Correlated variation between the splanchnocranium and basicranium in the Toy rabbit

The aim of this study was to explore and compare patterns of morphological covariation, including symmetrical deviations, between splanchnocranium and the basicranium in Toy rabbit, a type of paedomorphic rabbit. A sample of 32 skulls of adult Toy rabbits was studied on digital pictures on ventral aspects by means of geometric morphometric methods. A set of 7 landmarks were located on the horizontal plane of the splanchnocranial ventral bones (palatine process of the maxillary bone [processus palatinus maxillae] + palatine bone [lamina horizontalis ossis palatini]), and a set of 8 landmarks were on the basicranium (sphenoid [os sphenoidale] + basilar part of the occipital bone [pars basilaris] + bulla tympanica). Both fluctuating and directional asymmetries were detected on both blocks, being the asymmetry more important among splanchnocranial bones. It appeared also a significant relationship (allometry) between size and shape, especially in the basicranium, as well a significant relationship between the two blocks. From results we deduce that, although normally cranial base usually reaches adult size before the face, in paedomorphic animals the face stops its growth earlier than basicranium, resulting in their proportionally reduced splanchnocranium, the typical brachyfacial morphology for paedomorphy. In other words, our results support the hypothesis of an early stop of facial pattern development in neoteny -the retention of juvenile characteristics into adulthood-, which can affect vital structures. So, further research should expand on clinical data of paedomorphic animals in order to advance in the understanding of pathological results of this growth anomaly.