Sanzinia Gray, 1849

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

Sanzinia Gray, 1849

Material examined.

Sanzinia madagascariensis ( Duméril & Bibron, 1844) (MNHN-ZA-AC-1900.0122A; NHMUK 1967.77; SMF PH 55; SMF PH 56; UMMZ 190752; UMMZ 131713).

Description (Figs 74-79).

Trunk vertebrae. Centrum much shorter than wide; cotyle and condyle slightly depressed; neural arch vaulted; posterior median notch of the neural arch deep; neural spine higher than long; prezygapophyseal accessory processes vestigial; hypapophyses disappearing posteriorly to the 60th vertebra; haemal keel in more posterior vertebrae well-developed, ridge-like; paracotylar foramina absent in most vertebrae - in Sanzinia examined by Kluge (1991) only one out of 10 sampled vertebrae possessed unilaterally a tiny foramen.

Hoffstetter (1961:157) remarked the constant presence of a distinct foramen situated next to the dorsolateral corner of each side of the zygantrum that he regarded as somehow distantly analogue of the parazygantral foramina of madtsoiids. We confirm the presence of these foramina in Sanzinia but we note that they are less prominent than those in certain specimens of Candoia (and certainly less prominent than those of madtsoiids; see also Discussion below). Furthermore, Smith (2013) highlighted that the shape of the subcentral structures of Sanzinia could be subjected to ontogenetic variation, with very small individuals possessing distinct hypapophyses (or hypapophyses-like structures) throughout the trunk vertebrae, medium-sized individuals possessing sharp, projecting keels on their mid-trunk vertebrae and blunt haemal keels on their posterior trunk vertebrae, while large individuals possessed acute haemal keels in their mid-trunk vertebrae.

Trunk / caudal transition. The last trunk vertebrae possess a short hypapophysis, diminished in size in the following first cloacal vertebrae and then reduced entirely in the remaining cloacal vertebrae and three anteriormost caudal vertebrae. The remaining caudal vertebrae are provided with a distinct haemal keel; some of these keels, however, are bifurcated distally into two short spurs and thus may be interpreted as (distinctly reduced) haemapophyses. These “quasi-haemapophyses” together with normally developed keels are distributed at random (without any clear constant pattern) along the caudal portion of the column. In one specimen (SMF PH 56), however, all caudal vertebrae except for the four anteriormost ones, possess tiny haemapophyses. Moreover, the middle / posterior caudal vertebra of ZFMK 70428 (an individual slightly larger than UMMZ 131713) possesses distinct haemapophyses (Martin Ivanov and Krister Smith, personal communications). Posteriormost caudal vertebrae are fused.

Smith (2013) highlighted that in a very small individual (CM 145342), delicate haemapophyses were present on all caudal vertebrae except the anteriormost approximately two ones and the same pattern more or less observed also in mid-sized individuals he studied. Therefore, this reduction of haemapophyses in larger ontogenetic stages and adults could be potentially subjected to some degree of ontogenetic (or generally intraspecific) variation.

Number of vertebrae (all for Sanzinia madagascariensis ): SMF PH 55: 286 (231+4+51 [including a final fusion]); SMF PH 56: 266 (220+4+42 [including a final fusion]); UMMZ 131713: 256 (217+4+35).

Data from literature (all for Sanzinia madagascariensis ): ~300 vertebrae in total, of which ~225 trunk (based on Hoffstetter 1960: fig. 3); 261 vertebrae in total, of which 192 trunk ( Jourdran 1904); 208 trunk and cloacal vertebrae plus 42+ caudal vertebrae ( Alexander and Gans 1966).