The ontogeny of the shell in side‐necked turtles,with emphasis on the homologies of costal and neural bones

Although we are starting to understand the molecular basis of shell development based on the study of cryptodires, basic comparative ontogenetic data for the other major clade of living turtle, the pleurodires, are largely missing. Herein, the developmental and phylogenetic relation between the bony shell and endoskeleton of Pleurodira are examined by studying histological serial sections of nine specimens of three different species, including an ontogenetic series of Emydura subglobosa. Emphasis is given to the portion of the carapace in which ribs and vertebral spinous processes become part of the carapace. Central questions are how neurals and costals are formed in pleurodiran turtles, whether costals and neurals are of endoskeletal or exoskeletal origin, and what ontogenetic factors relate to neural reduction of some Pleurodira. The neurals and costals do not develop as independent ossification centers, but they are initial outgrowths of the periosteal collar of endoskeletal ribs and neural arches. Slightly later in development, the ossification of both shell elements continues without a distinct periosteum but by metaplastically ossifying precondensed soft‐tissue integumentary structures. Through ontogeny, ribs of the turtles studied are closely associated with the hypaxial intercostalis musculature while epaxial interspinalis musculature connects the neural arches. We here propose an alternative structural hypothesis for the neural reduction and, ultimately, the complete loss of the neural series. The complete reduction of neurals in Emydura spp. may be linked to heterochrony, accompanied by a restricted influence of epaxial musculature and epidermal–dermal interaction in shell bone formation. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Derived appendicular morphology in Early Cretaceous aquatic turtles evidenced by the track record

A well‐preserved isolated manus impression evidences the presence of derived aquatic adaptations in the forelimb morphology of Berriasian turtles. Size and the abundant co‐occurring turtle fauna indicate that the track was left by a large‐sized, bottom‐walking basal pancryptodiran. The footprint shows an interesting mosaic of primitive and derived features. The basic turtle pattern is reflected by a short and broad autopodium but thin phalanges, claw reduction and extensive webbing enclosing the digits and lateral and medial margins of the distal metapodium are clearly specialized features related to the aquatic environment. Some characters including the proportional elongation of the first digit, which reached as far distally as the other digits and was probably highly mobile at the metacarpal‐phalangeal joint, indicate an even higher degree of specialization. The specimen gives evidence on a hitherto unknown range of appendicular modification in Early Cretaceous turtles, and redundantly proves the aquatic habitat and locomotion of large‐sized turtles from the Berriasian of northwestern Germany.     

Autopodial development in the sea turtles Chelonia mydas and Caretta caretta

The manus and pes were studied using whole-mount and histological preparations of ontogenetic series of Chelonia mydas and Caretta caretta. Patterns of connectivity and sequences of chondrification events are similar to those reported for other turtle species, with respect to both the primary axis and the digital arch. There is no evidence of anterior condensations in the region distal to the radius and the tibia, supporting the hypothesis that the radiale and tibiale are absent in turtles. The three middle metacarpals are the first elements to start ossification in the manus of C. mydas, while ossification has not started in the pes. In the hatchling of C. mydas, most carpals have started ossification, whereas tarsals are mostly still cartilaginous. In C. caretta, the first carpals to ossify are the ulnare and intermedium, followed by the pisiform. Among metatarsals, the fifth hooked metatarsal is the last one to start ossification. The fibulare and intermedium fuse early in chondrogenesis, later becoming the astragalocalcaneum. Ossification in the carpals of C. caretta starts while tarsals are still cartilaginous. The derived autopodial proportions in each autopodium of adults are laid out at the condensation stage, and features that were present in basal turtles are absent at all stages examined (developmental penetrance). In contrast to this, conservatism is expressed in the presence of similar patterns of connectivity during early chondrogenesis, and in the development of overall proportions of the manus versus pes. As in adult anatomy, the development of the autopodium of marine turtles is a mosaic of derived and plesiomorphic features.     

