January 7, 2013
First Fossil Bird Discovered With Teeth For A Tough Diet
Alan McStravick for redOrbit.com - Your Universe Online
A trip to the Galapagos islands will bring you face to face with 14 closely related species of finch that Charles Darwin discovered on his adventure abroad in the 1830s. The finches he noted, still referenced in essentially every biology textbook, had beak sizes of varying lengths and sizes. This was true of both the ground- and tree-dwelling birds, and Darwin postulated that differing diets might have required the birds´ unique beaks for their specialized feeding tasks.It was these birds, catalogued in 1835, that first helped Darwin to arrive at his theory of evolution. He was able to realize that each of the finch species had originally arisen from one ancestral form and that each of the successive forms — with their individual ecological niches and diets — were what he considered the most perfect examples of adaptive radiation, the process where one species undergoes several distinct changes to survive and thrive in a wider variety of habitats.
If Darwin had lived some 121-125 million years ago, he might have experienced the same sense of wonder at the site of a Sulcavis geeorum, a species of early bird that existed in the Liaoning Province of what is now modern-day China. It was here that a new fossil discovery was made showing that these early ancestors of the dinosaurs had evolved teeth adapted to their specialized diets.
In a report of the finding published in the latest issue of the Journal of Vertebrate Paleontology, researchers say they believe that S. geeorum existed on a so-called ℠durophagous diet´, one that included lots of prey with hard exoskeletons such as insects or crabs.
S. geeorum was an enantiornithine bird, a primitive group of early birds that were abundant in the Mesozoic era and carried over into the Cretacious. With the discovery of S. geeorum, researchers are enjoying their own Darwin-like moment as they see this discovery as representing a huge leap forward in the known diversity of tooth shape in early birds. This diversity of shape also leads them to believe that they may have stumbled upon an as yet unrecognized degree of ecological diversity.
According to the research team, S. geeorum is the first fossilized bird discovery that has ornamented tooth enamel. Looking back to the specific dinosaurs from which birds are believed to have evolved, researchers find that their tooth structure was specialized mainly for a carnivorous diet. The enanitiornithine family of birds have undergone the most minimal tooth reductions from their dinosaur cousins compared to any other extinct or extant groups of birds, and they also displayed a wide diversity of individual dental patterns.
In this newest enantiornithine discovery, researchers say that they have discovered a robust set of teeth that are marked with grooves on the inside surface. It is from these grooves, they hypothesize, that the teeth received their strength that allowed them to ingest harder food items.
“While other birds were losing their teeth, enantiornithines were evolving new morphologies and dental specializations. We still don´t understand why enantiornithines were so successful in the Cretaceous but then died out — maybe differences in diet played a part,” according to Jingmai O´Connor, lead author of the new study. One thing that is known is that until this discovery, no previous known bird species had preserved ridges, striations, serrated edges, or any other form of dental ornamentation.
"This study highlights again how uneven the diversity of birds was during the Cretaceous. There are many more enantiornithines than any other group of early birds, each one with its own anatomical specialization," said the study´s co-author Luis Chiappe, from Natural History Museum of Los Angeles County.