Extinction and replacement among predatory mammals in the North American late Eocene and Oligocene: Tracking a paleoguild over twelve million years

Changes in taxonomic and morphologic diversity within the paleoguild of predatory mammals were explored within a mammalian chronofauna spanning a twelve million year interval, from the latest Eocene to the end of the Oligocene of North America (36–24 ma). The timespan encompassed a modest extinction event among terrestrial mammals (circa 34 ma) followed by a period of relative stability. Morphological diversity was assessed with estimates of body mass, relative tooth size, and tooth shape. Principal component, nearest‐neighbor, and minimum‐spanning‐tree analyses were used to compare morphological diversity and species packing within predator paleoguilds in the mid‐Chadronian (37–34 ma), Orellan (34–32), Whitneyan (32–29.5), and early Arikareean (29.5–24) land mammal ages. Species richness of predators throughout the interval was relatively constant, fluctuating between 15 and 18 total taxa. Moreover, despite significant differences in taxonomic composition and a modest extinction event among terrestrial mammals, morphological diversity within the paleoguild was very similar in the Chadronian and Orellan. In the Whitneyan and especially the early Arikareean, the diversity of feeding adaptations among species declined slightly, largely due to the loss of several highly specialized meat‐eaters (creodonts, nimravids) and the addition of small omnivores (canids).     

地点覆盖度、集合群落、地质时期动物群:联接古生物学和现代种群生物学的概念

在古生物群落中新近出现的地点覆盖度或发生率的概念,以及对生物集合种群的空间动态学的深入了解,使古生物学和现代生物学的联系更加紧密。集合群落的概念以及地质时期动物群的古生物学认识显示,将古生物学和生态学结合在一起是大有希望的。评述了目前对这些概念的理解,并以欧亚大陆大型食草动物群落的发育作为范例,介绍了运用这些理论来研究化石记录的方法。研究结果表明,化石记录中种群覆盖度的研究可以在以化石为基础的进化研究和以现生有机体为基础的进化研究之间架起一座桥梁。地点覆盖度最大的类群,像现代生态学中发生率最大的类群一样,往往是地理分布最广泛、在当地最丰富的类群。