A new Late Jurassic turtle from Spain: phylogenetic implications,taphonomy and palaeoecology

Abstract: The Jurassic was an important period in the evolution of Testudinata and encompasses the origin of many clades, and this is especially true of Jurassic turtles from Western Europe. A new genus and species of Late Jurassic turtle, Hispaniachelys prebetica gen. et sp. nov. from the upper Oxfordian of the Prebetic (Southern Spain), is described on the basis of postcranial material. The specimen is the only known tetrapod from the Mesozoic of the Prebetic and the oldest turtle from southern Europe. A mosaic of characters indicates this is a new genus: it displays basal features including dorsal epiplastral processes/reduced cleithra, no medial contact of the extragulars and a long first thoracic rib, alongside derived characters including an absence of mesoplastra and the vertebral 3/4 sulcus crossing neural 5. The phylogenetic position of the new taxon is hard to resolve, and it might be either a paracryptodire or a basal testudine, but it is distinct from Plesiochelys. A complex taphonomic history is shown by a range of overlying grazing traces and bioerosion on the carapace. The carapace was subsequently overturned and buried ventrally up, terminating grazing activity, and was then bored by sponges before final burial. Scanning electron microscopy reveals phosphatic microspheroids associated with bacterial decay in the vascular cavities of the cancellous bone, suggesting the carapace may have acted as a closed microenvironment in which decay‐derived authigenic minerals formed.     

放射纹蛇颈龟的新材料及其有关问题的探讨

放射纹蛇颈龟 (Plesiochelys radiplicatus) 系1953年杨钟健、周明镇所建,由一不完整的背甲和部分腹甲为代表.本文记述了一件可归该种的基本完整的背甲,补充了种的一些特征.并结合目前资料,对龟甲上的某些幼体特征,以及蛇颈龟类的系统分类和我国的蛇颈龟等问题,作了探讨.     

A new, nearly complete stem turtle from the Jurassic of South America with implications for turtle evolution

Turtles have been known since the Upper Triassic (210Myr old); however, fossils recording the first steps of turtle evolution are scarce and often fragmentary. As a consequence, one of the main questions is whether living turtles (Testudines) originated during the Late Triassic (210Myr old) or during the Middle to Late Jurassic (ca 160Myr old). The discovery of the new fossil turtle, Condorchelys antiqua gen. et sp. nov. from the Middle to Upper Jurassic (ca 160-146Myr old) of South America (Patagonia, Argentina), presented here sheds new light on early turtle evolution. An updated cladistic analysis of turtles shows that C. antiqua and other fossil turtles are not crown turtles, but stem turtles. This cladistic analysis also shows that stem turtles were more diverse than previously thought, and that until the Middle to Upper Jurassic there were turtles without the modern jaw closure mechanism.     

Morphogenetic and constructional differences of the carapace of aquatic and terrestrial turtles and their evolutionary significance

The postembryonic development of the turtle carapace was studied in the aquatic Еmys orbicularis and the terrestrial Тestudo graeca. Differences in the structure of the bony shell in aquatic and terrestrial turtles were shown to be associated with varying degrees of development of epidermal derivatives, namely, the thickness of the scutes and the depth of horny furrows. Sinking of the horny furrows into the dermis causes local changes in the structure of the collagen matrix, which might precondition the acceleration of the ossification. Aquatic turtles possess a relatively thin horny cover, whose derivatives are either weakly developed or altogether absent and thus make no noticeable impact on the growth dynamics of bony plates. Carapace plates of these turtles outgrow more or less evenly around the periphery, which results in uniform costals, relatively narrow and partly reduced neurals, and broad peripherals extending beyond the marginal scutes. In terrestrial turtles (Testudinidae), horny structures are much more developed and exert a considerable impact on the growth of bony elements. As a result, bony plates outgrow unevenly in the dermis, expanding fast in the zones under the horny furrows and slowly outside these zones. This determines the basic features of the testudinid carapace: alternately cuneate shape of costals, an alternation of broad octagonal and narrow tetragonal neurals, and the limitation of the growth of peripherals by pleuro-marginal furrows. The evolutionary significance of morphogenetic and constructional differences in the turtle carapace, and the association of these differences with the turtle habitats are discussed.     

