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Giant Cretaceous Crocs Grew More Slowly Than Their Dinosaur Cousins



>From Business Wire--look for Chris Brochu's name as one of the 
authors of this Nature paper.
________

"Giant Cretaceous Crocs Grew More Slowly Than Their Dinosaur Cousins"

     STANFORD, Calif.--(BUSINESS WIRE)--March 17, 1999--Imagine a 
crocodile that is more than 30 feet long and weighs about 10,000 pounds.

     Such a creature actually existed 80 million years ago, when dinosaurs 
still ruled the Earth. Paleontologists Gregory Erickson, a postdoctoral 
fellow in mechanical engineering at Stanford University, and Christopher
 A. Brochu at the Field Museum of Natural History in Chicago, have figured
 out how they grew so large.

     The giant crocs, dubbed Deinosuchus, or terror crocodile, needed 
their large stature to compete with the dinosaurs that also tended to be
 extremely large by today's standards. The prehistoric crocs achieved 
their large size by growing at about the same annual rate as modern 
crocodilians but continuing to grow for decades longer, the researchers
 report in the March 18 issue of the journal Nature.

     The researchers studied the annual growth layers in the fossilized 
bony armor plates called scutes from two terror crocs that were 
unearthed in Texas and Montana. By comparing them with the scutes 
of existing crocodilians, the researchers have found that the Deinosuchus
 grew a foot a year, about the same as modern crocodiles, but they 
continued to grow for a much longer period, taking about 35 to 40 years 
to reach adult size. By comparison, today's crocodiles seldom live 
beyond the age of 30 in the wild.

     "This is a much different growth pattern from that found in dinosaurs," 
says Erickson. "For example, duckbilled dinosaurs that were about the 
same size as Deinosuchus grew to adult size in only seven to eight years.
It illustrates ne of the key differences between dinosaurs and other
reptiles."

     Scutes are bony plates within the skin of crocodiles that serve as 
body armor located on their back and sides. The plates contain a series 
of layers that are laid down annually. The thickness of a given layer is 
proportional to how much the animal grew that year. The scientists 
counted these layers to determine the age of the terror crocs that they 
examined. Then, by taking the relative thickness of the annual layers
 into account, the researchers reconstructed how much each of the 
crocs grew each year.

     They also examined jaws, ribs, vertebrae and other long bones 
on the Deinosuchus skeletons. They found that the giant crocs of 
yesteryear had the same type of slow-growing bones, called lamellar-
zonal bones, as do today's crocodilians: a finding consistent with the 
slow growth indicated by their analysis of the scutes.

     This slow but steady growth pattern is characteristic of cold-blooded
 creatures like reptiles. At one time, scientists thought dinosaurs grew 
in a similar fashion and reached such large sizes because they continued 
growing for a long time, like the terror croc. In the last 20 years, however,
 they have found considerable evidence that dinosaurs grew much more 
quickly, at rates comparable to those of large mammals today. This has 
led some paleontologists to argue that dinosaurs must have had a high 
metabolic rate, one comparable to warm-blooded animals. But exactly 
how dinosaurs managed to grow so large and so fast remains a scientific 
mystery.
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Mary
mkirkaldy@aol.com