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Generally speaking, the males of most species are smaller than
the females of the same species. Their vent (cloaca) openings are
positioned farther from the margin of the bottom shell (plastron)
than those of females. The tails of male water turtles tend to be
relatively long and tapered, but thick at their base. The tails of
females are generally short and stubby. The males of some water
turtle species also have unusually long claws on their front feet.
Certain species of water turtles have been successfully bred in
captivity. During mating, the male's penis may protrude during
sexual excitement and resembles an "opening flower". Inexperienced
observers often regard this structure with bewilderment. Copulation
takes place when the male inserts this structure into the female's
cloacal opening.
Eggs can be incubated by burying them in 1-2 inches of sand or
dirt kept at 75-85 F. Incubators can be rudimentary to elaborate.
The eggs should not be disturbed in any way during the incubation
period. The eggs usually hatch in 65-140 days (average 80-110 days).
The eventual sex of a water turtle may be influenced by egg
incubation temperatures. Red-Eared Slider eggs, for example,
incubated at 85 F yield primarily female turtles, while those
incubated at 75 F yield primarily male turtles. The numbers of each
sex tend to be equal when eggs are reared at 80 F. This interesting
phenomenon does not occur in all water turtle species. Among other
chelonian species (certain tortoises), high environmental temperatures
produce more male offspring.
Some scientists speculate that temperature-induced sex
determination is the major factor responsible for the demise of
dinosaurs. They theorize that a meteor collision produced a massive
dust cloud, blocking out much of the sunlight and greatly reducing
the environmental temperature. Such cooling may have resulted in
drastic changes in sex ratios of dinosaur offspring. Such an
imbalance in the number of males and females could have, in turn,
greatly compromised the dinosaurs' reproductive success.
A specialized sharp projection (called an "egg tooth") on the
"upperbeak" of hatchling water turtles aids them in emerging from the
egg. Premature hatching may occur from time to time. When this
occurs, the yolk sac is conspicuous as it hangs from its attachment
to the lower shell. These hatchlings can be saved as long as the
yolk sac is kept moist and not injured. The baby can be suspended
with the yolk sac gently wrapped in saline-soaked gauze until the
material within the sac has been completely absorbed. The hatchling
will not eat on its own during this period because of the adequate
nourishment it receives from the yolk sac material.
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