Igor G. Danilov

A REDESCRIPTION OF ‘PLESIOCHELYS’ TATSUENSIS FROM THE LATE JURASSIC OF CHINA, WITH COMMENTS ON THE ANTIQUITY OF THE CROWN CLADE CRYPTODIRA

Abstract A reexamination of the holotype of ‘Plesiochelys’ tatsuensis Yeh, 1963, from the Late Jurassic of China, allows us to establish previously unknown characters of this species. A phylogenetic analysis places ‘P.’ tatsuensis on the stem of Trionychia, near the clades Adocidae and Nanhsiungchelyidae. Given the hypothesized phylogenetic position of ‘P.’ tatsuensis, a new genus, Yehguia gen. nov., is erected for this species. The phylogenetic position of Y. tatsuensis pushes the origin of the crown clade Cryptodira into the Late Jurassic. This is remarkable in light of recent studies that moved the origin of crown group turtles (Testudines) from the Triassic to the Late Jurassic. This means that the establishment of basal cryptodiran lineages must have quickly followed the origin of Testudines in the Late Jurassic. The fact that the most ancient fossil Cryptodira is hypothesized to be on the stem of Trionychia is concordant with recent molecular hypotheses that place Trionychia as the most basal extant lineage of Cryptodira. Finally, our results further highlight that the Late Jurassic of China is important for understanding the earliest evolution of cryptodiran turtles.

A reassessment of some poorly known turtles from the Middle Jurassic of China, with comments on the antiquity of extant turtles

Abstract Recent studies have shown that the Middle Jurassic is a key time for understanding the origin and early evolution of crown group turtles, but few turtle-bearing localities from this epoch are known. This study adds to our knowledge by providing a detailed description of two poorly characterized specimens (IVPP-V6507 and IVPP-V8805) from the Middle Jurassic of China that previously were both assigned to the poorly known species Chengyuchelys baenoides. This reappraisal allows us to present new observations, images, and taxonomic conclusions about these specimens and others from the same locality (Dashanpu, Zigong Prefecture, Sichuan Province, China). With at least four species, Dashanpu is the most diverse locality from the Middle Jurassic; all other turtle localities from this time have only one species each. We place Chengyuchelys into a cladistic analysis of turtle relationships for the first time. Our analysis places Chengyuchelys as sister to Xinjiangchelys latimarginalis and solidly on the stem of Cryptodira. This result is surprising because Chengyuchelys retains mesoplastra. Nevertheless, derived osteological and scalation characters of this taxon drive its phylogenetic position as a relatively advanced stem cryptodire. This finding, combined with a reappraisal of other Middle Jurassic turtles from Asia, shows that the crown group Testudines had evolved by the Middle Jurassic. Unfortunately, many key specimens from Sichuan Province are still poorly characterized morphologically and stratigraphically. This lack of phylogenetic and temporal resolution hinders our understanding of the origins of extant turtle clades, but also highlights the importance of Jurassic Asian turtles for ultimately resolving these issues.

New Material and a Reassessment of Soft-Shelled Turtles (Trionychidae) from the Late Cretaceous of Middle Asia and Kazakhstan

ABSTRACT In this paper we describe previously unpublished trionychid turtle material, consisting of numerous shell fragments, from two Late Cretaceous (Santonian—early Campanian) localities from Middle Asia and Kazakhstan (Central Asia in the U.S. tradition): Kansai (Tadjikistan) and Shakh-Shakh (Kazakhstan). This material can be attributed to two forms of trionychids present in both localities. One of them is the named species Trionyx riabinini Kuznetsov and Chkhikvadze, 1987, described from Shakh-Shakh. New data on its shell morphology provided by our study allow attribution to the genus Aspideretoides Gardner et al., 1995, known previously only from the Campanian—Maastrichtian of North America. The presence of this taxon in both Middle Asia and North America provides the first clear evidence for the relationship between Cretaceous Asian and North American trionychids. The second form is established as a new species, “Trionyx” kansaiensis, sp. nov., with unclear systematic position within Trionychinae. We lastly present a brief review of other named taxa of Cretaceous trionychids of Middle Asia and Kazakhstan.

Osteology, relationships, and ecology of Annemys (Testudines, Eucryptodira) from the Late Jurassic of Shar Teg, Mongolia, and phylogenetic definitions for Xinjiangchelyidae, Sinemydidae, and Macrobaenidae

ABSTRACT A complete description of the xinjiangchelyid turtles Annemys levensis and A. latiens is provided, based on all available material from the Upper Jurassic type locality of Shar Teg, Mongolia. Annemys latiens was previously known almost exclusively from shell material, but an undescribed skull from Shar Teg is referable to this species and its distinct morphology confirms the presence of two taxa at this locality. Annemys latiens has an elongated skull that markedly differs in proportions from those of A. levensis and resembles the shape of some recent, piscivorous turtles. The overall similarity of the shells of the two Annemys species combined with significant differences in the skull indicate that these turtles probably partitioned the aquatic niche by exploring different feeding strategies. Among xinjiangchelyids, at least three different skull morphotypes can be differentiated, which implies a moderate level of ecological diversification among Late Jurassic Asian turtles. Phylogenetic analysis weakly supports the inclusion of Annemys spp. into Xinjiangchelyidae and places xinjiangchelyids at the stem of Testudines, but the latter result is considered tentative. Phylogenetic definitions of Xinjiangchelyidae, Sinemydidae, and Macrobaenidae are provided for nomenclatural clarity and precision.

