# Morphometric Assessment of Pelvic Asymmetry in Domestic Cats and Dogs

## TL;DR

This study examines left-right pelvic asymmetry in domestic cats and dogs, finding consistent patterns and individual variation that could aid veterinary anatomy and comparative research.

## Contribution

The study introduces a repeatable geometric morphometric framework to quantify pelvic asymmetry in cats and dogs, revealing distinct species and sex-related patterns.

## Key findings

- Cats showed a stronger and more consistent left-right asymmetry pattern compared to dogs.
- Males exhibited greater fluctuating asymmetry than females.
- Pelvic asymmetry patterns were not significantly associated with age or body mass.

## Abstract

Pelvic bones are expected to exhibit left–right symmetry; however, small differences between sides can arise due to growth, daily movement, and individual life history. Evidence was found for two patterns: a small but consistent left–right difference across the overall sample and additional individual-to-individual variation in asymmetry. High consistency was observed across repeated landmark digitizations, indicating that the detected patterns were not primarily driven by digitizing error. When groups were compared, the patterns described for cats and dogs reflect descriptive summaries of the sample rather than formal between-group statistical inference. In these descriptive summaries, cats tended to exhibit a stronger and more consistent left–right pattern, whereas dogs showed greater individual variation. Differences in asymmetry magnitude were also observed between males and females. No clear association was detected with age, and only a weak trend was observed with body mass. These findings provide a reliable reference for understanding pelvic shape differences in cats and dogs and may be useful for veterinary anatomy and comparative research.

This study used 3D landmark-based geometric morphometrics under an object-symmetry framework to quantify pelvic asymmetry in domestic cats and dogs while explicitly accounting for measurement error through replicate digitizations. Procrustes ANOVA revealed significant components of both directional asymmetry (DA) and fluctuating asymmetry (FA) in the overall dataset, and DA was further visualized as a structured, non-random pattern across the landmark configuration. Measurement error remained smaller than the FA component, yielding high repeatability, indicating that the detected asymmetry patterns were not driven by landmarking imprecision. Group-wise summaries are presented as descriptive patterns of the sample (rather than direct between-group inference). In these descriptive summaries, cats tended to show a more coherent DA pattern, whereas dogs showed greater individual variation consistent with a relatively stronger FA component; males also tended to exhibit greater FA-related dispersion than females. In regression models of FA, age showed no association, body mass exhibited only a weak trend, and sex emerged as a significant predictor, while species showed no detectable effect when covariates were included. Collectively, these results support the hypothesis that pelvic shape contains both systematic (DA) and individual-specific (FA) asymmetry components, with sex-related differences in FA magnitude, but limited evidence for age- or weight-related effects within the sampled range. The study provides a repeatable framework and baseline reference for pelvic asymmetry in cats and dogs.