Paramyine ischyromyids are one of the first ancestral rodent groups to appear in North America. Studying ecological indicators of these extinct animals enables us to better understand how they integrated into North American mammalian communities. In this study we reassess the locomotor behavior of a nearly complete skeleton of a paramyine, Paramys delicatus (AMNH FM 12506), using functional limb indices and living squirrels as extant analogues. We then used the results of the functional limb index study to select an appropriate locomotor group for body mass estimations of Paramys delicatus and other early North American (Wasatchian-Bridgerian) paramyines. This was done because body mass is strongly tied to locomotor patterns and more reliable body mass estimates can be generated from an extant sample that functionally resembles the fossils being studied. Functional limb indices were calculated for three locomotor groups (arboreal, semifossorial, and gliding) of living sciurids. Comparisons among arboreal, semifossorial, and gliding sciurids show that the functional indices related to mechanical advantage of muscles and limb robusticity enable distinction among locomotor groups; however, there is considerable overlap between arboreal and semifossorial taxa. Paramys delicatus was found to have generally greater mechanical advantages and limb robusticity than most living squirrels, including semifossorial taxa. As these traits are associated with semifossorial squirrels that frequently use scratch-digging, this suggests that Paramys delicatus and perhaps other early paramyines were likely proficient scratch-diggers. However, indices reflecting limb proportions of paramyines suggest that these early rodents may have used more hind limb dominated locomotion than do living squirrels. Body mass estimations for early paramyines were therefore derived from a semifossorial squirrel sample. Statistical comparisons suggest that many of the most reliable estimators for body mass in Paramys delicatus and other paramyines are those derived from humeral dimensions, with the most reliable estimate being humeral head superoinferior breadth. Using these estimators, individual body mass estimates of early paramyines range from 3391 to 4005 g for Paramys delicatus, 1137–1329 g for Paramys copei, 1291 g for Paramys taurus, and 3357 g for Notoparamys costilloi. All body mass estimations derived from postcranial elements are substantially larger than previously published estimates derived from the dentition, which may be because postcranial elements play a larger role in supporting body weight.

中文翻译：

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Paramys delicatus (Ischyromyidae, Rodentia) 的运动行为和身体质量以及对其他早期北美 Paramyines 的评论

Paramyine ischyromyids 是最早出现在北美的祖先啮齿动物群体之一。研究这些灭绝动物的生态指标使我们能够更好地了解它们如何融入北美哺乳动物群落。在这项研究中，我们使用功能性肢体指数和活松鼠作为现存的类似物，重新评估了近乎完整的副赖氨酸骨架的运动行为，Paramys delicatus (AMNH FM 12506)。然后，我们使用功能性肢体指数研究的结果来选择合适的运动组，用于估计 Paramys delicatus 和其他早期北美（Wasatchian-Bridgerian）paramyines 的体重。这样做是因为体重与运动模式密切相关，并且可以从功能类似于所研究化石的现存样本中生成更可靠的体重估计值。计算了活的 sciurids 的三个运动组（树栖、半窝和滑翔）的功能性肢体指数。树栖类、半窝类和滑行类动物之间的比较表明，与肌肉机械优势和肢体健壮性相关的功能指标可以区分运动组；然而，树栖类群和半化石类群之间存在相当大的重叠。Paramys delicatus 被发现通常比大多数活松鼠（包括半化石类群）具有更大的机械优势和肢体健壮性。由于这些特征与经常使用刮挖的半化石松鼠有关，这表明Paramys delicatus 和其他早期的paramyines 可能是熟练的刮挖者。然而，反映副肌腱肢体比例的指数表明，这些早期啮齿动物可能比活松鼠使用了更多的后肢主导运动。因此，早期副肌氨酸的体重估计来自半仓鼠样本。统计比较表明，许多最可靠的Paramys delicatus 和其他paramyines 体重估计值来自肱骨尺寸，最可靠的估计值是肱骨头上下宽度。使用这些估计量，对于Paramys delicatus，早期副肌氨酸的个体体重估计范围为3391至4005克，Paramyscopei 1137–1329 g，Paramys taurus 1291 g，以及Notoparamys costilloi 3357 g。从颅后要素得出的所有体重估计值都大大大于先前公布的从牙列得出的估计值，这可能是因为颅后要素在支持体重方面发挥了更大的作用。