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The mara Dolichotis patagonum (Caviomorpha, Caviidae) is probably the extant rodent with the most pronounced postcranial specializations for fast locomotion. When running the species can reach a speed of ~40 km/h. It has been suggested that its body posture and limb bones show evolutionary parallelism regarding small-sized artiodactyl species. Due to its elongated limbs and relatively large body mass (average 8 kg) compared to other rodents, its limb bones may experience large loads at high speeds. Using kinematic data from high speed video films and skeletal dimensions of museum specimens, ground reaction forces and stresses acting on the humerus and tibia during different gaits were estimated. Values of bending stress obtained for the tibia were greater than those for the humerus during walking, gallop and "pronk". The stress experienced by the tibia when running doubled the value obtained when walking (54.5 vs. 26.1 MPa, respectively). Estimated bone safety factors were less than half during fast locomotion (3.1) compared to walking (6.4). It is discussed how maras' body posture and skeletal dimensions affect bone stress experienced during locomotion. [ABSTRACT FROM AUTHOR]

Mandibles from separate populations of free-living mouflons (Ovis aries musimon) from Southern Spain, submitted to different ecological conditions, were studied. Searching for ontogenetic shape variations we used geometric morphometrics tools and we explored the use of several mathematical models for describing growth rate variations between populations and sexes. A strong allometry was detected with variations in shape mainly matching with molar and premolar eruption. Mandible shape did not vary significantly with sex nor was sexual size dimorphism detected in adults, whatever the population. By modeling growth we detected differences between populations in all parameters such as the maturity rate describing precocity, and the time it took to reach asymptotic size (varying from 9 up to 18 months). A longer period of growth did not result in a larger asymptotic size, but it led to smaller mandibles. Mouflons with relatively late teeth replacement, lower maturation rate and smaller adult size were those of the population submitted to extreme environmental conditions, like epizootic disease, droughts and ungulate overpopulations. We discuss how a delay in reaching mature size has probably an important subsequent impact on reproductive and life-history traits in this species. Being able to record the effects of density-dependent and densityindependent factors, mandibles become a target of interest for ecological and management studies also on mouflons. [ABSTRACT FROM AUTHOR]