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Re: Sauropod Necks

Stanley Friesen said:

Elephants have been seen rearing up to get at foliage.  This sort of
behavior is not that energy intensive with an animal like _Diplodocus_ with
a properly placed center of mass.

Elephants do, on occasion, rear up to reach foliage. For reasons I have previously outlined, we don't know for sure that Diplodocus and other sauropods could rear up on their hindlimbs. How do you know that tripodal rearing in a sauropod is "not that energy intensive"?

I have heard this before [grazing sauropods with horizontal necks], and continue to find it unconvincing. What other
group of land animals has developed an analogous feeding mechanism? I can
think of none. To my mind this makes its value doubtful, as I would think
it would have evolved more than once if it were truly useful.

All well-known animals with long necks use them for one purpose - access to
elevated food sources.

Careful, careful, careful. I can think of no other group of graviportal (elephants, etc.) animals that: 1) achieved the sizes of many sauropods; 2) had a U-shaped manus in which all the metacarpals formed a vertical, doric column-like structure; 3) are graviportal and yet have large claws on the hand and foot; 4) have no olecranon process (regained in titanosaurs, but different); 5) have extremely hollow and pneumatic vertebrae; 6) have tiny heads; 7) have a semi-plantigrade hindfoot; etc.

There really are no good extant analogs for sauropods. This is the danger implicit in any kind of analogy with an elephant, giraffe, etc. Plus, the animals with long necks you site are mammals. There is an oftentimes an unconscious bias toward using mammals as a yardstick for evaluating locomotion, behavior, physiology, etc., in dinosaurs, and this has lead, in my opinion, to overlooking interesting aspects of all dinosaurs. Why do sauropods have this really weird hand that no other graviportal mammals, let alone other dinosaurs, have? (I gave a talk on this at SVP last year and am trying to get a paper out on it ASAP) Does the absence of an ossified patella and other sesamoids mean that dinosaurs were inferior to mammals in their locomotor abilites, or were they just different?

For the long necks: if sauropods are descendants of animals like prosauropods (a very sticky systematics issue still!), perhaps becoming bigger gives you a longer neck that later becomes exapted for more efficient feeding, but perhaps these weird dinosaurs didn't evolve a long neck initially for feeding purposes. Evolution often works by producing structures that are later adapted to new functions -- there is often the temptation to assume that the evolution of various structures is guided purely by "need."

Again, who says that mammals have to be a yardstick by which we judge dinosaurs? Mammals are derived in many strange ways themselves. Suggesting that because mammals with long necks (giraffes) use them for high browsing and therefore possession of a long neck in sauropods implies the same feeding strategy is the mammalian bias writ large. We're dealing with archosaurs that lived in an ecosystem without flowering plants, where gymnosperms were dominant, and where numerous other, different evolutionary factors were at work. We must always keep this in mind and be judicious about how we choose analogies (if we do at all), and what parts of those analogies we choose.

Finally, grazing with a long neck in sauropods may not have evolved outside of dinosaurs, or within other groups of dinosaurs, due to the historical and evolutionary constraints of anatomy. All mammals have only 7 cervical vertebrae, and while the range of neck length and motion in mammals is amazing, it pales in comparison to what is available in dinosaurs, and by extension, birds. Perhaps this evolutionary program of 7 neck verts in mammals has prevented long-necked forms from evolving. Or, perhaps something about the Mesozoic ecosystem combined with dinosaur ancestry had something to do with the success of sauropods. Or, because mammals have to chew their food and have larger skulls and teeth, sticking a heavy head on the end of long neck is not feasible. The big heads and grinding teeth of many ornithischians may have also been a factor working against them evolving long necks for grazing. Perhaps accidental consequences of size, ancestry, ecology, physiology, etc., all came together to select for animals such as sauropods. Analogies are limiting.

Matt Bonnan
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