Applying synchrotron X-ray microtomography to a study of Morganucodon and Kuehneotherium: two of the earliest stem mammals.

将同步加速器 X 射线显微断层扫描应用于摩根古龙 (Morganucodon) 和 Kuehneotherium 的研究：两种最早的干哺乳动物。

• 批准号: NE/E010431/1
• 负责人: Emily Rayfield
• 金额: $ 6.58万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE010431%2F1
• 关键词: Applying; synchrotron; ray; microtomography; study

Although the era following the extinction of the dinosaurs is often referred to as 'The Age of Mammals', mammalian history actually stretches back three times as far to the Late Triassic, about 220Ma ago. Their Mesozoic fossil record is frustratingly sparse, and the part that mammals played in Mesozoic ecosystems is sketchy. Exceptionally though, the fissure fillings of Glamorganshire have yielded truly enormous collections of teeth and disarticulated bones. Morganucodon and Kuehneotherium are tiny ancestral mammals from these fissures and this proposed study will reveal new information about the ecology and evolution of these mammalian ancestors, using a rigorously quantified modelling approach. We know a lot about certain aspects of the mammalian transition from their ancestors, the cynodonts, particularly how parts of the jaw hinge transformed to the mechanism of the middle ear; one of the great case studies of vertebrate evolutionary morphology. Basal mammals such as Morganucodon and Kuehneotherium, which have an intermediate condition, have helped in the understanding of this transition. There are still many things that we do not understand about these earliest mammals though. Were they fully homeothermic, and so probably hairy, and did the mother provide milk for the babies? We can get some answers to these questions by a study of the teeth and jaws, by assessing adaptations for efficient feeding and looking at the replacement pattern of the teeth. Reptiles continue to replace their teeth throughout life but mammals have only two sets of teeth. This keeps the upper and lower teeth in position to process the food efficiently and indicates a mammalian physiology and growth pattern. Palaeontologists are using many new technological applications to help them interpret fossils. Detailed high resolution scans can be produced using synchrotron radiation. The small size of Morganucodon and Kuehneotherium, with teeth between 1-2mm in size, is here an advantage as they can be accommodated in the high resolution facilities at the Swiss Light Source (SLS) near Zurich. One method to decipher functional clues in the jaw is the engineering technique Finite Element Analysis (FEA). Researchers build a digital model of the structure they wish to test (i.e. bridge, Morganucodon jaw), apply elastic properties and loading forces that mimic the behaviour (i.e. biting) to be tested. The analysis calculates strain and stress within the structure in response to these loading forces. Non-invasive techniques such as computed tomography scans can be used to generate accurate three-dimensional images of structures, such as jaws, which are required to form the basis of an accurate finite element model. Tiny early mammals are assumed to be insectivores but this covers a very wide range of possible food. This study will use FEA to test whether the jaws of Morganucodon and Kuehneotherium are adapted for biting beetles or snapping at passing moths. It will estimate the force of their bite / e.g. could they penetrate insect cuticles? This is important, as it will inform on feeding specialization and ecological niches. Morganucodon and Kuehneotherium both have an intermediate double jaw joint and one aspect of the transition to the mammalian jaw joint which has not been previously investigated is whether there is a change in priority of the two joints during the growth of an individual. Is there some indication for this from the relative size of the different jaw bones? If so it will help us to understand the mechanism of the transition. High resolution synchrotron scans will also provide detailed information about the tooth replacement pattern in these basal mammals and so tell us more about how the transition to a mammalian dentition occurred. Some ancestral replacement patterns still occurred but we shall be able to study the mechanism with these internal scans in unprecedented detail.

