Grooved enamel in the teeth of an Early Cretaceous bird:

Jingmai K. O’Connor , Yuguang Zhang , Luis M. Chiappe , Qingjin Meng , Li Quanguo & Liu Di (2013): A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization, Journal of Vertebrate Paleontology, 33:1, 1-12. http://dx.doi.org/10.1080/02724634.2012.719176

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