But as Witton noted in an email, a lot of uncertainty remains, particularly around the missing elements of the skeleton and the possible chimeric nature of the reconstruction. “Many of the more famous components of the 2014 Spinosaurus paper have to be regarded as problematic,” he said. “As demonstrated by subsequent papers, there are multiple ways to interpret fossils of this animal. Some of these seem to explain current Spinosaurus data better than the hypothesis put forward by Ibrahim et al, and they do undermine the radical reinterpretation publicized in 2014.” Only the recovery of more fossil material, collected under well-documented conditions, will resolve the problem, he said.
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All of this is business as usual in paleontology—claims are made and disputed all of the time, as various scientists attempt to interpret scanty evidence. What made the 2014 Spinosaurus reboot different was the sheer scale of the PR effort surrounding the paper: a 5,000 square foot exhibit, a science paper, a television special, and a cover story in National Geographic.
However, there’s a problem with this kind of overwhelming PR—it often implicitly represents a hypothesis as established certainty when there’s still intense debate. “The artwork, exhibitions, and models we've seen of this animal are really impressive,” Witton said, “so much so that many lay folk will take this interpretation of Spinosaurus as definitive. ... The reality is that scientists have already highlighted issues at the heart of the 2014 reconstruction, but the media campaign continues with the same confidence we saw in 2014.” Looking at the National Geographic presentation, a non-specialist might easily conclude that the appearance of Spinosaurus as a knuckle-walking swimmer has been decided for good.
These issues are complicated and unlikely to be resolved any time soon. Yet the new Spinosaurus material does offer some intriguing ideas about the appearance and lifestyle of the great sailed predator. To begin with, it seems clear that Spinosaurus and Sigilmassosaurus, if they are indeed different animals, shared a short-legged body plan unique among predatory dinosaurs. These short hind limbs don’t necessarily preclude bipedal motion—a great deal will depend on the posture of the neck and arms, if that information ever comes to light. Animals that appear to be confined to all fours, like pangolins, sometimes are adept at moving on their hindlimbs.
Paradoxically, after all the fuss over the hind legs, spinosaurs may have been terrible swimmers. In recent analysis of his team’s findings, Sereno came to the conclusion that the animal’s center of gravity would have left it struggling to keep its head above water when floating. “It sucks!” Sereno said, laughing. “I get the sense that it’s in the subaquatic zone, not really adapted for deep water … the thing is very unstable.” Perhaps, Sereno said, Spinosaurus represents an unsuccessful experiment by dinosaurs attempting to move into aquatic niches.