Abstract
The body morphology of harbour porpoises (Phocoena phocoena), like that of other fully aquatic mammals, differs greatly from terrestrial species due to adaptations to aquatic life. Thus, the developmental processes of the osteochondral unit (OCU) and its postnatal adaptation in harbour porpoises remain poorly understood. Here, we compared the humeral head microarchitecture in neonate, juvenile and adult harbour porpoises to better understand the relationship between environmental loading and the organisation of the OCU within diarthrodial joints. In neonates, the superficial layer of hyaline cartilage showed parallel collagen fibres, while the remaining cartilage exhibited an oblique orientation. Neither a calcified cartilage layer (CCL) nor a subchondral bone plate (SBP) was present. In juveniles the early formation of distinct zones in the articular cartilage, initial cartilage calcification and SBP formation were observed. Adults exhibited a layered hyaline cartilage structure within an arcade-like collagen arrangement, similar to terrestrial mammals. The formation of the CCL and SBP was age-dependent, as in terrestrial species, but appeared to occur later in the maturation process towards adults. These findings provide new insight into how aquatic environments shape age-related remodeling and structural adaptation of the OCU in cetacean diarthrodial joints.
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The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.
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Acknowledgements
We sincerely thank the stranding network volunteers and organizations for reporting and retrieving deceased harbour porpoises for our research. The post-mortem investigations were conducted at Utrecht University with the help of many colleagues, students, and volunteers, for which we specifically want to acknowledge Andrea Gröne, Linde van Schalkwijk, Nadiah van Eijk, Manon Lock, Louis van den Boom, Marc Kranenburg, Darryl Leydekkers, Mattie van Rijen, and Ruby Wagensveld.
Funding
Necropsies of harbour porpoises in The Netherlands are commissioned by the Ministry of Agriculture, Fisheries, Food Security and Nature, and since 2016 embedded under the Legal Research Tasks Nature & Environment unit of Wageningen UR (project reference numbers 140000353, WOT-04-009-045, WUR1482821). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon Europe research and innovation programme (Re-COLL; grant agreement No [101142063]) and by the Summit Program “DRIVE-RM”, funded by The Dutch Research Council (NWO)(SUMMIT.1.027).
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M.M.K. conceptualised the study, carried out the data collection, data preparation, formal analysis, visualisation, painted illustrations and wrote the initial manuscript draft. L.L.I.J. was involved in the data collection and preparation and reviewed and edited the final manuscript. J.M. conceptualised the study. P.R.v.W., R.L., and J.M. supervised the study, and critically reviewed and edited the manuscript.
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Ethical review and approval was not required for the animal study because the animals described in this study were harbour porpoises which died of natural causes or were euthanized on welfare grounds and not for the purpose of this, or other, studies. No consent from an Animal Use Committee was required, as the animals described in this study were not used for scientific or commercial testing. Consequently, animal ethics committee approval was not applicable to this work.
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Księżarczyk, M.M., IJsseldijk, L.L., van Weeren, P.R. et al. Age-dependent development and microarchitecture of the osteochondral unit of the humeral head in harbour porpoises (Phocoena phocoena). Sci Rep (2026). https://doi.org/10.1038/s41598-026-39726-7
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DOI: https://doi.org/10.1038/s41598-026-39726-7
