Spinosaurus the paradigm buster

Figure 1. Spinosaurus from Ibrahim 2014. Yes, the proportions are correct. It's a non bipedal swimming theropod.

Figure 1. Spinosaurus from Ibrahim 2014. Yes, the proportions are correct. It’s a non bipedal swimming theropod. The red bones are known. The gray ones are hypothetical.

Generally I avoid all but the most basal dinosaurs.
However, just a few posts ago we looked at Spinosaurus and Arizonasaurus, two archosauriformes with a similar dorsal sail.  Well, it seems the proportions of Spinosaurus were a little off in the hind leg department. And that makes the new data fascinating.

And POP there goes a paradigm
The Spinosaurus tale has been told by Nat Geo, Science, Nature, and other places. I found the reaction to this heretical pile of facts just as fascinating. There was shock. And there were skeptics! (something I’ve grown accustomed to from the first vampire pterosaur abstract onward).

Skeptics are good. But facts are facts.

From the Abstract
We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position near the mid-region of the skull and an elongate neck and trunk that shift the center of body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle is downsized, the hind limbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy control in water. The short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic foot-propelled locomotion. Surface striations and bone microstructure suggest that the dorsal “sail” may have been enveloped in skin that functioned primarily for display on land and in water.

From the Dinosaur Mailing List
There’s something fishy about the new Spinosaurus
the pelvis and hind limbs are too small.”

Note sure if these questions have been answered
1. Did Spinosaurus knuckle-walk to protect its fore claws? After all, it had to come out of the water, at least to lay its eggs. Perhaps it ventured out only to mud and sand bars as crocs do.
2. Other than display, was the sail used for thermoregulation? Keeping it dry in a hot sun would have allowed it to soak in heat. Wetting it would have cooled the sail by evaporative heat loss.
3. Was the sail used in transportation? If there was a current in the water, the orientation of the sail to the current could have been aligned for minimum impact or at right angles for maximum impact.

When we have missing parts, it is usually okay to fill them in with parts gleaned from sister taxa — until the actual parts become found. Then we have to give up our cherished paradigms and let the facts speak for themselves.

References
Ibrahim N, Sereno PC, Dal Sasso C, Maganuco S, Fabbri M, Martill DM, Zouhri S, Myhrvold N, Iurino DA 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science. doi:10.1126/science.1258750.

History of Spinosaurus with old reconstruction of long hind limbs

Paul Sereno on YouTube

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