Trionychid Turtles Research Articles

Development of Skin and Dermal Bone of the Shell in <i>Pelodiscus maackii</i> (Testudines: Trionychidae)

The article is devoted to the study of the ontogenetic development of the skin and the structure of the skin-bone shell of the trionychid turtle Pelodiscus maackii (Brandt, 1858). The process of formation of the epidermis and dermis, as well as their derivatives (epidermal scales and dermal ossifications), is described. The development of epidermal scales in Pelodiscus maackii has been shown to be similar to the development of asymmetric scales in other reptiles. Five stages of formation of the definitive structure of the dermal bones have been identified. Structural differences between the internal and external parts of the bony plates (rod-shaped elements and bony callosities) are due to the previous stratification of the dermis into histologically distinct strata: hypodermal, fibrous and papillary. In particular, the fibrous stratum, consisting of several layers of orthogonally oriented collagen bundles, is a precursor to the plywood-like structure of the trionychid bony plates. The growth of bone tissue around the vascular network in the papillary layer is the reason for the formation of surface ornamentation of the trionychid callosities. Some questions of the evolutionary significance of the unique features of the trionychid shell are discussed.

Cranial and mandibular anatomy of Plastomenus thomasii and a new time-tree of trionychid evolution

Trionychid (softshell) turtles have a peculiar bauplan, which includes shell reductions and cranial elongation. Despite a rich fossil record dating back to the Early Cretaceous, the evolutionary origin of the trionychid bauplan is poorly understood, as even old fossils show great anatomical similarities to extant species. Documenting structural detail of fossil trionychids may help resolve the evolutionary history of the group. Here, we study the cranial and mandibular anatomy of Plastomenus thomasii using µCT scanning. Plastomenus thomasii belongs to the Plastomenidae, a long-lived (Santonian–Eocene) clade with uncertain affinities among trionychid subclades. The skulls of known plastomenids are characterized by unusual features otherwise not known among trionychids, such as extremely elongated, spatulate mandibular symphyses. We use anatomical observations for updated phylogenetic analyses using both parsimony and Bayesian methods. There is strong support across methods for stem-cyclanorbine affinities for plastomenids. The inclusion of stratigraphic data in our Bayesian analysis indicates that a range of Cretaceous Asian fossils including Perochelys lamadongensis may be stem-trionychids, suggesting that many features of trionychid anatomy evolved prior to the appearance of the crown group. Divergence time estimates from Bayesian tip-dating for the origin of crown Trionychia (134.0 Ma) and Pan-Trionychidae (123.8 Ma) constrain the evolutionary time span during which the trionychid bauplan has evolved to a range of < 11 million years. Bayesian rate estimation implies high morphological rates during early softshell turtle evolution. If correct, plastomenids partially fill the stratigraphic gap which results from shallow divergence times of crown cyclanorbines during the late Eocene.

Histological evidence for dermal-endochondral co-ossification of the dorsal blades in the late Paleozoic amphibian Platyhystrix rugosus (Temnospondyli: Dissorophidae)

ABSTRACT We provide a detailed histological report of the dorsal blades of the Permo-Carboniferous dissorophid Platyhystrix rugosus. The blades, originally interpreted as hyperelongated neural spines, show compelling histological evidence of a dermal contribution that includes mineralized fibers and plywood-like tissue remarkably similar to extant osteoderm-bearing ceratophryid frogs and trionychid turtles. Their fusion to the vertebrae suggests homology with the osteoderm series of related Permian dissorophids. Although the mode of ossification is difficult to ascertain, both dermal ossification and metaplasia of the surrounding fibrous connective tissue (such as ligaments interconnecting the blades) likely combined to produce the fused blades observed in the closely allied Carboniferous platyhystricine Astreptorhachis. These represent the oldest examples of the phenomenon of dermal-endochondral co-ossification of osteoderms and vertebrae in the postcranial skeleton of a Paleozoic tetrapod. Our findings also highlight the adoption of different developmental mechanisms to produce convergent ecomorphology in sail-backed Paleozoic dissorophid amphibians (dermal blades derived from osteoderms) versus contemporary synapsids (hyperelongated neural spines). Future histological studies should sample additional dissorophid taxa to map the development of osteoderms within a broader phylogenetic context and to better understand their functional diversity.

A new vertebrate fauna from the Lower Cretaceous Holly Creek Formation of the Trinity Group, southwest Arkansas, USA.