虽然恐龙灭绝后的时代通常被称为“哺乳动物时代”，但哺乳动物的历史实际上可以追溯到晚三叠世的三倍，大约220 Ma前。它们的中生代化石记录少得令人沮丧，哺乳动物在中生代生态系统中所起的作用也很粗略。然而，在格拉摩根郡的裂缝填充物中，却发现了数量巨大的牙齿和断骨。Morganucodon和Kuehneotherium是来自这些裂缝的微小的祖先哺乳动物，这项拟议的研究将揭示有关这些哺乳动物祖先的生态和进化的新信息，使用严格的量化建模方法。我们对哺乳动物从它们的祖先犬齿兽转变的某些方面了解很多，特别是下颌铰链的部分如何转变为中耳的机制;这是脊椎动物进化形态学的一个伟大案例。基栖哺乳动物，如摩根齿兽和Kuehneotherium，具有中间状态，有助于理解这种转变。然而，关于这些最早的哺乳动物，我们仍然有许多不了解的事情。它们是完全恒温的吗，所以可能有毛，母亲是否为婴儿提供乳汁？我们可以通过对牙齿和颌骨的研究，通过评估有效进食的适应性和观察牙齿的更换模式来回答这些问题。爬行动物一生中不断更换牙齿，但哺乳动物只有两套牙齿。这使上下牙齿保持在适当的位置，以有效地处理食物，并表明哺乳动物的生理和生长模式。古生物学家正在使用许多新的技术应用来帮助他们解释化石。使用同步辐射可以产生详细的高分辨率扫描。摩根齿象和屈氏兽的牙齿大小在1- 2毫米之间，它们的小尺寸在这里是一个优势，因为它们可以容纳在苏黎世附近的瑞士光源（SLS）的高分辨率设施中。一种解读颌骨功能线索的方法是工程技术有限元分析（FEA）。研究人员建立了他们希望测试的结构的数字模型（即桥梁，Morganucodon颌骨），应用弹性特性和加载力来模拟待测试的行为（即咬合）。该分析计算响应于这些载荷力的结构内的应变和应力。诸如计算机断层扫描的非侵入性技术可用于生成诸如颌的结构的精确三维图像，这是形成精确有限元模型的基础所需的。微小的早期哺乳动物被认为是食虫动物，但这涵盖了非常广泛的可能食物。这项研究将使用有限元分析来测试摩根齿象和Kuehneotherium的下颚是否适合咬甲虫或咬经过的飞蛾。它将估计它们的咬合力/例如，它们能否穿透昆虫表皮？这一点很重要，因为它将为饲养专业化和生态位提供信息。Morganucodon和Kuehneotherium都有一个中间的双颚关节和一个方面的过渡到哺乳动物的颚关节，以前没有调查的是是否有一个变化的优先级的两个关节在个人的成长。从不同颌骨的相对大小上有没有什么迹象表明这一点？如果是这样的话，这将有助于我们理解这种转变的机制。高分辨率同步加速器扫描还将提供有关这些基础哺乳动物牙齿替换模式的详细信息，从而告诉我们更多有关哺乳动物牙列过渡的信息。一些祖先的替换模式仍然发生，但我们将能够以前所未有的细节研究这些内部扫描的机制。

项目成果

Molar microwear of insectivorous bats: implications for the trophic ecology of two early mammals.

食虫蝙蝠的磨牙微磨损：对两种早期哺乳动物营养生态的影响。

• 作者: Nicholas Crumpton (Author)

A functional investigation into the dietary ecology of two of the earliest stem mammals, Morganucodon watsoni and Kuehneotherium praecursoris.

对两种最早的干哺乳动物（Morganucodon watsoni 和 Kuehneotherium praecursoris）的饮食生态学进行功能性调查。

• 作者: Pamela Gill (Author)

How the cingula of basal mammal teeth may alleviate strain in the enamel caused by a soft food diet.

哺乳动物基底牙齿的扣带带如何减轻由软食饮食引起的牙釉质压力。

• 作者: Philip Anderson (Author)

Within-guild dietary discrimination from 3-D textural analysis of tooth microwear in insectivorous mammals.

• DOI: 10.1111/jzo.12068
• 发表时间: 2013-12
• 期刊: Journal of zoology (London, England : 1987)
• 作者: Purnell MA;Crumpton N;Gill PG;Jones G;Rayfield EJ
• 通讯作者: Rayfield EJ

Did the Cretaceous monotreme Teinolophos trusleri possess an internal mandibular trough for postdentary bones?

白垩纪单孔类Teinolophos trusleri是否拥有用于容纳齿后骨的内部下颌槽？

• 作者: Hopson James (Author)