Abstract
Lamniform sharks are apex marine predators undergoing dramatic local and regional decline worldwide, with consequences for marine ecosystems that are difficult to predict. Through their long history, lamniform sharks have faced widespread extinction, and understanding those ‘natural experiments’ may help constrain predictions, placing the current crisis in evolutionary context. Here we show, using novel morphometric analyses of fossil shark teeth, that the end-Cretaceous extinction of many sharks had major ecological consequences. Post-extinction ecosystems supported lower diversity and disparity of lamniforms, and were dominated by significantly smaller sharks with slimmer, smoother and less robust teeth. Tooth shape is intimately associated with ecology, feeding and prey type, and by integrating data from extant sharks we show that latest Cretaceous sharks occupied similar niches to modern lamniforms, implying similar ecosystem structure and function. By comparison, species in the depauperate post-extinction community occupied niches most similar to those of juvenile sand tigers (Carcharias taurus). Our data show that quantitative tooth morphometrics can distinguish lamniform sharks due to dietary differences, providing critical insights into ecological consequences of past extinction episodes.
Highlights
The end-Cretaceous mass extinction event witnessed the loss of 40% of marine genera and is ranked as the fifth most severe such event of the Phanerozoic [1]
Our analyses demonstrate that Maastrichtian lamniforms were ecologically diverse, occupying similar ecomorphospace compared to extant taxa, whereas post-extinction Danian lamniforms were significantly smaller with much reduced ecological diversity
The disappearance of the more common Maastrichtian taxa cannot be attributed to preservation or sampling biases because they are represented by large, robust teeth (e.g. Serratolamna maroccana and Squalicorax pristodontus), unlikely to be preferentially lost during diagenesis or overlooked during collection
Summary
The end-Cretaceous mass extinction event witnessed the loss of 40% of marine genera and is ranked as the fifth most severe such event of the Phanerozoic [1]. 34% of genera and 45% of species became extinct [3]. Documenting rates of taxonomic extinction does not, provide a measure of ecological impact, the magnitude of which is decoupled from the associated loss of taxa during past events [1,5]. In terms of its ecological impact, the end-Cretaceous event was the second most severe crisis of the Phanerozoic [1]. Studies of predatory bony fish demonstrate significant ecological selectivity during the end-Cretaceous extinction [8,9], but no similar study has been attempted for sharks even though they represent an ideal model
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