We present a previously discovered but undescribed late Early Cretaceous vertebrate fauna from the Holly Creek Formation of the Trinity Group in Arkansas. The site from the ancient Gulf Coast is dominated by semi-aquatic forms and preserves a diverse aquatic, semi-aquatic, and terrestrial fauna. Fishes include fresh- to brackish-water chondrichthyans and a variety of actinopterygians, including semionotids, an amiid, and a new pycnodontiform, Anomoeodus caddoi sp. nov. Semi-aquatic taxa include lissamphibians, the solemydid turtle Naomichelys, a trionychid turtle, and coelognathosuchian crocodyliforms. Among terrestrial forms are several members of Dinosauria and one or more squamates, one of which, Sciroseps pawhuskai gen. et sp. nov., is described herein. Among Dinosauria, both large and small theropods (Acrocanthosaurus, Deinonychus, and Richardoestesia) and titanosauriform sauropods are represented; herein we also report the first occurrence of a nodosaurid ankylosaur from the Trinity Group. The fauna of the Holly Creek Formation is similar to other, widely scattered late Early Cretaceous assemblages across North America and suggests the presence of a low-diversity, broadly distributed continental ecosystem of the Early Cretaceous following the Late Jurassic faunal turnover. This low-diversity ecosystem contrasts sharply with the highly diverse ecosystem which emerged by the Cenomanian. The contrast underpins the importance of vicariance as an evolutionary driver brought on by Sevier tectonics and climatic changes, such as rising sea level and formation of the Western Interior Seaway, impacting the early Late Cretaceous ecosystem.

A new plastomenid trionychid turtle, Plastomenus joycei , sp. nov., from the earliest Paleocene (Danian) Denver Formation of south-central Colorado, U.S.A.

ABSTRACT North American soft-shelled turtles, including trionychines and plastomenids, are incredibly abundant in latest Cretaceous through earliest Paleocene sediments. Here we describe a new species of plastomenid turtle, Plastomenus joycei, based on a nearly complete early Danian skeleton from the Denver Formation in the Denver Basin, Colorado. Plastomenus joycei is differentiated from all other plastomenid turtles based on the presence of large eighth costals that are much longer than wide, sinusoidal raised ridges on the carapace, flat posterior edge of the carapace, spike-like epiplastra that lack callosities, a broad entoplastron that lacks a callosity, hyoplastra with two lateral processes, presence of metaplastically ossified hyoplastral shoulders (i.e., anteriorly protruding lappets), and a broad midline contact between the hypo- and xiphiplastra. Plastomenus joycei broadly resembles the Cretaceous Gilmoremys spp. and the Eocene Plastomenus thomasii and exhibits intermediate morphology between the two, most notably in the degree of ossification of the plastron. The increase in plastral ossification, as well as a decrease in overall size and an increase in the doming of the shell, co-occurs with the Cretaceous–Paleogene mass extinction and these morphological changes may be in response to an increase in mammalian predators during the early Paleogene. Plastomenus joycei is most commonly found in riverine sandstone sediments and is hypothesized to be a riverine turtle. http://zoobank.org/urn:lsid:zoobank.org:pub:F4FE56A9-3E63-4BF0-A5CB-0CF0F9B6B045

Geochemical analyses suggest stratigraphic origin and late Miocene age of reworked vertebrate remains from Penanjong Beach in Brunei Darussalam (Borneo)

ABSTRACT We report on sporadic fossil vertebrates from Brunei Darussalam (Borneo). Most of these isolated remains are reworked and derive from Penanjong Beach known for former coastal cliffs used to be rich in marine molluscs. Previously, the only vertebrate remains reported were shark teeth. With new material, the fish fauna is now represented by six shark and a single ray taxa, while remains of three turtle families were discovered (Trionychidae, Cheloniidae, Geoemydidae). This fauna is compared to nearby upper Miocene fossiliferous beds from where remains of cheloniid and trionychid turtles were unearthed. To assess the origin of the reworked remains, rare earth element (REE) concentrations of the fossil bioapatite were compared between the reworked and the geographically closest in-situ Ambug Hill fauna. The obtained trend in REE variations are identical, revealing similar REE uptake mechanism and early diagenetic conditions. With the additional fact that the succession outcropping at Ambug Hill cuts the coastline imply that the majority of the reworked fossils derive from the local Miocene beds. This is supported by Sr-isotope ages from reworked calcite bivalve shells ranging from 9.74 to 6.62 Ma. These turtle remains thus represent the hitherto known first Neogene fossil tetrapods from Borneo.

