After my own literature review and consulting with Mark Witton,* let me officially declare that RIFT's Leviathan subscribes to the Hone & Holtz wading model. This is evidenced further by my art direction for Fred Wierum's incredible rendition of the animal above. Mark also suggested the posture and even gait of the animal may have resembled something akin to modern day pangolin. So, there you have it. RIFT's Spinosaurus is the pangolin-egret hybrid from your nightmares. I hope RIFT gives you nightmares, too.
*Note: to my knowledge, Mark has not taken a stance yet on the aquatic pursuit vs. wading model. In his excellent Spinosaurus blog post, and in our back-and-forth, he has pointed out different anatomical and histological features of the animal--and their possible implications--but has stressed the need for more data, studies, and fossils before committing firmly to any conclusions about its behavior and lifestyle. I agree, though for the sake of the novel I have taken the wading stance (which I believe to be the likeliest dominant behavior, though it is unlikely that it was strictly one and never the other).
Spinosaurus References Used in RIFT:
Hone DWE, and Holtz TR. Evaluating the ecology of Spinosaurus: Shoreline generalist or aquatic pursuit specialist? Palaeontologia Electronica, 24(1):a03. https://doi.org/10.26879/1110 palaeo-electronica.org/content/2021/3219-the-ecology-of-spinosaurus
Ibrahim N, Sereno PC, Varricchio DJ, Martill DM, Dutheil DB, Unwin DM, Baidder L, Larsson HCE, Zouhri S, Kaoukaya A (2020) Geology and paleontology of the Upper Cretaceous Kem Kem Group of eastern Morocco. ZooKeys 928: 1–216. https://doi.org/10.3897/zookeys.928.47517
Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature581, 67–70 (2020). https://doi.org/10.1038/s41586-020-2190-3
Arden, T.M.S., Klein, C.G., Zouhri, S., Longrich, N.R., Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurus, Cretaceous Research (2018), doi: 10.1016/j.cretres.2018.06.013.