四川中侏罗世的龟化石

本文对产自四川自贡中侏罗世的三件龟甲标本作了鉴定,认为均可归成渝龟属(Chengyuchelys)。一为自贡成渝龟,新种(Chengyuchelys zigongensis,sp.nov.),一为似贝氏成渝龟(C.baenoides, Young et Chow),一为成渝龟未定种(Chengyuchelys sp.)。在形态描述的基础上,讨论了成渝龟属的系统分类。     

A NEW SPINICAUDATAN GENUS (CRUSTACEA: ‘CONCHOSTRACA’) FROM THE LATE CRETACEOUS OF MADAGASCAR

Abstract: A new spinicaudatan genus and species, Ethmosestheria mahajangaensis gen. et sp. nov., is described from the Anembalemba Member (Upper Cretaceous, Maastrichtian) of the Maevarano Formation, Mahajanga Basin, Madagascar. This is the first spinicaudatan reported from the post‐Triassic Mesozoic of Madagascar. The new species is assigned to the family Antronestheriidae based on the cavernous or sievelike ornamentation on the carapace. Of well‐documented Mesozoic spinicaudatan genera, Ethmosestheria mahajangaensis is most closely related to Antronestheria Chen and Hudson from the Great Estuarine Group (Jurassic) of Scotland. However, relatively poor documentation of the ornamentation of most Gondwanan Mesozoic spinicaudatan species precludes detailed comparison among taxa. Ethmosestheria mahajangaensis exhibits ontogenetic trends in carapace growth: a change in carapace outline from subcircular/subelliptical to elliptical, and from very wide juvenile growth bands to narrow adult growth bands. Ornamentation style, however, does not vary with ontogeny. Ethmosestheria mahajangaensis individuals lived in temporary pools in a broad channel‐belt system within a semiarid environment; preserved desiccation structures on carapaces indicate seasonal drying out of pools within the river system. Specimens of Ethmosestheria mahajangaensis are preserved with exquisite detail in debris flow deposits; these are the first spinicaudatans reported from debris flow deposits. These deposits also contain a varied vertebrate fauna, including dinosaurs, crocodyliforms, turtles, and frogs. Rapid entombment of the spinicaudatan carapaces likely promoted early fossil diagenesis leading to highly detailed preservation.     

四川内江晚侏罗世中国龟科一新属

描述了产自四川内江晚侏罗世的中国龟科（Ｓｉｎｅｍｙｄｉｄａｅ）化石一新属新种──叶氏香港龟Ｈｏｎｇｋｏｎｇｏｃｈｅｌｙｓ ｙｅｈｉ。它以椎盾较横宽、第７、８椎板较退化、上臀板缺失、具腹甲后窗等特征区别于中国龟属（Ｓｉｎｅｍｙｓ）和满洲龟属（Ｍａｎｃｈｕｒｏｃｈｅｌｙｓ）。这是中国龟科化石在四川的首次发现．     

AN ALMOST COMPLETE JUVENILE SPECIMEN OF THE CHELONIID TURTLE CTENOCHELYS STENOPORUS (HAY, 1905) FROM THE UPPER CRETACEOUS NIOBRARA FORMATION OF KANSAS,USA

Abstract: A new, unusually well‐preserved juvenile specimen of Ctenochelys stenoporus from the Niobrara Formation is described. The skull has come apart at its sutures and all bones of the braincase and ear region are preserved three‐dimensionally. This allows a detailed reconstruction of the important brain structures of a basal juvenile cheloniid turtle. It is compared with adult Ctenochelys specimens, and the major ontogenetic changes in the skull and postcranial skeleton are described. Furthermore, the specimen is compared with other fossil and extant cheloniids with well‐known braincases and the differences between basal and advanced cheloniids turtles are specified.     

