Premaxillae of the Extinct Megalonychid Sloths Acratocnus, Neocnus, and Megalonyx, and their Phylogenetic Implications (Mammalia, Xenarthra)
Premaxillae of the Extinct Megalonychid Sloths Acratocnus, Neocnus, and Megalonyx, and their Phylogenetic Implications (Mammalia, Xenarthra)
复制标题
已灭绝巨爪树懒 Acratocnus、Neocnus 和 Megalonyx 的前颌骨及其系统发育意义（哺乳动物、Xenarthra）
DOI：
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发表时间：
2016
影响因子：
1.9
通讯作者：
T. Gaudin
中科院分区：
文献类型：
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作者：
Lauren M. Lyon;Chelsea Powell;H. Gregory McDonald;T. Gaudin
在大多数食叶动物中，前上颌骨松散地附着在上颌骨上，因此在其他保存完好的头骨化石中经常缺失。尽管在树懒中很少保存，但在保存该元素的分类群中，前颌骨已被证明具有显著的遗传变异。在巨爪科中，前颌骨仅在早期分类群Eucholoeops（Santacrucian South American Land Mammal Age [SALMA]）、现存的两趾树懒Choloepus和北美新近纪分类群Megalonyx中被发现，后者仅在未发表的硕士论文中被描述。我们在此报告在两个已灭绝的巨爪类属，新爪类和巨爪类中发现了前颌骨。这些身体小，半树栖的巨爪树懒是大安的列斯群岛的特有物种。虽然树懒在加勒比海的出现至少可以追溯到渐新世晚期，但最著名的分类群来自更新世至全新世的洞穴沉积物，分布在波多黎各、伊斯帕尼奥拉岛和古巴。本文还描述了产于北美的两种巨爪兽的前颌骨，即北美陆地哺乳动物时代（NALMA）M。Leptostomus和Rancholabrean NALMA M.乔氏菌。这些物种表现出一个渐进的重定向的前颌骨内巨爪类从原始的水平元素到一个几乎垂直的元素，和一些显着的变化，解剖的切牙孔。形态学证据表明，一个扩大，板状前颌骨构成了整个分支Megalonychidae的突触。此外，虽然Eucholoeops保留了一个短的前颌骨前突，像megatherioid树懒，这一过程是缺乏在其他巨爪类，这表明这一过程的损失可能团结晚中新世到现代megalonychids。
In most folivorans, the premaxilla is loosely attached to the maxilla, so that it is often missing in otherwise very well-preserved fossil skulls. Despite its infrequent preservation in sloths, the premaxilla has been shown to have phylogenetically significant variation among the taxa that do preserve the element. In the family Megalonychidae, the premaxilla is known only in the early taxon Eucholoeops (Santacrucian South American Land Mammal Age [SALMA]), the extant two-toed sloth Choloepus, and the North American Neogene taxon Megalonyx, the last described only in an unpublished Master’s thesis. We report here the discovery of the premaxilla in two genera of extinct megalonychids, Neocnus and Acratocnus. These small bodied, semiarboreal megalonychid sloths are endemic to the islands of the Greater Antilles. Though the presence of sloths in the Caribbean dates at least to the late Oligocene, the best known taxa derive from Pleistocene to Holocene cave deposits in Puerto Rico, Hispaniola, and Cuba. We also describe the premaxilla in two species of Megalonyx from North America, the Blancan North American Land Mammal Age (NALMA) M. leptostomus and Rancholabrean NALMA M. jeffersonii. These species show a progressive reorientation of the premaxilla within Megalonyx from a primitive horizontal element to a nearly vertical element, and some significant changes in the anatomy of the incisive foramen. Morphological evidence suggests that a broadened, plate-like premaxilla constitutes a synapomorphy for the entire clade Megalonychidae. Furthermore, although Eucholoeops retains a short anterior process of the premaxilla like that of megatherioid sloths, this process is lacking in the other megalonychids, suggesting that the loss of this process may unite late Miocene to Recent megalonychids.