Natricidae Bonaparte 1840

Family NATRICIDAE Bonaparte, 1840 Diagnosis. North American natricid vertebrae have well-developed, pointed hypapophyses directed posteriorly on the trunk vertebrae (Holman, 2000). These hypapophyses are usually sigmoid in shape (Szyndlar, 1991). The vertebrae overall are lightly built and elongate, with long centra, strong subcentral ridges, posteriorly vaulted neural arches, and somewhat short parapophyseal processes (Szyndlar, 1991). Remarks. Szyndlar (1991) differentiated natricid snakes from other snake groups known to possess hypapophyses on their trunk vertebrae. Natricids differ from viperids in exhibiting hypapophyses that are somewhat sigmoidal in shape, and in possessing a relatively longer centra, posteriorly vaulted neural arches, and shorter parapophyseal processes. They differ from elapids in being more lightly build overall, with much longer centra and prominent subcentral ridges. Despite the hypapophyses being presented as a definitive character for natricids as a whole, McDowell (1961), Malnate (1972), and Ikeda (2007) showed that there are a few exceptions to this rule outside of North America, possibly representing a loss of this character later in the evolution of some species.