A new species of trionychid turtle, Axestemys infernalis sp. nov., from the Late Cretaceous (Maastrichtian) Hell Creek and Lance formations of the Northern Great Plains, USA

A new species of trionychid turtle, Axestemys infernalis sp. nov., from the Late Cretaceous (Maastrichtian) Hell Creek and Lance formations of the Northern Great Plains, USA

A new species of trionychid turtle from the Upper Cretaceous (Campanian) Fruitland Formation of New Mexico, USA

AbstractNew shell material of a trionychid turtle from the Upper Cretaceous (upper Campanian) Fossil Forest Member of the Fruitland Formation of northwestern New Mexico represents a new species,Gilmoremys gettyspherensis. The material consists of right costals I–III, V, VI, and VIII, left costals V, VII, and VIII, the left half of the entoplastron, the right hypo- and xiphiplastron, and the left hyo-, hypo-, and xiphiplastron. The specimen shows great similarities to the Late Cretaceous (Maastrichtian) trionychidGilmoremys lancensis(Gilmore, 1916) by having a relatively thin shell, carapacial sculpturing consisting of fine pits combined with extended sinusoidal ridges or grooves, free costal rib ends, presence of a preneural, a distally constricted costal I and distally expanded costal II, two lateral hyoplastral processes, low hyoplastral shoulders, and full midline contact of the elongate xiphiplastra, but differs by being smaller, having raised sinusoidal ridges on the carapace instead of grooves, less distally expanded costals II, and less elongate xiphiplastra. Phylogenetic analysis placesGilmoremys gettyspherensisn. sp. as sister toGilmoremys lancensisnear the base of the clade Plastomenidae. Like the majority of previously described plastomenid materials, the type specimen ofGilmoremys gettyspherensisn. sp. was collected from a mudstone horizon, suggesting a preference for ponded environments.UUID:http://zoobank.org/e7165061-d86b-46b7-a1f8-c31f5a8ed628

The first record of a trionychid turtle (Testudines: Trionychidae) from the Cretaceous of the Pacific Coast of North America

Trionychid turtles were widespread throughout much of the Western Interior Basin of North America during the Cretaceous, represented by a wide variety of taxa. Despite their widespread abundance east of the Rocky Mountains, they have not previously been reported from Cretaceous deposits along the Pacific Coast of North America. We report here on an isolated trionychid costal from Vancouver Island, British Columbia. The fossil was recovered from the Late Cretaceous (Turonian to Maastrichtian) Nanaimo Group, on Vancouver Island, British Columbia. While the fossil is generically indeterminate, its presence adds an important datapoint in the biogeographic distribution of Trionychidae.

Amphibians and reptiles of the state of San Luis Potosí, Mexico, with comparisons with adjoining states.

A summary of the species of amphibians and reptiles of the state has been compiled, including their geographic distributions, habitats, and conservation statuses. The herpetofauna of San Luis Potosí consists of 41 species of amphibians and 141 species of reptiles. San Luis Potosí shares the highest number of species with Hidalgo and Tamaulipas, and the least number of species with Nuevo León. In San Luis Potosí, there are several taxa of particular conservation concern including salamanders, emydid and trionychid turtles, anguid and xenosaurid lizards, and natricid and colubrid snakes.

Fauna and setting of the &lt;em&gt;Adelolophus hutchisoni&lt;/em&gt; type locality in the Upper Cretaceous (Campanian) Wahweap Formation of Utah

We report new data on the type locality of the hadrosaurid ornithischian Adelolophus hutchisoni Gates et al., 2014 from the Campanian-aged Wahweap Formation of southern Utah, and the remainder of the vertebrate assemblage from the site. The type locality (UCMP V98173) is a previously-reported U.S. Geological Survey locality (USGS D815) and is stratigraphically low in the upper member of the Wahweap Formation. Additional taxa from the same site include acipenseriforms (sturgeon), amiiforms (bowfin), and lepisosteiforms (gar fish), baenid and trionychid turtles, and both theropod and ornithischian dinosaurs.

The furculae of the dromaeosaurid dinosaur Dakotaraptor steini are trionychid turtle entoplastra.

