ABSTRACT

We describe a partial skeleton of a large-sized owl from Wasatchian strata of the Willwood Formation (Wyoming, U.S.A.). The holotype of Primoptynx poliotauros, gen. et sp. nov., includes all major postcranial bones and is one of the most substantial Paleogene records of the Strigiformes. The fossil shows that owls exhibited a considerable morphological diversity in the early Eocene of North America and occupied disparate ecological niches. As in the protostrigid taxon Minerva from the late early to early middle Eocene of North America, but unlike in extant owls, the ungual phalanges of the hallux and the second toe of the new species are distinctly larger than those of the other toes. Primoptynx poliotauros gen. et sp. nov., however, does not exhibit the derived tibiotarsus morphology of the Protostrigidae. Even though the new species may well be a stem group representative of protostrigid owls, current data do not allow an unambiguous phylogenetic placement. Concerning the size of the ungual phalanges, the feet of P. poliotauros correspond to those of extant hawks and allies (Accipitridae). We therefore hypothesize that it used its feet to dispatch prey items in a hawk-like manner, whereas extant owls kill prey with their beak. Primoptynx and protostrigid owls were possibly specialized in foraging on prey items that required an accipitrid-like killing strategy, such as larger-sized or more defensive mammals. The extinction of these peculiar owls may have been related to the radiation of accipitrid diurnal birds of prey, which appear to have diversified in the late Eocene and early Oligocene.

摘要

我们描述了威尔伍德组（美国怀俄明州）的沃萨奇阶地层中的一只大猫头鹰的部分骨骼。的模式标本Primoptynx poliotauros，根。等。十一月，包括所有主要的后颅骨，并且是剑形目最重要的古近纪记录之一。化石表明，猫头鹰在北美始新世早期表现出相当大的形态多样性，并占据了不同的生态位。就像北美始新世早期至中期初生的密涅瓦分类群一样，但与现存的猫头鹰不同，拇指的趾骨和新物种的第二趾明显比其他趾大。Primoptynx poliotaurosgen。等。但是，nov。并未显示出原头龙的胫bio的形态。即使新物种很可能代表原刚猫头鹰的茎群，但目前的数据仍不能明确地将系统发育定位。关于指甲指骨的大小，的脚P. poliotauros对应于现存鹰和同盟（鹰科）的。因此，我们假设它用脚以鹰般的方式分发猎物，而现存的猫头鹰则用喙杀死猎物。Primoptynx以及原宿猫头鹰可能专门用于觅食那些需要采取类似杀戮策略的猎物，例如大型或更具防御性的哺乳动物。这些特有的猫头鹰的灭绝可能与放射状的昼夜猛禽的放射有关，后者在始新世晚期和渐新世早期已经多样化。