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| THAICHELYS Szczygielski et al. [A] Thaichelys ruchae (Broin, 1984) [B-C] Proterochersis robusta. [F] Proganochelys quenstedtii in Szczygielski, Dróżdż, Chanthasit, Manitkoon et Ditbanjong, 2025. ไทยเชลิส |
Abstract
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 i. 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.
Systematic paleontology
AMNIOTA Haeckel, 1866 sensu Laurin and Reisz, 2020
TESTUDINATA Klein, 1760 sensu ITNC et al., 2020
PROTEROCHERSIDAE Nopcsa, 1923 (converted clade name)
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| Comparison of the bridge region morphology in Triassic pantestudinates (ventral view, scaled to roughly the same shell length). A, Thaichelys ruchae SM2017-1-124. B, Proterochersis robusta SMNS 18440. C, Proterochersis robusta SNBS 17561. D, Proterochersis porebensis ZPAL V. 39/49 (pratype). E, Proganochelys quenstedtii SMNS 17204. F, Proganochelys quenstedtii SMSN 16980. G, Proganochelys quenstedtii MB.1910.45.2. H, Palaeochersis talampayensis PULR 068 (holotype). Scute sulci in A indicated with grey lines, dashed lines indicate poorly defined or ambiguous sulci. |
THAICHELYS Szczygielski et al. gen. nov.
Etymology: Referring to Thailand, as the origin place of the described specimens, and incorporating -chelys (gr. Χέλυς, turtle): „Thai turtle”.
Type and only species: Thaichelys ruchae (Broin, 1984)
Thaichelys ruchae (Broin, 1984) comb. nov.
Holotype: SM2015-1-001 (former TF 1440-6), incomplete left side of the anterior plastral lobe (Figs 6, 8A, 9).
Type locality: Ban Suan Sawan Banana Farm, Si Chomphu, Khon Kaen, Thailand.
Type horizon and age: Huai Hin Lat Formation, Late Triassic (Norian).
Revised diagnosis: Testudinate characterized by a unique combination of characters: (1) carapace not reduced in thickness (unlike in Chinlechelys tenertesta, Palaeochersis talampayensis, and Waluchelys cavitesta); (2) pleurals with shelf-like, anteroposteriorly elongated bosses (unlike in Proganochelys quenstedtii); (3) three supramarginals present (unlike in Palaeochersis talampayensis, Proganochelys quenstedtii, and Waluchelys cavitesta); (4) bridge-level marginals (a) not wedging between the supramarginals (unlike in Proganochelys quenstedtii), (b) with anterolaterally projected, V-shaped in lateral view intermarginal sulci (unlike in Proganochelys quenstedtii), (c) with the dorsal exposition smaller ...
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| Thaichelys ruchae, life restoration as a proterochersid turtle. Digital drawing by Sita Manitkoon. |
Tomasz Szczygielski, Dawid Dróżdż, Phornphen Chanthasit, Sita Manitkoon and Pitaksit Ditbanjong. 2025. The Triassic Turtle of Thailand –Revision of ‘Proganochelys’ ruchae. PLoS ONE. 20(3): DOI: doi.org/10.1371/journal.pone.0316338 [March 19, 2025]
