Researchers gained significant insight into how dinosaur arms developed into bird wings.
The researchers made their findings by looking at how the wings of modern birds develop in growing embryos as well as the bones of dinosaurs and early birds, PLOS reported. In the past researchers have been unsure of how dinosaur wrists morphed from straight to "bent and hyperflexible," allowing ancient birds to fold up their wings.
The team found the evolutionary transformation is characterized by a halving in the number of wrist bones, but developmental biologists and paleontologists have different classifications for these types of bones.
This new study combines both groups' research and used an interdisciplinary approach that re-examined fossils in museum collections and collected new data on seven modern bird species by looking at specific proteins in 3-D embryonic skeletons.
Early dinosaur ancestors were believed to have as many as nine wrist bones, but birds only held onto four over the course of evolution. There has been a long-lived debate over which original bones are still seen in birds today.
In the 1970s, Yale professor John Ostrom suggested a modern bone called the semilunate was the product of a merging of two bones present in dinosaurs. The finding suggests the common idea that birds evolved from dinosaurs, but the theory has never before been confirmed.
This new data backs up the idea that the two dinosaur bones merged to become one. Another bone called the pisiform was believed to have been lost in bird-like dinosaurs and re-emerged as birds began to evolve. The researchers also identified the other two wrist bones seen in modern birds, which have often been misidentified.
"This emphasizes the downsides of not integrating all data sources, and reveals a situation perhaps akin to that of astronomy and experimental physics in the pursuit of cosmology: Together, palaeontology and development can come much closer to telling the whole story of evolution - this integrative approach resolves previous disparities that have challenged the support for the dinosaur-bird link and reveals previously undetected processes, including loss of bones, fusion of bones, and re-evolution of a transiently lost bone," the researchers said in a statement.
The findings were published Sept. 30 in the journal PLOS Biology.