A REASSESSMENT OF THE REFERRAL OF AN ISOLATED SKULL FROM THE LATE CRETACEOUS OF UZBEKISTAN TO THE STEM-TESTUDINOID TURTLE GENUS LINDHOLMEMYS

Abstract A fossil turtle skull (ZISP PH 1/17) from the Late Cretaceous (upper Turonian, Bissekty Formation) of Dzharakuduk (Uzbekistan, Asia) was used to score the skull characters for the genus Lindholmemys (a stem testudinoid) in a recent phylogenetic analysis. A description of ZISP PH 1/17 and a new cladistic analysis reveals no characters to support its referral to Lindholmemys elegans or to the stem-testudinoid lineage. ZISP PH 1/17 is very similar to North American Adocus, differing mainly in characters of the upper jaw. Therefore, we hypothesize that ZISP PH 1/17 is the skull of either Shachemys ancestralis or “Adocus” aksary, adocid shell taxa from Dzharakuduk. Pending additional discoveries and description of turtles from Dzharakuduk, we refer ZISP PH 1/17 to Adocidae, gen. et sp. indet.

Cretaceous soft-shelled turtles (Trionychidae) of Mongolia: New diversity, records and a revision

This paper is devoted to the description and revision of material of Cretaceous soft-shelled turtles (Trionychidae) of Mongolia. It includes the description of seven trionychid species, six of which are new, and two new genera: the cyclanorbine Nemegtemys conflata gen. et sp. nov. from the Nemegt Formation (Maastrichtian), and the trionychines Gobiapalone breviplastra gen. et sp. nov. from the Nemegt and Barungoyot (Campanian) formations, G. orlovi from the Baynshire Formation (Cenomanian–Santonian), ‘Trionyx’ baynshirensis sp. nov. from the Baynshire Formation, ‘T.’ gilbentuensis sp. nov. from the Nemegt Formation, ‘T.’ gobiensis sp. nov. from the Nemegt Formation, and ‘T.’ shiluutulensis sp. nov. from an unknown formation (Campanian). In addition, one shell from the ?Baynshire Formation of Khermin Tsav is assigned to Gobiapalone sp. The type material of Amyda menneri is considered to be Trionychidae indet. and Amyda menneri to be a nomen dubium. Finally, we revise other available materials of Cretaceous trionychids from 45 localities in Mongolia. Nemegtemys conflata, if correctly assigned, is the earliest known member of Cyclanorbinae. The two species of the new genus Gobiapalone are included in two phylogenetic analyses of Trionychidae. In both analyses Gobiapalone is monophyletic. In the first analysis, Gobiapalone is placed within Apalonina. In the second analysis, Gobiapalone is sister to Apalonina. Thus, the results of both analyses show that Apalonina, which is a rather advanced and well-supported trionychid clade, or its closest sister taxon (stem-Apalonina), were present in the Late Cretaceous of Asia. These results suggest that most other supra-generic clades of modern trionychids had been established in Asia by the Late Cretaceous. That suggestion is supported by the discovery of a cyclanorbine Nemegtemys conflata in the Late Cretaceous of Mongolia. Finally we summarize the latest data on temporal and geographical distributions of Cretaceous Trionychidae of Asia and North America. http://zoobank.org/urn:lsid:zoobank.org:pub:921DA1C5-C4B2-463D-A49D-608024C6036A

The first ‘true’ Adocus (Testudines, Adocidae) from the Paleogene of Asia

ABSTRACT This paper describes a new species of the genus Adocus (A. inexpectatus, sp. nov.), based on an almost complete shell from the upper Eocene Youganwo (= Youkanwo) Formation of the Maoming Basin, China. The inclusion of A. inexpectatus in a phylogenetic analysis of Adocusia resulted in a polytomy with Adocus aksary and A. amtgai (both from the Upper Cretaceous of Asia). This clade formed a polytomy with the North American species of Adocus. Like other ‘true’ Adocus, A. inexpectatus has overlapping of the marginals onto the costals in the middle and posterior parts of the carapace and sculpturing of the shell surface with small grooves and pits. Thus, A. inexpectatus represents the first ‘true’ Adocus from the Paleogene of Asia. Other specimens from the Paleogene of Asia that have been referred to Adocus, characterized by shell sculpturing with small dots and unknown condition of the marginal/costal overlapping, are distinct from ‘true’ Adocus and herein referred to as ‘Adocus’ spp. Here we also report the presence of ‘Adocus’ from the Paleocene of North America. Our study indicates that the evolutionary and biogeographic history of the Adocidae was more complicated than considered previously, including previously unrecognized dispersal events between Asia and North America. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Two New Plastomenine Softshell Turtles from the Paleocene of Montana and Wyoming