Studies on skeleton formation in reptiles: Patterns of ossification in the skeleton of Chelydra serpentina (Reptilia, Testudines)

Patterns and sequence of ossification are described throughout the skeleton of Chelydra serpentina Linnaeus. Evidence is adduced documenting the decoupling of ossification processes from sequence and patterns of chondrification. Convergence of ontogenetic repatterning in the ossification of the axial skeleton in Chelydra and Squamata is discussed, as are problems of adaptive modification of ossification patterns. The development of a carapace may be correlated with changes of ossification patterns in the postcranial axial skeleton of turtles, but the most striking evidence for the adaptive modification of ossification sequence obtains from a comparison of the limb skeleton and its ossification in Chelydra and in sea turtles     

A new Xinjiangchelyid turtle (Testudines, Eucryptodira) from the Jurassic Qigu Formation of the southern Junggar Basin, Xinjiang, north-west China

A new eucryptodiran turtle, Xinjiangchelys qiguensis sp. nov. from the Upper Jurassic (Oxfordian — ?Kimmeridgian) Qigu Formation of the southern Junggar Basin (north‐west China) is described. The type material consists of a partial skeleton, including the complete carapace, plastron, nearly all cervical vertebrae, both scapulae, the pelvis and one ulna. It is clearly identifiable as a basal eucryptodire since it lacks the mesoplastron. It is distinguished from other species of Xinjiangchelys by several autapomorphies of the carapace and plastron, such as the first and fifth vertebrals extending on the peripherals, the plastron with three pairs of gulars, and an intergular which does not contact the hyoplastron. In the postcranium, the scapula with a long acromial and a small scapular process, the pelvis with a short ilial shaft and the elongated cervical vertebrae are characteristic. A new phylogenetic analysis of the in‐group phylogeny of the Xinjiangchelyidae is proposed and discussed, resulting in a new classification of the family. Xinjiangchelys (Toxocheloides) narynensis is regarded as a nomen dubium. Shartegemys is referred to Xinjiangchelys, whereas the holotypes of ‘Plesiochelys’chungkingensis and ‘P’. latimarginalis are excluded from the genus Xinjiangchelys but included in the Xinjiangchelyidae.     

A juvenile eurysternid turtle (Testudines: Eurysternidae) from the upper Kimmeridgian (Upper Jurassic) of Nusplingen (SW Germany)

A juvenile turtle from the upper Kimmeridgian (Upper Jurassic) of Nusplingen is identified as an eurysternid turtle. It differs in plastral morphology from a juvenile eurysternid turtle from the latest Kimmerdigian of Kelheim described in the 19th century, which represents a comparably early developmental stage. Both juveniles have primordial ribs not yet transformed into costals and lack all other carapacial elements whereas the plastral elements are well developed. The new specimen from Nusplingen has a more robust plastron type when compared to the very gracile, bow- or arc-shaped plastron type of the formerly described juvenile. Both plastron types are also represented by yet undescribed additional juvenile, medium-sized and/or larger eurysternid specimens. The juvenile specimens thus likely document the presence of two morphologically very similar eurysternid taxa in the Upper Jurassic of southern Germany. Both plastron types are different from those described for Idiochelys and Solnhofia but may resemble plastron morphology of Eurysternum, which is, however, only incompletely known.     

A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods

Background

Secondary adaptation to aquatic life occurred independently in several amniote lineages, including reptiles during the Mesozoic and mammals during the Cenozoic. These evolutionary shifts to aquatic environments imply major morphological modifications, especially of the feeding apparatus. Mesozoic (250–65 Myr) marine reptiles, such as ichthyosaurs, plesiosaurs, mosasaurid squamates, crocodiles, and turtles, exhibit a wide range of adaptations to aquatic feeding and a broad overlap of their tooth morphospaces with those of Cenozoic marine mammals. However, despite these multiple feeding behavior convergences, suction feeding, though being a common feeding strategy in aquatic vertebrates and in marine mammals in particular, has been extremely rarely reported for Mesozoic marine reptiles.

