Stover Kristin K, Sidote JoAnna, Williams Susan H
Department of Biological Sciences, Ohio University, Athens, OH 45701, USA.
Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, 228 Irvine Hall, Athens, OH 45701, USA.
Zoology (Jena). 2017 Oct;124:95-105. doi: 10.1016/j.zool.2017.06.006. Epub 2017 Jun 17.
A primary hypothesis for the evolution of mandibular symphyseal fusion in some mammals is that it functions to resist loads incurred during routine mastication. Anecdotal support for this hypothesis is based on the fact that when the symphysis fuses, it typically does so early during postnatal ontogeny prior to or around the time of weaning. However, little is known about the process of fusion, particularly relative to feeding behaviors and the dynamics of mastication, including occlusion and masticatory loading. In the present study, we investigate the timing and process of symphyseal fusion in alpacas (Vicugna pacos) in the context of maturation of the oral apparatus and oral behavior. We also report on in vivo strains from the symphysis and corpus in young alpacas prior to and following full fusion and M occlusion. Results show that fusion begins rostrally by 1 month and is complete by 6-7 months whereas all deciduous premolars and M come into occlusion by 6 months. Although symphyseal loading patterns are maintained throughout ontogeny, in young alpacas symphyseal strain magnitudes are low compared with adults but corpus strain magnitudes are comparable to those found in adults. Reduced symphyseal loading in young individuals is contrary to what might be predicted given that the symphysis is still fusing. When considered in light of the development of occlusion and rumination, strain magnitudes may be necessarily low and reflect an overall delay in the maturation of masticatory dynamics.
一些哺乳动物下颌联合融合进化的一个主要假说是，它的功能是抵抗日常咀嚼过程中产生的负荷。对这一假说的轶事性支持基于这样一个事实，即当联合融合时，它通常在出生后个体发育早期，即在断奶前或断奶前后发生。然而，关于融合过程，尤其是相对于进食行为和咀嚼动力学（包括咬合和咀嚼负荷）的融合过程，人们所知甚少。在本研究中，我们在口腔器官成熟和口腔行为的背景下，研究了羊驼（小羊驼）联合融合的时间和过程。我们还报告了年轻羊驼在完全融合和M咬合之前和之后，联合和下颌体的体内应变情况。结果表明，融合从1月龄时在吻侧开始，6 - 7月龄时完成，而所有乳牙前磨牙和M在6月龄时开始咬合。尽管联合负荷模式在整个个体发育过程中保持不变，但与成年羊驼相比，年轻羊驼联合部位的应变幅度较低，而下颌体的应变幅度与成年羊驼相当。鉴于联合仍在融合，年轻个体联合部位负荷的降低与预期情况相反。从咬合和反刍的发育情况来看，应变幅度可能必然较低，反映出咀嚼动力学成熟的总体延迟。
