WASHINGTON, Mar 8 (Reuters) For big beasts, dinosaurs like Tyrannosaurus rex sure had small genomes.
In a study published, scientists estimated the size of the genome -- the genetic composition of an organism -- for 31 species of dinosaurs and extinct birds, and found that the meat-eating types like T-rex had relatively small genomes.
The research further adds to scientific understanding of dinosaurs, animals that dominated the Earth from about 230 to 65 million years ago and continue to fascinate people today.
While dinosaurs have been extinct for 65 million years, researchers at Harvard University in Massachusetts and the University of Reading in Britain studied cells from fossilized bones to extrapolate the size of their genomes.
But don't worry, T-rex fans. Having a small genome doesn't imply inferiority. As the researchers noted, a lungfish has a bigger genome than a human.
The study in the journal Nature described significant differences between the major dinosaur lineages.
The type of bipedal carnivorous dinosaurs known as theropods -- like Tyrannosaurus, Allosaurus and Deinonychus -- had very small genomes in the range of modern birds, the study found.
The same was true for the extinct birds they studied, including the diving seabird Hesperornis, which lived during the age of dinosaurs, and the large, flightless, carnivorous Diatryma, which lived after the dinosaurs went extinct.
It is widely accepted among paleontologists that birds arose from small feathered theropod dinosaurs.
''It's clear that all of the theropods, including birds, have a very consistently restricted size range for their genome,'' the study's lead author, Harvard's Chris Organ, said in an interview.
But plant-eating dinosaurs known as Ornithischians -- including the armored Stegosaurus, the horned Triceratops and Styracosaurus and the duckbilled Maiasaura -- had more moderately sized genomes in the range of today's lizards and crocodilians.
The researchers did not focus on the genome of the massive long-necked dinosaurs known as sauropods, like Diplodocus.
DINOSAUR TRAITS The researchers wrote that their work showed streamlined genomes arose long before the first birds appeared. They said small genome size should be added to the list of dinosaur traits that previously had been thought to be found only in modern birds, including feathers, pulmonary innovations, parental care and nesting.
The research indicated that the small genomes associated with birds -- whose genetic composition is the smallest of any land vertebrates -- appeared very early in dinosaur evolution, roughly 230 million years ago.
''One of the problems with genomics is that we don't have any information for a lot of life because most species that have ever lived are extinct,'' Organ said.
The size of certain kinds of cells can reflect the size of an organism's genome. While soft tissues rarely are left behind in fossils, bones fossilize very well.
After analyzing 26 living animal species, the researchers determined that bone cells called osteocytes are good indicators of genome size. These cells are housed in durable small pockets within bone tissue that can be preserved nicely in fossilized dinosaur and bird bones.
''What's so cool about fossil bone is that a lot of it looks identical to bone from living animals,'' Organ said.
By measuring these pockets in fossil specimens at Harvard and a museum in Bozeman, Montana, they determined the size of these cells in the extinct animals in order to gauge genome size.
Reuters BDP DB0931
In a study published, scientists estimated the size of the genome -- the genetic composition of an organism -- for 31 species of dinosaurs and extinct birds, and found that the meat-eating types like T-rex had relatively small genomes.
The research further adds to scientific understanding of dinosaurs, animals that dominated the Earth from about 230 to 65 million years ago and continue to fascinate people today.
While dinosaurs have been extinct for 65 million years, researchers at Harvard University in Massachusetts and the University of Reading in Britain studied cells from fossilized bones to extrapolate the size of their genomes.
But don't worry, T-rex fans. Having a small genome doesn't imply inferiority. As the researchers noted, a lungfish has a bigger genome than a human.
The study in the journal Nature described significant differences between the major dinosaur lineages.
The type of bipedal carnivorous dinosaurs known as theropods -- like Tyrannosaurus, Allosaurus and Deinonychus -- had very small genomes in the range of modern birds, the study found.
The same was true for the extinct birds they studied, including the diving seabird Hesperornis, which lived during the age of dinosaurs, and the large, flightless, carnivorous Diatryma, which lived after the dinosaurs went extinct.
It is widely accepted among paleontologists that birds arose from small feathered theropod dinosaurs.
''It's clear that all of the theropods, including birds, have a very consistently restricted size range for their genome,'' the study's lead author, Harvard's Chris Organ, said in an interview.
But plant-eating dinosaurs known as Ornithischians -- including the armored Stegosaurus, the horned Triceratops and Styracosaurus and the duckbilled Maiasaura -- had more moderately sized genomes in the range of today's lizards and crocodilians.
The researchers did not focus on the genome of the massive long-necked dinosaurs known as sauropods, like Diplodocus.
DINOSAUR TRAITS The researchers wrote that their work showed streamlined genomes arose long before the first birds appeared. They said small genome size should be added to the list of dinosaur traits that previously had been thought to be found only in modern birds, including feathers, pulmonary innovations, parental care and nesting.
The research indicated that the small genomes associated with birds -- whose genetic composition is the smallest of any land vertebrates -- appeared very early in dinosaur evolution, roughly 230 million years ago.
''One of the problems with genomics is that we don't have any information for a lot of life because most species that have ever lived are extinct,'' Organ said.
The size of certain kinds of cells can reflect the size of an organism's genome. While soft tissues rarely are left behind in fossils, bones fossilize very well.
After analyzing 26 living animal species, the researchers determined that bone cells called osteocytes are good indicators of genome size. These cells are housed in durable small pockets within bone tissue that can be preserved nicely in fossilized dinosaur and bird bones.
''What's so cool about fossil bone is that a lot of it looks identical to bone from living animals,'' Organ said.
By measuring these pockets in fossil specimens at Harvard and a museum in Bozeman, Montana, they determined the size of these cells in the extinct animals in order to gauge genome size.
Reuters BDP DB0931
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