Exiliboa Bogert, 1968

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

Exiliboa Bogert, 1968

Material examined.

Exiliboa placata Bogert, 1968 (MVZ Herps 137126 [Morphosource.org: Media 000076130, ark:/87602/m4/ M76130 ]; UTACV R 37871 ) .

Description (Figs 118-123).

Trunk vertebrae. Centrum longer than wide; cotyle and condyle slightly depressed; neural arch slightly depressed; posterior median notch of the neural arch deep; neural spine dorsoventrally high with a distinct thickening and lateral widening of its dorsal margin, crossing around two thirds of the midline of the neural arch; cotyle and condyle orbicular; prezygapophyseal accessory processes absent to vestigial; hypapophyses present on anterior trunk vertebrae, being sigmoid until around V 25 and subsequently plate-like until around V 40, and gradually diminishing in size to be replaced by a prominent haemal keel in mid-trunk and posterior trunk vertebrae; paracotylar foramina absent.

The mid-trunk vertebra of the same species, illustrated by Bogert (1968a: fig. 8) closely matches the same morphology. Note that Bogert (1968a) also claimed that hypapophyses were restricted to only the first 20 anterior trunk vertebrae, however, this was apparently because he preferred to use the term "haemal keel" for smaller, blade-like hypapophyses ( Bogert 1968a).

Trunk / caudal transition. A blade-like and thick hypapophysis is present in the last trunk and in cloacal vertebrae. In caudal vertebrae, this is replaced by a distinct, moderately developed, and thick haemal keel; the keel is still present in the tip of the tail; pleurapophyses long, robust, and laterally directed throughout the caudal series; the posteriormost (approximately) two caudal vertebrae are fused.

Smith (2013) highlighted that the long, robust and laterally directed pleurapophyses throughout the tail represent an autapomorphy for Exiliboa . We figure this feature here for this taxon - we also note that this prominence and lateral direction is also the case for Ungaliophis though not to the same extent.

Number of vertebrae (all for Exiliboa placata ). UTACV R 37871: 196 (159+4+33, including a final fusion); MVZ Herps 137126: 195 (165+4+26, including a final fusion).

Data from literature and unpublished data from personal communications (all for Exiliboa placata ): 166 trunk vertebrae plus 3 cloacal vertebrae plus 28 caudal vertebrae (the posteriormost 4 or 5 are partially fused) ( Bogert 1968a); 165 trunk vertebrae plus 27 cloacal and caudal vertebrae plus a final fusion (NMNH 209414B; Krister Smith, unpublished data, personal communication to GLG).