Smith B Holly
Museum of Anthropological Archaeology, University of Michigan, Ann Arbor, MI 48109, USA.
Center for the Advanced Study of Human Paleobiology, George Washington University, Washington, DC 20052, USA.
Biology (Basel). 2024 Aug 12;13(8):612. doi: 10.3390/biology13080612.
The young of toothed mammals must have teeth to reach feeding independence. How tooth eruption integrates with gestation, birth and weaning is examined in a life-history perspective for 71 species of placental mammals. Questions developed from high-quality primate data are then addressed in the total sample. Rather than correlation, comparisons focus on equivalence, sequence, the relation to absolutes (six months, one year), the distribution of error and adaptive extremes. These mammals differ widely at birth, from no teeth to all deciduous teeth emerging, but commonalities appear when infants transit to independent feeding. Weaning follows completion of the deciduous dentition, closest in time to emergence of the first permanent molars and well before second molars emerge. Another layer of meaning appears when developmental age is counted from conception because the total time to produce young feeding independently comes up against seasonal boundaries that are costly to cross for reproductive fitness. Mammals of a vast range of sizes and taxa, from squirrel monkey to moose, hold conception-to-first molars in just under one year. Integrating tooth emergence into life history gives insight into living mammals and builds a framework for interpreting the fossil record.
有齿哺乳动物的幼崽必须拥有牙齿才能实现独立进食。本文从生命史的角度，对71种胎盘哺乳动物的牙齿萌出与妊娠、出生和断奶过程的整合情况进行了研究。随后，基于高质量灵长类动物数据提出的问题在整个样本中得到解答。研究重点并非相关性，而是等效性、顺序、与绝对时间（六个月、一年）的关系、误差分布以及适应性极值。这些哺乳动物在出生时差异很大，有的没有牙齿，有的则已萌出所有乳牙，但当幼崽过渡到独立进食时，共性就显现出来了。断奶发生在乳牙列完成之后，时间上最接近第一恒磨牙的萌出，且远早于第二恒磨牙的萌出。从受孕开始计算发育年龄时，会出现另一层意义，因为幼崽实现独立进食的总时间会遇到季节性界限，跨越这些界限对繁殖适应性来说成本高昂。从松鼠猴到驼鹿，各种各样大小和类群的哺乳动物从受孕到第一恒磨牙萌出的时间都略少于一年。将牙齿萌出纳入生命史有助于深入了解现存哺乳动物，并为解释化石记录构建一个框架。
