The Mesozoic plate tectonic and paleogeographic history of the final break up of West Gondwana had a profound effect on the distribution of terrestrial vertebrates in South America. As the supercontinent fragmented into a series of large landmasses (South America, Antarctica, Australia, New Zealand, the Indian subcontinent, and Madagascar), particularly during the Late Jurassic and Cretaceous, its terrestrial vertebrates became progressively isolated, evolving into unique faunal assemblages. The episodic nature of South American mammalian Cenozoic faunas became apparent in its modern formulation after George Gaylord Simpson's seminal works on this topic. Two aspects add complexity to this generally accepted scheme: first, the fact that South America is not (and was not) a biogeographic unit, as the Neotropical Region does not include its southernmost tip (the Andean Region, including Patagonia and the southern Andes). Second, and intimately linked with the first one, that South America was not an island continent during the Late Cretaceous and the beginning of the Cenozoic, being its southernmost portion closely linked with West Antarctica up to the late Paleocene at least. Here we stress on this second aspect; we summarize a series of recent, detailed paleogeographical analyses of the continental breakup between Patagonia (including the Magallanes Region) and the Antarctic Peninsula crustal block, beginning with the opening of the Atlantic Ocean in the Early Cretaceous and running up to the Early Paleogene with the expansion of the Scotia Basin. In second place, we comment on the implications of these distinct paleogeographic and paleobiogeographic scenarios (before and after their geographic and faunistic isolation) for the evolution of South American terrestrial mammalian faunas. Summarizing, (1) we recognize a West Weddellian terrestrial biogeographic unit with the assemblage of the southern part of South America (Patagonia and the Magallanes Region) and the Antarctic Peninsula (and probably Thurston Island) crustal block of West Antarctica, spanning from the Late Cretaceous (Campanian) through the Early Paleogene (Paleocene); (2) we suggest that the Antarctic Peninsula acted as a double "Noah's Ark” regarding, first, the probable migration of some non-therian lineages into southern South America; later, the migration of metatherians to Australasia.

西冈瓦纳最终解体的中生代板块构造和古地理史对南美陆生脊椎动物的分布产生了深远的影响。随着超大陆分裂成一系列大型陆地（南美，南极洲，澳大利亚，新西兰，印度次大陆和马达加斯加），特别是在侏罗纪晚期和白垩纪时期，其陆生脊椎动物逐渐被隔离，演变成独特的动物群落。在乔治·盖洛德·辛普森（George Gaylord Simpson）就该主题所做的开创性工作之后，南美哺乳动物新生代动物的情节性质在其现代表述中变得显而易见。这个普遍接受的方案增加了两个方面的复杂性：首先，南美不是（过去也不是）生物地理单位，因为新热带地区不包括其最南端（安第斯地区，包括巴塔哥尼亚和安第斯山脉南部）。其次，与第一个密切相关，在白垩纪晚期和新生代初期，南美不是一个岛屿大陆，它是最南端的部分，至少与西南极洲直到古新世都息息相关。在这里，我们强调第二方面。我们总结了一系列近期，详细的古地理分析，分析了巴塔哥尼亚（包括麦哲伦地区）和南极半岛地壳块之间的大陆破裂，始于白垩纪早期的大西洋开放，一直到白垩纪早期的古近纪。斯科舍盆地的扩张。第二名 我们评论了这些独特的古地理和古生物地理场景（在地理和动物隔离之前和之后）对南美陆生哺乳动物区系演化的影响。总而言之，（1）我们认识到一个Weddellian陆地生物地理单位，其组成为南美南部（巴塔哥尼亚和马加拉内斯地区）和南极洲的南极半岛（可能还有瑟斯顿岛）地壳块体，其范围从晚期开始。白垩纪（Campanian）至早期古近纪（古新世）；（2）我们建议，南极半岛起着双重“诺亚方舟”的作用，首先涉及一些非以太宗族可能迁入南美洲南部；其次是通过迁徙迁徙到大洋洲。