Data and code from: Cross-species applicability of a bone-ageing method in delphinids
Data files
Feb 05, 2026 version files 2.98 MB
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Flipper_development.Rmd
23.28 KB
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Inter-observer_error.R
6.35 KB
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Pectoral_fin_data.xlsx
2.94 MB
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README.md
8.03 KB
Abstract
Radiographic evaluation of flipper ossification is a reliable technique for age estimation in bottlenose dolphins (Tursiops truncatus), although its applicability to other odontocetes remains untested. Interspecific differences in flipper morphology and bone development may limit transferability or require adjustments for robust application. This study applies the bottlenose dolphin framework to common dolphins (Delphinus delphis) to characterise developmental patterns, describe morphological differences, and evaluate the interspecific application of this method. Radiographs from 137 common dolphins aged 0–31 years were examined, with bone maturation scored at 16 anatomical sites on the pectoral flipper. Several differences were identified, including bilateral asymmetry between left and right flippers and the need to adjust long and delta bone scoring systems due to interspecific variation in bone maturation. Despite these differences, reproducibility between observers was high, and ossification scores correlated strongly with age, underscoring the reliability of the method. This study provides the groundwork for a species-specific bone ageing model for common dolphins by addressing interspecific variation in skeletal maturation. One caveat concerns the subtle expression of degenerative changes in this species compared with bottlenose dolphins, which may limit age estimation precision in older individuals but is unlikely to affect accuracy across most of the lifespan. Thus, our findings provide the first evidence that, despite morphological differences, the method can be successfully applied to common dolphins.
Dataset DOI: 10.5061/dryad.8931zcs4t
Description of the data and file structure
Files:
- Pectoral_fin_data.xlsx – raw data including bone maturation scores and metadata.
- Flipper_development.Rmd – R code for main analyses.
- Inter-observer_error.R – R code for reproducibility assessment.
Regarding Pectoral_fin_data.xlsx:
'Left' and 'Right'
Sheet "Left" and "Right" show the bone maturation scores for the left and the right pectoral flipper. The values for individual bone locations range from -1 to 8 scored based on morphological maturation stages. Total bone scores are defined as the sum of discrete morphological maturation stages across all flipper bone.
Abbreviations are as follows:
| Abbreviations | Explanations |
|---|---|
| M2pr | Metacarpal 2, proximal epiphysis |
| M3pr | Metacarpal 3, proximal epiphysis |
| M4pr | Metacarpal 4, proximal epiphysis |
| M5 | Metacarpal 5 |
| M2dis | Metacarpal 2, distal epiphysis |
| M3dis | Metacarpal 3, distal epiphysis |
| M4dis | Metacarpal 4, proximal epiphysis |
| D2P1pr | First phalanx of digit 2, proximal epiphysis |
| D3P1pr | First phalanx of digit 3, proximal epiphysis |
| D4P1 (delta) | Proximal phalanx of digit 4, (delta bone) |
| D2P1dis | Proximal phalanx of digit 2, distal epiphysis |
| D3P1dis | Proximal phalanx of digit 3, distal epiphysis |
| D2P2average | Average score for the second phalanx of digit 2 (calculated from the individual scores of proximal and distal epiphysis) |
| D3P2average | Average score for the second phalanx of digit 3 (calculated from the individual scores of proximal and distal epiphysis) |
| D2P2max | Maximum score for the second phalanx of digit 2 (calculated from the individual scores of proximal and distal epiphysis) |
| D3P2max | Maximum score for the second phalanx of digit 3 (calculated from the individual scores of proximal and distal epiphysis) |
| D2P2min | Minimum score for the second phalanx of digit 2 (calculated from the individual scores of proximal and distal epiphysis) |
| D3P2min | Minimum score for the second phalanx of digit 3 (calculated from the individual scores of proximal and distal epiphysis) |
| Total_score_detailed | The total bone score was calculated using all individual bone scores, with the proximal and distal epiphyses of the second phalanges of digits 2 and 3 treated as separate scores. |
| Total_score_average | The total bone score was calculated using all individual bone scores, with the proximal and distal epiphyses of the second phalanges of digits 2 and 3 represented by their average score. |
| Total_score_max | The total bone score was calculated using all individual bone scores, with the proximal and distal epiphyses of the second phalanges of digits 2 and 3 represented by their maximum score. |
| Total_score_min | The total bone score was calculated using all individual bone scores, with the proximal and distal epiphyses of the second phalanges of digits 2 and 3 represented by their minimum score. |
'Proximal-distal development'
Ossification typically begins in the radius, followed by the ulna and then progresses distally into the metacarpals and phalanges. The sheet 'Proximal-distal development' lists individuals which showed abnormalities with regard to the typical proximal-distal progression of bone maturation.
'Spearman'
The sheet comprises pooled raw data from the left and right pectoral flippers used to calculate Spearman correlations between bone maturation and age.
'Bilaterality'
The sheet presents total bone scores for the left and right pectoral flippers and compares them to assess whether bilateral differences in bone maturation occurred.
'Delta bone anomalies'
Delta bone maturation typically follows a unidirectional sequence; whereby distal mineralization is not expected until proximal consolidation is complete. In a subset of common dolphins, however, distal ossification frequently began before the proximal center had fully consolidated. This sheet lists the affected animal codes and the maturation stages of the affected delta bones.
'Ashley vs me (R)'
This sheet provides bone scores for animals that were scored by two observers. These raw data were used to assess inter-observer error in assigning morphological bone maturation stages.
Code/ Software
Analyses were performed in R v4.3.2.
- Inter-observer error: potential observer-related bias was tested using generalized linear mixed-effects models (GLMMs; lme4 package) on a subset of 40 radiographs scored by two independent observers.
- Correlation of ossification scores with age: relationships between ossification stage and dental age were assessed using Spearman’s rank correlation (ρ), run separately for males and females.
- Precedence matrix analysis: pairwise comparisons among bones were used to establish the typical developmental order of ossification and to visualize sex- and side-specific variation.