Chatar Narimane, Boman Romain, Fischer Valentin, Segura Valentina, Julémont Cara, Tseng Z Jack
Evolution and Diversity Dynamics Lab, UR Geology, Université de Liège, Liège, Belgium.
Functional Anatomy and Vertebrate Evolution Lab, Department of Integrative Biology, University of California, Berkeley, California, USA.
Anat Rec (Hoboken). 2024 May 27. doi: 10.1002/ar.25504.
The evolution of organisms can be studied through the lens of developmental systems, as the timing of development of morphological features is an important aspect to consider when studying a phenotype. Such data can be challenging to obtain in fossil amniotes owing to the scarcity of their fossil record. However, the numerous remains of Rancho La Brea allow a detailed study of the postnatal changes in an extinct sabertoothed felid: Smilodon fatalis. Despite numerous previous studies on the ontogeny of Smilodon, an important question remained open: how did the cubs of Smilodon acquire and process food? By applying 3D geometric morphometrics and finite element analyses to 49 mandibles at various developmental stages (22 of S. fatalis, 23 of Panthera leo, and 4 of early diverging felids), we assess the changes in mandibular shape and performance during growth. Both lions and sabertooths exhibit a shift in mandibular shape, aligning with eruption of the lower carnassial. This marks the end of weaning in lions and suggests a prolonged weaning period in S. fatalis owing to its delayed eruption sequence. We also highlight distinct ontogenetic trajectories, with S. fatalis undergoing more postnatal mandibular shape changes. Finally, although S. fatalis appears more efficient than P. leo at performing an anchor bite, this efficiency is acquired through ontogeny and at a quite late age. The delayed shape change compared with P. leo and the low biting efficiency during the growth in Smilodon could indicate an extended duration of the parental care compared with P. leo.
生物体的进化可以通过发育系统的视角来研究，因为在研究一个表型时，形态特征发育的时间是一个需要考虑的重要方面。由于化石记录稀少，在化石羊膜动物中获取此类数据可能具有挑战性。然而，拉布雷亚牧场的大量遗骸使得对一种已灭绝的剑齿猫科动物——致命刃齿虎的出生后变化进行详细研究成为可能。尽管之前有许多关于刃齿虎个体发育的研究，但一个重要问题仍然悬而未决：刃齿虎幼崽是如何获取和处理食物的？通过对49个处于不同发育阶段的下颌骨（22个致命刃齿虎的、23个狮子的以及4个早期分化猫科动物的）应用三维几何形态测量学和有限元分析，我们评估了生长过程中下颌形状和性能的变化。狮子和剑齿虎在下颌形状上都表现出一种转变，这与下裂齿的萌出一致。这标志着狮子断奶的结束，并表明致命刃齿虎断奶期延长，因为其萌出顺序延迟。我们还强调了不同的个体发育轨迹，致命刃齿虎出生后下颌形状变化更大。最后，尽管致命刃齿虎在进行锚式咬噬时似乎比狮子更高效，但这种效率是在个体发育过程中且在相当晚的年龄才获得的。与狮子相比，致命刃齿虎形状变化延迟以及生长过程中咬噬效率较低，这可能表明与狮子相比，其亲代抚育期更长。
