Fossil Record 18(1): 1-16, doi: 10.5194/fr-18-1-2015
The rarity of gastroliths in sauropod dinosaurs – a case study in the Late Jurassic Morrison Formation, western USA
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‡ Institut für Geowissenschaften, Universität Tübingen, Sigwartstraße 10, 72076 Tübingen, Germany and Museum für Naturkunde Berlin, Invalidenstraße 43, 10115 Berlin, Germany
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Occurrences of suspected sauropod geo-gastroliths and"exoliths" (exotic clasts) are compared with authentic finds of stomach stonesin the sauropods Diplodocus, Cedarosaurus, and Camarasaurus.Sedimentological and taphonomical evidence fromclassic sauropod dinosaur localities in the Late Jurassic Morrison Formation(Cleveland-Lloyd Dinosaur Quarry, Dry Mesa Dinosaur Quarry, CarnegieQuarry/Dinosaur National Monument, Howe Quarry, Como Bluff, and Bone CabinQuarry) reveals very few sauropod finds with unambiguous gastroliths. Thescarcity of clasts in the fine-grained sediments of most of the localitiessuggests that only a small number of sauropods possessed gastroliths. Theoccurrence of a hypothetical avian-style gastric mill in sauropods is notsupported by taphonomical evidence. Exoliths that are abundant in the EarlyCretaceous of the western USA are nearly absent in Late Jurassic sediments.Without an association with fossil bone, there is no convincing evidencethat such clasts represent former gastroliths. It is more plausible thatmost exoliths have been transported in hyperclastic flows or thatsurface-collected stones are weathering relicts of former conglomeratelayers.