Institute of Geology and Paleontology, Linyi University, Linyi, Shandong 276000, China.
Proc Natl Acad Sci U S A. 2011 Sep 20;108(38):15904-7. doi: 10.1073/pnas.1112694108. Epub 2011 Sep 6.
The crop is characteristic of seed-eating birds today, yet little is known about its early history despite remarkable discoveries of many Mesozoic seed-eating birds in the past decade. Here we report the discovery of some early fossil evidence for the presence of a crop in birds. Two Early Cretaceous birds, the basal ornithurine Hongshanornis and a basal avian Sapeornis, demonstrate that an essentially modern avian digestive system formed early in avian evolution. The discovery of a crop in two phylogenetically remote lineages of Early Cretaceous birds and its absence in most intervening forms indicates that it was independently acquired as a specialized seed-eating adaptation. Finally, the reduction or loss of teeth in the forms showing seed-filled crops suggests that granivory was possibly one of the factors that resulted in the reduction of teeth in early birds.
该作物是当今食籽鸟类的特征，但尽管过去十年中发现了许多中生代食籽鸟类，但其早期历史却鲜为人知。在这里，我们报告了一些关于鸟类存在嗉囊的早期化石证据的发现。两种早白垩世鸟类，基干的长尾鸟 Hongshanornis 和一种基干的鸟类 Sapeornis，表明一种本质上现代的鸟类消化系统在鸟类进化的早期就已经形成。在两个亲缘关系较远的早白垩世鸟类谱系中发现了嗉囊，而在大多数中间形式中却没有发现嗉囊，这表明它是作为一种专门的食籽适应而独立获得的。最后，在显示有种子填充嗉囊的形态中牙齿的减少或缺失表明，食籽可能是导致早期鸟类牙齿减少的因素之一。
