Department of Ecology and Evolutionary Biology, Brown University, Providence, RI, USA
Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA, USA.
Proc Biol Sci. 2018 May 30;285(1879). doi: 10.1098/rspb.2018.0727.
Studies of soft tissue effects on joint mobility in extant animals can help to constrain hypotheses about joint mobility in extinct animals. However, joint mobility must be considered in three dimensions simultaneously, and applications of mobility data to extinct taxa require both a phylogenetically informed reconstruction of articular morphology and justifications for why specific structures' effects on mobility are inferred to be similar. We manipulated cadaveric hip joints of common quail and recorded biplanar fluoroscopic videos to measure a 'ligamentous' range of motion (ROM), which was then compared to an 'osteological' ROM on a ROM map. Nearly 95% of the joint poses predicted to be possible at the hip based on osteological manipulation were rendered impossible by ligamentous constraints. Because the hip joint capsule reliably includes a ventral ligamentous thickening in extant diapsids, the hip abduction of extinct ornithodirans with an offset femoral head and thin articular cartilage was probably similarly constrained by ligaments as that of birds. Consequently, in the absence of extraordinary evidence to the contrary, our analysis casts doubt on the 'batlike' hip pose traditionally inferred for pterosaurs and basal maniraptorans, and underscores that reconstructions of joint mobility based on manipulations of bones alone can be misleading.
对现存动物软组织对关节活动性影响的研究有助于约束关于已灭绝动物关节活动性的假说。然而，关节活动性必须同时在三个维度上进行考虑，并且将活动性数据应用于已灭绝分类群需要对关节形态进行系统发育信息重建，以及对为什么推断特定结构对活动性的影响相似的理由进行说明。我们操纵了普通鹌鹑的尸体髋关节，并记录了双平面荧光透视视频，以测量“韧带”活动范围 (ROM)，然后将其与 ROM 图谱上的“骨骼”ROM 进行比较。根据骨骼操作预测的髋关节的近 95%的可能姿势被韧带限制而变得不可能。由于现生物种的髋关节囊在腹侧可靠地包含一个韧带增厚部分，因此具有偏移股骨头和薄关节软骨的已灭绝的鸟跖类动物的髋关节外展可能与鸟类一样受到韧带的限制。因此，在没有相反的特殊证据的情况下，我们的分析对传统上为翼龙和基础手盗龙类推断的“蝙蝠样”髋关节姿势提出了质疑，并强调了仅基于骨骼操纵重建关节活动性可能会产生误导。