Dakotaraptor steini is a recently described dromaeosaurid dinosaur from the Upper Cretaceous (Maastrichtian) Hell Creek Formation of South Dakota. Included within the D. steini hypodigm are three elements originally identified as furculae, one of which was made part of the holotype specimen. We show that the elements described as D. steini ‘furculae’ are not theropod dinosaur furculae, but are rather trionychid turtle entoplastra referable to cf. Axestemys splendida. The hypodigm of D. steini should be adjusted accordingly.

A LATE CRETACEOUS SHARK COPROLITE WITH BABY FRESHWATER TURTLE VERTEBRAE INCLUSIONS

A small (3.4 cm) coprolite from the Upper Cretaceous (middle Campanian age) Coachman Formation in South Carolina, contains six cervical vertebrae from a very small, freshwater, trionychid turtle. Four of the vertebrae included in the coprolite are aligned and partly articulated. The coprolite shows typical selachian heteropolar shape with traces of spiral morphology, and is attributed to one of several common lamniform shark taxa in the associated marine fauna, most probably Squalicorax kaupi. Based on the minute size of the included vertebrae, with the largest 4.5 mm long, the turtle must have been very small and likely newly hatched. Assuming the selachian producing the specimen was a marine or estuarine species, this coprolite specimen indicates that the shark was feeding in or proximal to a fluvial environment, as observed in modern species of Carcharhinus. Given the small size of the coprolite, the shark was likely also small, suggesting that a juvenile Late Cretaceous shark was feeding far upstream, perhaps near its pupping area.

The first reliable record of trionychid turtles in the Paleocene of Asia

A new soft-shelled turtle species (Trionychidae), Gobiapalone palaeocenica sp. nov. is described based on an incomplete articulated juvenile skeleton from an unnamed Upper Paleocene locality in the Bugin Tsav Basin of Mongolia. This is the first reliable trionychid record in the Paleocene of Asia.

A new trionychid turtle from the Early Cretaceous of Heilongjiang Province, Northeastern China

A new soft-shelled turtle (“Trionyx” jixiensis sp. nov.) from the Lower Cretaceous Chengzihe Formation, Jixi city, Heilongjiang Province, China is described on the basis of a nearly complete carapace. The new species is diagnosed by the absence of suprascapular fontanelles and absence of a preneural; eight neurals, tetragonal fifth neural; and eight pairs of costals, with the large eighth costals meeting after the eighth neural. Due to the incompleteness of the specimen and confused classification of the genera of trionychids, the new species cannot be included in any genus of Trionychinae and is temporarily assigned to “Trionyx” (sensu lato). “Trionyx” jixiensis is one of the earliest trionychids, its discovery indicates that the family was already diversified during the Early Cretaceous in Asia.

A phylogeny of softshell turtles (Testudines: Trionychidae) with reference to the taxonomic status of the critically endangered, giant softshell turtle, Rafetus swinhoei

Several important aspects of the evolution of the softshell turtle (family Trionychidae) have not been addressed thoroughly in previous studies, including the pattern and timing of diversification of major clades and species boundaries of the critically endangered Shanghai Softshell Turtle, Rafetus swinhoei. To address these issues, we analyzed data from two mitochondrial loci (cytochrome b and ND4) and one nuclear intron (R35) for all species of trionychid turtles, except Pelochelys signifera, and for all known populations of Rafetus swinhoei in Vietnam and one from China. Phylogenetic analyses using three methods (maximum parsimony, maximum likelihood, and Bayesian inference) produce a well resolved and strongly supported phylogeny. The results of our time-calibration and biogeographic optimization analyses show that trionychid dispersals out of Asia took place between 45 and 49 million years ago in the Eocene. Interestingly, the accelerated rates of diversification and dispersal within the family correspond surprisingly well to global warming periods between the mid Paleocene and the early Oligocene and from the end of the Oligocene to the mid Miocene. Our study also indicates that there is no significant genetic divergence among monophyletic populations of Rafetus swinhoei, and that previous taxonomic revision of this species is unwarranted.

