The holotypic locality of the brachiosaurid titanosauriform sauropod, Abydosaurus mcintoshi, is quarry DNM-16, located in Dinosaur National Monument. The bones are preserved near the base of a heterolithic, trough cross stratified to planar bedded sandstone channel complex. The trough cross to planar bedded sandstones mark times of variable flow with times of high flow velocity based on bones whose upper surfaces were eroded before final burial. The abundance of mud with the dominant medium to fine sand, and poorly confined sandstone channels indicate the bones were transported and buried in medial to distal intermittent flows of a distributive fluvial system. The quarry is at the base of the Naturita Formation, the base of which is latest Albian in age. The sauropods lived and died in the middle Cretaceous as the Cretaceous seaway advanced southward. The unconformity below the Naturita Formation and on top of the underlying the Ruby Ranch Member represents the LK-2 sequence boundary. The quarry produced ~260 bones, all of which represent Abydosaurus, except for several small theropod teeth, denoting a single catastrophic event acting on a group of sauropods. About one-third of the bones occur in close association or articulation, including three skulls (one articulated with the first five cervical vertebrae), five limbs, and strings of caudal vertebrae. There is no evidence of preburial weathering or breakage, and trample scratch marks are rare. More than 20% of the bones exhibit irregular, mm-scale pits occur on the shafts and the articular ends of limb bones are commonly hollowed out. The irregular pits are termite foraging traces, and hollows indicate extensive mining by these insects. At least seven individuals of Abydosaurus are present, representing at least two ontogenetic stages (juveniles and subadults).Together, these observations indicate the following: (1) the catastrophic death of a sauropod herd; (2) partial carcass maceration; (3) minor transportation, including articulated units (skulls, vertebrae, limbs); (4) rapid burial in migrating, ephemeral, branches of a distributary fluvial system; (5) channel migration resulting in in-situ scouring of the upper surface of some bones; (6) burial of scoured bones. Termite infestation occurred both prior to, and after, fluvial entrainment and burial.



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Physical and Mathematical Sciences; Geological Sciences



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Abydosaurus, Naturita Formation, taphonomy, sedimentology, distributive fluvial system, Dinosaur National Monument, DNM-16

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