Despite their heft, many dinosaurs had surprisingly tiny genomesMarch 08, 2007Two major classes of dinosaurs show genomes distinctly aligned with modern birds, reptiles CAMBRIDGE, Mass. — They might be giants, but many dinosaurs apparently had genomes no larger than that of a modern hummingbird. So say scientists who've linked bone cell and genome size among living species and then used that new understanding to gauge the genome sizes of 31 species of extinct dinosaurs and birds, whose bone cells can be measured from the fossil record. The researchers, at Harvard University and the University of Reading, were led by Chris Organ and Scott V. Edwards, both at Harvard. They report their findings this week in the journal Nature. "We see distinct differences between two major lineages of dinosaurs," says Organ, a postdoctoral fellow in organismic and evolutionary biology supported by the National Institutes of Health. "The theropods — carnivores such as Tyrannosaurus rex and Velociraptor — had very small genomes, in the range of modern birds. Ornithischians — which include Stegosaurus and Triceratops — had more moderately sized genomes, akin to those of living lizards and crocodilians. We aren't sure about the genomes of the long-necked sauropods yet." Organ and Edwards say the clear-cut dichotomy in dinosaur genomes is likely due to different amounts of repetitive and non-coding DNA in the two groups' genetic material, a factor largely responsible for variation in genome size across animal species. They estimate that active repetitive DNA might have comprised an average 12 percent of the ornithischian genome but just 8.4 percent of theropod genetic constitution. The work indicates that the small genomes typically associated with birds — whose genetic composition is noticeably sparer than that of other vertebrates — evolved in dinosaurs some 230 to 250 million years ago, rather than with the emergence of modern living birds just 110 million years ago. Organ and Edwards suggest after this shrinking, theropod genomes then stabilized in size for hundreds of millions of years, a process that continues in modern birds. "Our work debunks the theory that the small, repeat-poor genomes typical of birds may have co-evolved with flight as a means of conserving energy," says Edwards, professor of organismic and evolutionary biology in Harvard's Faculty of Arts and Sciences and Alexander Agassiz Professor of Zoology and curator of ornithology in Harvard's Museum of Comparative Zoology. "In fact, our work shows these streamlined genomes arose long before the first birds and flight, and can be added to the list of dinosaur traits previously thought to be found only in modern birds, including feathers, pulmonary innovations, and parental care and nesting." Other researchers had previously determined that the sizes of various cell types, across species, tend to reflect the size of an organism's genome. Analyzing 26 living species, Organ and Edwards are the first to show that the same applies to the bone cells called osteocytes. These cells reside in individual lacunae, small pockets inside bone tissue. This uniquely durable cellular housing allowed the scientists to look back in time at the size of 31 extinct species' genomes: By measuring lacunae in dinosaur and extinct bird specimens housed at Harvard's Museum of Comparative Zoology and at the Museum of the Rockies in Bozeman, Mont., they were able to determine just how big the various extinct species' osteocytes had been. "These fossils let us sample species through evolutionary time," Edwards says, "providing genomic information that's often unavailable for long-extinct ancestors." Harvard University |
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| Related Dinosaur Current Events and Dinosaur News Articles Warm-blooded dinosaurs worked up a sweat Were dinosaurs "warm-blooded" like present-day mammals and birds, or "cold-blooded" like present day lizards? The implications of this simple-sounding question go beyond deciding whether or not you'd snuggle up to a dinosaur on a cold winter's evening. The last European hadrosaurs lived in the Iberian Peninsula Spanish researchers have studied the fossil record of hadrosaurs, the so-called 'duck-billed' dinosaurs, in the Iberian Peninsula for the purpose of determining that they were the last of their kind to inhabit the European continent before disappearing during the K/T extinction event that occurred 65.5 million years ago. The humble beginnings of a king Tyrannosaurus rex and related large carnivorous dinosaurs together form the family Tyrannosauridae. A long forgotten fossil skull in the collections of the Natural History Museum in London has now provided crucial clues to the early stages of the lengthy evolutionary history of these fearsome predators. New dinosaur species from Montana A husband and wife team of American paleontologists has discovered a new species of dinosaur that lived 112 million years ago during the early Cretaceous of central Montana. New analyses of dinosaur growth may wipe out one-third of species Paleontologists from the University of California, Berkeley, and the Museum of the Rockies have wiped out two species of dome-headed dinosaur, one of them named three years ago - with great fanfare - after Hogwarts, the school attended by Harry Potter. Do 3 meals a day keep fungi away? The fact that they eat a lot - and often - may explain why most people and other mammals are protected from the majority of fungal pathogens, according to research from Albert Einstein College of Medicine of Yeshiva University. Crushed bones reveal literal dino stomping ground Imagine the gruesome sound of bones snapping as a thirsty, 30-ton dinosaur tramples a heap of fresh carcasses on his way to a rapidly shrinking lake. Chinese and American paleontologists discover a new Mesozoic mammal An international team of paleontologists has discovered a new species of mammal that lived 123 million years ago in what is now the Liaoning Province in northeastern China. Archaeopteryx was not very bird-like New research published this week clips the wings of Archaeopteryx. First found in Germany in the 1860's and dating to 150 million years ago, Archaeopteryx has long been considered the iconic first bird. Inside the first bird, surprising signs of a dinosaur The raptor-like Archaeopteryx has long been viewed as the archetypal first bird, but new research reveals that it was actually a lot less "bird-like" than scientists had believed. More Dinosaur Current Events and Dinosaur News Articles |
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