Locomotor reconstruction of Leptictidium from the Eocene of Messel using bone structure patterns in the postcranial skeleton of running and hopping extant mammals

已灭绝的Leptictidium(Leptictida目)是梅塞尔坑(德国始新世)的一种小型哺乳动物化石属，自1962年发现以来一直存在争议。到目前为止，仅根据其外部形态，有人交替地提出Leptictidium是两足漏斗或跑步者(参见表1)。2)。然而，骨内结构(如皮质和小梁部分)也记录了与运动和姿势相关的功能特化。骨骼的内部结构和特性可以作为一个可靠的指标来描述已灭绝的类群的运动行为。这种内部信号在Leptictidium的附属物中仍有待探索。因此，这项初步研究的目的是描述现代哺乳动物奔跑和跳跃时颅后骨骼元素的外部和内部解剖结构。由此产生的比较数据库将成为我们研究项目的核心，这些项目将试图重建像Leptictidium这样的鳞片类动物的运动类型。对于每个已研究的现存分类单元，关于肢体和腰带外部形态的描述性数据将与这些分子的内部骨结构相关联(使用μCT成像技术)，并与动物的已知运动行为相关联。这种外部和内部分析相结合的方法是研究陆地哺乳动物化石运动的一种创新方法。

The locomotion of the extinct Leptictidium (order Leptictida), a small fossil mammal genus from the Messel Pit (Eocene, Germany) has been debated since its discovery in 1962. To date, it has been alternately suggested that Leptictidium was a bipedal hopper or runner, based on its external morphology only (App. 2). However, bone endostructures (e.g. cortical and trabecular components) also record functional specialisation related to locomotion and posture. The inner configuration and properties of the bone can be used as a reliable proxy to characterise locomotor behaviours of extinct taxa. Such inner signal remains to be explored in the appendicular elements of Leptictidium. Accordingly, the aim of this pilot study is to characterise the external and inner anatomical structures of postcranial skeletal elements in running and hopping modern mammals. The resulting comparative database will be the core of our research projects that will try to reconstruct the type of locomotion of leptictids like Leptictidium. For each studied extant taxon, the descriptive data on the external morphology of the limbs and girdles, will be associated with the inner bone structures of these elements (using μCT imaging techniques), and correlated with the known locomotor behaviour of the animal. This combination of external and internal analyses is an innovative approach for the study of the locomotion of fossil terrestrial Mammals.