Ungaliophiidae McDowell, 1987 (sensu Burbrink et al. 2020), 1861

Szyndlar, Zbigniew & Georgalis, Georgios L., 2023, An illustrated atlas of the vertebral morphology of extant non-caenophidian snakes, with special emphasis on the cloacal and caudal portions of the column, Vertebrate Zoology 73, pp. 717-886 : 717

Ungaliophiidae McDowell, 1987 (sensu Burbrink et al. 2020)

General information.

Long considered as a subfamily of Tropidophiidae ( Ungaliopheinae of McDowell [1987] - spelling formally emended to Ungaliophiinae by ICZN [2020]), ungaliophiids were recently demonstrated as being distinct booids, on the basis of molecular data ( Slowinski and Lawson 2002; Wilcox et al. 2002; Lawson et al. 2004; Wiens et al. 2008; Pyron et al. 2013; Burbrink et al. 2020), with this view supported also by their distinctive skulls ( Bogert 1968a), vertebrae ( Bogert 1968a; Smith 2013), and external morphology and myology ( Zaher 1994) (see entry of Tropidophiidae above). Therefore, according to recent taxonomic schemes, Ungaliophiidae form the sister group of Charinaidae ( Pyron et al. 2014; Georgalis and Smith 2020; Scanferla and Smith 2020b). More particularly, in such taxonomic schemes and phylogenies, they have been considered either as a subfamily (i.e., Ungaliophiinae ) of (an expanded) Charinaidae (e.g., Pyron et al. 2014; Georgalis and Smith 2020) or either as their own family, Ungaliophiidae ( Zaher 1994; Wilcox et al. 2002; Burbrink et al. 2020; Zaher et al. 2023). We select here the latter nomenclature, especially because caudal vertebral morphology of charinaids is strikingly most similar to erycids and not to ungaliophiids (see also the entry of Charinaidae above).

Ungaliophiidae currently comprise two genera, Exiliboa and Ungaliophis , with only three species in total, inhabiting continental Central and northern South America ( Wallach et al. 2014; Boundy 2021). The fossil record though attests to a much larger past distribution including the Eocene of North America ( Smith 2013) and Europe ( Scanferla et al. 2016; Scanferla and Smith 2020b).

Vertebral morphology of Ungaliophiidae possesses striking differences compared to that of other booids and constrictors in general. More particularly, their trunk vertebrae are characterized by a distinctive elongation (with the CL/NAW ratio ≥1.1) and light construction, while their caudal vertebrae are characterized by the presence of a haemal keel (instead of haemapophyses) throughout the caudal series which only disappears near the tip of tail. Indeed, Smith (2013) has highlighted these two diagnostic features of ungaliophiids as synapomorphies within constrictors.

Ungaliophiid vertebrae have only been rarely figured. In fact, previous figures of vertebrae of extant Ungaliophiidae have been so far only presented by Bogert (1968a, 1968b) and Smith (2013). Among these, vertebrae from the cloacal and/or caudal series have been presented by Smith (2013). Besides this figuring, Szyndlar and Böhme (1996), Szyndlar and Rage (2003), Szyndlar et al. (2008), and Smith (2013) emphasized considerably on the pattern of subcentral structures in the cloacal and caudal series of ungaliophiids.