Blackburn, D.G. (1993) Standardized criteria for the recognition
of reproductive modes in squamate reptiles.
Herpetologica 49: 118-132.
Abstract: This
paper reviews the various criteria for the recognition of oviparity and
viviparity in squamates and proposes a hierarchy of these criteria based on
reliability and practicality. The best
evidence for oviparity includes field observations of oviposition and of
developing eggs of certain identity, and observations of hatching eggs that
were not freshly-oviposited. Other
strong evidence of oviparity includes egg-tending behavior, and the oviposition
of developing eggs in captivity.
Viviparous reproduction is strongly indicated by observations of
parturition in the field and in captivity, as well as by ovulation of minuscule
ova. Somewhat weaker evidence of
viviparity includes the presence of advanced oviductal fetuses and the absence
of an opaque eggshell around moderately-developed oviductal embryos. However, the presence of an eggshell around
oviductal eggs does not necessarily indicate oviparity, and its absence during
early development does not exclusively indicate either reproductive mode. Likewise, the presence of immature embryos
in the oviduct does not distinguish between oviparous and viviparous habits,
nor do field observations of females in proximity to a clutch of unidentified
eggs, or the emergence of young from thin-shelled (or shell-less)
"eggs" of unknown history.
Unsubstantiated reports in the literature warrant corroboration and must
be treated cautiously. The use of
criteria to recognize reproductive modes is illustrated with literature on the
genus Eumeces. Future reports on
squamates should detail how reproductive modes of individual species and higher
taxa were inferred.
Reprints: daniel.blackburn@mail.trincoll.edu