Dean M C, Shellis R P
Evolutionary Anatomy Unit, Department of Anatomy and Developmental Biology, University College London, Gower Street, London, WC1E 6BT.
J Hum Evol. 1998 Oct-Nov;35(4-5):401-10. doi: 10.1006/jhev.1998.0243.
The enamel of certain primates (orang-utans, siamangs and the early Miocene fossil hominoid, Proconsul) occasionally contains striae of Retzius that appear distinct from those more typical of the lateral and cervical enamel of other anthropoids. These striae can be described as "S-shaped" since their contour is markedly sinuous as it passes from the enamel dentine junction (EDJ) to the tooth surface. "S-shaped" striae have never been described in the comparative literature on primate enamel and yet they may be of some phylogenetic significance. This study explores the interrelationship between four variables in the enamel of an orang-utan, a siamang and a specimen of Proconsul heseloni (from Rusinga Island, Kenya) all of which contain "S-shaped" striae. The morphological components of this form of stria have been quantified here. The four variables measured were (1) prism width; (2) the angle the prisms make to the EDJ; (3) the angle the striae of Retzius make with respect to the EDJ, and (4) the daily rate of enamel formation. Each of these four variables was measured in inner enamel close to the EDJ, in enamel mid-way between the EDJ and the enamel surface, and in outer enamel. Our aim was both to quantify the components of "S-shaped" striae and to attempt to offer a developmental explanation for the appearance of these striae in fully formed enamel. We conclude that "S-shaped" striae may be associated with regions of lateral enamel where prism width either remains constant or even reduces as the enamel surface is approached. This, together with an increase in the linear daily rate of enamel secretion towards the outer enamel, a cervical inclination in the angulation of the prisms with respect to the EDJ, and an increased angulation of the striae of Retzius to the EDJ are all features that characterize "S-shaped" striae. This description will facilitate identification and quantification of any similar striae in the enamel of other primates. It will also allow careful comparison of each of the four variables one with another which may in turn help in establishing "S-shaped" striae as developmentally homologous between species.
某些灵长类动物（猩猩、合趾猿以及中新世早期的化石类人猿——原康修尔猿）的牙釉质偶尔会含有芮氏线，这些芮氏线与其他类人猿侧面和颈部牙釉质中更典型的芮氏线明显不同。这些芮氏线可被描述为“S形”，因为其轮廓从牙釉质牙本质界（EDJ）延伸至牙齿表面时明显蜿蜒曲折。在关于灵长类动物牙釉质的比较文献中从未描述过“S形”芮氏线，但它们可能具有一定的系统发育意义。本研究探讨了一只猩猩、一只合趾猿以及一个肯尼亚鲁辛加岛的赫氏原康修尔猿标本牙釉质中四个变量之间的相互关系，所有这些标本都含有“S形”芮氏线。此处已对这种形式的芮氏线的形态成分进行了量化。所测量的四个变量分别为：（1）棱柱宽度；（2）棱柱与牙釉质牙本质界的夹角；（3）芮氏线与牙釉质牙本质界的夹角，以及（4）牙釉质形成的每日速率。这四个变量中的每一个都在靠近牙釉质牙本质界的内层牙釉质、牙釉质牙本质界与牙釉质表面中间位置的牙釉质以及外层牙釉质中进行了测量。我们的目的既是量化“S形”芮氏线的成分，也是试图对这些芮氏线在完全形成的牙釉质中的出现提供一种发育学解释。我们得出结论，“S形”芮氏线可能与侧面牙釉质区域相关，在该区域，随着接近牙釉质表面，棱柱宽度要么保持不变，甚至减小。这一点，再加上朝着外层牙釉质牙釉质分泌的线性每日速率增加、棱柱相对于牙釉质牙本质界的角度的颈部倾斜以及芮氏线相对于牙釉质牙本质界的角度增加，都是“S形”芮氏线的特征。这一描述将有助于识别和量化其他灵长类动物牙釉质中任何类似的芮氏线。它还将允许对这四个变量中的每一个进行仔细的相互比较，这反过来可能有助于确定“S形”芮氏线在不同物种之间在发育上是同源的。