Soft-shelled turtles (Trionychidae) from the Cenomanian of Uzbekistan

Localities from the Cenomanian of Uzbekistan are the oldest in Middle Asia and Kazakhstan to preserve two broadly sympatric species of trionychid turtle. Material described here comes from multiple Cenomanian formations from the Itemir locality, and from multiple localities in the Cenomanian Khodzhakul Formation. The first taxon from the locality, “Trionyx” cf. kyrgyzensis, has multiple morphological similarities with the older, Early Cretaceous “Trionyx” kyrgyzensis. In contrast, the second taxon, “Trionyx” dissolutus, has multiple similarities with “Trionyx” kansaiensis, one of two species of trionychid found in younger Late Cretaceous localities. “Trionyx” dissolutus bears some superficial resemblance to other trionychid taxa within the clade Plastomenidae because of its highly ossified plastron with a hyoplastral lappet and an epiplastral notch. However, Plastomenidae is diagnosed primarily through characters that are absent or cannot be observed in the available material of “T.” dissolutus, and other shared features are plesiomorphic. In addition, “T.” dissolutus shares other synapomorphies with Trionychinae. A heavily ossified plastron may be more homoplastric within Trionychidae than has been previously recognized. Finally, we provide an improved understanding of the subtle similarities and differences between several closely related Cretaceous turtle assemblages of Middle Asia and Kazakhstan.

Soft-shelled turtles (Trionychidae) from the Bissekty Formation (Upper Cretaceous: Turonian) of Uzbekistan: Skull-based taxa and probable skull-shell associations

In this paper we describe previously unpublished trionychid turtle material, consisting of skull fragments, from the Late Cretaceous (late Turonian) Bissekty Formation of the Dzharakuduk locality in Uzbekistan. This material is assigned to two taxa: the skull-based Khunnuchelys kizylkumensisBrinkman et al. (1993, Can. J. Earth Sci. 30, 2214-2223) and Trionychini indet. Two specimens which cannot be confidently attributed to these two taxa are considered Trionychidae indet. In addition to these trionychid taxa known from skulls, the Dzharakuduk turtle assemblage includes at least two shell-based taxa, Aspideretoides cf. A. riabinini and “Trionyx” cf. “T.” kansaiensis. For this and other Late Cretaceous localities of Middle Asia and Kazakhstan, we suggest the probable skull-shell associations of Khunnuchelys spp. with “Trionyx” kansaiensis-like forms and Trionychini indet. with Aspideretoides-like forms.

A new softshelled trionychid turtle of the genus Khunnuchelys from the Upper Cretaceous Bostobe Formation of Kazakhstan

Previously unpublished trionychid turtle material from the Upper Cretaceous (Santonian—lower Campanian) Bostobe Formation from the Baybishe and Baykhozha localities in Kazakhstan is described. The material represents a new species of Khunnuchelys, a large, skull-based clade of Cretaceous Asian trionychids. Concordant with other partial skulls and fragmentary specimens described previously, Khunnuchelys lophorhothon sp. nov. has the unusual features of a beaklike maxilla and a vaulted, expanded triturating surface. In addition, the specimens reveal novel features including a constricted skull roof. Although estimates of the length of the carapace differ depending on estimation method, the skull belonged to a turtle of comparable size to the shell-based species “Trionyx” kansaiensis from the same formation. It is likely that K. lophorhothon and T. lophorhothon kansaiensis are synonymous, but this can be proved only by a find of associated skull and shell material.

Soft-shelled turtles (Trionychidae) from the Bissekty Formation (Late Cretaceous: late Turonian) of Uzbekistan: Shell-based taxa

In this paper we describe previously unpublished trionychid turtle material, consisting of numerous shell fragments, from the Late Cretaceous (late Turonian) Bissekty Formation of the Dzharakuduk locality in Uzbekistan. This material is assigned to two shell-based taxa: Aspideretoides cf. riabinini and “Trionyx” cf. kansaiensis. The material which cannot be confidently attributed to these two taxa is identified as Trionychidae indet. In addition to these shell-based trionychid taxa, the Dzharakuduk turtle assemblage includes two skull-based taxa of trionychids (Khunnuchelys kizylkumensis and Trionychini indet.). The trionychids from the Bissekty Formation are most similar to trionychids from the younger (Santonian – early Campanian) Bostobe Formation of Kazakhstan, represented by three shell-based taxa (Aspideretoides riabinini, Paleotrionyx riabinini and “Trionyx”kansaiensis), and one skull-based taxon (Khunnuchelys sp.). We provide an improved understanding of the subtle similarities and differences between four closely related Cretaceous turtle assemblages of Middle Asia and Kazakhstan.