Chelsea M. Comans, Sandi M. Smart, Emma R. Kast, YueHan Lu, Tina Lüdecke, Jennifer N. Leichliter, Daniel M. Sigman, Takehito Ikejiri, Alfredo Martínez-García
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引用次数: 0
Abstract
The nitrogen isotopic composition (15N/14N ratio, or δ15N) of enameloid-bound organic matter (δ15NEB) in shark teeth was recently developed to investigate the biogeochemistry and trophic structures (i.e., food webs) of the ancient ocean. Using δ15NEB, we present the first nitrogen isotopic evidence for trophic differences between shark taxa from a single fossil locality. We analyze the teeth of four taxa (Meristodonoides, Ptychodus, Scapanorhynchus, and Squalicorax) from the Late Cretaceous (83–84 Ma) Trussells Creek site in Alabama, USA, and compare the N isotopic findings with predictions from tooth morphology, the traditional method for inferring shark paleo-diets. Our δ15NEB data indicate two distinct trophic groups, with averages separated by 6.1 ± 2.1‰. The lower group consists of Meristodonoides and Ptychodus, and the higher group consists of Scapanorhynchus and Squalicorax (i.e., lamniforms). This δ15NEB difference indicates a 1.5 ± 0.5 trophic-level separation between the two groups, a finding that is in line with paleontological predictions of a higher trophic level for these lamniforms over Meristodonoides and Ptychodus. However, the δ15NEB of Meristodonoides is lower than suggested by tooth morphology, although consistent with mechanical tests suggesting that higher trophic-level bony fishes were not a major component of their diet. Further, δ15NEB indicates that the two sampled lamniform taxa fed at similar trophic levels despite their different inferred tooth functions. These two findings suggest that tooth morphology alone may not always be a sufficient indicator of dietary niche. The large trophic separation revealed by the δ15NEB offset leaves open the possibility that higher trophic-level lamniforms, such as those measured here, preyed upon smaller, lower trophic-level sharks like Meristodonoides.
期刊介绍:
The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time.
Geobiology invites submission of high-quality articles in the following areas:
Origins and evolution of life
Co-evolution of the atmosphere, hydrosphere and biosphere
The sedimentary rock record and geobiology of critical intervals
Paleobiology and evolutionary ecology
Biogeochemistry and global elemental cycles
Microbe-mineral interactions
Biomarkers
Molecular ecology and phylogenetics.