A fondly-held belief about long-necked sauropods, the giant four-footed dinosaurs beloved of monster movies and children, is most probably untrue, a dino expert said on Wednesday.
At the zenith of the dinosaurs' reign, some sauropods evolved necks of extraordinary length -- more than nine metres (29.25 feet) in the case of the Mamenchisaurus, a titan of the Late Jurassic period around 150 million years ago.
Prevailing wisdom has it that these leviathans used their necks like giraffes today. They reached up high into the trees, munching leisurely on forest canopy that was out of reach for rival herbivores.
Not so, says a paper appearing in Biology Letters, a journal published by Britain's prestigious Royal Society.
It argues that giant sauropods most probably preferred to feed horizontally, rather than vertically, on the grounds of energy cost.
Australian evolutionary biologist Roger Seymour did a simulation of how much blood pressure a gigantic sauropod would need in order to place its head vertically.
He then calculated how much energy the creature would require in order to pump around blood at this high pressure.
"It would have required the animal to expend approximately half of its energy intake just to circulate the blood," says Seymour.
"A vertical neck would have required a high systemic arterial blood pressure. It is therefore energetically more feasible to have used a more or less horizontal neck to enable wide browsing while keeping blood pressure low."
There are sauropod experts and I'll defer to them. I'm skeptical: there have been no long necked mammalians that were NOT intended to go into the trees, sooo...
This also sounds rather familiar for some reason. *shrugs*
Didn't we already know this for most of the sauropods, except perhaps those few macronarians who had their necks point upwards (I'm thinking brachiosaurs)?
ReplyDeleteIn Brachiosaurs the shoulders were higher than the hips, so, it'd logical that their necks go upward, wouldn't it?
ReplyDeleteRight now, experts disagree (dissenters include Gregory S. Paul, Scott Hartman and Mike Taylor).
ReplyDeleteAt some point. we may see a response in print.
Stevens & Parrish, as well as Berman & Rothschild, have also suggested a horizontal feeding posture for sauropods, so this just further confirms it. I know that the guys at SV-POW have problems with it, though.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteI finally came across the actual paper here: http://rsbl.royalsocietypublishing.org/content/early/2009/03/31/rsbl.2009.0096.full
ReplyDeleteWell, it's fairly short, I read it, and it doesn't seem like its well done at all. He assumes inexplicably that a semi-divided cold-blooded reptilian heart would somehow be MORE efficient in getting blood up a vertical neck than a fully divided endotherm's heart! (who knew this sort of pseudoscience was even publishable?)
Then he also assumes that even despite having such long necks, sauropods had the exact same circulatory configuration as short-necked animals with no modifications to their necks. We already know that sauropod necks were highly pneumatic and unusual in many other ways compared to things like cows and horses...
So why not have a specially adapted circulatory system too? Even a giraffe has its own specialized vessels and muscles to pump blood to to the brain.
I don't really buy the whole "multiple hearts" theory, but I think it's very likely that sauropods had some sort of adaptation like valves in their arteries to prevent backflow. This would have made it possible to pump blood up a vertical incline without grossly exaggerating the size and energy needs of the heart.
Now it's interesting that Roger Seymour actually attempts to disprove this possibility... but he only cites HIS OWN RESEARCH and that of his partisan colleague Lillywhite in his defense.
Seymour's BIGGEST mistake is in assuming that sauropods needed a LOT of blood pumped to the brain and therefore ridiculously high blood pressure.
Knowing how the natural world works, there is undoubtedly a simple and elegant explanation for all this that likely avoids the whole blood pressure dilemma altogether (and no, it got nothing to do with wacko quack-science catastrophists and their BS claims that the earth was smaller and had less gravity in the Jurassic).
Simply put, sauropods had very small brains that were nevertheless capable of controlling every behavior these creatures needed to master.
Now the question is, WHY evolve such a small brain when your smaller, shorter-necked ancestors had a proportionally larger one?
It's OBVIOUS - the brain evolved to become more compact to REDUCE its energy and blood needs! Most sauropods had a brain the size of a lemon. Something like that doesn't need a lot of blood ANYWAY - it was probably fed by tiny capillaries - only a tiny fraction of the number needed for a human brain. So you wouldn't need a lot of volume in the neck arteries to get blood up to the head. Indeed, the less internal volume they had, the thicker and stronger the arterial walls and muscles could be, so that a change in neck posture would not cause disastrous bursting.
Now let's look at Dr. Seymour himself... He is a PhD zoologist, but it seems his research is ALL OVER THE PLACE.
ReplyDeletehere's the URL:http://www.adelaide.edu.au/directory/roger.seymour
He's actually specialized in Physiology more than Zoology, and his papers range from cabbages to beetles to tuna fish. Overall MOST of his curriculum vitae focuses on fish and insects, a little background on birds - but from reading his articles it seems he has little interest in the unique metabolic and physical adaptation of dinosaurs and is not a paleontologist - and he tackles the neck issue with some very primitive and oversimplified physics such as a plumbing engineer would use in an aqueduct.
BTW I'm not in any way attacking Seymour personally, I'm just doubting his research and methods. It's basically a rehash of all the "dinosaurs couldn't lift this or move that" stuff that was taught in the 1950s. Back then they also used some very speculative physics and catastrophic assumptions to claim that this that and the other were "impossible" for dinosaurs living on land.
I contend that there is no point in evolving a long neck if you are not going to use it vertically at least SOME of the time (otherwise they could simply walk forward to the food not that hard, is it?) - and there's also not much point in evolving such a highly specialized, pneumatic neck that's clearly designed for lightness and vertical carriage WITHOUT ALSO evolving the circulatory adaptations above and beyond those of ordinary short-necked creatures such as most modern zoologists have at their disposal.
Next time somebody attempts this sort of thing, they should make CLEAR what parts of their research are speculative (i.e. the hypothetical volume of blood, the hypothetical width and thickness of the arteries, the mathematical implications of capillary action through small vessels, etc... and NOT just present a short, overly simplistic paper with a bunch of sensational, catastrophic blood pressure estimates as fact).
so, why is'nt a giraffe a sauropod? Warm blood?
ReplyDelete