I tried to emphasise in the last post that there is still more to come here. I’m sure other people are writing more about Spinosaurus and its behaviour, ecology and functional biology right now and there will inevitably be further discoveries and data coming out in future. While I am confident in the wading / heron-like idea, further work could easily provide major modifications to that or overturn it. Such is the way of science: things are not settled. Below, I thought I would put together a few ideas of hypotheses or aspects of the model that could be tested or assessed further to show how much more there is to come and move away from the ‘this is settled’ idea that I’m sure at least a few people will have articulated. Some of these are much easier than others to tackle (measuring toes is way easier than working out drag) but all are, I think, something we as a scientific community can tackle in the coming years based on the techniques we have and the available fossils.
What does naris and orbit position look like in an even wider range of reptiles and in birds?
What is the overall density and distribution of mass? In particular, how buoyant would it be?
What was the exact arrangement of the neck muscles?
How flexible is the neck?
How stiff is the dorsal series?
What is the exact arrangement of the dorsal sail?
How much drag would the sail / legs produce when swimming?
How much wave drag would there be at different depths?
How spread were the toes? Is this more than other theropods?
What swimming form would it use? (Whole body or just the tail)?
Would leg thrusts help in propulsion or add more drag than thrust?
How flexible is the tail?
How strong are the caudal neural spines?
How much muscle did it have in the tail and where?
Would increased flexibility help it provide propulsion?
Would a leg and tail driven thrust in water be effective, even for a single thrust?
How efficient would it be walking?
What would the efficiency calculations for the tail look like with a more accurate model with variable flexibility and different degrees of submergence?
Are there more general common features of various aquatic and semi-aquatic reptile lineages and can we quantify things like leg reduction, tail musculature, drag reduction etc. to look at this as more of a continuum than a binary state?
Is ungual curvature driven in part by size / evolutionary relationships / habitats?
What are the isotopic signatures like for teeth that are in situ in jaws?
How many different habitats and environments did Spinosaurus occupy? And what were these like?
I think that all shows that we can push this forwards considerably. The new paper covers all kinds of different bits of anatomy, ecology, mechanics and possible behaviours and some considerations of the environments too, but this is still all just starting points. This of course is all based on existing fossils and any future discoveries (an arm would be nice, or a complete skull for that matter) is only going to provide most data (or fuel to the fire, take your pick). Still, this hopefully provides a few ideas for people to be getting on with.
If you want even more discussion on Spinosaurus (and why wouldn’t you) then the first episode of the new series of my Terrible Lizards podcast is now up and it’s a whole hour of wading hell-herons (copyright Andrea Cau).
Dave Hone's Archosaur Musings 
How about comparing the shape and thicknes of ribs to other aquatic animals?
And to throw additional issues in here, requiring larger sample sizes:
* What changes, if any, are there during ontogeny to the anatomy?
* What differences, if any, are there between sexes? (Particularly relevant if the sail and tail-sail have a stronger socio-sexual component than otherwise)
* WHAT THE HECK ARE THE PROPORTIONS OF ANY SINGLE INDIVIDUAL OF THE SPECIES?!?!?!?! (Seriously, we still don’t have a single good snout-to-tail, with limbs, specimen. Everyone’s reconstruction is a chimera of multiple individuals of different sizes.)
Pers obs – if you are swimming with the fishes, they are (very) hard to catch. If you are wading, it is doable. They can be pinned to the bottom, splashed onto shore and / or knocked unconscious en masse and then scooped up like loaves of scaly bread. When large animals wade in still water (read deltaic environment), silt-stunned fishes float belly-up. Flattened tail, webbed feet, and dorsal sail can serve to enhance creation of turbidity. Terrestrial nesting requires maintenance of terrestrial locomotive competence, albeit minimal….
You can count me in as a wader.
Pers obs – if you are swimming with the fishes, they are (very) hard to catch. If you are wading, it is doable. They can be pinned to the bottom, splashed onto shore and / or knocked unconscious en masse and then scooped up like loaves of scaly bread. When large animals wade in still water (read deltaic environment), silt-stunned fishes float belly-up. Flattened tail, webbed feet, and dorsal sail can serve to enhance creation of turbidity. Terrestrial nesting requires maintenance of terrestrial locomotive competence, albeit minimal….
You can count me in as a wader.
This pretty much sums up my problem with the underwater pursuit predator hypothesis: its advocates seem to have rushed into print without doing any real analysis, beyond making superficial comparisons, particularly concerning that tail.
Berislav mentioned comparison of the ribs; how certain are we of the proportions of the ribcage anyway? Skeletals always make it look so oddly thin. Maybe that’s just a result of compositing so many specimens together.