The Science of Nature

, 102:58

Cranial symmetry in baleen whales (Cetacea, Mysticeti) and the occurrence of cranial asymmetry throughout cetacean evolution

Original Paper

DOI: 10.1007/s00114-015-1309-0

Cite this article as:
Fahlke, J.M. & Hampe, O. Sci Nat (2015) 102: 58. doi:10.1007/s00114-015-1309-0

Abstract

Odontoceti and Mysticeti (toothed and baleen whales) originated from Eocene archaeocetes that had evolved from terrestrial artiodactyls. Cranial asymmetry is known in odontocetes that can hear ultrasound (>20,000 Hz) and has been linked to the split function of the nasal passage in breathing and vocalization. Recent results indicate that archaeocetes also had asymmetric crania. Their asymmetry has been linked to directional hearing in water, although hearing frequencies are still under debate. Mysticetes capable of low-frequency and infrasonic hearing (<20 Hz) are assumed to have symmetric crania. This study aims to resolve whether mysticete crania are indeed symmetric and whether mysticete cranial symmetry is plesiomorphic or secondary. Cranial shape was analyzed applying geometric morphometrics to three-dimensional (3D) cranial models of fossil and modern mysticetes, Eocene archaeocetes, modern artiodactyls, and modern odontocetes. Statistical tests include analysis of variance, principal components analysis, and discriminant function analysis. Results suggest that symmetric shape difference reflects general trends in cetacean evolution. Asymmetry includes significant fluctuating and directional asymmetry, the latter being very small. Mysticete crania are as symmetric as those of terrestrial artiodactyls and archaeocetes, without significant differences within Mysticeti. Odontocete crania are more asymmetric. These results indicate that (1) all mysticetes have symmetric crania, (2) archaeocete cranial asymmetry is not conspicuous in most of the skull but may yet be conspicuous in the rostrum, (3) directional cranial asymmetry is an odontocete specialization, and (4) directional cranial asymmetry is more likely related to echolocation than hearing.

Keywords

Directional asymmetry Hearing 3D geometric morphometrics Photogrammetry 

Supplementary material

114_2015_1309_MOESM1_ESM.pdf (23 kb)
ESM 1(PDF 23.1 kb)
114_2015_1309_MOESM2_ESM.pdf (24 kb)
ESM 2(PDF 24.1 kb)
114_2015_1309_MOESM3_ESM.pdf (36 kb)
ESM 3(PDF 35 kb)
114_2015_1309_MOESM4_ESM.tif (174 kb)
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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.Museum für NaturkundeLeibniz-Institut für Evolutions- und BiodiversitätsforschungBerlinGermany

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