ABSTRACT The many fossil turtle remains collected by Princeton University throughout the 1950s and 1960s from Paleocene sediments in Montana and Wyoming include two new species of plastomenine softshell turtles (Trionychidae) that are referred to Hutchemys gen. nov., which corresponds to the previously used informal taxon “Plastomenine Type A.” Hutchemys is unique among trionychids in having a broadly rounded entoplastron that is underlain by a large rectangular callosity and fully immobilized through lateral processes of the hyoplastra. Hutchemys rememdium sp. nov. is documented by specimens from the Torrejonian of Montana and the Tiffanian of Wyoming, whereas Hutchemys arctochelys sp. nov. is only known from a collection of shells from a single Clarkforkian locality in Montana. The holotype of a third taxon, Aspideretes nassau Hay 1908, is diagnostic for Hutchemys, but cannot be diagnosed to the species level and is thus considered a nomen dubium. A phylogenetic analysis places the new species in a clade that is sister to Plastomenus aff. thomasii along the phylogenetic stem of Cydanorbinae, thus tentatively confirming monophyly of Plastomeninae and a close relationship to cyclanorbines. However, given that many supposedly diagnostic postcranial characters of Plastomeninae are often found among trionychines as well, in particular characters pertaining to the extensively ossified plastron, we suggest that a wide and rounded entoplastron is a more useful character in diagnosing this clade. Representatives of Hutchemys seem to have preferred swampy habitats and their shell converges on that of testudinoid or pleurodiran pond turtles in the degree of ossification and the presence of an anterior plastral hinge.

Middle Jurassic turtles from the Sichuan Basin, China: a review

The turtle fauna of the Middle Jurassic Xiashaximiao Formation in the Sichuan Basin and the type series of Chengyuchelys baenoides Young & Chow, 1953 are revised. By the absence of a mesoplastron and other shell characters, both the holotype and paratype of Chengyuchelys baenoides belong to the family Xinjiangchelyidae and come probably from the Upper Jurassic Shangshaximiao Formation. The Middle Jurassic turtle assemblage of the Sichuan Basin is composed of two entities: the Bashuchelyidae fam. nov. ( Bashuchelys gen. nov., Chuannanchelys gen. nov.) and Protoxinjiangchelys gen. nov. on the one hand, and Sichuanchelys on the other hand, with the former as the dominant group. Bashuchelyids and xinjiangchelyids are closely related to one another, while Sichuanchelys is more primitive and has no shared apomorphic features with bashuchelyids. The whole assemblage appears to be endemic to the Sichuan Basin at genus level and distinct from the Late Jurassic turtle fauna of the same basin in its relict nature and absence of the Polycryptodira.

Cretaceous Trionychids of Asia: An Expanded Review of Their Record and Biogeography

This chapter presents an expanded review of all described and/or figured specimens and taxa of trionychids from the Cretaceous (Barremian to Maastrichtian) of Asia. Cretaceous occurrences in Asia are limited to indeterminate trionychids and to the subfamily Trionychinae; cyclanorbines are unknown and previous reports of plastomenids are based on misidentified trionychine material. For the Trionychinae, we recognize 13 taxa of uncertain placement within the subfamily (“Aspideretes” maortuensis, four species of Khunnuchelys, “Paleotrionyx” riabinini, “Trionyx” kansaiensis and “T.” kyrgyzensis, and Trionychinae indet. 1–5), seven taxa within the tribe Trionychini (“Amyda” menneri and “Am”. orlovi, “Aspideretes” alashanensis, Aspideretoides riabinini and Aspideretoides sp., and Trionychini indet. 1 and 2), and three taxa within the subtribe Apalonina (Apalonina indet. 1–3). We also recognize Sinamyda and four indeterminate taxa as Trionychidae incertae sedis. Although two other tribes (Ulutrionychini and Rafetini) have been proposed to include some Asian Cretaceous trionychines, monophyly of those tribes has yet to be satisfactorily demonstrated. During the Cretaceous, earlier and more basal trionychids (i.e., trionychines with eight neurals) were more broadly distributed across Asia, whereas later and more derived taxa had more restricted ranges. The recognition of Aspideretoides spp. and three indeterminate Apalonina in the Cretaceous of Asia provides evidence for a shared history with North American trionychids.