Sauropod Neck Posture, Energy Costs

[Mark Hallett <marksabercat@yahoo.com>]

Thanks David for following up on my accidentally truncated messages. As I 
originally said in the longer of the two I first sent to Guy and Kent, I agree 
that the seeming existence of an avian-like respiratory system has strong 
implications for a similarly avian-like circulatory system that might permit at 
least a temporarily vertical or subvertical neck posture for most sauropods. As 
we know, "absence of evidence is not not evidence of absence", and in 
considering this issue I'm always reminded of the incredible, and often 
unlikely, adaptations that life forms have evolved to get around a specific 
problem; as such auxilliary "hearts" and other circulatory specializations, 
whether they existed or not, are therefore not inconceivable in this light. On 
a broader level, to me it doesn't make sense to me that sauropods would evolve 
such a large, complex structure (the neck) to access a ground level food source 
that could be reached, at relatively little
 energy cost, by simply walking up to it. If an extremely long neck "vacuum 
cleaner" adaptation was a successful solution to this problem, I think we 
should expect to have seen it in at least a few mammalian forms which 
specialized in utilizing a superabundant, low nutritional plant material. IMHO, 
it seems more likely that arboreal browsing was a basal condition among early 
sauropods arising from prosauropod-like ancestors, persisting as a main feeding 
strategy (quadrupedally, or in the case of diplodocids, bipedally/tripodally) 
in most lineages but giving way in specialized, short necked forms like 
Nigersaurus to crop ground vegetation. A thought to keep in mind is that the 
ability to switch from one trophic feeding level to another as seasonal or 
geographic food abundance dictated may have meant that most sauropods could 
adapt to a variety of conditions, probably the key to their persistence 
throughout most of the Mesozoic. --Mark Hallett