Ravosa M J, Simons E L
Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, IL 60611-3008.
Am J Phys Anthropol. 1994 Sep;95(1):63-76. doi: 10.1002/ajpa.1330950106.
Ontogenetic changes in the morphology of the mandibular symphysis are described in Archaeolemur so as to infer the functional significance of symphyseal fusion in this subfossil Malagasy lemur. The first regions of the symphysis to show a more complex morphology were the lower and anterior borders of the joint and, to a lesser extent, the lingual borders of the superior and inferior transverse tori. During growth, these regions became increasingly rugose and encroached upon a centrally located, smooth, "oval" region, which may have been a principal pathway for neurovascular structures communicating with the unfused joint. In subadults, the symphysis was completely fused except for the lingual surface of the inferior transverse torus, where a patent suture and potential space were present between dentaries. Thus, in Archaeolemur there was an age- and size-related pattern of increased symphyseal ossification or fusion that was complete by adulthood. The morphology of the interlocking bony processes and the sequence of ossification in the symphysis suggest that increased dorsoventral shear stress during mastication was the most likely determinant of symphyseal fusion in Archaeolemur. The allometric pattern of greater symphyseal fusion may be linked to the presence of relatively greater dorsoventral shear in adults due to an increased recruitment of balancing-side jaw-muscle force. There is little indication that the symphysis of juvenile Archaeolemur was buttressed to resist forces associated with "wishboning" during mastication or vertical bending during incision. Our observations, as well as those of others, suggest that symphyseal fusion in primates occurs initially as a response to increased dorsoventral shear during mastication. Therefore, wishboning stress might only become a major determinant of symphyseal form and function in those taxa that develop a fused symphysis to counter increased dorsoventral shear.
本文描述了古原狐猴下颌联合形态的个体发育变化，以推断这种马达加斯加亚化石狐猴联合融合的功能意义。联合处最早呈现出更复杂形态的区域是关节的下边缘和前边缘，以及程度稍轻的上下横嵴的舌侧边缘。在生长过程中，这些区域变得越来越粗糙，并侵蚀了位于中央的光滑“椭圆形”区域，该区域可能是与未融合关节连通的神经血管结构的主要通道。在亚成体中，联合处除了下横嵴的舌面外完全融合，在齿骨之间存在一条开放的缝线和潜在间隙。因此，在古原狐猴中，存在一种与年龄和大小相关的联合骨化或融合增加的模式，成年时完成。联合处相互嵌合的骨突形态和骨化顺序表明，咀嚼过程中背腹向剪切力增加是古原狐猴联合融合最可能的决定因素。联合融合程度更高的异速生长模式可能与成年个体中由于平衡侧颌肌力增加而导致的相对更大的背腹向剪切力有关。几乎没有迹象表明幼年古原狐猴的联合处得到加强以抵抗咀嚼过程中与“叉骨状”相关的力或切割过程中的垂直弯曲力。我们以及其他人的观察表明，灵长类动物的联合融合最初是对咀嚼过程中背腹向剪切力增加的一种反应。因此，叉骨状应力可能仅在那些发育出融合联合以应对增加的背腹向剪切力的类群中成为联合形态和功能的主要决定因素。