Principal Findings

A relative of fossil protostegid and dermochelyoid sea turtles, Ocepechelon bouyai gen. et sp. nov. is a new giant chelonioid from the Late Maastrichtian (67 Myr) of Morocco exhibiting remarkable adaptations to marine life (among others, very dorsally and posteriorly located nostrils). The 70-cm-long skull of Ocepechelon not only makes it one of the largest marine turtles ever described, but also deviates significantly from typical turtle cranial morphology. It shares unique convergences with both syngnathid fishes (unique long tubular bony snout ending in a rounded and anteriorly directed mouth) and beaked whales (large size and elongated edentulous jaws). This striking anatomy suggests extreme adaptation for suction feeding unmatched among known turtles.

Conclusion/Significance

The feeding apparatus of Ocepechelon, a bony pipette-like snout, is unique among tetrapods. This new taxon exemplifies the successful systematic and ecological diversification of chelonioid turtles during the Late Cretaceous. This new evidence for a unique trophic specialization in turtles, along with the abundant marine vertebrate faunas associated to Ocepechelon in the Late Maastrichtian phosphatic beds of Morocco, further supports the hypothesis that marine life was, at least locally, very diversified just prior to the Cretaceous/Palaeogene (K/Pg) biotic crisis.     

Patterns of ossification in the manus of the harbor porpoise (Phocoena phocoena): hyperphalangy and delta-shaped bones

With the transition from terrestrial to aquatic habitats, cetacean forelimbs have undergone significant modifications in bone morphology and soft tissue distribution. Some, but not all, of these modifications are also demonstrated in other lineages of extant and extinct secondarily aquatic tetrapods. This study examines the ontogenetic pattern of ossification of the manus of the harbor porpoise (Phocoena phocoena), using plain film radiography. Two modifications examined are hyperphalangy (number of phalanges per digit increased beyond the typical mammalian number) and the morphology of delta-shaped bones. Hyperphalangy in Phocoena phocoena is apparent in digits 2 and 3. Phalangeal counts in all digits are variable (sometimes between the right and left flippers of the same individual) and are not necessarily correlated with age. Phalangeal ossification and epiphyseal fusion proceeds along the proximo-distal axis within each digit. In addition, digits 2 and 3 are at a more advanced stage of ossification than more abaxial digits. Delta-shaped bones appear to be a normal stage in the ossification of phalanges in all digits except the third, and may persist in the adult in certain digits. In humans, this morphology is a developmental anomaly usually associated with other malformations, such as polydactyly or syndactyly. Delta-shaped bones in the cetacean manus display a consistent orientation and the process by which they are formed may be similar to that in extinct marine reptiles.     

The ontogeny of morphological defenses in Kemp's ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) sea turtles

Marine turtles are large reptiles that compensate for high juvenile mortality by producing hundreds of hatchlings during a long reproductive lifespan. Most hatchlings are taken by predators during their migration to, and while resident in, the open ocean. Their survival depends upon crypticity, minimizing movement to avoid detection, and foraging efficiently to grow to a size too difficult for predators to either handle or swallow. While these behavioral antipredator tactics are known, changes in morphology accompanying growth may also improve survival prospects. These have been only superficially described in the literature. Here, we compare the similarities and differences in presumed morphological defenses of growing loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii) posthatchlings, related species that differ in growth rate, timing of habitat shift (the return from oceanic to neritic locations), and size at maturity. In both species, vertebral spination and carapace widening increase disproportionally as small turtles grow, but later in ontogeny, the spines regress, sooner in ridley than in loggerhead turtles. Carapace widening occurs in both species but loggerheads are always longer than they are wide whereas in Kemp's ridley turtles, the carapace becomes as wide as long. Our analysis indicates that these changes are unrelated to when each species shifts habitat but are related to turtle size. We hypothesize that the spines function in small turtles as an early defense against gape‐limited predators, but changes in body shape function throughout ontogeny—initially to make small turtles too wide to swallow and later by presenting an almost flat and hardened surface that large predators (such as a sharks) are unable to grasp. The extremely wide carapace of the Kemp's ridley may compensate for its smaller adult size (and presumed greater vulnerability) than the loggerhead. J. Morphol. 276:929–940, 2015. © 2015 Wiley Periodicals, Inc.