The skull morphology of four species of cottontails from the mountains and plateaus of southwestern United States and northern Mexico, currently recognized as Sylvilagus nuttallii, S. cognatus, S. robustus, and S. holzneri (=S. floridanus holzneri), was analyzed using multivariate statistics. Based on 26 or 30 measurements taken on each of 350 adult skulls, and formulation of 16 pooled samples, with each representing a different geographic population, the results show there are two species-level distinctions in skull type. Cottontails from southern Utah, northern and east-central Arizona, and northern New Mexico show morphological overlap among geographically adjacent samples and all have a highly arched skull. These are referable to S. nuttallii. Cottontails from central Arizona, central New Mexico, and western Texas southward along the Sierra Madre Occidental to Durango, Mexico, and Sierra Madre Oriental to central Coahuila, Mexico show morphological overlap among geographically adjacent samples and all have a relatively flat skull. These are referable to S. holzneri. Both S. nuttallii and S. holzneri are polytypic in the study area. Sylvilagus n. pinetis is restricted to the White Mountains of Arizona. Those north and west of the Colorado River in Arizona and Utah are referable to S. n. nuttallii and those from southeastern Utah, northeastern Arizona and northern New Mexico are referable to S. n. grangeri. The population of cottontails previously referred to S. cognatus from central New Mexico is indistinguishable from topotypical S. holzneri from southeastern Arizona as well as populations from southwestern New Mexico, Chihuahua, and Sonora, Mexico. Cottontails previously referred to S. robustus, from the Guadalupe Mountains of New Mexico and Texas, southward in the mountains of western Texas, and the Sierra Madre Oriental to central Coahuila, Mexico, average larger in overall size and, on average, have proportionately larger auditory bullae and are referable to S. holzneri robustus. The relationship of S. holzneri to other mountain/plateau-inhabiting taxa, outside the study area in central and southern Mexico remains to be resolved.

四个品种从山上和美国西南部和墨西哥北部的高原棉尾的头骨形态，目前公认Sylvilagus藻，S. cognatus，S.粗壮，和S. holzneri（= S. floridanus holzneri)，使用多元统计进行分析。基于对 350 个成人头骨中的每一个进行 26 或 30 次测量，以及 16 个汇集样本的公式化，每个样本代表不同的地理种群，结果显示头骨类型存在两种物种级别的差异。来自犹他州南部、亚利桑那州北部和中东部以及新墨西哥州北部的棉尾辫在地理上相邻的样本之间显示出形态重叠，并且都有一个高度拱形的头骨。这些可参考S. nuttallii. 从亚利桑那州中部、新墨西哥州中部和德克萨斯州西部沿西马德雷山脉向南到墨西哥杜兰戈和东马德雷山脉到墨西哥科阿韦拉中部的棉尾辫在地理上相邻的样本之间显示出形态重叠，并且都具有相对平坦的头骨。这些可参考S. holzneri。无论S.乐藻和S. holzneri都在研究区域多型。西尔维拉古斯 pinetis仅限于亚利桑那州的怀特山脉。位于亚利桑那州和犹他州的科罗拉多河以北和以西的地区可称为S. n. nuttallii和来自犹他州东南部、亚利桑那州东北部和新墨西哥州北部的那些被称为S. n. 格兰杰里. 先前被称为来自新墨西哥州中部的S. cognatus的棉尾鱼种群与来自亚利桑那州东南部的典型S. holzneri以及来自新墨西哥州西南部、奇瓦瓦州和墨西哥索诺拉州的种群无法区分。Cottontails 以前称为S.robustus，来自新墨西哥州和德克萨斯州的瓜达卢佩山脉，向南的德克萨斯州西部山区，以及东部的马德雷山脉到墨西哥科阿韦拉州中部，平均整体尺寸更大，平均比例更大听觉大疱，可参考S. holznerirobustus。S. holzneri的关系 墨西哥中部和南部研究区之外的其他山地/高原栖息分类群仍有待解决。