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Biogeography a key influence on distal forelimb variation in horses through the Cenozoic
Proceedings of the Royal Society B: Biological Sciences ( IF 4.7 ) Pub Date : 2021-01-13 , DOI: 10.1098/rspb.2020.2465
Jamie A MacLaren 1, 2
Affiliation  

Locomotion in terrestrial tetrapods is reliant on interactions between distal limb bones (e.g. metapodials and phalanges). The metapodial–phalangeal joint in horse (Equidae) limbs is highly specialized, facilitating vital functions (shock absorption; elastic recoil). While joint shape has changed throughout horse evolution, potential drivers of these modifications have not been quantitatively assessed. Here, I examine the morphology of the forelimb metacarpophalangeal (MCP) joint of horses and their extinct kin (palaeotheres) using geometric morphometrics and disparity analyses, within a phylogenetic context. I also develop a novel alignment protocol that explores the magnitude of shape change through time, correlated against body mass and diet. MCP shape was poorly correlated with mass or diet proxies, although significant temporal correlations were detected at 0–1 Myr intervals. A clear division was recovered between New and Old World hipparionin MCP morphologies. Significant changes in MCP disparity and high rates of shape divergence were observed during the Great American Biotic Interchange, with the MCP joint becoming broad and robust in two separate monodactyl lineages, possibly exhibiting novel locomotor behaviour. This large-scale study of MCP joint shape demonstrates the apparent capacity for horses to rapidly change their distal limb morphology to overcome discrete locomotor challenges in new habitats.

中文翻译:

生物地理学对新生代马远端前肢变异的关键影响

陆地四足动物的运动依赖于远端肢体骨骼(例如,metapodials 和趾骨)之间的相互作用。马(Equidae)四肢的掌指关节高度专业化,促进重要功能(减震;弹性后坐力)。虽然在整个马的进化过程中关节形状发生了变化,但尚未对这些修改的潜在驱动因素进行定量评估。在这里,我在系统发育背景下使用几何形态测量学和差异分析检查了马的前肢掌指关节 (MCP) 及其已灭绝的亲属 (palaeotheres) 的形态。我还开发了一种新的对齐方案,探索随时间变化的形状变化幅度,与体重和饮食相关。MCP 形状与质量或饮食代理的相关性很差,尽管在 0-1 Myr 间隔检测到显着的时间相关性。新世界和旧世界hipparionin MCP形态之间恢复了明确的划分。在 Great American Biotic Interchange 期间观察到 MCP 差异和高形状差异率的显着变化,MCP 关节在两个独立的单指谱系中变得广泛而坚固,可能表现出新的运动行为。这项对 MCP 关节形状的大规模研究表明,马具有快速改变其远端肢体形态以克服新栖息地中离散运动挑战的明显能力。在 Great American Biotic Interchange 期间观察到 MCP 差异和高形状差异率的显着变化,MCP 关节在两个独立的单指谱系中变得广泛而坚固,可能表现出新的运动行为。这项对 MCP 关节形状的大规模研究表明,马具有快速改变其远端肢体形态以克服新栖息地中离散运动挑战的明显能力。
更新日期:2021-01-13
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