中国科学院南京地质古生物研究所机构知识库

We investigated the sexual dimorphism and reconstructed the body ofPlesiaceratherium gracilebased on the numerous new specimens from the Early Miocene Shanwang Basin, China. The sexual dimorphism ofP. gracileis reflected by the size of both the lower incisor i2 [length male/female (M/F) ratio = 2.69, width M/F = 1.63] and the upper incisor I1 (length M/F = 1.63). Other mensural variations reveal their ranges greatly overlapping on both genders, with a low M/F ratio; hence, they cannot be interpreted as sexual dimorphism. The large-sized body and the strong sexual difference of incisors suggest thatP. gracileis polygynous and has a solitary lifestyle. When we reconstructed the body ofP. gracile, we found that the head-body length is 2,796-3,117 mm, the shoulder height is 1,476-1,627 mm, and the body weight is about 1,198 kg. All skeletons have the ventral edge of the thorax at the level of the olecranon of the ulna. The spinous processes of the posterior thoracic vertebrae and the lumbar vertebrae are always vertical, the metatarso-femur ratio and the tibio-femur ratio are high, and the two joint angles between the scapula, the humerus, and the radius are 102 degrees-143 degrees and 115 degrees-160 degrees, respectively, indicating thatP. gracilehas a mediportal limb and a horse-gallop running type. Furthermore, the limb-segment comparisons ofP. gracileand other rhinoceroses demonstrate that the proximal long bones, including the scapula, the humerus, and the femur, are important for the body height, regardless of whether their body is large or small-sized; the distal parts of the limb, including the metacarpus and the metatarsus, are sensitive to body mass changes.