Trachyboa Peters, 1860

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

Trachyboa Peters, 1860

Material examined.

Trachyboa boulengeri Peracca, 1910 (NHMUK 1901.3.29.77; NHMUK 1907.3.29.26.77; UMMZ 190753); Trachyboa gularis Peters, 1860 (AMNH R28982 ; UMMZ 239492 [Morphosource.org: Media 000070188, ark:/87602/m4/ M70188 ]) .

Description (Figs 26-30).

Trunk vertebrae. The description is based on Trachyboa boulengeri . The vertebrae display a number of peculiarities unparalleled with other extant snakes: they are relatively very dorsoventrally tall and anteroposteriorly short in lateral view, with strongly laterally expanded zygapophyses in dorsal and ventral view; centrum much shorter than wide; cotyle and condyle orbicular; neural arch depressed, provided with distinct tubercles (or minute pterapophyses) above the postzygapophyseal areas; posterior median notch of the neural arch deep; neural spine twice as high as long, relatively very thick, surmounted by a broad plate, the latter produced anteriorly and posteriorly into distinct paired spurs; prezygapophyseal accessory processes not projecting laterally beyond the articular facets, but expanded posteriorly in dorsal view; short plate-like hypapophyses with a distinct anteroventral corner present throughout the trunk portion of the column; paracotylar foramina absent.

The trunk vertebrae of the type species of the genus, Trachyboa gularis , generally resemble those of Trachyboa boulengeri , but differ from the latter in the absence of additional structures on the neural spine and neural arch, and the?absent (or at least vestigial) prezygapophyseal accessory processes in the former species (see also Bogert 1968b: fig. 7C).

Trunk / caudal transition. The peculiarities observed in the trunk vertebrae of Trachyboa boulengeri are retained also in those from the cloacal and caudal portions of the column (except for the posteriormost caudal vertebrae). Notably, in the most complete available specimen (NHMUK 1907.3.29.26.77), skeletonized personally by one of us (ZS; see also above section "Parts of the vertebral column"), there are only two cloacal vertebrae (Fig. 27 ) - it is not clear though if this is the standard case for this particular species, or if it simply represents a variation (or even pathology) of this single particular specimen - in Trachyboa gularis (UMMZ 239492), nevertheless, there are four cloacal vertebrae. The hypapophysis of the last trunk vertebra is distinctly larger than in mid-trunk vertebrae; that structure (slightly shorter but thicker) is retained in the cloacal and nine anterior caudal vertebrae (Fig. 28 ). Paired haemapophyses first appear on the 10th caudal vertebra, although they display the shape of grooved hypapophyses or keels rather than standard haemapophyses typical for most snakes; subcentral structures observed on the 16th and 21st caudal vertebrae are not grooved (i.e., these vertebrae possess a non-grooved haemal keel instead of haemapophyses; Fig. 28 ). Distinct tubercles (or minute pterapophyses) above the postzygapophyseal areas continue also to be present in the cloacal and caudal vertebrae.

In Trachyboa gularis (UMMZ 239492), the tiny paired haemapophyses (resembling grooved hypapophyses) appear already from the last cloacal (S 4) and continue until around C 12. The remaining few posterior caudal vertebrae possess a small keel, which is (in a random pattern) either ungrooved or slightly grooved.

Number of vertebrae. Trachyboa boulengeri (NHMUK 1907.3.29.26.77):? (?+2+25); Trachyboa gularis (UMMZ 239492): 179 (154+4+21, plus a final fusion).

Data from literature: Trachyboa boulengeri : 131-134 trunk and cloacal vertebrae plus 24 caudal vertebrae ( Alexander and Gans 1966).

Figures

Figure 27. Tropidophiidae: Trachyboa boulengeri (NHMUK 1907.3.29.26.77), trunk vertebrae and cloacal vertebrae. Note that there are only two cloacal vertebrae in this specimen.

Figure 28. Tropidophiidae: Trachyboa boulengeri (NHMUK 1907.3.29.26.77), caudal vertebrae.