Crocodylian princess in Taiwan: Revising the taxonomic status of Tomistoma taiwanicus from the Pleistocene of Taiwan and its paleobiogeographic implications

Toyotamaphimeia, deriving from a mythological princess in Japan into a crocodile, refers to an extinct crocodylian lineage. Here, we reexamine the holotype of a long-forgotten species: Tomistoma taiwanicus from the Pleistocene of Tainan (Taiwan) and revise its taxonomic status to Toyotamaphimeia taiwanicus comb. nov., leading to the first recognized species of Toyotamaphimeia outside Japan. Our phylogenetic analyses also support this taxonomic assignment and, more interestingly, further suggest an East Asian lineage. In addition, Toyotamaphimeia taiwanicus represents a tropical species, resolving a long-lasting puzzle of why Toyotamaphimeia only inhabited the much higher latitudinal area (Japan). Given the large body size of Toyotamaphimeia taiwanicus (about 7 m) and geologically older than Toyotamaphimeia machikanensis from Japan, we propose a novel evolutionary scenario: the genus Toyotamaphimeia originated in Taiwan and evolved to a large body size with gigantothermic physiology, allowed an Out-of-Taiwan scheme, and dispersed further north to Japan. Our taxonomic identification shows the presence of an extinct endemic crocodylian species from the Pleistocene of Taiwan with large-scale paleogeographic implications, and this study, with our recent progress in vertebrate paleontology in Taiwan, should provoke more in-depth paleontological research on elucidating a larger picture of the Pleistocene extinction.

丰田鳄属（Toyotamaphimeia）得名自日本神话中化为鳄鱼的公主，是一类已灭绝的鳄形类（crocodylian）支系。本研究重新检视了一件长期被忽视的物种正模标本（holotype）：产自中国台湾台南更新世（Pleistocene）的台湾假长吻鳄（Tomistoma taiwanicus），并将其分类地位修订为台湾丰田鳄（Toyotamaphimeia taiwanicus），新组合（comb. nov.），这也是日本以外首个被正式确认的丰田鳄属物种。本研究的系统发育分析（phylogenetic analyses）支持该分类修订结论，更具意义的是，分析结果进一步表明该类群隶属于东亚支系。此外，台湾丰田鳄为热带物种，这一发现解决了长期困扰学界的谜题：为何此前仅知丰田鳄属分布于纬度更高的日本区域。鉴于台湾丰田鳄体型庞大（体长约7米），且地质年代早于日本的马甘丰田鳄（Toyotamaphimeia machikanensis），本研究提出全新的演化假说：丰田鳄属起源于台湾，通过巨温性（gigantothermic）生理机制演化出大体型，借此实现“走出台湾”的扩散模式，并进一步向北迁徙至日本。本研究的分类学鉴定确认了中国台湾更新世存在一种特有已灭绝鳄形类物种，该发现具有重要的古地理学意义；结合团队近期在台湾脊椎动物古生物学（vertebrate paleontology）领域的研究进展，本研究有望推动更深入的古生物学研究，以阐明更新世灭绝事件的整体图景。