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Age prediction model for adult male Galapagos sea lions based on skull measures

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Abstract

The age of adult mammals is required for studies related to ontogeny patterns, growth rate, and life history. However, the reliable age determination from skulls with no canine teeth is generally inaccurate. This research aims to develop an age prediction model for adult male sea lions by measures of a particular skull section, which was validated by counting dentine growth layers in their upper canine teeth. We used skulls and teeth of 49 Galapagos sea lions (GSL, Zalophus wollebaeki) aged between 13 and 20 years old collected in different breeding rookeries of the Galapagos archipelago between 2000 and 2018. Two groups of skull measures were considered: (1) measures correlating with total skull length and (2) measures used in growth models in the literature. A generalized additive model was adjusted to estimate ages on skulls. The measures that best described the age prediction model were maxillary tooth row length (MTRL), occipital plate height (OPH), anterior nasal width (ANW), braincase posterior width (BPW), braincase width (BW), jugal supraorbital process height (JSPH), nasal length (NL), orbital length (OL), and postpalate length (PosL) (r2 = 0.93; AIC = 56.16). The predicted ages were close to those counted in teeth with a standard deviation between 0.10 and 0.45 of the average age. This validates the usefulness of our approach to determine age in skulls of GSL even with missing teeth. We recommend the assessment and application of this methodology in morphometric research of pinnipeds but considering morphological characteristics and the skull development of each species.

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Acknowledgments

We thank the Galapagos National Park Directorate (GNPD) for providing logistical support and for granting us permission to collect the samples used in this study. We also thank the Universidad San Francisco de Quito (USFQ) for logistical support during the preparation of this manuscript. We are grateful to GNPD rangers and the crew “Sierra Negra” ship for their help in collecting and processing the biological material used in this study. We offer special gratitude to all members of GNPD/USFQ/UNC research expeditions for providing their invaluable work during the collection of osteological material. Finally, we thank Dr. Carlos F. Mena and all staff of Galapagos Science Center (GSC) for providing the facilities for information processing and samples analysis.

Funding

Financial support was provided by the Universidad San Francisco de Quito (USFQ).

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Authors and Affiliations

  1. Galapagos Science Center, Universidad San Francisco de Quito, Isla San Cristóbal, Islas Galápagos, Ecuador

    Salomé Izurieta-Benítez, Diego O. Urquía, Marjorie Riofrío-Lazo & Diego Páez-Rosas

  2. Dirección del Parque Nacional Galápagos, Oficina Técnica San Cristóbal, Isla San Cristóbal, Islas Galápagos, Ecuador

    Jorge Torres & Diego Páez-Rosas

Authors
  1. Salomé Izurieta-Benítez
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  2. Diego O. Urquía
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  3. Jorge Torres
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  4. Marjorie Riofrío-Lazo
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  5. Diego Páez-Rosas
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Contributions

Conceptualization: S.I-B. and D.P-R. Collected data: S-I-B., J.T. and D.P-R. Designed methodology: D.O.U., D.P-R. and M.R-L. Funding acquisition: D.P-R. Formal analysis: D.O.U., D.P-R., and M.R-L. Writing-original draft: S.I-B. and D.P-R. Writing-review and editing: S.I-B., D.O.U., J.T., M.R-L. and D.P-R. All authors gave final approval for publication.

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Correspondence to Diego Páez-Rosas.

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Communicated by: Cino Pertoldi

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Izurieta-Benítez, S., Urquía, D.O., Torres, J. et al. Age prediction model for adult male Galapagos sea lions based on skull measures. Mamm Res 66, 201–210 (2021). https://doi.org/10.1007/s13364-020-00553-4

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