Fry et al. (2008) described the maxillary teeth of
H. nasicus
and
H. plati-
rhinos
as having smooth surfaces and lacking an “enclosed venom canal.” These
investigators also reported that the “venom” duct opened directly into the oral cavity
rather than into the “lumen of the fang sheath” and the surface of the “fang” (Fry et
al., 2008). The notably enlarged, smooth posterior maxillary teeth of
H. platirhinos
,
H. simus
, and
H. nasicus kennerlyi
are shown in
Plate 4.79A-E
.
The enlarged posterior maxillary teeth of
Heterodon
spp. have been popularly per-
ceived to perform prey manipulation and “deflation” functions. The deflation function,
specifically, puncturing a grasped toad with the enlarged maxillary teeth during deglu-
tition, was considered to be a response to the toads' (
Bufo
spp.—a favored prey item
of
Heterodon
spp.) antipredator defense mechanism of inflating themselves with air
(Edgren, 1955; McAlister, 1963; Pope, 1947). However, these teeth have been consid-
ered too short to effectively perform this function (Kroll, 1976). An opposing view opines
that the enlarged maxillary teeth probably only reinforce the grip on prey (Ditmars, 1896;
Kroll, 1976), as well as possibly facilitate entry of Duvernoy's secretion into the result-
ing wounds (Averill-Murray, 2006; Weinstein and Kardong, 1994). Although the latter
hypothesis is probably correct, close examination of the markedly enlarged, ungrooved,
posterior maxillary teeth suggests that these could support such a prey-handling function
(toad “deflation”) if approximately two-thirds of the length of the respective teeth pro-
trude from the buccal mucosa during deglutition (see
Plate 4.79A-E
). This interesting
question deserves further formal study, as it may clarify
Heterodon
prey-handling strate-
gies as well as add some clues about Duvernoy's secretion function(s).
The source of toxic oral secretions of
Heterodon
spp. has been long debated.
Hay (1892) indicated that the enlarged posterior maxillary teeth were “
…
not con-
nected with any source of poison
…
.” Similarly, McAlister (1963) reported that the
“superior labial gland” lacked posterior enlargement. He concluded that the enlarged
posterior maxillary teeth were not primarily associated with facilitating penetra-
tion of “saliva” into prey. Kapus (1964) reported the presence of a “parotid” gland
in
H. nasicus
,
H. n. kennerlyi
, and
H. simus
, and that the gland of
H. nasicus
was
notably larger than that of
H. simus
. Some authors hypothesized that local effects
of
Heterodon
spp. bites in humans were possibly due to residual toxic skin secre-
tions from anuran prey left in the snake's buccal cavity (Anderson, 1965). Smith and
Brodie (1982) considered that
Heterodon
spp. may have a generalized salivary toxic-
ity: “
…
the fangs do not deliver a venom, although the saliva is believed to be toxic.”
However, several authors favored probable toxic secretions produced in a specific
oral gland (Bragg, 1960; Morris, 1985). This was demonstrated by Kroll (1976), who
identified in
H. nasicus
and
H. platirhinos
a “seromucous venom gland” (Duvernoy's
gland) associated with the enlarged posterior maxillary teeth. This gland is readily
found in dissected specimens of
H. nasicus
and
H. platirhinos
and clearly produces
a secretion with variable toxicity and probable specificity for anuran amphibians
(McAlister, 1963; Young, 1992). Taub (1967) found that the Duvernoy's glands of
H. nasicus
and
H. platirhinos
had moderately thick-“heavy” thick capsules and mod-
erate numbers of moderately thick trabeculae. Ninety percent of the intraglandular
