Sanziniidae Romer, 1956, 1858

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

Sanziniidae Romer, 1956

General information.

Sanziniidae represents a small lineage of booids, pertaining to two genera ( Acrantophis and Sanzinia ) and four species, that are endemic to Madagascar ( Pyron et al. 2014). Originally established as a subfamily of boids by Romer (1956), who also included in it the bolyeriids from the Mascarene Islands. Recent taxonomic schemes have elevated them to the family level ( Pyron et al. 2014; Burbrink et al. 2020; Georgalis and Smith 2020).

Vertebral morphology of Sanziniidae is reminiscent of other constrictors. However, a principal difference lies within their caudal vertebrae, where they possess keels (that are partly grooved or bifurcated in Sanzinia ) instead of haemapophyses. Actually, there appears to be a contradiction in the existing literature as far as it regards the subcentral structures of sanziniid vertebrae: Romer (1956) erroneously mentioned the presence of hypapophyses throughout the trunk vertebrae with McDowell (1975) also using the term "strongly projecting crest" for these structures. However, this observation was refuted by Hoffstetter (1960) and Szyndlar and Böhme (1996), who specified that there are no hypapophyses (by any definition of this term) in mid- and posterior trunk vertebrae. In an attempt to clarify this controversy, Smith (2013) suggested that ontogenetic variation may be the source of this confusion, as he highlighted that in a very small individual of Sanzinia madagascariensis there were distinct hypapophyses-like structures throughout the trunk vertebrae but these were progressively shifted to “regular” haemal keels in larger individuals. As for the cloacal and caudal region, Szyndlar and Böhme (1996) and Szyndlar et al. (2008) noted that sanziniids possess haemal keels and no haemapophyses in their caudal vertebrae, with some keels of Sanzinia bifurcated distally into two short spurs that may be interpreted as short haemapophyses. Smith (2013) nevertheless considered that this could also be ontogenetically variable, as he reported that in a very small individual, delicate haemapophyses were present on all caudal vertebrae except for the anteriormost approximately two ones, with the same pattern also generally present in mid-sized individuals.

Previous figures of vertebrae of extant Sanziniidae were so far only presented by Auffenberg (1958), Dowling (1959), and Gasc (1974). Among these, vertebrae from the cloacal and/or caudal series of sanziniids have never been figured so far. Figures of the microanatomy and histology of sanziniid vertebrae were presented by Houssaye et al. (2013). Quantitative study on the intracolumnar variability of sanziniid vertebrae was conducted by Hoffstetter (1960).