T. rex grew beefier than museum fossils suggest

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Big bones belong to adults that have finished growing, smaller bones to juveniles that are still sprouting up. It seems like the safest of assumptions, but it is one that is fraught with peril when applied to dinosaurs.

Presenting this week at the Society of Vertebrate Paleontology's meeting in Los Angeles, California, palaeontologist Jack Horner of the Museum of the Rockies in Bozeman, Montana, revealed that when he cut open the fossilized bones of dinosaurs in the museum’s collection and studied the layers of bone within, he found signs in most specimens that the animals were still growing at the time of their death.

In fossils labelled as juveniles, the outer bone layers contained canals that would once have held blood vessels, as well as large groups of osteocytes — cells that are important for bone formation. But the researchers were surprised to find similar signs of growth in adult fossils, because in most animals that are alive today, the skeleton tends to stop growing once adulthood is reached.

The key thing that Horner was looking for was arrested growth: closely packed bone layers bereft of osteocytes and blood vessels that are almost always found in skeletons that have finished growing. He did find them in a few fossils, indicating that dinosaur bones had the potential to eventually stop growing. But the vast majority of the bones he looked at did not have them.

 

Written By: Matt Kaplan
continue to source article at nature.com

4 COMMENTS

  1. I think it was illustrations like this that got me interested in science as a child.

    Me and my brothers had two choices as a young kids on Sundays when our grandparents were in the process of failing to ensure the church of England remained viable for future generations:

    1. Be a good child and endure an acutely boring church service.
    2. Play up and so be sent outside to wait in the library next door until the adults and well-behaved kids were finished.

    Given that the library was full of fantastically illustrated books about dinosaurs, early humans, aircraft, spacecraft, and war machines there really was no contest.

    If it turns out to be normal practise to collocate public libraries (open for reading on Sundays) with churches then maybe these kinds of dinosaur illustrations were a contributing reason why all good and well-socialised people go to church and faithfully believe what they’re told to believe, while mostly rude and ill-behaved misfits grow up to become atheists.

  2. There are engineering constraints on the possible size of living structures, and furthermore, organisms do not automatically scale up their organs as they increase in size (- It takes millennia of evolution) so if they just kept right on growing, eventually they would be too big to live or too big to move, or their body parts would be dysfunctionally out of proportion.
    >

    Elephants Took 24 Million Generations to Evolve From Mouse-Size – http://news.nationalgeographic.co.uk/news/2012/02/120203-mammals-evolution-body-size-science-elephants-mice/ -

    Using both fossil and living specimens, scientists calculated growth rates for 28 different mammalian groups during the past 65 million years—and found that, for mammals, getting big takes longer than shrinking.

    It takes a minimum of 1.6 million generations for mammals to achieve a hundredfold increase in body size, about 5 million generations for a thousandfold increase, and about 10 million generations for a 5,000-fold increase, the team discovered.

    The study also found that mammals shrink up to 30 times faster than they increase.

    “That’s quite amazing that there’d be such a difference in the rate of decreasing in size compared to increasing,” said Evans, whose study appears this week in the journal Proceedings of the National Academy of Sciences.

    Evans and colleagues suspect their findings might also apply to other animal groups, such as dinosaurs.

    “We have actually started looking into dinosaurs, but the difficulty with them,” he said, is that it’s unknown how long a dinosaur’s generation lasted.

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