Department of Archaeology, Simon Fraser University, Burnaby, British Columbia, Canada.
Kunming Natural History Museum of Zoology, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.
Am J Biol Anthropol. 2024 Dec;185(4):e25014. doi: 10.1002/ajpa.25014. Epub 2024 Nov 7.
Reconstruction of life histories for fossil and living primates draws on rate of enamel layering, termed Retzius periodicity (RP in days) expressed as surface perikymata, during dental crown formation. Disclosure of RP through thin sectioning is destructive; consequently, sample sizes are inadequate to detect the range of RPs present in discrete taxa. We propose an additional method to detect RPs at the population level based on twice-yearly average recurrence of linear enamel hypoplasia (rLEH) in apes shown by prior studies.
Casts of teeth from orangutans (Pongo pygmaeus) (n = 40) and Lufengpithecus lufengensis (n = 57) from Late Miocene Shihuiba, China, (133 and 138 LEH, respectively) were recorded with scanning electron microscope (SEM) and confocal microscopy to yield perikymata counts between episodes of LEH. Frequency distributions of aggregated perikymata counts between LEH were compared to frequency distribution of tooth-specific ratios of perikymata counts between successive LEH (this latter step removes effects of RP differences within a sample).
Drawing on prior research, two successive intervals between LEH span 1 year on average. Ratios of successive to previous intervals between LEH show that orangutans and Lufengpithecus exhibit two asymmetric intervals centered on 5.3 and 6.7 months, likely reflecting the effect of axial tilt insolation on phenology. Estimated RPs are not unimodal but show a range from 7 to 12 in Lufenpithecus and 8 to 11 in Pongo, comparable to published values.
Repetitive LEH is sufficiently regular to detect additional RPs which, in the case of Lufengpithecus, have yet to be demonstrated histologically.
重建化石和现生灵长类动物的生活史，需要根据牙齿冠部形成过程中釉质分层的速率（以每天的 Retzius 周期性表示，用表面釉小皮纹表示）。通过薄片揭示 RP 是具有破坏性的；因此，样本量不足以检测离散分类群中存在的 RP 范围。我们提出了一种在种群水平上检测 RP 的附加方法，该方法基于先前研究中展示的类人猿中每年两次的线性釉质发育不全（rLEH）的平均复发。
来自中国晚中新世始新世化石的猩猩（Pongo pygmaeus）（n=40）和禄丰古猿（Lufengpithecus lufengensis）（n=57）的牙齿铸型，用扫描电子显微镜（SEM）和共聚焦显微镜进行记录，以在 LEH 之间的釉小皮纹计数。在 LEH 之间的聚集釉小皮纹计数的频率分布与牙齿之间连续 LEH 之间釉小皮纹计数的比例的频率分布进行了比较（后一步骤消除了样本内 RP 差异的影响）。
根据先前的研究，两次 LEH 之间的连续间隔平均为 1 年。连续到前一个 LEH 之间的间隔的比例表明，猩猩和禄丰古猿表现出两个不对称的间隔，中心分别为 5.3 和 6.7 个月，这可能反映了轴向倾斜对光照的影响。估计的 RP 不是单峰的，但在禄丰古猿中显示出 7 到 12 的范围，在猩猩中显示出 8 到 11 的范围，与已发表的值相当。
重复的 LEH 足够规律，可以检测到额外的 RP，在禄丰古猿的情况下，这些 RP 尚未通过组织学证明。
