Duck‐billed dinosaurs (Hadrosauridae) were the most common ornithopods of the Late Cretaceous. Second only to sauropods and in many cases exceeding the sizes of the largest land mammals (such as indricotheres or proboscideans), they are among the largest terrestrial herbivores to have walked the Earth. Despite their gigantic size, diversity and abundance, their growth strategies remain poorly understood. Here, we examine the bone microstructure of several Mongolian hadrosauroids of varied adult sizes. The small and middle‐sized species have lines of arrested growth (LAGs). On the other hand, one of the largest duck‐billed dinosaurs, Saurolophus angustirostris, shows uninterrupted growth, comparable with other big hadrosaurs for which the lack of cyclical growth arrests was interpreted as a result of living in the polar region. Since both of the studied taxa inhabited warmer, continental, monsoon‐influenced environments of the Late Cretaceous Mongolia, we propose that the absence of LAGs is not a climatic‐driven condition but rather connected with the animal's size (i.e. ontogeny). Our results show that, like sauropods, hadrosaurs changed their growth dynamics from cyclical to continuous during their evolution, which made it possible for them to achieve comparable body sizes.

中文翻译：

---

非极性鸭嘴龙的不间断生长解释了鸭嘴恐龙之间的巨大差异

鸭嘴恐龙（鸭嘴龙科）是白垩纪晚期最常见的鸟类。它们仅次于蜥脚类动物，而且在许多情况下超过了最大的陆生哺乳动物（如indotherotheres或proboscideans）的大小，它们是在地球上行走的最大的陆生食草动物之一。尽管它们的规模巨大，种类繁多且数量众多，但对其增长策略的了解仍然很少。在这里，我们检查了成年大小不同的几种蒙古类鸭嘴龙的骨微结构。中小型物种具有停滞生长线（LAG）。另一方面，最大的鸭嘴恐龙之一Saurolophus angustirostris表现出不间断的增长，与其他大型鸭嘴龙类似，后者被解释为由于生活在极地地区而缺乏周期性的生长停滞。由于所研究的两个分类单元都居住在晚白垩世蒙古的温暖，大陆性，季风影响的环境中，因此我们提出，LAG的缺失不是气候驱动的条件，而是与动物的体型（即个体发育）有关。我们的结果表明，像蜥脚类动物一样，鸭嘴龙在进化过程中将其生长动力学从周期性改变为连续，这使其具有可比的体型。