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Dear Ken,

Stephan has told me that he'll shortly be re-posting some comments I made 
earlier last month, in answer to Rothschild's claims at the last SVP that most, 
if not all, sauropods reared only infrequently, and probably not at all to 
feed. G. Paul's statements in his recent post in response to your comments are 
on this subject, and here are some other points to consider.

In terms of energy expenditure, moving towards a standing food source 
consumes only a trivial percentage of an animal's total energy budget (this is 
proportionately even less for large animals, which although their absolute 
expenditure is greater than that of small ones when they do this, use fewer 
calories relative to their size), the only situations in which an animal must 
evolve long reach are those in order to obtain access to foods it otherwise 
cannot get to. Long-legged, herbivorous forms that graze or browse from the 
or lower levels (elephants, ungulates, and flamingos, for example) have 
developed trunks or moderate to hyper-long necks to compensate for the length 
their height and/or legs to get their food-gathering apparatus down to what 
are eating. Some short-legged birds like swans have hyper-long necks, but this 
is primarily an underwater adaptation to feeding on submerged vegetation 
growing on lake and river bottoms while the body remains at the surface of the 
water. Geese, with their habit of horizontally grazing their way across an open 
space, are the closest living analogues that would fit in with Martin et al's 
"vacuum-cleaner" hypothesis for sauropods, but geese have much more flexible 
necks than sauropods did, and their small size and rapid cropping capability 
them into a very different econiche than sauropods.

The concept of diplodocids and some other taxa as primarily 
riparian/lacustrine margin feeders also has problems. In the best known 
ecosystems like the Morrison, there simply aren't very many extensive 
lake systems where you could have the resource portioning among diplodocoids 
that Holland, Haas and others have postulated. The one or two large ones that 
are thought to have existed probably were seasonally variable in their extent, 
and may well have been alkaline-not likely to support the range of aquatic 
plants that would ultimately lead to the evolution of long necks and 
resource portioning for this kind of feeding adaptation. The Morrison's system 
of shallow, braided streams and shallow, moderately-sized rivers are also not 
good prospects for this kind of feeding scenario.

I think that Martin et al are correct in assessing the abilities of the two 
major neck bracing systems of sauropods as effective adaptations to supporting 
the neck horizontally, but I disagree that this would not be effective in 
holding the neck in a subvertical position as well for feeding. In 
sauropod necks as adaptations for vertical/ subvertical feeding, we have to 
answer at least two basic questions: (1) why do two basically separate systems 
neck bracing evolve, more than once, among sauropods? If a largely cervical 
rib, compression-braced system (brachiosaurids, etc.) was adequate for holding 
the neck in a subvertical pose for feeding, why evolve, as diplodocoids did, a 
bifurcate/high neural spine, tensionally-braced system? Conversely, if a 
tensionally-braced system was needed top maintain a "neutral" pose (sensu 
Stevens), why didn't all hyper-long necked forms develop this? As I might have 
mentioned, a multi-segmented, subvertical beam is best supported by two, not 
one tension cable to minimize the tendency of lateral torque; we find this 
both among diplodocoids and typical human engineered construction cranes. (2) 
diplodocoids were not specialists for upright rearing, how do we explain the 
excessively wide, massive pelves (proportionately larger for these forms than 
in brachiosaurids, with smaller pelves), the short forelimbs, the tall neural 
spines (not apparently necessary for long neck support, as evidenced by other 
sauropods), the sled chevrons (similar in function to those of ground sloths, 
which Paul has consistently pointed out), the short trunk, and the 
sub-horizontal position of the foramen magnum, which would place the head at 
the ideal 
angle for backwards pulling of vegetation in a vertical/subvertical neck?

For myself and some other students, the features found in the best-known 
diplodocoid taxa like Diplodocus, Apatosaurus, Dicraeosaurus and others all 
strongly suggest that these forms were primarily adapted as upright feeders of 
coniferous foliage and fruiting bodies, with cherry pickers as the best human 
analogy for the diplodocoids. The evolution of sauropods strongly coincides 
the rise of conifers as the dominant tree forms of the Mesozoic, and a form of 
resource partitioning among mid-late sauropod taxa in this light makes a great 
deal of sense. This doesn't mean I think that they never ate other plants; the 
extreme geological longevity of sauropods in seasonally arid ecosystems like 
the Morrison shows that they were flexible feeders, and in a pinch they 
probably could and did eat plants like ferns and cycads, the latter if they 
stout-toothed macronarians. They were survivors. 

--Mark Hallett