COLUBRIDAE Oppel, 1811

Jacisin Iii, John J. & Lawing, A. Michelle, 2024, Fossil snakes of the Penny Creek Local Fauna from Webster County, Nebraska, USA, and the first record of snakes from the Early Clarendonian (12.5 - 12 Ma) of North America, Palaeontologia Electronica (a 2) 27 (1), pp. 1-42 : 11-12

Family COLUBRIDAE Oppel, 1811

Diagnosis. Vertebral characters of Colubridae include: trunk vertebrae lightly built and longer than wide ( Holman, 2000); neural spines long, thin, uniformly wide, and as high as or higher than they are long ( Holman, 2000; Head et al., 2016); subcentral ridges of the centrum are deep ( Holman, 2000; Jurestovsky, 2021); prezygapophyseal accessory processes are prominent ( Holman, 2000); epizygophyseal spines extending posteriorly from the postzygapophyses present in some species ( Holman, 2000); synapophyses distinctly divided into diapophyses and parapophyses ( Holman, 2000); cotyle circular-to-oval in shape ( Jurestovsky, 2021). The hemal keel is typically thin and may appear similar to one of three types: hemal keels present without parapophyseal process development, both hypapophysis and parapophyseal processes present, and hemal keel thin with somewhat round prezygpophyseal articular processes ( Rage, 1984; Holman, 2000; Ikeda, 2007).

Remarks. The defining characters for colubrids are complicated by the diversity and degree of variation within the group, and are partially dependent on whether groups such as the natricids and dipsadids are included within the group. Post-cervical hypapophyseal characters would seem to be inappropriate for defining colubrids as a whole if natricids are included because, as noted in Ikeda (2007), several studies have pointed out that some natricids lack hypapophyses on their trunk vertebrae ( McDowell, 1961; Malnate, 1972), while a small number of homalopsine snakes exhibit prominent hypapophyses on their trunk vertebrae ( Gyi, 1970; McDowell, 1987). Furthermore, Ikeda (2007) noted the highly variable shape of the prezygapophyseal facets and hemal keel within Colubridae , and pointed out that the neural spine is often more long than high in small-bodied species, but more high than long in large-bodied species.