Szczygielski Tomasz, Dróżdż Dawid, Chanthasit Phornphen, Manitkoon Sita, Ditbanjong Pitaksit
Institute of Paleobiology, Polish Academy of Sciences, Warsaw, Poland.
Independent Researcher, Cieszyn, Poland.
PLoS One. 2025 Mar 19;20(3). doi: 10.1371/journal.pone.0316338. eCollection 2025.
True turtles (Testudinata) appeared in the Norian (Late Triassic) and quickly attained a worldwide distribution and relatively high diversity. Their remains are currently known from that time from Asia, Europe, North America, and South America, and represent at least three separate clades. Whereas the generic and suprageneric attribution of comparatively well-preserved and studied European and South American taxa, such as Proganochelys quenstedtii, Proterochersis robusta and Proterochersis porebensis, Palaeochersis talampayensis, and Waluchelys cavitesta sparks no controversy, the more fragmentary and less common species have been variably considered representatives of separate genera or referred to already existing ones - most commonly, Proganochelys. This uncertainty is unfortunate, as it severely muddles the picture of the evolution, diversity, and geographical distribution of the earliest turtles. One such problematic species, coming from the Norian Huai Hin Lat Formation of Thailand, was described in 1980s as Proganochelys ruchae. However, this generic attribution was subsequently put into question and the recent increase of available Triassic turtle material allows to remove the species ruchae from Proganochelys to a new genus, Thaichelys gen. nov., and place it in the clade of Proterochersidae, together with Proterochersis spp., Keuperotesta limendorsa, and Chinlechelys tenertesta. As a result, the genus Proganochelys is considered here to be solely a central Pangean (modern-day European) taxon. Moreover, Thaichelys ruchae exhibits in some respects a transitional morphology between other Triassic taxa and Proterochersis spp., and may constitute a sister taxon to the grouping of Proterochersis spp. and Keuperotesta limendorsa from Europe. This, in turn, considering the lack of a Carnian record of pantestudinates outside of Asia, suggests that Thaichelys ruchae could represent an early radiation of the Proterochersidae which branched off before the Testudinata dispersed into the western Pangea.
真龟类（龟鳖目）出现于诺利期（晚三叠世），并迅速在全球范围内分布且具有较高的多样性。目前已知它们在那个时期于亚洲、欧洲、北美洲和南美洲均有化石遗迹，且至少代表了三个独立的分支。虽然保存相对完好且研究充分的欧洲和南美洲类群，如原颚龟（Proganochelys quenstedtii）、粗壮原鳄龟（Proterochersis robusta）、孔氏原鳄龟（Proterochersis porebensis）、塔拉帕耶古鳄龟（Palaeochersis talampayensis）和卡维特斯瓦鲁切龟（Waluchelys cavitesta）的属级和超属级归属并无争议，但那些更为破碎且不常见的物种，却被不同地视为独立属的代表，或被归入已有的属——最常见的是原颚龟属。这种不确定性很不幸，因为它严重混淆了最早龟类的演化、多样性和地理分布情况。一个这样有问题的物种，来自泰国诺利期的怀欣拉特组，在20世纪80年代被描述为鲁氏原颚龟（Proganochelys ruchae）。然而，这个属级归属后来受到质疑，并且最近三叠纪龟类材料的增加使得鲁氏龟种从原颚龟属移出，归入一个新属——泰国龟属（Thaichelys gen. nov.），并将其与原鳄龟属物种、莱门多萨凯珀鳄龟（Keuperotesta limendorsa）和纤细钦勒龟（Chinlechelys tenertesta）一起置于原鳄龟科的分支中。因此，在这里原颚龟属仅被视为一个泛古大陆中部（现代欧洲）的分类单元。此外，鲁氏泰国龟在某些方面展现出其他三叠纪分类单元与原鳄龟属物种之间的过渡形态，并且可能构成原鳄龟属物种与来自欧洲的莱门多萨凯珀鳄龟组合的姐妹分类单元。反过来，考虑到亚洲以外地区卡尼期泛龟类化石记录的缺失，这表明鲁氏泰国龟可能代表了原鳄龟科在龟鳖目扩散到西泛古大陆之前就已分支的早期辐射类群。
