Land Mammals and the Great American Interchange

摘要: Xhe continents of South America, Africa, Antarctica, Australia, and India were once joined in a large land mass the southern hemisphere called Gondwana. About 100 million years ago (mya) America began to separate from moving primarily westward direction. There is no convincing geological evidence indicate that had continuous connection with any other continent _ until about 3 mya, when Bolivar Trough marine barrier disappeared Americas united by emergence Panamanian bridge. The long-isolated continental biotas North brought into contact, resulting an intermingling has come be known as Great American Interchange (Webb 1976; Fig. 1). site former thus gateway for this event, de noting historical boundary tween two biotic provinces (Fig. 2). Although many different groups plants animals took part interchange, I will focus on mammals, which are most thoroughly studied participants. was first recog nized Wallace (1876), but it taken another hun dred intense paleontological study Amegh ino, Matthew, Scott, Patterson, Simpson, Webb, others clarify patterns dispersal (see, example, Marshall 1981, 1985; Webb bridge three permitted mingling long-separated faunas 1982). It only during last decade, moreover, greater precision dating sediments containing interchange taxa provided firm time frame various aspects event. now possible assess detail, analyze tempo mode rates extinction origina tion successive through time. As result, repre sents best-documented example fossil record intermin