Data from: Ground squirrels (Rodentia, Sciuridae) of the late Cenozoic Meade Basin sequence: diversity and paleoecological implications

The Meade Basin, SW Kansas, yields a rich vertebrate fossil record from the late Cenozoic. Here, we review fossil ground squirrels (Sciuridae) from the region as a contribution to the broader Meade Basin Rodent Project. We recognize 14 species in 7 genera: 2 species of giant ground squirrels (Paenemarmota Hibbard and Schultz, 1948) from the early Pliocene, and at least 12 species in 6 extant genera (Ammospermophilus Merriam, 1892; Otospermophilus Brandt, 1844; Ictidomys J. A. Allen, 1877; Poliocitellus A. H. Howell, 1938; Urocitellus Obolenskij, 1927; Cynomys Rafinesque, 1817) from the Pliocene-Pleistocene sequence, including the first regional records of Ammospermophilus. Based on dental morphology and the ecology of modern congeners, we interpret faunal change through the sequence as primarily reflecting a shift from a Pliocene assemblage of “southwestern” taxa with granivorous/omnivorous diets (relatively low-crowned, transversely narrow cheek teeth) in warm and at least occasionally dry shrub or shrub-steppe habitats (Ammospermophilus, Otospermophilus, Ictidomys meadensis), to a Pleistocene temperate assemblage of grazing taxa that either exhibited relatively high-crowned, transversely wider cheek teeth (Urocitellus, Cynomys, Ictidomys tridecemlineatus) or were otherwise dependent on grassland habitats (Poliocitellus). The early Pleistocene Borchers assemblage was transitional in this regard, heralding a "revolution" observed as well with other clades in the Meade Basin rodent community. This interpretation is broadly congruent with evidence of Pliocene climatic change and the staged development of regional grasslands, with the modern proportion of C3/C4 plants established in the Meade Basin during the early Pleistocene.

堪萨斯州西南部的米德盆地（Meade Basin）产出了晚新生代时期的丰富脊椎动物化石记录。作为广义米德盆地啮齿类研究项目的一项研究成果，本研究对该区域产出的化石陆栖松鼠（松鼠科Sciuridae）进行了系统综述。本研究共鉴定出7属14种：其中2种为产自早上新世的巨型地松鼠（Paenemarmota Hibbard and Schultz, 1948），另有6个现生属共至少12个物种产自上新世-更新世沉积序列，其中包含漠黄鼠属（Ammospermophilus Merriam, 1892）在该区域的首个化石记录；其余现生属包括Otospermophilus Brandt, 1844、Ictidomys J. A. Allen, 1877、Poliocitellus A. H. Howell, 1938、Urocitellus Obolenskij, 1927以及草原犬鼠属（Cynomys Rafinesque, 1817）。基于牙齿形态学特征与现代近缘类群的生态习性，本研究认为该沉积序列中的动物群更替主要反映了生态环境的转变：从上新世以“西南型”类群为主的组合——这些类群多为食谷/杂食性，拥有相对低冠、横向窄缩的颊齿，栖息于温暖且偶伴干旱的灌丛或灌丛草原生境（包括漠黄鼠属、Otospermophilus以及Ictidomys meadensis）——转变为更新世的温带放牧型类群组合；这类放牧型类群要么具有相对高冠、横向更宽的颊齿（如Urocitellus、草原犬鼠属以及Ictidomys tridecemlineatus），要么特化依赖草原生境（如Poliocitellus）。早更新世的博彻斯（Borchers）动物群组合在该生态转变中处于过渡阶段，预示了一场“演化革命”——这一转变同样见于米德盆地啮齿类群落的其他演化支。该解释与上新世气候变化及区域草原阶段性发育的相关证据高度吻合，现代C3/C4植物的占比格局于早更新世在米德盆地得以确立。