We explore hypothetical ecologies to explain diversity among predatory dinosaurs in North America's medial Cretaceous, based on occurrence, tooth morphology, and stable isotope analysis. The Mussentuchit local fauna, Utah, USA, is among the best-known terrestrial vertebrate assemblages from the Cretaceous. Study samples include teeth from six microvertebrate sites, ranging in depositional setting from distal floodplain to channel lags. We recognize four theropod morphotypes: a comparatively large theropod (morph 1), a medium-sized dromaeosaurid (morph 2), a small dromaeosaurid (morph 3), and a tooth-morph similar to the genus Richardoestesia (morph 4). These four morphotypes vary significantly in mean size, from 15.1 mm in the largest theropod to 3.7 mm in Richardoestesia. Further, tooth representation from two of the best-sampled microsites (representing a channel/splay and floodplain deposit) show differing patterns of abundances with morphs 1 and 3 having roughly the same abundance in both sites, while morph 2 was more abundant in the floodplain setting and morph 4 was more abundant in the channel/splay. Stable isotope analysis (δ¹³C; δ¹⁸O) of tooth carbonate from the theropod morphotypes, goniopholidid crocodilians, and matrix (to test for diagenesis) from these sites were also analyzed. The theropods show modest differences in δ¹³C values between each other, with carbonate from the teeth of morphs 1, 3, and 4 being enriched in ¹³C for the channel/splay relative to the floodplain environments, possibly indicative of dietary plasticity in these species. We hypothesize that these data indicate that the Mussentuchit theropods had different niches within the predator guild, suggesting plausible means by which ecospace was divided among the predatory dinosaurs of the Mussentuchit local fauna.

中文翻译：

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在兽脚亚目恐龙中的小生境划分：来自最高雪松山地层（美国犹他州）的食肉动物的饮食和栖息地偏好。

我们基于发生，牙齿形态和稳定同位素分析，探索假设生态学来解释北美内侧白垩纪捕食性恐龙之间的多样性。美国犹他州Mussentuchit当地动物群是白垩纪最著名的陆地脊椎动物组合之一。研究样本包括来自六个微脊椎动物部位的牙齿，其沉积环境从远洪泛滥到河道滞后不等。我们认识到四种兽脚亚目的形态类型：相对较大的兽脚亚目（变体1），中等大小的屈毛龙（变体2），较小的屈毛龙（变体3）和类似于理查德斯氏菌属的牙齿变体（变体4）。这四种形态型的平均大小差异很大，从最大的兽脚亚目中的15.1毫米到理查德氏症的3.7毫米。进一步，来自两个采样率最高的微型站点的牙齿表示（表示通道/展开和洪泛区沉积物）显示出不同的丰度模式，形态1和3在两个站点中具有大致相同的丰度，而形态2在洪泛区设置中更丰富。通道4中的变形4更为丰富。稳定同位素分析（δ¹³ ℃；δ ¹⁸从兽脚形态从这些站点齿碳酸盐，goniopholidid鳄鱼和基质（测试为成岩）的O）进行了分析。在兽脚显示δ适度差异^13个彼此之间C值，与来自变种1,3的齿碳酸盐，和4中富集¹³ ℃下相对漫滩环境中的信道/喷射，可能指示在这些膳食可塑性的物种。我们假设这些数据表明，肉食性兽脚类动物在食肉动物行会中具有不同的生态位，这表明将生态空间划分为肉食性恐龙本地动物区系的合理手段。