The keratinous beak is inferred to have evolved multiple times in the Archosauria and in Aves. Unfortunately, this feature rarely preserves in the fossil record. Here we examine a collection of 603 specimens belonging to the Confuciusornithiformes, a clade of edentulous basal avians, only two of which preserve visible traces of the rhamphotheca. Preservation is very different between the two specimens, offering no clues as to the taphonomic conditions that are conducive to preservation of this feature. These differences suggest that preservation of the rhamphotheca is not limited to a very narrow set of specific chemical conditions. We suggest the more common preservation of feathers over rhamphotheca is due to the higher melanin content in the former. The well-preserved traces in one specimen described here suggests that the rhamphotheca covering the upper and lower jaws each may consist of a pair of right and left elements, thus differing from the condition in neornithines in which the premaxillary nail and mandibular nail covering the rostral half of the upper and lower jaws respectively each form a single unit.

角蛋白喙被推断在始祖鸟和Aves中已经进化了多次。不幸的是，这一特征很少保存在化石记录中。在这里，我们检查了603个标本，这些标本属于孔子基类，是无齿的基底禽类的进化枝，其中只有两个标本保留了可见的黄麻。这两个标本之间的保存有很大不同，没有提供有关有助于保存该特征的最合理条件的线索。这些差异表明，红腐菌的保存不限于非常狭窄的特定化学条件。我们建议，比起大黄蜂，更常见的羽毛保存是由于前者中较高的黑色素含量。