Sigilmassaurus brevicollis shown here reconstructed with and without a prominent “hump.” The neck of the “humped” spinosaur is reflexed according to Evers et al. (2016), following a strong upward cant of the cervical series at its base. The spines being nearly absent in these vertebrae, the muscles of the neck are reconstructed following several birds in which the muscles are rendered into ligaments creating a “nuchal” array. Dinosaurs with a likely similar structure include hadrosaurs.
This reconstruction remains modest, and the tissue depth is similar between the two reconstructions; the ligaments are reconstructed such that they span merely 4 or so vertebrae at once. However, the vertebral supporting ligaments and muscle sheets lying above the base of the neck could be much more extensive and bridge more vertebrae can be spanned by the nuchal muscles, which would considerably thicken the appearance of the neck, but also reduce the prominence of the implied hump.
It can be said that Sigilmassasaurus was a spinosaur imitating a hadrosaur.