pointy vertebral region) of Beibeilong had low neural spines (bony spines developing upward from the top surface of the neural arch) and were X-shaped in top view. The (hip vertebrae) of Beibeilong was formed by six sacral vertebrae. The was strap-like and co-joined by the furcula. The was a large pelvic bone with a gently convex top border, and its (a recurved anterior ilium expansion, also known as "ala") was longer than the squared off (posterior ilium expansion), another feature of Beibeilong. The (hole in the pelvic girdle formed by the ilium, ischium, and pubis) had its top border formed by the ilium with a broad gentle arch. Both ilium and were united by the (lower ilium protuberance). The shaft of the was relatively skinny and rod-like shaft. The was robust compared to other bones, somewhat bowed, and elongated, slightly larger than the pubis. Unlike most oviraptorosaurs, its femur lacked a ridge-like feature extending along the shaft between the and the lower mid-condyle (rounded region for articulation). Furthermore, the accessory trochanter of the femur was badly developed, unique trait of Beibeilong. The lacked the distinctive boss that is present on the lower end of the cnemial crest in most oviraptorosaurs. Both crest and its condyle were low and poorly defined but connected to each other. Eggs The eggs of Beibeilong are identified as belonging to the oospecies Macroelongatoolithus xixiaensis. They were very elongated with rather rounded poles and/or ends, and measured between in length. In its microscopic composition, the eggshell was a two-layered structure with an outer "continuous" layer and inner "mammillary/cone" layer. Although not considered a layer, the boundary separating both outer and inner layers was notably demarcated, undulatory, and wavy. Eggshell thickness varied from to . The eggshell of Beibeilong eggs was ornamented on its external surface, characterized by a rugose texture composed by scattered nodes and additional nodes forming ridge-like structures and irregular chain-like structures. Like other Macroelongatoolithus nests, a complete Beibeilong nest would have been ring-shaped with a center devoid of eggs. Classification Pu and team in 2017 considered Beibeilong to have been anatomically similar to, but more basal (primitive) than Gigantoraptor. This conclusion was consistently recovered in their phylogenetic analyses incorporating ontogenetically (growth) variable characteristics. Beibeilong was recovered within the oviraptorosaur family Caenagnathidae in a relatively basal position; below is the obtained cladogram by Pu and team: Paleobiology Ontogeny In their 2017 description of Beibeilong,