Abstract Asian hesperornithiforms are extremely rare in contrast to North American records; thus, their diversity in Asia during the Cretaceous is unclear. Maastrichtian hesperornithiform materials have been reported from both fluvial and marine deposits in North America but only from fluvial deposits in Asia. Asian hesperornithiforms from Maastrichtian deposits have been considered as freshwater taxa because of their occurrence from fluvial sediments and their histological features. Here, we report the first hesperornithiform record from marine Maastrichtian deposits in Asia. It is represented by an isolated left tibiotarsus from the inter-arc basin deposit of the Kita-ama Formation (lower Maastrichtian), Izumi Group of southwest Japan. It has a shallow tibial incision, fibular crest extending to the mid shaft, and laterally angled lateral articular surface. Although its phylogenetic position within Hesperornithiformes is ambiguous, these characters are similar to non-hesperornithid hesperornithiforms. Unossified proximal and distal epiphyses indicate that this individual was immature. A remarkably thick cortical area of the tibiotarsus suggests that this hesperornithiform was a sea-dwelling bird and that the habitat of this group during the Maastrichtian extended to both terrestrial and marine environments in Asia and North America.

中文翻译：

---

来自日本马斯特里赫特的海洋 Hesperornithiform (Avialae: Ornithuromorpha)：对白垩纪末最早潜水鸟类古生态多样性的影响

摘要 与北美的记录相比，亚洲的 hesperornithiforms 极为罕见。因此，它们在白垩纪期间在亚洲的多样性尚不清楚。Maastrichtian hesperornithiform 材料已从北美的河流和海洋沉积物中报告，但仅来自亚洲的河流沉积物。来自马斯特里赫特沉积物的亚洲 hesperornithiforms 被认为是淡水类群，因为它们来自河流沉积物及其组织学特征。在这里，我们报告了亚洲海洋马斯特里赫特沉积物的第一个 hesperornithiform 记录。它以日本西南部和泉群北天组（马斯特里赫特下段）弧间盆地沉积物的孤立左胫跗骨为代表。它有一个浅胫骨切口，腓骨嵴延伸到中轴，和横向成角度的外侧关节面。虽然它在 Hesperornithiformes 中的系统发育位置不明确，但这些特征与非 hesperornithid hesperornithiforms 相似。未骨化的近端和远端骨骺表明该个体不成熟。胫跗骨的一个非常厚的皮质区域表明这种hesperornithiform 是一种海栖鸟类，并且该类群在马斯特里赫特时期的栖息地扩展到亚洲和北美洲的陆地和海洋环境。 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .