DIPSADIDAE Bonaparte, 1838

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 : 18

Family DIPSADIDAE Bonaparte, 1838

Diagnosis. Vertebrae can be assigned to Dipsadidae through a combination of characters that individually are not necessarily exclusive to the group. Dipsadid snakes generally have vertebrae that are square to slightly longer than wide in dorsal view, an elongated centrum, and long, low, and narrow neural spines that overhang posteriorly (some taxa also overhang anteriorly) ( Holman, 2000; Parmley and Hunter, 2010; Holman et al., 2011; Mead and Steadman, 2017; Jurestovsky, 2021; Syromyatnikova et al., 2021). The neural arch is depressed to moderately vaulted in different species, and the zygosphene is usually crenate, but can be concave in some species when viewed dorsally ( Holman, 2000; Mead and Steadman, 2017). The prezygapophyses generally protrude only slightly beyond the ovoid prezygapophyseal facets to form small points ( Mead and Steadman, 2017). The cotyle and condyle are round to slightly dorsoventrally compressed, where the cotyle is flattened on the ventral portion in anterior view ( Mead and Steadman, 2017; Jurestovsky, 2021) Epizygapophyseal spines are absent ( Holman, 2000; Mead and Steadman, 2017; Jurestovsky, 2021). The synapophyses are divided into distinct diapophyses and parapophyses ( Holman, 2000; Syromyatnikova et al., 2021). Distinct hemal keels with adjacent subcentral ridges are present, and hypapophyses are absent from trunk vertebrae except potentially in a few species ( Holman, 2000; Ikeda, 2007; Head et al., 2016; Mead and Steadman, 2017; Syromyatnikova et al., 2021)

Remarks. The vertebrae of many extant dipsadid snakes have not yet been described and is outside the scope of this study, making it difficult to confirm the above characters across the entire group. We have, however, assembled the common characters expressed across several publications ( Holman, 2000; Parmley and Hunter, 2010; Holman et al., 2011; Mead and Steadman, 2017; Jurestovsky, 2021; Syromyatnikova et al., 2021) – and our personal observations of some North American and West Indian taxa – as a way to delimit dipsadids from colubrids and natricids through a combination of characters.