Odobenus rosmarus; geometric morphometrics; ontogeny; sexual dimorphism; subspecies
Abstract :
[en] As both iconic Arctic megafauna and long-exploited marine resources, walruses (Odobenus rosmarus) have left an abundant osteological record across the Holarctic. However, distinguishing sex, ontogenetic stage, and subspecies assignation from disarticulated skeletal elements remains challenging. Quantifying cranial and mandibular shape variation while disentangling the effects of individual intrinsic factors (sexual dimorphism, ontogeny, geographic distribution) but also their combined influence offers new insights into these key axes of morphological differentiation. Here, two-dimensional geometric morphometric analyses are applied to 166 skulls and 143 mandibles representing the Atlantic (O. r. rosmarus) and Pacific (O. r. divergens) subspecies. Analyses revealed that sexual dimorphism is the dominant morphological signal: males develop more compact and reinforced skulls and mandibles, reflecting strong constraints to grow tusks and handle combat stresses, whereas females retain more gracile morphologies. Juveniles closely resemble adult females, with males diverging later through delayed hypermorphic growth. Subspecific comparisons confirmed significant differences, with Pacific walruses exhibiting more robust morphologies and greater developmental canalization, while Atlantic walruses show higher variability, likely linked to heterogeneous ecological conditions. Population-level analyses highlighted additional structuring, with Pacific groups tightly constrained and Atlantic groups occupying a broader morphospace. Unlike previous studies that examined sexual dimorphism, ontogeny, or subspecific differences separately, our study evaluates all three factors within a unified framework, revealing a hierarchical organization of craniomandibular variation shaped by sexual selection, developmental timing, and ecological divergence. These results provide new insights into walrus evolutionary history and their differential vulnerability to past human exploitation and ongoing Arctic environmental change.
Disciplines :
Zoology
Author, co-author :
Boisville, Mathieu ; Earth Historical Analysis, Earth Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
Chatar, Narimane ; Université de Liège - ULiège > Département de géologie > Evolution and diversity dynamics lab ; Functional Anatomy and Vertebrate Evolution Lab, Department of Integrative Biology, University of California Berkeley, Berkeley, California, USA
Ruiz-Puerta, Emily J; Section for Molecular Ecology and Evolution, Globe Institute, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Kobenhavn, Denmark ; Arctic Centre & Groningen Institute of Archaeology, Faculty of Arts, University of Groningen, Groningen, The Netherlands
Rule, James P ; School of Biological Sciences, Monash University, Victoria, Australia
Kohno, Naoki ; Earth Historical Analysis, Earth Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan ; Department of Paleontology and Anthropology, National Museum of Nature and Science, Tsukuba, Japan
Language :
English
Title :
Exploring factors shaping the craniomandibular shape of extant walrus.
Publication date :
03 April 2026
Journal title :
Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology
The authors thank the following individuals and institutions for providing access to and assistance, or photographs of, specimens under their care: Academy of Natural Sciences of Drexel University (Philadelphia, USA): Ned Gilmore, Ted Daeschler; Canadian Museum of Nature (Ottawa, Canada): Scott Rufolo, Shyong En Pan, Aaraya Aad; Chiba Environmental Research Center (Chiba, Japan): Takahiro Kojima; Chiba Natural History Museum and Institute (Chiba, Japan): Satoshi Maruyama, Hisayoshi Kato; Icelandic Institute of Natural History (Gar\u00F0ab\u00E6r, Iceland): Sn\u00E6bj\u00F6rn P\u00E1lsson; Icelandic Museum of Natural History (Seltjarnarnes, Iceland): Hilmar Malmquist; Museum of Zoology, University of Cambridge (Cambridge, UK): Robert Asher; Natuurhistorisch Museum (Rotterdam, the Netherlands): Hidde Bakker, Bram Langeveld, Klaas Post; National Museum of Nature and Science (Tokyo, Japan): Yuko Tajima; Naturalis Biodiversity Center (Leiden, the Netherlands): Anne Schulp, Jelle Reumer, Anne van de Weerd, Willem Renema, Klaas Post; Royal Belgian Institute of Natural Sciences (Brussels, Belgium): Pascal Godefroit, S\u00E9bastien Bruaux, Terry Walschaert, Olivier Pauwels, Olivier Lambert, Leonard Dewaele; Smithsonian National Museum of Natural History (Washington DC, USA): Darrin Lunde, Michael McGowen, John Ososky; The Natural History Museum (London, UK): Phaedra Kokkini; University of Cambridge (Cambridge, UK): Daniel Field; University of Copenhagen (Copenhagen, Denmark): Morten Tange Olsen, Sarah Saboya de Medeiros, Anne Birgitte Gotfredsen; Zoological Institute, Russian Academy of Sciences (St. Petersburg, Russia): Gennady F. Baryshnikov, Alexei Tikhonov. The authors also express their sincere gratitude to Olivier Lambert and Leonard Dewaele, with whom the initial ideas for this project were developed during a research stay at the Royal Belgian Institute of Natural Sciences (Brussels) in 2020. Mathieu Boisville was supported by the Overseas Musha Training Support Program for Graduate Students and the Support Program for Participation in Overseas Conferences of the Habatake! Program from the University of Tsukuba. Additional support was provided by the Jackson School of Travel Grant from the Society of Vertebrate Paleontology and by the Hans de Bruijn Foundation, which funded visits to museum collections in the Netherlands. Narimane Chatar was supported by a Belgian American Educational Foundation (BAEF) post\u2010doctoral fellowship as well as a grant from the National Science Foundation (NSF DBI\u20102128146).
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