Investigation of growth pattern and life mode of Desmostylus using X ray CT and serial tissue sections

本文通过对中新世北太平洋绳纹介（Desmostylus）的头颅骨、下颌骨和臼齿的X射线CT图像分析，研究了该物种的生长模式和生活方式。对于0.1.2.3/2.1.2.3早中新世物种D.hesperus和中中新世物种D.hesperus，先前被认为是0.1.3.3/1.1.3.3，应分别修订为www.example.com和0.0.2-1.3/2.1.2-1.3。分析还揭示了他们一生中牙齿替换和移位的模式。Desmostylus物种的实质性特点是几乎所有第二代牙齿的顺序移位：即，下第二、第三门齿和犬齿像臼齿一样相继萌出，上下前臼齿的每颗牙齿都有一个 ...更多信息 在14个样本中的10个头骨中，发现了明显的两性异形。其表现为臼齿和犬齿相对于颅骨大小的大小差异。在从组织学角度研究硬组织发育与生活方式的关系时，我们在一些离体牙齿和颅骨原位牙齿中观察到了Retzius线的周期性集中。这些线的浓度被认为是从出生，断奶，繁殖（或分娩），病理经验等生理反应的结果。在Desmostylus样本的情况下，这种周期性的Retzius线的浓度也观察到在女性头骨上的第二和第三磨牙爆发。因为这些牙齿是在它们生命的后期发育的，所以在索柱兽雌性个体的第二和第三磨牙中看到的这些周期性的Retzius线的集中可能是繁殖历史的信号，对于这些灭绝的神秘哺乳动物，如索柱兽，这仍然是未知的。少

The growth pattern and life mode of the Miocene North Pacific tethythere, Desmostylus, was investigated based on X-ray CT images of skulls and mandibles and serial tissue sections of molar teeth.Examinations of more than 14 cranial and 20 mandibular material, represented by the individuals of juveniles, sub-adults, adults, and sexually both males and females using X-ray CT revealed that the dental formula of Desmostylus, previously considered as 0.1.3.3/1.1.3.3, should be revised as 0.1.2.3/2.1.2.3 for the Early Miocene species D.japonicus and 0.0.2-1.3/2.1.2-1.3 for the Middle Miocene species D.hesperus, respectively. The analyses also revealed the patterns of tooth replacements and displacements during their life. The substantial peculiarity in the species of Desmostylus is the sequential displacements of almost all second-generation teeth : i.e., the lower second, third incisors and canine have erupted sequentially just like the molars, and each tooth of upper and lower premolars ha … More s also erupted sequentially throughout their life.Among the 10 skulls out of 14 samples, distinct sexual dimorphism was recognized. It was expressed by the size differences of molar teeth as well as canine teeth relative to the skull size. It suggests that the sexual dimorphism in Desmostylus may be continually emphasized by male individuals during their later life.As for the examination of hard tissue development from histological perspective in relation to answering questions for their life mode, periodic concentrations of Retzius lines were observed in some isolated teeth and those in situ on a skull. The concentrations of such lines are thought to be results of physiological responses from birth, weaning, breeding (or give birth), pathological experiences and so on. In the case of samples of Desmostylus, such periodic concentrations of Retzius lines were also observed in the second and third molars erupted on a female skull. Because such teeth are developed during the later stage of their life, these periodic concentrations of Retzius lines seen in the second and third molars in a female individual of Desmostylus maybe signals of the reproduction histories, which are still unknown for such extinct, enigmatic mammals as desmostylians at all. Less