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Re: What did Spinosaurus eat? New species of Lepidotes found

On 2/21/2011 1:18 AM, Tim Williams wrote:

Nevertheless, IMHO it is curious that it was not until the evolution
of Avialae that dinosaurs became specialized for fully aquatic habits.
  Some (like the spinosaurids) flirted; but none 'took the plunge'.

I think there is a size constraint here -- taking as working assumptions that the ability to nest competently on dry land was critical to individual dinosaurs, and also that the occasional forced overland trek is a part of most semi-aquatic lifestyles -- the larger dinosaurs were logically limited to a foot design that functioned well on land, whatever their daily habits.

Is it even theoretically possible to construct a foot/leg system that continues to work well on dry land for a massive and fully-erect animal, yet contains "aquatic improvements" that would be obvious to someone looking at the bones?

Heh -- as to spinosaurs -- given the potential of a spinosaurid body to clog a shallow water column w/ silt, and their general tactical capacity to adopt heron-like or bear-in-a-salmon stream tactics, I doubt they had to swim well to catch lepidotes or nile perch anyway.