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Toothy beak bridges gap between dinosaurs and birds

Ichthyornis dispar illustration. (Credit: Yale)

Researchers have pieced together the 3D skull of an iconic, toothed bird that represents a pivotal moment in the transition from dinosaurs to modern-day birds.

Ichthyornis dispar lived nearly 100 million years ago in North America, looked something like a toothy seabird, and drew the attention of such famous naturalists as O.C. Marsh (who first named and described it) and Charles Darwin.

“Right under our noses this whole time was an amazing, transitional bird…”

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, researchers report 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—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,” says paleontologist Bhart-Anjan Bhullar of Yale University, principal investigator of a study in the journal Nature. “It has a modern-looking brain along with a remarkably dinosaurian jaw muscle configuration.”

Perhaps most interesting of all, Bhullar says, is that Ichthyornis dispar shows us what the bird beak looked like as it first appeared in nature.

At its origin, the beak was a precision grasping mechanism that served as a surrogate hand as the hands transformed into wings.

“The first beak was a horn-covered pincer tip at the end of the jaw,” says 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 research team conducted its analysis using CT-scan technology, combined with specimens from the Yale Peabody Museum of Natural History; the Sternberg Museum of Natural History in Hays, Kansas; the Alabama Museum of Natural History; the University of Kansas Biodiversity Institute; and the Black Hills Institute of Geological Research.

“The fossil record provides our only direct evidence of the evolutionary transformations that have given rise to modern forms,” says Field. “This extraordinary new specimen reveals the surprisingly late retention of dinosaur-like features in the skull of Ichthyornis—one of the closest-known relatives of modern birds from the Age of Reptiles.”

The researchers say their findings offer new insight into how modern birds’ skulls eventually formed. Along with its transitional beak, Ichthyornis dispar had a brain similar to modern birds but a temporal region of the skull that was strikingly like that of a dinosaur—indicating that during the evolution of birds, the brain transformed first while the remainder of the skull remained more primitive and dinosaur-like.

How birds evolved such crazy beaks

Ichthyornis would have looked very similar to today’s seabirds, probably very much like a gull or tern,” says Hanson. “The teeth probably would not have been visible unless the mouth was open but covered with some sort of lip-like, extra-oral tissue.”

In recent years Bhullar’s lab has produced a large body of research on various aspects of vertebrate skulls, often zeroing in on the origins of the avian beak. “Each new discovery has reinforced our previous conclusions. The skull of Ichthyornis even substantiates our molecular finding that the beak and palate are patterned by the same genes,” Bhullar says.

“The story of the evolution of birds, the most species-rich group of vertebrates on land, is one of the most important in all of history. It is, after all, still the age of dinosaurs.”

Additional co-lead authors of the study are from the Milner Centre for Evolution at the University of Bath and from Yale. Additional coauthors are from the University of Kansas, Fort Hays State University, the Alabama Museum of Natural History, and the McWane Science Center.

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Yale University, the Yale Peabody Museum of Natural History, the University of Bath, the Alexander Wetmore Memorial Research Award, the Stephen J. Gould Award, and grants from the National Science Foundation, the Yale Institute for Biospheric Studies, the Evolving Earth Foundation, and the Frank M. Chapman Memorial Fund supported the research, in part.

Source: Yale University