ABSTRACT

The Early Carboniferous stem tetrapod Whatcheeria deltae is among the earliest-branching limbed tetrapods represented by multiple near-complete specimens, making it an important taxon in understanding the vertebrate water-to-land transition. However, all preserved skulls of Whatcheeria suffer from post-mortem crushing and lateral compression, which has made cranial reconstruction problematic. In this study, computed tomography data of three Whatcheeria specimens were segmented using visualization software to digitally separate each individual skull bone from matrix. Digital methods were used to repair and retrodeform the bones and produce the first complete three-dimensional skull reconstruction of Whatcheeria. We provide a revised description of the cranial and lower jaw anatomy of Whatcheeria based on CT data, focusing on sutural morphology and previously unknown anatomical details. Our findings suggest that Whatcheeria had one of the narrowest skulls of any known early tetrapod, a gap between the nasals, and significant overlap of the lacrimal onto the nasal and prefrontal. Sutural morphology is used to infer loading regime in the skull during feeding and suggests the skull of Whatcheeria was well adapted to resist stresses induced by biting large prey with its enlarged anterior fangs.

摘要

早石炭世干四足动物Whatcheeria deltae是最早分支的四足动物之一，以多个近乎完整的标本为代表，使其成为了解脊椎动物水陆过渡的重要分类群。然而，所有保存的Whatcheeria头骨都遭受了死后挤压和横向压缩，这使得颅骨重建成为问题。在这项研究中，三个Whatcheeria标本的计算机断层扫描数据使用可视化软件进行分割，以数字方式将每个颅骨与矩阵分开。数字方法被用于修复和变形骨骼，并产生了第一个完整的Whatcheeria三维颅骨重建. 我们根据 CT 数据提供了对Whatcheeria颅骨和下颌解剖结构的修订描述，重点关注缝合线形态和以前未知的解剖细节。我们的研究结果表明，Whatcheeria的头骨是任何已知的早期四足动物中最窄的头骨之一，鼻腔之间存在间隙，并且泪腺在鼻腔和前额叶上有明显的重叠。缝合线形态用于推断进食过程中颅骨的负载情况，并表明Whatcheeria的颅骨很好地适应了通过其扩大的前牙咬住大型猎物而引起的压力。