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Tyrannosaurus growth rate articles



From: Ben Creisler bh480@scn.org

I don't have the full reference and abstract yet from the 
new Nature, but in case these news items have not been 
mentioned yet:
http://www.newscientist.com/

 Teen T-rex had monster growth spurt 
18:00 11 August 04 NewScientist.com news service 
Towering Tyrannosaurus rex reached its colossal 
proportions due to a monster growth spurt in its teenage 
years, reveals a new study.
Once the world was stalked by giants, from the six-tonne 
flesh-eating T. rex to Brachiosaurus, a lumbering 
vegetarian sauropod that weighed in at an impressive 88 
tonnes. But 65 million years after the dinosaurs 
disappeared, relatively little is known about how they 
became so big.
Now, Gregory Erickson, a palaeontologist at Florida State 
University in Tallahassee, US, has collected a large 
number of small, discarded T. rex bones sitting in museum 
drawers, and found the bones contain a treasure trove of 
well preserved growth rings inside. These cast-offs have 
allowed Erickson and his colleagues to chart out the first 
growth curve for T. rex.
The team shows that T. rex became a giant only in its 
teenage years, undergoing an exponential growth spurt for 
around four years during adolescence.
It therefore achieved its gigantic size not by growing for 
longer, as do modern mammals and lizards, but by growing 
dramatically faster. An adolescent T. rex would have 
gained about 2 kilogrammes a day between the ages of 14 
and 18, before slowing down and settling into adulthood.

Live fast, die young 
By using polarising light microscopes to examine bone 
growth rings, the team was also able to age the skeletons 
of 20 different specimens, including the famous Sue, on 
display at the Field Museum in Chicago, US.
Sue it emerges, is not only the largest T. rex known, but 
also the oldest. But even she died at just 28. ?T. rex 
lived fast and died young,? says Erickson. ?They were like 
the James Dean of dinosaurs.? The youngest specimen ? 
which had previously been labelled as a dwarf 
Tyrannosaurus ? was only two years old.
?We really have a new quantitative tool that will open up 
new avenues of research, because now we can start asking 
questions about the biology of extinct creatures like we 
can for living ones,? says Peter Makovicky, one of the 
team.
One such question is how did such dinosaurs move their 
gigantic bodies? Some answers were presented at the 
International Congress of Vertebrate Morphology, held in 
Florida, US, in August. For instance, John Hutchinson at 
the Royal Veterinary College in Hatfield, UK described how 
interactive software, which models a creature?s mass, 
centre of mass and inertia based on skeletal evidence, is 
revealing more about how T. rex walked.
Hutchinson has previously shown that T. rex?s size would 
limit it to running at no more than 25 miles per hour. To 
run any faster, the dinosaur?s skeleton would have to 
support a biologically impossible amount of muscle (New 
Scientist print edition, March 2002).
However, the weight limit on running fast only kicks in 
for animals over about one tonne, which corresponds to a 
juvenile T. rex around 12 years old.
His new models, which have been validated using ostrich 
skeletons, which move in a similar way to T. rex, show 
that the dinosaur?s posture was rather unsteady, hampered 
by a strong tendency for the head to pitch forward. 
However, inertia was a strong stabilising force for large 
dinosaurs like T. rex.
Journal reference: Nature (vol 430, p 772)
Anna Gosline


http://www.newswise.com/articles/view/506494/
Newswise ? Most teenagers have growing pains, but none 
probably compared to those of Tyrannosaurus rex as it 
ascended to adulthood more than 65 million years ago, 
according to a Florida State University researcher.
>From around age 14 to 18, T. rex took on about 70 percent 
of its adult mass, growing from a 1-ton carnivorous lizard 
to a bone-crushing, 6-ton dinosaur eating machine with few 
rivals in the prehistoric kingdom, according to FSU 
biologist Gregory Erickson. At the peak of this spurt, T. 
rex grew more than 4.5 pounds a day.
Erickson and his team of paleontologists are the first to 
establish an accurate picture of how T. rex accelerated 
its growth over a relatively few years to become 
gargantuan while earlier, smaller relatives had much 
slower growth. The scientists did this by counting growth 
rings in the bones of T. rex and other members of its 
family and calculating the corresponding body size by 
measuring the circumference of the femur.
The research is featured as the cover story for the Aug. 
12 edition of the journal Nature.
T. rex's growth rate is comparable to that of the modern 
day elephant. But while elephants have a lifespan of more 
than 70 years, T. rex lived no more than 30 years.
"We now know that T. rex lived fast and died young," said 
Erickson.
Erickson and Peter Makovicky, dinosaur curator at The 
Field Museum and a coauthor of the study, will join with 
other team members at the Chicago museum on Wednesday to 
announce their findings. The museum is home to Sue® [The 
Field Museum], the world's largest, oldest and most 
complete T. rex fossil, which was discovered in South 
Dakota in 1990.
Erickson has spent much of his career exploring how some 
dinosaurs got so big. The first dinosaurs to roam the 
Earth some 225 million years ago were about a yard long 
and weighed between 50 to 100 pounds, he said. The giants, 
such a T. rex and A. sarcophagus, came along about 150 
million years later.
"Almost every child asks: 'How did dinosaurs get so big?' 
That has remained one of the great mysteries in 
paleontology," Erickson said. "Here we cracked the code 
for one family of dinosaurs, the Tyrannosauridae."
Like trees, dinosaur bones are marked by growth rings, 
with a new one developing every year. But there was one 
giant obstacle to counting the rings: Most of the big, 
meat-eating dinosaurs' bones remodeled themselves as they 
grew and become hollow, erasing much of the growth record.
A possible solution to this dilemma came to Erickson about 
four years ago while examining Sue. He noticed that Sue's 
rib bones were solid. Further investigation revealed that 
the fibula (a leg bone) and some hipbones were also solid 
and retained the full compliment of growth rings.
Erickson assembled a team of researchers from the American 
Museum of Natural History, The Field Museum, Canada's 
Royal Tyrrell Museum of Palaeontology, Stanford University 
and the University of Iowa. They examined cross sections 
of bones from 20 Tyrannosaurs that ranged from 2 to 28 
years of age and establish T. rex's accelerated growth 
rate during its teenage years.
The researchers verified their results by comparing the 
dinosaurs' growth rings to those of modern-day alligators 
and lizards, whose rings are similar.
Ten years ago such research may have been impossible, 
Erickson said. Museums wouldn't have allowed scientists to 
cut away at T. rex bones to examine growth rings because 
there were only a few good specimens. But a flurry of 
discoveries in the past decade - there are now more than 
30 known T. rex specimens worldwide - have given museums a 
greater comfort level and allowed more invasive scientific 
research.