Biology Reference
In-Depth Information
(A)
(B)
Plate 2.2
(A) Tropical rattlesnake; Neotropical rattlesnake; cascabel; cascavel;
maraca-boia; numerous other names (
Crotalus durissus collilineatus
) (Brazil) with
fangs erected.
Central and South American rattlesnakes have markedly variable venoms
among different populations. Some secrete venoms that contain the potent heterodimeric
presynaptic neurotoxin, crotoxin, historically, the first toxin isolated from any snake venom.
Other populations lack this toxin, and secrete venoms that only contain toxins common to
many
Crotalus
spp. (procoagulants, hemorrhagins, hypotensive peptides, and numerous other
components). Bites from these snakes can cause severe systemic envenoming. Given their
sizable fang structure, venom reservoir, and potent venom, fatalities are common. Note the
distensible, strongly recurved, canaliculated front-fangs typical of “solenoglyphous” dentition.
The fang on the right side of the photo is expressing a drop of venom at the fang aperture.
(B) Close-up view of Western diamondback rattlesnake (
Crotalus atrox
) anterior maxilla and
fangs.
This specimen has fangs that contain a visible groove that corresponds with the venom canal
or lumen. Viperid and elapid fangs have significant morphological variability. Several hypotheses
have attempted to establish evolutionary models for the development of dentition adapted for
venom delivery. One of these suggests that selective apoptosis (programmed cell death) contributes
to the formation of a fang lumen, or an external groove (see text).
Plate 2.2
A, photo copyright to David A. Warrell;
Plate 2.2B
, AMNH specimen #137173,
photo copyright to Arie Lev.
R. subminiatus
) lack grooves in their enlarged posterior maxillary teeth (Section 4.3).
This supports the accuracy of Stejneger's contention that the presence of a grooved “rear
fang” is not strictly necessary for the introduction of Duvernoy's secretion into a bite-
inflicted wound (Stejneger, 1893).
Although their morphology is variable (Fry et al., 2008; Weinstein et al., 2010),
the typical storage capacity of venom glands also emphasizes the functional differ-
ence between these and Duvernoy's glands (
Figure 2.1
). One notable aspect of this
