英国爱丁堡大学Stephen L. Brusatte、Gregory F. Funston等研究人员合作揭示胎盘类哺乳动物生活史的起源。这一研究成果于2022年8月31日在线发表在国际学术期刊《自然》上。

研究人员用古组织学和地球化学的方法介绍了最早的胎生动物生活史记录，它是一个6200万年前的全齿目，这个演化支包括第一个达到真正大体型哺乳动物。研究人员将牙齿微量元素图谱的应用范围扩大了6000万年，确定了出生和断奶的化学标记，并将这些标记与牙齿的每日生长记录进行了校准。漫长的妊娠期（约7个月）、快速的牙齿发育和短的哺乳间隔（约30-75天）表明，Pantolambda bathmodon是高度早熟的，与非胎生哺乳动物和已知的中生代前体不同。这些结果表明，P. bathmodon像胎生动物一样进行繁殖，并以其身体大小的速度进行生活。如果假设P. bathmodon反映了胎生动物的近亲，这些研究结果表明，生产发育良好的早熟幼体的能力在胎生动物演化的早期就已建立，较大的新生儿尺寸可能是早期胎生动物体型快速增长的一个机制。

据了解，白垩纪末灭绝后，胎生哺乳动物迅速实现了多样化，占据了关键的生态位，并增大了体型，但其他动物却没有做到这一点。胎生动物幼体独特的延长妊娠期可能是其成功和体型增长的因素，但早期胎生动物的繁殖方式仍然是未知的。

附：英文原文

Title: The origin of placental mammal life histories

Author: Funston, Gregory F., dePolo, Paige E., Sliwinski, Jakub T., Dumont, Matthew, Shelley, Sarah L., Pichevin, Laetitia E., Cayzer, Nicola J., Wible, John R., Williamson, Thomas E., Rae, James W. B., Brusatte, Stephen L.

Issue&Volume: 2022-08-31

Abstract: After the end-Cretaceous extinction, placental mammals quickly diversified1, occupied key ecological niches2,3 and increased in size4,5, but this last was not true of other therians6. The uniquely extended gestation of placental young7 may have factored into their success and size increase8, but reproduction style in early placentals remains unknown. Here we present the earliest record of a placental life history using palaeohistology and geochemistry, in a 62 million-year-old pantodont, the clade including the first mammals to achieve truly large body sizes. We extend the application of dental trace element mapping9,10 by 60 million years, identifying chemical markers of birth and weaning, and calibrate these to a daily record of growth in the dentition. A long gestation (approximately 7 months), rapid dental development and short suckling interval (approximately 30–75 days) show that Pantolambda bathmodon was highly precocial, unlike non-placental mammals and known Mesozoic precursors. These results demonstrate that P. bathmodon reproduced like a placental and lived at a fast pace for its body size. Assuming that P. bathmodon reflects close placental relatives, our findings suggest that the ability to produce well-developed, precocial young was established early in placental evolution, and that larger neonate sizes were a possible mechanism for rapid size increase in early placentals.

DOI: 10.1038/s41586-022-05150-w

Source: https://www.nature.com/articles/s41586-022-05150-w