Temporal differences in fossil assemblages of small mammals can generate important insights into associated environmental conditions. Moreover, by including modern assemblages in such comparisons, it may also be possible to identify the effects of recent human colonization on mammal communities and their habitats. To explore potential signals of European colonization in northwestern Patagonia, we compared fossil and modern assemblages of small mammals from two newly characterized paleontological sites in the Limay Valley region of Río Negro Province, Argentina. The material analyzed consisted of 18 species of small-bodied terrestrial mammals identified from a sample of 27,992 specimens. Fossil assemblages dating from 6453 to 1002 calibrated years before present were relatively stable in taxonomic composition and displayed only minor differences in relative species abundances. In contrast, the modern assemblages examined were clearly distinct, containing a different suite of numerically dominant taxa and lacking three previously abundant grassland species that are presumed to have gone extinct in the vicinity of our study sites. We suggest that these changes reflect substantial post-colonization modifications of surrounding landscapes, including establishment of pine plantations, changes in fire regimes, and introductions of livestock and invasive species of plants. If correct, this supposition raises important concerns regarding the use of modern assemblages as a baseline for reconstructing paleoenvironmental conditions. To avoid potential misinterpretations associated with the use of modern faunal assemblages, we suggest two potential alternative strategies for inferring temporal changes in environmental conditions.

中文翻译：

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巴塔哥尼亚北部小型哺乳动物群落的近期变化：古环境重建的警告

小型哺乳动物化石组合的时间差异可以产生对相关环境条件的重要见解。此外，通过在此类比较中包括现代组合，还可以确定最近人类殖民对哺乳动物群落及其栖息地的影响。为了探索欧洲在巴塔哥尼亚西北部殖民的潜在信号，我们比较了来自阿根廷里奥内格罗省利迈河谷地区两个新特征古生物学遗址的小型哺乳动物的化石和现代组合。分析的材料包括从 27,992 个样本中鉴定出的 18 种小型陆生哺乳动物。从 6453 年到 1002 年校准之前的化石组合在分类组成上相对稳定，并且在相对物种丰度上仅显示出微小的差异。相比之下，所检查的现代组合明显不同，包含一组不同的数量优势类群，并且缺乏三种以前丰富的草原物种，这些物种被认为在我们的研究地点附近已经灭绝。我们认为这些变化反映了殖民化后对周围景观的实质性修改，包括松树种植园的建立、火灾状况的变化以及牲畜和入侵植物物种的引入。如果正确，这一假设会引起人们对使用现代组合作为重建古环境条件基线的重要担忧。