Dinosaur Stance Changes

coming out of the swamp

(part of the Zallinger Mural - Yale/Peadody Museum)

Fixing Iguanadon's Broken Tail

Our picture of the dinosaur has changed dramatically. At times nearly impossible to recognize the "finished product" of 200 years of scientific thought. Iguanadon, one of the first dinosaurs to be discovered, was first portrayed as a sprawled out lizard based on current scientific beliefs (see Early Dinosaurs). Later skeletons that were discovered were all mounted in a kangaroo-like posture (bipedal), with their tails as support. Today we know that all of these previous constructions of Iguanadon are wrong. In order for Iguanadon to assume a bipedal pose using it's tail for support, it would have had to have broken several vertabrae in the lower part of it's tail. We view Iguanadon as a primarily quadrapedal animal, walking on all four of its legs. (See video of Iguandon walking)

1800....................................1820....................................1860.......................................1960

A Duck out of Water

Duckbilled dinosaurs were given this name because of their distinctive, broad, toothless beak. They have long been associated with the swamp and are often posed much like Iguanadon: bipedal, feeding in the shallow water. Bakker and other Renaissance paleontologists are pulling this stereotype apart piece by piece and taking the duckbill out of the water.

Early supporters of the duckbill-swamp theory felt that they had a lot of evidence to support thier ideas. Duckbilled dinosaurs had no front teeth, and so they must have been able to eat only water plants, cropping them gently. They saw the strange hollow crests on the duckbills as snorkels or air storage chambers for when the animals foraged under water. Early paleontologists believed their most conclusive evidence to come in the shape of a mummified duckbill that had been found. The front paws of the duckbill seemed to have been webbed, an obvious adaptation for swimming. Bakker tears each of these arguments apart and offers sound evidence that the duckbill's true home was the woodlands, not the swampy shore.

Bakker begins by offering new evidence against the theory. He points to the fossilized bony tendons which run along the greater part of the duckbill's lower back. (See red box in picture below) These tendons, says Bakker, would have given the animal a very limited range of movement in its tail, so it could not have been used to push against the water. Instead it would have created enormous amounts of drag when animal tried to swim.(Bakker 152-154)

quadrapedal duckbill........................duckbill skeleton with bony back corset - in red box

enlarged view of duckbill tail - from blue box above

Bakker next tackles the controversy of the duckbill's paw. The paw, says Bakker, was not webbed at all. Instead fleshy, with a pad for walking underneath. Bakker claims that, compared to all web footed animals today, duckbill's toes and fingers were too short to have efficient webbing stretched in between them.(Bakker 146-150, 157-159)

Bakker and other current paleontologist believe that the duckbill's hollow crests were used for sexual display and not as air storage chambers. Recent CT scans and reconstruction of one duckbill skull showed that the crest could have been used as a resonating chamber for calling to other dinosaurs. Computer simulations have even recreated this noise. (See Dinosaur Communication)(Bakker 344)

Out of the Swamps and into the Tree Tops

Apatosaurus has long been portrayed as a swamp-bound heavyweight. However, its similarities to birds are amazing. Marsh showed that it would be impossible for Apatosaurus to have been sprawled by the riverside like a crocodile (see All American Dinosaur). Bakker agrees and says he sees more mammalian characteristics than simply leg posture. A hollow area under the foot allows the large sauropod (class of similar dinosaurs) to comfortably support it's weight much like an elephant. This would have allowed the animal to forage on land without having to worry about it's weight getting stuck in the mud. (Video of Apatosaurus and Elephant walking)

While early scientists argued that it was necessary for sauropods to stay near soft food sources (swamps) because of their few week teeth, Bakker disagrees. He believes that he has found evidence of gizzards and gizzard stones in these dinosaurs. Bakker believes that these dinosaurs foraged in the trees by taking a tripod stance (See illustration below). They would have cropped pine needles with their small front teeth and then swallowed them without chewing. The food would instead be crushed in the gizzard by rocks, much like a modern day bird.(Bakker 125-139)

The apatosaur skeleton seems perfectly suited for this kind of feeding. The spines on the lower vertabrae over the back are taller and form a sort of arch. This arch better supports the weight of the dinosaur when it is in its tripod stance. The back of Apatosaurus was built like a high tension bridge to support its tree top feeding, while the back of other dinosaurs, like the Brachiosaurus pictured below, had smaller spines. (Bakker 190-193)

People are still trying to figure out exactly how sauropods supported their weight, especially their necks. Recently, several groups of engineers completed work on a project called DinoMorph. They scanned in sauropod skeletons and then generated the full skeleton of the original dinosaur on computers. They then ran the program through some modern flexibility equations to determine how well these large animals could move. The result of their experiments were fascinating to paleontologists around the globe. From a standing position, Apatosaurus would have been unable to raise it's head more than a few degrees. (view video of neck movement ) The full results of their findings can be viewed at National Geographic's website. To find out more about how exactly how their project worked visit the engineers at DinoMorph.

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