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| Fossil reconstruction and illustration of Ichthyornis dispar. Photo Credit: Michael Hanson/Yale University |
Yet another piece of the jigsaw puzzle completing the picture of how a sub-order of dinosaurs transitioned into modern birds was put in place yesterday when researchers from Yale published a paper showing how the beak evolved from a dinosaur jaw. The paper was published in Nature. Unfortunately, it sits behind a paywall and the copyright holders require payment for reproducing even the abstract. However, it can be read here, and the Yale press release contains much of the essential information.
Ichthyornis dispar holds a key position in the evolutionary trail that leads from dinosaurian species to today’s avians. It lived nearly 100 million years ago in North America, looked something like a toothy seabird, and drew the attention of such famous naturalists as Yale’s O.C. Marsh (who first named and described it) and Charles Darwin.
Yet despite the existence of partial specimens of Ichthyornis dispar, there has been no significant new skull material beyond the fragmentary remains first found in the 1870s. Now, a Yale-led team reports on new specimens with three-dimensional cranial remains — including one example of a complete skull and two previously overlooked cranial elements that were part of the original specimen at Yale — that reveal new details about one of the most striking transformations in evolutionary history.
Right under our noses this whole time was an amazing, transitional bird,” said Yale paleontologist Bhart-Anjan Bhullar, principal investigator of a study published in the journal Nature. “It has a modern-looking brain along with a remarkably dinosaurian jaw muscle configuration.”
Perhaps most interesting of all, Bhullar said, is that Ichthyornis dispar shows us what the bird beak looked like as it first appeared in nature.
“The first beak was a horn-covered pincer tip at the end of the jaw,” said Bhullar, who is an assistant professor and assistant curator in geology and geophysics. “The remainder of the jaw was filled with teeth. At its origin, the beak was a precision grasping mechanism that served as a surrogate hand as the hands transformed into wings.”
The skull shows a mosaic of features, typical of a species intermediate on the evolutionary pathway between two orders. The beach is clearly transitional and functions as a toothed projection, able to be used as precision grasping tool, taking on some of the functions of hands that were becoming wings.
The brain was bird-like but the temporal region was very dinosaur-like, showing how some dinosaur features were retained late into the evolution of birds. The beak and the end of the extended jaw was covered in horn and the teeth were probably behind lip-like tissues, so would only have been visible when the beak was open.
This is just another piece of the picture of the evolution of birds from dinosaurs, or as some people would contend, the continuation of theropod dinosaurs over time as they evolved to become what we now classify as birds. It adds to the genetic and morphological evidence that birds are really modern, feathered, bipedal dinosaurs.
No doubt creationists will continue to deny this growing evidence and this example of yet another transitional species.
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