Long Katherine, Prothero Donald, Madan Meena, Syverson Valerie J P
Department of Geological Sciences, California State Polytechnic University, Pomona, California, United States of America.
Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, California, United States of America.
PLoS One. 2017 Sep 27;12(9):e0183175. doi: 10.1371/journal.pone.0183175. eCollection 2017.
Previous studies have demonstrated that the Pleistocene saber-toothed cat Smilodon fatalis had many forelimb adaptations for increased strength, presumably to grapple with and subdue prey. The Rancho La Brea tar pits yield large samples of juvenile limb bones forming a growth series that allow us to examine how Smilodon kittens grew up. Almost all available juvenile limb bones were measured, and reduced major axis fits were calculated to determine the allometric growth trends. Contrary to expectations based on their robust limbs, Smilodon kittens show the typical pattern of growth found in other large felids (such as the Ice Age lion, Panthera atrox, as well as living tigers, cougars, servals, and wildcats) where the limb grows longer and more slender faster than they grow thick. This adaptation is thought to give felids greater running speed. Smilodon kittens do not grow increasingly more robust with age. Instead, they start out robust and follow the ancestral felid growth pattern, while maintaining their robustness compared to other felids. Apparently, the growth of felid forelimbs is highly canalized and their ontogeny is tightly constrained.
先前的研究表明，更新世的剑齿虎致命刃齿虎在前肢有许多适应性变化以增强力量，推测是为了抓住并制服猎物。拉布雷亚沥青坑出土了大量幼年肢体骨骼样本，形成了一个生长序列，使我们能够研究刃齿虎幼崽是如何成长的。几乎所有可用的幼年肢体骨骼都进行了测量，并计算了主轴拟合度以确定异速生长趋势。与基于其粗壮四肢的预期相反，刃齿虎幼崽呈现出其他大型猫科动物（如冰河时期的狮子、美洲拟狮，以及现存的老虎、美洲狮、薮猫和野猫）中发现的典型生长模式，即四肢变长变细的速度比变粗的速度更快。这种适应性变化被认为能让猫科动物跑得更快。刃齿虎幼崽不会随着年龄增长而变得越来越强壮。相反，它们一开始就很强壮，并遵循祖先猫科动物的生长模式，同时与其他猫科动物相比保持其强壮性。显然，猫科动物前肢的生长具有高度的定向性，其个体发育受到严格限制。
