Zheng Xiaoting, O'Connor Jingmai K, Huchzermeyer Fritz, Wang Xiaoli, Wang Yan, Zhang Xiaomei, Zhou Zhonghe
Institute of Geology and Paleontology, Linyi University, Linyi, Shandong, China; Tianyu Natural History Museum of Shandong, Pingyi, Shandong, China.
Key Laboratory of Vertebrate Evolution and Human Origin of the Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China.
PLoS One. 2014 Apr 14;9(4):e95036. doi: 10.1371/journal.pone.0095036. eCollection 2014.
A crop adapted for an herbivorous diet of seeds has previously been documented in the Early Cretaceous birds Sapeornis and Hongshanornis. Here we report on several specimens of Yanornis that preserve a crop containing fish. One specimen preserves two whole fish in the oesophagus, indicating that Early Cretaceous birds shared trophic specializations with Neornithes for the increased energetic demands of flight--namely the storing of food for later consumption when the stomach is full. Whole fish also indicate that despite their presence, teeth were not used to orally process food, suggesting the hypertrophied dentition in this taxon were utilized in prey capture. The presence of macerated fish bones in the crop of other specimens indicates the highly efficient advanced muscular system of peristalsis responsible for moving ingested items between different segments of the alimentary canal was also in place. Despite the fact many features of the modern avian alimentary canal are inferred to compensate for the absence of teeth in birds (expandable oesophagus, grinding gizzard), the derived alimentary canal was apparently present in toothed Cretaceous birds. Although Yanornis was considered to have switched their diet from piscivorous to herbivorous, based on position and morphology we reinterpret the gastroliths reported in one specimen as sand impacted in the intestines, and reconstruct the taxon as primarily piscivorous. This is a novel interpretation for fossilized gastroliths, and the first documentation of this condition in the fossil record.
此前在早白垩世鸟类孔子鸟和红山鸟中已记录到一种适应以种子为食的草食性饮食的嗉囊。在此，我们报告了几个保存有含鱼嗉囊的燕鸟标本。一个标本在食管中保存了两条完整的鱼，这表明早白垩世鸟类与今鸟亚纲具有共同的营养特化特征，以满足飞行增加的能量需求——即当胃已满时储存食物以供稍后食用。完整的鱼还表明，尽管它们存在，但牙齿并未用于口腔处理食物，这表明该分类群中肥大的齿系用于捕食猎物。其他标本嗉囊中存在被浸软的鱼骨，这表明负责在消化道不同部分移动摄入物的高效先进蠕动肌肉系统也已存在。尽管现代鸟类消化道的许多特征被推断是为了弥补鸟类没有牙齿的缺陷（可扩张的食管、研磨砂囊），但这种衍生的消化道显然在有齿的白垩纪鸟类中就已存在。尽管燕鸟曾被认为已从食鱼性转变为草食性，但基于位置和形态，我们将一个标本中报告的胃石重新解释为肠道中堵塞的沙子，并将该分类群重建为主要食鱼性。这是对化石胃石的一种新颖解释，也是化石记录中这种情况的首次记录。
