Colubroidea

Diagnosis. Vertebral characters used to identify to Colubroidea include: vertebrae longer than wide (length at least 1.2 - 1.3 times as wide at the neural arch) and relatively lightly built (Holman, 2000; Smith, 2013); neural spines thin and long when compared to other groups (Holman, 2000); zygosphenal and zygantral areas less massive than in booids (Holman, 2000); synapophyses distinctly divided into parapophyseal and diapophyseal processes (Holman, 2000); mid- and posterior trunk vertebrae with sharp, relatively thin hemal keels, with hypapophyses often absent in these regions (Rage, 1984; Holman, 2000; Ikeda, 2007; Smith, 2013; Head et al., 2016). When present, trunk vertebral hypapophyses are relatively long and often pointed (Holman, 2000; Ikeda, 2007); both paracotylar and lateral foramina present (Rage, 1984; Ikeda, 2007).

Remarks. There is some disparity in what constitutes the defining characters of colubroid vertebrae because of the vast diversity of the group. As such, we saw it fitting to summarize known characters in this study. Zaher et al. (2009, 2019) point out that no known vertebral synapomorphies currently define Colubroidea, and vertebrae are typically assigned through the combination of the characters listed above. However, Rage (1984) and Ikeda (2007) identified the presence of both paracotylar and lateral foramina together on the vertebrae as consistent throughout the group. Holman (2000) provided a number of additional characters, but some of the proposed characters describe only some groups of colubroids, and as such, are not included in the diagnosis of the group at this time. These disputed characters include the lack of hypapophyses beyond the cervical region in several groups, and possibly the presence of well-developed prezygapophyseal accessory processes, which Ikeda (2007) was unable to find in several Asian viperids. It should be noted that Holman (2000) focused only on North America colubroids, and therefore may have defined the group primarily for North American taxa.