Reading this I am more and moreconvinced that this class of reptiles was wonderfully adapted to living in weedchoked tropical lakes. They had thecapacity to go on land, but mostly stayed semi submerged in lakes full of waterplants which they could easily vacuum up and digest. When small they likely stayed away fromwater, but as they became larger, they would naturally return to it as theirsize made attacks rather unlikely. Theirhollowed bones would provide excellent buoyancy to handle the immense amount offodder they ate.
On land, they would have to eatfar less digestible plant material, without any of the necessary adaptationssported by elephants and mastodons to handle woody material. In lakes, the sheer mass of water weed wouldeasily support such a creature.
Once again, I find that both the Sauropodsand the Theropods were aquatic adapted dinosaurs that competed with crocodiles and tookadvantage of their buoyancy and of water’s ability to maintain a stabletemperature.
There were plenty of dinosaursadapted to land based livelihoods. Yet the sauropod appears to be perfect for vacuuming up water weeds and at times also browsing on land plants.
Giants Who Scarfed Down Fast-Food Feasts
CENTERPIECE A life-size model of a 60-foot female Mamenchisaurus,whose fossilized bones were discovered in China ,was close to ready at the American Museum of Natural History in New York
Published: April 11, 2011
Nothing in the dinosaur world was quite like the sauropods. They werehuge, some unbelievably gigantic, the biggest animals ever to lumber across theland, consuming everything in sight. Their necks were much longer than agiraffe’s, their tails just about as long and their bodies like an elephant’s,only much more so.
Wide-eyed first graders are not the only ones fascinated by sauropods,particularly those outsize friends Apatosaurus (formerly known asBrontosaurus), Brachiosaurus and Diplodocus. Scientists are redoubling theirstudy of the unusual biology of these amazing plant-eaters. They are askingquestions not unlike, in spirit, those of schoolchildren.
By what physiological strategy of heart, lungs and metabolism were thelargest of sauropod species able to thrive over a span of 140 million years?How did they possibly get enough to eat to grow so hefty, to lengths of 15 to150 feet and estimated weights of up to 70 tons? A mere elephant has to eat 18hours a day to get its fill. Even in the Mesozoic era, there were only 24 hoursin a day.
For more than seven years, a group of German and Swiss scientists hasmade a concerted effort to test the limits of body size in terrestrialvertebrates and, in the process, try to answer these and other questionsrelated to the enigma of sauropod gigantism.Findings by many other scientists have been reviewed and analyzed, then testedwith new experiments and more observations.
“We actually have been re-engineering a sauropod,” said P. MartinSander, a paleontologist at the University of Bonn
One clear explanation has emerged: These were the ultimate fast-foodgourmands. Reaching all around with their long necks, these giants gulpeddown enormous meals. With no molars in their relatively small heads, they wereunequipped for serious chewing. They let the digestive juices of theircapacious bodies break down their heaping intake while they just kept packingaway more chow.
This was seemingly the only efficient way for sauropods to satisfytheir appetites and to diversify into some 120 genera, beginning more than 200million years ago. They eventually dominated the landscape for a long runthrough the Cretaceous, only to die out with all nonavian dinosaurs 65 millionyears ago.
The German-Swiss team of paleontologists, biologists and otherscientists, financed by the German Research Foundation, has now weighed in withits comprehensive report “Biology of the Sauropod Dinosaurs,” a bookpublished last month by Indiana University Press.Dr. Sander is one of the book’s editors and also guest curator of a major exhibition,“TheWorld’s Largest Dinosaurs,” opening Saturday at the American Museumof Natural History in Manhattan and scheduled to run until Jan. 2,2012.
A centerpiece of the show will be a life-size model of a 60-foot femaleMamenchisaurus, whose fossilized bones were discovered in China
Early in their investigations, material scientists in the German-Swissgroup proposed that sauropod bone had superior mechanical properties comparedwith large mammal bone, which would have given these dinosaurs strongerskeletons to support heftier bodies. The hypothesis was tossed aside aftertests showed that sauropod and cow bone tissue had the same strength.
Then the investigators found no evidence that availability of foodand the physical and chemical conditions in the Mesozoic era were sufficientlydifferent to have accounted for sauropod gigantism. If anything, theenvironment then was probably less favorable for plant and animal life thanit is today. So the researchers directed their efforts to a detailedexamination of the biological makeup of these giants.
Dr. Sander noted in the book that the new study was one of the fewdinosaur projects in which paleontologists were outnumbered bynonpaleontologists, mainly biologists. Mark A. Norell, a dinosaurpaleontologist at the American Museum and principal curator of the exhibition,remarked, “This shows how biological our field has become.”
In a recent interview televised from his office in Bonn
The animals had the longest necks for their body size of any dinosaurknown. Dr. Sander and his colleagues think that two of the sauropod’s primitiveinheritances probably account for this. One was the absence of mastication, andthe other its egg-laying reproduction.
