Fossil Bird Had Tough Teeth

Every now and then, chicken embryos sprout teeth. The developing birds don’t survive – the recessive condition is lethal – but the nascent beginnings of chicken dentition confirm something that paleontologists have known since the late 19th century. For millions of years, birds had teeth.

Yale paleontologist Othniel Charles Marsh called such birds “Odontornithes.” The term is regarded as obsolete now, but it still has a ring to it. The loon-like Hesperornis and the seabird Ichthyornis, found in the ancient chalk of a vanished Cretaceous sea and described by Marsh in 1880, provided intellectual ammunition to Thomas Henry Huxley and other naturalists who saw an undeniable connection between reptiles and birds. Huxley didn’t believe such birds were on the direct line of descent from ancient reptiles and birds of modern aspect, but fossils such as the early birds Archaeopteryx and the later Hesperornis showed that such a transition was possible.

Paleontologists have discovered multiple forms of toothed birds since Marsh’s day. The structures vary in minor detail from species to species, but, for the most part, fossil bird teeth were relatively smooth and simple – useful for snatching fish or crunching insects, but not slicing up carcasses or chewing. In the latest issue of the Journal of Vertebrate Paleontology, though, Jingmai O’Connor and coauthors describe a new genus of fossil bird with unusual teeth not quite like any seen before.

Named Sulcavis geeorum, the 121-125 million year old bird was an enantiornithine. This totally extinct group was a radiation of unusual birds that were developing dental specializations while other avian lineages were losing their teeth. Indeed, Sulcavis expands the range of apparent niches these birds occupied by virtue of its “robust” teeth, marked by long grooves running down the side.  No bird has ever been found with such ornamented teeth.

O’Connor and colleagues stress that we need additional specimens to better understand the nature of Sulcavis. For one thing, it’s difficult to say whether the bird’s distinctive teeth were an abnormality or a “true feature.” But suppose that the stout, grooved teeth were an actual trait that evolved in this lineage of archaic birds. What was Sulcavis eating with its odd teeth?

In a way, teeth are like talons. They are tools that can be used in multiple ways. Determining their primary use – not to mention the reason they evolved this way and not that – relies on both comparative evidence and a touch of imagination. Since there are no toothed birds today, much less ones with ornamented enamel, it’s hard to say what Sulcavis fed on. Nevertheless, the bird’s teeth roughly resemble those of the mosasaur Globidens – a marine lizard with bulbous teeth it supposedly used to crush shelled mollusks and other shielded prey. If O’Connor and coauthors are correct, Sulcavis “may have been especially well adapted for a diet of hard food items.” The trick is testing that idea through searching for gut contents and other elusive indicators of ancient diet.

Reference:

O’Connor, J., Zhang, Y., Chiappe, L., Meng, Q., Quanguo, L., Di, L. 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology. 33, 1: 1-12