Evolutionary pathways toward gigantism in sharks and rays

Through elasmobranch (sharks and rays) evolutionary history, gigantism evolved multiple times in phylogenetically distant species, some of which are now extinct. Interestingly, the world’s largest elasmobranchs display two specializations found never to overlap: filter feeding and mesothermy. The co...

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Bibliographic Details
Published in:Evolution 2019-03, Vol.73 (3), p.588-599
Main Authors: Pimiento, Catalina, Cantalapiedra, Juan L., Shimada, Kenshu, Field, Daniel J., Smaers, Jeroen B.
Format: Article
Language:English
Subjects:
Animals
Biological Evolution
Body Size
Case studies
Cretaceous
Diet
Elasmobranchii - anatomy & histology
Elasmobranchii - physiology
elasmobranchs
Evolution
Feeders
Feeding
Filter feeders
filter feeding
Gigantism
mesothermy
Oceans
ORIGINAL ARTICLE
Paleogene
Phylogeny
Prey
Sharks
Sharks - anatomy & histology
Sharks - physiology
Species extinction
Trophic levels
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Summary:Through elasmobranch (sharks and rays) evolutionary history, gigantism evolved multiple times in phylogenetically distant species, some of which are now extinct. Interestingly, the world’s largest elasmobranchs display two specializations found never to overlap: filter feeding and mesothermy. The contrasting lifestyles of elasmobranch giants provide an ideal case study to elucidate the evolutionary pathways leading to gigantism in the oceans. Here, we applied a phylogenetic approach to a global dataset of 459 taxa to study the evolution of elasmobranch gigantism. We found that filter feeders and mesotherms deviate from general relationships between trophic level and body size, and exhibit significantly larger sizes than ectothermic-macropredators. We confirm that filter feeding arose multiple times during the Paleogene, and suggest the possibility of a single origin of mesothermy in the Cretaceous. Together, our results elucidate two main evolutionary pathways that enable gigantism: mesothermic and filter feeding. These pathways were followed by ancestrally large clades and facilitated extreme sizes through specializations for enhancing prey intake. Although a negligible percentage of ectothermic-macropredators reach gigantic sizes, these species lack such specializations and are correspondingly constrained to the lower limits of gigantism. Importantly, the very adaptive strategies that enabled the evolution of the largest sharks can also confer high extinction susceptibility.
ISSN:0014-3820
1558-5646
DOI:10.1111/evo.13680