By not chewing their food, the animals had no need for a full set oflarge teeth or strong jaws and associated muscles. They had only incisors upfront for cropping and cutting vegetation. As a result, their heads remainedsmall and lightweight. A plant-chewing African elephant, for example, has a1,000-pound head; a Mamenchisaurus head weighed 45 pounds.
A small head, of course, took a load off the sauropod neck, presumablyallowing it to grow longer. Even so, the neck had to be bolstered with morevertebrae than mammals have. These bones are light for their large size,because they are hollowed out with many air pockets. Mammals, even the giraffewith a six-foot neck, are limited to no more than seven neck vertebrae; theMamenchisaurus neck had 19.
The sauropod’s neck became what the hook-and-ladder is to afirefighter: a means of extended reach that could be critical. It gave theseanimals an ability to graze a much wider radius of ground vegetation withoutmoving a step. Dr. Norell said that biomechanical studies indicated that thelong necks may not have been able to stretch higher to browse in trees, asgiraffes do.
In any event, sauropods could outcompete other plant eaters and overtime, as one scientist wrote, “enter the niche of giants.” And their consequentgigantism was perhaps their best defense against predators, intimidating eventhe neighborhood T. rex.
Sauropods took a long while evolving their body plan, which, insilhouette, became the ubiquitous logo of Sinclair oil back in the mid-20thcentury. But the retention of another of its primitive features, egg-laying,increases the number of offspring and thus improves the chances of long-termsurvival of a family of species — and time enough to innovate.
In a 2008 summary in the journal Science of the project’s preliminaryfindings, Dr. Sander and Marcus Clauss, a dinosaur specialist at the University of Zurich
One conclusion is that their very young grew rapidly: A human babydoubles in weight in about five months, a sauropod in only five days; and anadolescent sauropod put on 3,500 pounds a year. These are growth rates higherthan in today’s reptiles. They enabled these dinosaurs to reach sexual maturityin their second decade of life and full size in their third.
Stopping at an exhibit being readied for the new museum show, Dr.Norell pointed to an illustration of how heart rates are related to anorganism’s size. The heart of a mouse beats 700 times a minute; a human, 72; anelephant, 28; a sauropod, less than 10.
Dr. Sander cited the bird-lung model as an important innovation. Ifcorrect, he said in the interview, this and other evidence suggests thatsauropods were warm-blooded to some extent. “If an elephant had birdlike lungs,it would grow even bigger,” he speculated.
The fact that dinosaurs’ distant relative the crocodile has arespiratory system somewhat like a bird’s suggested to scientists that it mightalso have been true of sauropods. All the air-sac cavities in their long neckand torso resemble those in birds. Also, it might explain how animals with suchlong windpipes managed to draw in and absorb sufficient oxygen.
In time, however, sauropods seemed to feast on their enormous size.Writing in the project’s book, Dr. Clauss said that these giants “mightrepresent a rare example of herbivores that actually benefit from an increasein body size, in terms of a larger gut and a longer retention of food in thatgut.”
The bigger they got, in other words, the greater their capacity tostore vast food intake in digestive chambers. Galapagos tortoises, which eatand don’t chew, have stomach chambers that hold food for up to 11 days, givingmicrobes time to break it down and extract the nourishment.
Dr. Clauss of Zurich and Jürgen Hummel of the University of Bonnconducted fermentation experiments mixing micro-organisms with contents ofsheep stomachs and various plants, including horsetail plants, cycads, pineneedles and ginkgo leaves known to have been growing when sauropods foraged.From this and other evidence, they estimate that the giants probably took twoweeks to digest an all-day dinner.
Other scientists, who are not involved in the study, said theexperiments and analysis by the German-Swiss group provide an impressive bodyof knowledge about how some dinosaurs grew so big and why sauropods, inevolutionary terms, were so successful over a span of 140 million years and aglobal range.
“I’m not sure they’ve hit the nail on the head, always,” Peter Dodson,a University ofPennsylvania paleontologist, said of Dr. Sander’s team. “But they havecertainly a number of important insights.”
Dr. Dodson agreed with the researchers on the long neck’s criticalplace in sauropod biology and the growth rates of sauropod bones that appear toshow the animals had metabolic rates closer to those of mammals than those ofreptiles. But this does not necessarily mean, he said, that sauropods werefully warm-blooded.
In the team’s book, Dr. Clauss conceded that there was debate on themetabolic rates and a lack of consensus on the nature of the sauropodcardiovascular system. He noted that among many scientists a direct linkbetween the sauropod respiratory system and gigantism “is not yet compelling.”
The research, Dr. Dodson added, raises the related question of whymammals have never approached in size the larger sauropods. Some extinct Asianrhinoceros species that reached weights of 15 tons were the closest mammalscame. “They were to mammals what sauropods were to dinosaurs,” he said. “But itwas not a successful body plan in their time, an idea that went nowhere.”
Paul Sereno, a dinosaur fossil hunter at the University of Chicago,said the new research “is very valuable,” but he doubted there was enough hardevidence to support the bird-lung hypothesis. Still, he said, the sauropod “isan incredible animal, one of the best land animals that’s been invented.”
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