Leptotyphlopidae

Palci, Alessandro, Hutchinson, Mark N., Caldwell, Michael W., Smith, Krister T. & Lee, Michael S. Y., 2020, The homologies and evolutionary reduction of the pelvis and hindlimbs in snakes, with the first report of ossified pelvic vestiges in an anomalepidid (Liotyphlops beui), Zoological Journal of the Linnean Society 188, pp. 630-652 : 636

Scolecophidia: Leptotyphlopidae

Leptotyphlopids typically show a complete triradiate pelvis and a strongly reduced femur located ventral to the lymphapophyses and anterior to the cloaca ( Fig. 2H). On each side of the body, the pelvis consists of a posterodorsally directed ilium, a posteroventrally directed ischium and an anteroventrally directed pubis. Moreover, the ilium typically points somewhat laterally, the pubis in a slightly medial to slightly lateral direction, and the ischium always points posteromedially ( List, 1966). In some species of leptotyphlopids, the ischia may meet in the midsagittal plane of the body but never form an immovable joint ( List, 1966). All three elements are rod-like in shape, and the ilium is typically the longest of the three, whereas the pubis is the shortest and least curved.

Variation occurs mostly by minor changes in the shape and size of the elements, fusion of the elements ( Fig. 2I) or by the patterns of ossification ( Fig. 2J). For example, a specimen of Leptotyphlops nigricans (Schlegel, 1839) figured by List (1966: plate 20, fig. 5) shows a cartilaginous femur, whereas a specimen of Leptotyphlops magnamaculata (Taylor, 1940) figured by the same author has a cartilaginous ischium ( List, 1966: plate 20, fig. 2). Variation can also be intraspecific; for example, List (1966) figures a specimen of Leptotyphlops dulcis dissectus (Cope, 1896) (MCZ 39681), in which the femur is cartilaginous, and another specimen (USNM 99821), in which the ischium is also unossified ( List, 1966: plate 19 fig. 1 and plate 20, fig. 3, respectively). In some other species, the pubis is fused to the ilium (e.g. Leptotyphlops bakewelli Oliver, 1937 and Leptotyphlops melanotermus Cope, 1862 ; List, 1966; present study). In Leptotyphlops albifrons (Wagler, 1824) , the whole pelvic girdle appears to be cartilaginous, where the three elements (pubis, ischium and ilium) are merged together and there is no trace of a femur ( Essex, 1927). The femur of leptotyphlopids, when present and well developed, is typically forked laterally, with the largest dorsal process providing attachment for the claw and the other process representing a trochanter for muscle attachment ( Essex, 1927; List, 1966).