| Summary: | The Confuciusornithiformes represent the most stem-ward avian occurrence of an edentulous rostrum. Although a keratinous beak is widely considered to have covered the rostrum in confuciusornithiforms, this feature is almost never preserved, having been previously reported only in the holotype of <i>Confuciusornis</i><i> dui </i>and the holotype of <i>Eoconfuciusornis</i><i> </i><i>zhengi</i>. This strongly contrasts with the widespread preservation of the keratinous sheaths that cover the manual and pedal ungual phalanges. Here, we report on a third occurrence of a preserved rhamphotheca in a specimen of <i>Confuciusornis</i><i> </i><i>sanctus</i>. We illuminated the preserved traces using laser-stimulated fluorescence. Similarly to <i>E. </i><i>zhengi</i>, the rhamphotheca has been preserved only as a two-dimensional trace, whereas ungual sheaths are preserved in three dimensions. In contrast to the traces preserved in <i>C. dui</i>, the rhamphotheca in the discussed specimen of <i>C. </i><i>sanctus</i> is straight rather than upturned. This hints towards hidden morphological diversity within the thousands of <i>Confuciusornis</i> specimens, in which species may be further differentiated by soft tissue features or behaviors, much like many living birds, that cannot be detected in fossils, even with exceptional preservation.
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