Submission Type

Poster

Abstract

Lamniform sharks (Elasmobranchii: Lamniformes) display diverse habitat preferences and lifestyles. Based on museum specimens and published illustrations, we examined the proportion of the anteroposterior length of the rostral, olfactory, optic, and otic regions with respect to the neurocranial length in each lamniform species as a proxy of relative importance of each sensory region (electroreception, olfaction, vision, and ‘coordination’) to its lifestyle. We show that: 1) Carcharias and Megachasma (ragged-tooth and megamouth) have short rostral and large otic regions indicative of slower-swimming pelagic lifestyles with elevated coordination for balancing in the water column; 2) Alopias pelagicus, A. vulpinus, Carcharodon carcharias, Lamna ditropis, Odontaspis ferox, and O. noronhai (pelagic and common threshers, white, salmon, and sandtigers) have moderately long rostral and large optic-otic regions suggestive of fast-swimming pelagic lifestyles with enhanced vision and coordination for prey hunting aided by electroreception; 3) Isurus oxyrinchus, I. paucus, and Lamna nasus (makos and porbeagle) have relatively long rostral and optic regions for a moderate reliance of electroreception and enhanced vision for capturing large prey; and 4) Cetorhinus (basking) has a small optic region with a moderately elongated rostrum and large otic region reflective of an active planktivorous pelagic lifestyle with migratory behaviors and moderate use of electroreception. Pseudocarcharias and A. superciliosus (crocodile and bigeye thresher) living in deeper waters have large optic regions, but the trend is not universal; most strikingly, Mitsukurina (goblin) has an exceptionally elongated rostrum with the smallest optic region among all the lamniforms likely reflecting its heavy reliance on electroreception relative to vision. We also investigated shape variation of the lamniform neurocranium using landmark-based geometric morphometric analyses, and determined that rostral shape is the most variable relative to the other regions. Our study provides new insights into their evolutionary history and implications for conservation biology.

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Kenshu Shimada

Department of Biological Sciences, DePaul University

Department of Environmental Sciences and Studies, DePaul University

Sternberg Museum of Natural History, Fort Hays State University

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Functional implications reflected in neurocranial morphology of lamniform sharks (Elasmobranchii: Lamniformes)

Lamniform sharks (Elasmobranchii: Lamniformes) display diverse habitat preferences and lifestyles. Based on museum specimens and published illustrations, we examined the proportion of the anteroposterior length of the rostral, olfactory, optic, and otic regions with respect to the neurocranial length in each lamniform species as a proxy of relative importance of each sensory region (electroreception, olfaction, vision, and ‘coordination’) to its lifestyle. We show that: 1) Carcharias and Megachasma (ragged-tooth and megamouth) have short rostral and large otic regions indicative of slower-swimming pelagic lifestyles with elevated coordination for balancing in the water column; 2) Alopias pelagicus, A. vulpinus, Carcharodon carcharias, Lamna ditropis, Odontaspis ferox, and O. noronhai (pelagic and common threshers, white, salmon, and sandtigers) have moderately long rostral and large optic-otic regions suggestive of fast-swimming pelagic lifestyles with enhanced vision and coordination for prey hunting aided by electroreception; 3) Isurus oxyrinchus, I. paucus, and Lamna nasus (makos and porbeagle) have relatively long rostral and optic regions for a moderate reliance of electroreception and enhanced vision for capturing large prey; and 4) Cetorhinus (basking) has a small optic region with a moderately elongated rostrum and large otic region reflective of an active planktivorous pelagic lifestyle with migratory behaviors and moderate use of electroreception. Pseudocarcharias and A. superciliosus (crocodile and bigeye thresher) living in deeper waters have large optic regions, but the trend is not universal; most strikingly, Mitsukurina (goblin) has an exceptionally elongated rostrum with the smallest optic region among all the lamniforms likely reflecting its heavy reliance on electroreception relative to vision. We also investigated shape variation of the lamniform neurocranium using landmark-based geometric morphometric analyses, and determined that rostral shape is the most variable relative to the other regions. Our study provides new insights into their evolutionary history and implications for conservation biology.