Ravosa M J, Noble V E, Hylander W L, Johnson K R, Kowalski E M
Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611-3008, USA.
J Hum Evol. 2000 May;38(5):667-93. doi: 10.1006/jhev.1999.0380.
A postorbital bar is one of a suite of derived features which distinguishes basal primates from their putative sister taxon, plesiadapiforms. Two hypotheses have been put forward to explain postorbital bar development and variation in circumorbital form: the facial torsion model and visual predation hypothesis. To test the facial torsion model, we employ strain data on circumorbital and mandibular loading patterns in representative primates with a postorbital bar and masticatory apparatus similar to basal primates. To examine the visual predation hypothesis, we employ metric data on orbit orientation in Paleocene and Eocene primates, as well as several clades of visual predators and foragers that vary interspecifically in postorbital bar formation.A comparison of galago circumorbital and mandibular peak strains during powerful mastication demonstrates that circumorbital strains are quite low. This indicates that, as in anthropoids, the strepsirhine circumorbital region is excessively overbuilt for countering routine masticatory loads. The fact that circumorbital peak-strain levels are uniformly low in both primate suborders undermines any model which posits that masticatory stresses are determinants of circumorbital form, function and evolution. This is interpreted to mean that sufficient cortical bone must exist to prevent structural failure due to non-masticatory traumatic forces. Preliminary data also indicate that the difference between circumorbital and mandibular strains is greater in larger taxa.Comparative analyses of several extant analogs suggest that the postorbital bar apparently provides rigidity to the lateral orbital margins to ensure a high level of visual acuity during chewing and biting. The origin of the primate postorbital bar is linked to changes in orbital convergence and frontation at smaller sizes due to nocturnal visual predation and increased encephalization. By incorporating in vivo and fossil data, we reformulate the visual predation hypothesis of primate origins and thus offer new insights into major adaptive transformations in the primate skull.
眶后棒是一系列衍生特征之一，它将基干灵长类动物与其假定的姐妹分类群plesiadapiforms区分开来。已经提出了两种假说来解释眶后棒的发育以及眶周形态的变化：面部扭转模型和视觉捕食假说。为了检验面部扭转模型，我们采用了具有眶后棒且咀嚼器官与基干灵长类动物相似的代表性灵长类动物眶周和下颌加载模式的应变数据。为了检验视觉捕食假说，我们采用了古新世和始新世灵长类动物以及几个在眶后棒形成上种间存在差异的视觉捕食者和觅食者类群的眼眶方向的测量数据。对倭丛猴在强力咀嚼时眶周和下颌峰值应变的比较表明，眶周应变相当低。这表明，与类人猿一样，狐猴型灵长类动物的眶周区域在应对日常咀嚼负荷方面过度构建。两个灵长类亚目眶周峰值应变水平均一致较低这一事实，削弱了任何认为咀嚼应力是眶周形态、功能和进化决定因素的模型。这被解释为意味着必须存在足够的皮质骨以防止因非咀嚼性创伤力而导致的结构破坏。初步数据还表明，在较大的分类单元中，眶周和下颌应变之间的差异更大。对几种现存类似物的比较分析表明，眶后棒显然为眼眶外侧边缘提供了刚性，以确保在咀嚼和咬时具有高水平的视力。灵长类动物眶后棒的起源与较小体型时由于夜行性视觉捕食和脑容量增加导致的眼眶会聚和朝前化的变化有关。通过纳入活体和化石数据，我们重新阐述了灵长类动物起源的视觉捕食假说，从而为灵长类动物头骨的主要适应性转变提供了新的见解。
