ABSTRACT

Trematosaurids were globally distributed Early Triassic temnospondyl amphibians characterized by elongate ‘crocodile-like’ skulls. Some of the most famous trematosaurid fossils were discovered on the island of Spitsbergen in the Arctic Svalbard archipelago. Among these, the short-snouted trematosaurine, Tertrema acuta, is one of the few taxa represented by virtually complete cranial remains. Unusually, however, the type specimens comprise only natural molds that were historically used to reconstruct three-dimensional casts. Here, we re-assess these restorations using the original impressions to phylogenetically analyze and re-diagnose the taxon. Unexpectedly, our first-hand scores differ markedly from previous literature-sourced interpretations and yield conflicting tree topologies that nest T. acuta with long-snouted lonchorhynchines, thus destabilizing the long-favored sub-division of trematosaurids based on their skull shape. We attribute this result to character state conflict and suggest that the traditional classification of trematosaurids may mask more complex evolutionary relationships, as well as possible trophic partitioning, and eco-morphological plasticity.

摘要

Trematosaurids 是全球分布的早三叠世 temnospondyl 两栖动物，其特征是细长的“鳄鱼样”头骨。在北极斯瓦尔巴群岛的斯匹次卑尔根岛上发现了一些最著名的吸音龙科化石。其中，短吻吸龙类Tertrema acuta是少数具有几乎完整颅骨遗骸的分类群之一。然而，不同寻常的是，模型标本仅包含历史上用于重建 3D 模型的天然模具。在这里，我们使用原始印象重新评估这些修复体，以对分类群进行系统发育分析和重新诊断。出乎意料的是，我们的第一手分数与之前文献来源的解释明显不同，并产生了嵌套的相互冲突的树拓扑T. acuta具有长吻 lonchorhynchines，从而破坏了长期以来基于头骨形状的吸音龙科的细分。我们将这一结果归因于特征状态冲突，并认为传统的吸音龙科分类可能掩盖了更复杂的进化关系，以及可能的营养分区和生态形态可塑性。