Morphological Characteristics Of Cranium And Vertebrae In Taihangshan Macaques(Macaca Mulatta Tcheliensis)

The cranium and vertebrae are important components of the axial skeleton in primates.The relatively complex and highly integrated structure of the cranium has been widely used in the study of primate taxonomy.The vertebrae play a critical role in supporting the body,attaching muscles and protecting the nerves or spinal cord.Currently,Taihangshan macaque(Macaca mulatta tcheliensis)is the northernmost naturally distributed rhesus macaque.Although scientists have carried out mountainous studies on the skeletal morphology,there is a lack of systematic morphological description and quantitative analysis of its cranium and vertebrae.In this study,the cranium and vertebrae of adult Taihangshan macaques,collected during 2009 and 2019,were used for,1)morphological characteristic description of the cranium and comparison with those of previous study of Taihangshan macaque and other rhesus macaques subspecies;2)morphological characteristic description of the vertebrae and its functional morphological analysis based on principal component analysis;3)preliminary diagnosis of abnormal specimens.1.Morphological characteristics of the skull in Taihangshan macaquesIn this section,the skull morphological characteristics of adult Taihangshan macaques were generally described and the selected variables were analyzed between sexes,and compared with results of previous studies and other rhesus macaque subspecies.The main results include that,1)the skull sutures of adult Taihangshan macaques are closely healed,the skull surface is generally smooth,there are protruding external sagittal cristae on both the left and right sides of the sagittal suture,the orbital orifice is elliptical,the number of both left and right suborbital foramen is mostly 3,and the number of left and right mental foramen is mostly 1;2)most of the measured cranial variables of adult males are significantly greater than that of the adult females,but the total facial angle of adult females is significantly greater than that of the adult males suggesting that adult male's face is more convex;3)the cranial length of Taihangshan macaques in this study is relatively bigger than that of the previous study but the cranial width is opposite,while most of the measured variables of Taihangshan macaques are bigger than that of the M.mulatta mulatta,but the Taihangshan macaques differs from Hunan and Hubei macaques,Fujian and Guangdong rhesus macaques mainly in cranial length and zygomatic width;4)principal component analysis showed that the first principal component(eigenvalue8.342,contribution 83.42%)could differentiate the Taihangshan macaques and the M.mulatta mulatta.These findings suggest that the skull of Taihangshan macaques differs from other rhesus subspecies generally which could support it is a valid subspecies.2.Morphological characteristics of the vertebrae in Taihangshan macaquesIn this section,the vertebrae morphological characteristics of the 17 adult Taihangshan macaques were described,and the ventral craniocaudal length of the vertebral body was measured and analyzed.The principal results include that,1)typical vertebral column of adult Taihangshan macaques consists of 7 cervical vertebrae,12 thoracic vertebrae,7 lumbar vertebrae,3 sacral vertebrae and 16 caudal vertebrae;2)the 1^st to 6^th cervical vertebrae are characterized with transverse foramen,the transverse processes in the 4^th to 6^th cervical vertebrae are bifurcated,the spinous processes of the 1^st to 8^th thoracic vertebrae are caudally oriented,the length of the spinous processes of the 10^th to 12^th thoracic vertebrae decreases sequentially and its direction is parallel to the sagittal plane,the transverse processes of the lumbar spine are cranially oriented and the spinous processes are plate-shaped,the 11^th and 12^ththoracic vertebrae and the 1^st to 6^th lumbar vertebrae have accessory processes,and the sacrum looks like an inverted triangle formed by the fusion of the three sacral vertebrae;3)the coccygeal vertebrae are classified as proximal(the 1^st 4 coccygeal vertebrae),transitional(the 5^th and 6^th coccygeal vertebrae)and distal(the remaining10 vertebrae)coccygeal vertebrae;4)the ventral craniocaudal length of presacral vertebral body shows firstly decreasing(from C3 to C7),secondly increasing(from T1 to L5),and then decreasing(from L6 to L7),while the ventral craniocaudal length of the coccygeal vertebral body shows overally increasing(from Cy1 to Cy6 but not Cy2),and then decreasing overally(from Cy7 to Cy15 but not Cy16).3.Functional morphology of the vertebrae in Taihangshan macaquesPrincipal component analysis was adopted to investigate the dominant functional factors in the vertebrae of 14 adult Taihangshan macaques.The main results include that,1)the morphological functions of the cervical,lumbar and caudal region of adult Taihangshan macaques are characterized by Stability factor,Locomotion factor,Load-bearing factor and Protection factor;2)the morphological functions of thoracic and sacral regions of adult Taihangshan macaques are characterized by Stability factor,Load-bearing factor and Protection factor.The findings suggest that the morphological functions of the vertebrae in adult Taihangshan macaques obviously differ reginonally.4.Abnormal cranium and vertebrae in Taihangshan macaquesAbnormal cranium and vertebrae in adult Taihangshan macaques were noted,and prelimilary disease diagnosis has been conducted.The main findings include that,1)several cranium showes obvious bone hyperplasia,erosion and enlargement of the temporomandibular joint;2)there occurs spnondyloarthritis(Sp A)in adult Taihangshan macaques,the main manifestations of Sp A are bilateral sacroiliac joint surface and symphysis pubis surface accompanied by erosion,proliferation and even fusion,and the vertebrae and appendicular bones also could show obvious lesions such as hyperplasia and erosion;3)there are transitional vertebrae occuring in the vertebral column of adult Taihangshan macaques.