Dinosaurs are ancestral birds
Posted by admin in Life, Palaeontology
Quest – New research from China, published in Science provides further evidence for those who think that dinosaurs are the direct ancestors of birds. Most scientists think that birds evolved from dinosaurs about 150 million years ago. But there are those who believe that birds evolved independently.
This new fossil find makes that idea almost impossible, according to Xu Xing and colleagues of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Bejing. They have recently unveiled the fossil of Haplocheirus sollers, a new genus of alvarezsauroid—a group of dinosaurs once thought to be flightless birds.
The nearly complete skeleton, unearthed from 160-million-year-old mudstone deposits in northwestern China’s Junggar Basin, extends the fossil record of alvarezsauroids back in time by 63 million years—making it about 15 million years older than the earliest known bird, Archaeopteryx.
A new bird-like alvarezsauroid is even older than the first bird, Archaeopteryx—powerful evidence that birds arose from dinosaurs. Fossilised pigment organelles reveal the true colors of Sinosauropteryx.
Alvarezsaurs (members of the group Alvarezsauridae, alternately Alvarezsauria or Alvarezsauroidea) are a family of small, long-legged running dinosaurs. They are thought to represent the earliest known flightless birds. Alvarezsaurs are highly specialised.
They bear tiny but heavy forelimbs with compact bird-like hands and their skeleton suggests they had massive breast and arm muscles, possibly adapted for digging or tearing. They have tubular snouts, elongate jaws, and minute teeth.
They may have been adapted to prey on colonial insects such as termites.
Feather evolution
One of the biggest puzzles in the evolution of birds is why the original dinosaurs evolved feathers in the first place. One idea is that they were used for insulation. Other ideas are that the feathers provided camouflage or attracted mates.
But until very recently evidence such as distinctive patterns or colours was hard to find. However, this week Mike Benton of the University of Bristol in the United Kingdom and colleagues offer the first report (in Nature) of organelles bearing the pigment melanin in dinosaurs. They found melanosomes in the theropods Sinornithosaurus and Sinosauropteryx and in a bird, Confuciusornis, that lived roughly 125 million years ago.
Sinosauropteryx’s protofeathers ran in alternating orange and white rings down its tail. To Benton, the vibrant pattern suggests that “feathers first arose as agents for color display and only later in their evolutionary history did they become useful for flight and insulation”. But other researchers are still not sure and it looks as though it will still be a while before the true nature of dinosaur feathers is revealed.
Science 29 January 2010: Vol. 327. no. 5965, pp. 571 – 574 DOI: 10.1126/science.1182143
Nature advance online publication 27 January 2010 | doi:10.1038/nature08740; Received 21 September 2009; Accepted 10 December 2009; Published online 27 January 2010
