Department of Earth and Environmental Sciences and Department of Biology, City University of New York, Graduate School and University Center, New York City, New York, United States.
Department of Earth and Environmental Sciences, City University of New York, Brooklyn College, Brooklyn, New York, United States.
PeerJ. 2023 Feb 7;11:e14665. doi: 10.7717/peerj.14665. eCollection 2023.
We report here the first dinosaur skeletal material described from the marine Fox Hills Formation (Maastrichtian) of western South Dakota. The find consists of two theropod pedal phalanges: one recovered from the middle part of the Fairpoint Member in Meade County, South Dakota; and the other from the Iron Lightning Member in Ziebach County, South Dakota. Comparison with pedal phalanges of other theropods suggests strongly that the Fairpoint specimen is a right pedal phalanx, possibly III-2, from a large ornithomimid. The Iron Lightning specimen we cautiously identify as an ornithomimid left pedal phalanx II-2. The Fairpoint bone comes from thinly bedded and cross-bedded marine sandstones containing large hematitic concretions and concretionary horizons. Associated fossils include osteichthyan teeth, fin spines and otoliths, and abundant teeth of common Cretaceous nearshore and pelagic chondrichthyans. Leaf impressions and other plant debris, blocks of fossilized wood, and burrows are also common. The Iron Lightning bone comes from a channel deposit composed of fine to coarse sandstone beds, some of which contain bivalves, and a disseminated assemblage of mammal teeth, chondrichthyan teeth, and fragmentary dinosaur teeth and claws. We interpret the depositional environment of the two specimens as marginal marine. The Fairpoint bone derives from a nearshore foreset setting, above wave base subject to tidal flux and storm activity. The Iron Lightning specimen comes from a topset channel infill probably related to deposition on a tidal flat or associated coastal setting. The taphonomic history and ages of the two bones differ. Orthogonal cracks in the cortical bone of the Fairpoint specimen suggest post-mortem desiccation in a dryland coastal setting prior to transport and preservation in the nearby nearshore setting described above. The pristine surface of the Iron Lightning specimen indicates little transport before incorporation into the channel deposit in which it was found. The Fairpoint bone bed most probably lies within the Ammonite Zone of the early late Maastrichtian, and would therefore have an approximate age of 69 Ma. The Iron Lightning bone is from the overlying Ammonite Zone, and is thus about one million years younger.
我们在此报告了首例从南达科他州西部福克斯山组（马斯特里赫特阶）海相地层中描述的恐龙骨骼材料。这一发现包括两个兽脚亚目恐龙的足趾骨：一个来自南达科他州米德县费尔波特段的中段；另一个来自南达科他州齐巴赫县的铁闪电段。与其他兽脚亚目恐龙的足趾骨比较表明，费尔波特段的标本很可能是一个大型似鸟龙类的右足第二趾骨，可能是第三趾的第二趾节。我们谨慎地将铁闪电段的标本鉴定为一个似鸟龙类的左足第二趾骨。费尔波特段的骨头来自于薄而交错的海相砂岩，其中含有大的赤铁矿结核和结核层。伴生的化石包括硬骨鱼牙齿、鳍刺和耳石，以及大量常见的白垩纪近岸和远洋软骨鱼类牙齿。叶子印痕和其他植物残骸、化石木块以及洞穴也很常见。铁闪电段的骨头来自于一个由细砂岩到粗砂岩床组成的河道沉积，其中一些床层含有双壳类，以及散布的哺乳动物牙齿、软骨鱼类牙齿和零碎的恐龙牙齿和爪子。我们将这两个标本的沉积环境解释为边缘海。费尔波特段的骨头来自近岸前积层，位于波浪基准面之上，受潮汐流动和风暴活动的影响。铁闪电段的标本来自一个顶积河道的填充物，可能与潮汐平原或相关的海岸环境的沉积有关。这两个标本的埋藏史和年龄不同。费尔波特段标本皮质骨中的正交裂缝表明，在被运移到上述近岸环境中保存之前，它曾在一个旱地海岸环境中经历过死后干燥。铁闪电段标本的原始表面表明，在被纳入其所在的河道沉积之前，它很少被搬运。费尔波特段的骨床最有可能位于早马斯特里赫特晚期的菊石带内，因此其年龄大约为 6900 万年。铁闪电段的骨头来自于上覆的菊石带，因此年龄要年轻大约一百万年。
