A hump-backed Spinosaurus, restored by R.E. Johnson and from Bailey 1997. Bailey 1997

Spinosaurus and Ouranosaurus were fundamentally different, and they remain among the most bizarre dinosaurs yet discovered. Both dinosaurs—a carnivore and herbivore, respectively—had elongated neural spines sticking out of many vertebrates along their backbones, creating prominent skeletal sails. In life, these structures are thought to have been covered by a thin layer of flesh. However, paleontologist Jack Bowman Bailey proposed an alternative idea in 1997: these dinosaurs were not sail-backed but hump-backed.

Bailey suggested that bison were a better analogue for the high-spined dinosaurs rather than the synapsids Dimetrodon and Edaphosaurus. He used basic anatomical comparison to illustrate the similarities between the back spines of dinosaurs and the thick, flattened spines near the shoulder region of bison. This led him to propose that the sails were sites for the attachments of powerful ligaments and large muscles.

According to Bailey’s hypothesis, if Spinosaurus had a thick hump, it probably walked on all fours instead of balancing on two legs like other large theropods. This suggests that Spinosaurus might not have been an agile sprinter like many other theropods but could have used its massive body to overpower prey or steal kills from smaller predators.

Bailey also suggested that other dinosaurs, such as Acrocanthosaurus, Protoceratops, and Stegosaurus, might have had humps for various purposes, such as storing energy or maintaining body temperature. While some paleontologists found Bailey’s notion plausible, the idea of dinosaurs being bison-backed has not gained widespread acceptance.

One reason for this is that Spinosaurus and Ouranosaurus likely lived in lush, swampy environments rather than hot, dry habitats where big sails or humps would have been advantageous. Additionally, the unique shape of their elongated spine rows suggests that they may have had different functions compared to those of bison or other mammals.

The exact purpose of the elongated spines of Spinosaurus and Ouranosaurus remains unknown. While they likely played roles in display and species recognition, reconstructing soft tissues on extinct animals is challenging, especially when there are no solid modern analogues for the structures in question.

In conclusion, Spinosaurus and Ouranosaurus were indeed unique dinosaurs, but whether they were bison-backed remains a subject of debate among paleontologists.

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