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Re: Sloping terrain Re: Woman against Abelisaur
On Jul 25, 2011, at 12:20 PM, Don Ohmes wrote:
> The intuitive 21st century perceptions just do not work when examined
That depends on which set of perceptions we're looking at. If by "21st century
perceptions" you mean the blanket concept that sauropods were always at a
disadvantage on compliant terrain compared to theropods, then yes - that 21st
century perception is overly simplistic. There are conditions in which we can
at least show, theoretically, that sauropods should have moved with greater
efficiency than theropods on compliant terrain (specifically, terrain with an
extremely soft layer over a harder one). However, to suggest that as a result
sauropods must have frequented such terrain is another supposition altogether.
The specific substrate circumstance that provides the tradeoff you're
suggesting would still be a difficult surface for a sauropod to move in (just
not as difficult as shorter animals). Those substrates conditions are also
likely to be localized, and provide insufficient food resources.
More to the point, we don't see any specific adaptations in sauropods to moving
on compliant terrain - by simple virtue of being large, they could wade through
semi-fluid substrates more easily than small animals, but that's really a
simple matter of height and mass. If sauropods were habitual swamp dwellers, I
would expect them to have feet adapted to such conditions (which they don't)
and the ability to maneuver in cluttered environments (which seems unlikely).
Furthermore, we should find sauropods regularly preserved in swamp-like
conditions *without* evidence for miring. To take your earlier analogy: yes,
penguins drown - but they also get eaten by sharks, starve to death, and die of
disease. Because penguins are primarily marine, they tend to show up in marine
deposits regardless of cause of death. If sauropods were habitual swamp
specialists, then we should find their remains in those conditions on a regular
basis, in a non-mired stance. If they keep showing up mired to death, then
that seems inconsistent with swamp specialization.
Of course, the caveat to all this is that I know from the previous
conversations that Don is looking for a predator escape strategy, which is
reasonable if one expects giant theropods to have been munching on big
sauropods. Personally, I think the baby-killer hypothesis for most big
theropods is more plausible, so I don't really worry too much about finding
some way to save the big herbivores as adults.