Anat Histol Embryol. 2019;00:1–6. wileyonlinelibrary.com/journal/ahe | 1 © 2019 Blackwell Verlag GmbH 1 | INTRODUCTION Paedomorphosis refers to underdevelopment, for example adults re‐ sembling a juvenile stage of its ancestor (Armbruster, Lee, Edwards, & Baldwin, 2013; Diogo & Ziermann, 2015; Goodwin, Bradshaw, & Wickens, 1997). It appears either when character development is delayed or through acceleration of sexual maturation (Leonova, 2015); paedomorphic animals require less growth to be developed as adult form (Geiger & Haussman, 2016; Skulachev et al., 2017). A large head and a round face, large eyes in relation to face size, bulg‐ ing cheeks, small nose and mouth are some of the components of this effect, perceived as juvenile traits. Such juvenile characteristics are perceived as attractive to humans (Borgi & Cirulli, 2013; Waller et al., 2013). Among domestic mammals, it has been described in domestic dogs (Goodwin, Levine, & McGreevy, 2008; Waller et al., 2013), which is characterized by a reduction in overall body size and retention of a juvenile head:body ratio (Goodwin et al., 2008), in cats (Parés‐Casanova, 2013; Waller et al., 2013), in companion Received: 1 October 2019 | Revised: 27 October 2019 | Accepted: 30 October 2019 DOI: 10.1111/ahe.12517 ORIGINAL ARTICLE Patterns of mandibular asymmetries in two types of companion rabbits Pere M. Parés‐Casanova | Maria Cabello Department of Animal Science, ETSEA, University of Lleida, Lleida, Spain Correspondence Pere M. Parés‐Casanova, Department of Animal Science, ETSEA, University of Lleida, Av. Rovira Roure, 191, Lleida, 25198 Catalonia, Spain. Email: peremiquelp@ca.udl.cat Abstract Developmental instability hypothesis suggests that asymmetric variation can par‐ tially reflect the body's inability to buffer environmental and/or genetic perturba‐ tions. Fluctuating asymmetry (FA), that is random differences between the left and right sides of body features that are symmetric at the population level, can assess this approach. Another kind of asymmetry is directional asymmetry (DA) which appears when the left and right sides differ consistently from each other. Extreme selection for morphological traits, as appear in some companion rabbits selected for a paedo‐ morphic (dwarf rabbits) or gerontomorphic (belier rabbits) appearance, may cause abnormal functional conditions, which in turn could be expressed as significative degrees of asymmetries. To study these phenomena, we analysed 62 mandibles of companion rabbits (20 beliers and 42 dwarfs) by means of geometric morphometric methods and quantified their size and shape asymmetric variation (both FA and DA) using 18 landmarks on the lateral side. FA was present in both types but in differ‐ ent degrees, being higher among dwarfs. It is considered that this type is subject to deeper changes than among beliers, and therefore, there is higher pressure on the phenotype. This observation could be assumed to be an adaptive response, com‐ ing out as FA. The presence of DA was significative and similar for two types. This likely indicates common masticatory lateralization, a pattern that has been detected in other domestic mammals. The methodological framework presented in this study can be valuable for future works focused on genetically and/or environmentally re‐ lated form study in pets. KEYWORDS craniometry, dwarf rabbit, gerontomorphy, laterality, paedomorphy