Natasha S. Vitek

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ABSTRACT In this paper we describe previously unpublished trionychid turtle material, consisting of numerous shell fragments, from two Late Cretaceous (Santonian—early Campanian) localities from Middle Asia and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.

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

A Review of the Fossil Record of New World Turtles of the Clade Pan-Trionychidae

Abstract Turtles of the clade Pan-Trionychidae have a rich, but fragmentary fossil record in the New World, ranging from the Late Cretaceous to the Holocene. The clade immigrated to North America from Asia no later than the Cenomanian. From the Campanian to the middle Eocene, pan-trionychid diversity in the New World was higher than it is today. In the Neogene, pan-trionychids inhabited southern North America and coastal regions of northern South America. Their range subsequently contracted, and extant New World pan-trionychids are now limited to the eastern third of temperate North America. The ecology of extinct pan-trionychids was likely similar to that of extant pan-trionychids, although novel feeding ecology has been hypothesized for some morphologically derived taxa. Current phylogenies of crown Trionychidae recognize two major clades, Cyclanorbinae and Trionychinae, but the placement of most fossil taxa remains poorly resolved relative to these two primary clades. A taxonomic review of 101 named New World taxa finds 31 nomina valida, 26 nomina invalida, 41 nomina dubia and 2 nomina nuda.

Giant fossil soft-shelled turtles of North America

Axestemys byssina, a large, potentially paedomorphic soft-shelled turtle (Trionychidae), and a number of other of giant trionychids were described over a century ago, but no rigorous analysis has been undertaken to investigate their relationships. These trionychids are unusual and are known from a broad temporal range spanning from the Cretaceous to the Eocene (70-46 m.y.a.). I examined all material previously assigned to Axestemys as well as previously undescribed material with traditional “Axestemys”like characteristics and provided a concept of Axestemys that is meaningful in both systematic and taxonomic contexts. Two new species are established. Axestemys byssina and Axestemys splendida comb. nov. are revised as a result of the description of new material, and Axestemys quinni is confirmed to be a member of Axestemys. Eugenichelys robertemryi Chkhikvadze, 2008 is synonymized with Axestemys byssina. Phylogenetic analysis and description of new material does not support the inclusion within the clade of “Axestemys” puercensis and Conchochelys admiribalis, previously hypothesized to belong to Axestemys. The taxon name ‘Axestemys’ is best defined phylogenetically as a stem-based clade rather than defined based on many of the characters traditionally ascribed to it, which are not consistently present throughout all species of Axestemys. All members of Axestemys reach a gigantic size that is today found only in a few tropical species of trionychid that independently evolved gigantism. The presence of Axestemys reflects both a warmer climate in the past in North America. Additionally, it reflects a high trionychid diversity and disparity comparable to those of Recent species confined to tropical climates today. Natasha S. Vitek. Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, P.O. Box 208109, New Haven, CT 06520, USA, nsvitek@utexas.edu

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.

Exceptional three-dimensional preservation and coloration of an originally iridescent fossil feather from the Middle Eocene Messel Oil Shale

A feather from the Eocene Messel Formation, Germany, has been demonstrated to have been originally structurally colored by densely packed sheets of melanosomes similar to modern iridescent feathers exhibiting thin-film diffraction. The fossil itself currently exhibits a silvery sheen, but the mechanism for generating this optical effect was not fully understood. Here we use scanning electron microscopy, electron probe microanalysis, and dual-beam focused ion beam scanning electron microscopy to investigate the source of the silvery sheen that occurs in the apical feather barbules. Focused ion beam scanning electron microscopy provides a powerful tool for studying three-dimensionality of nanostructures in fossils. Use of the method reveals that the flattened apical barbules are preserved almost perfectly, including smooth structural melanosome sheets on the obverse surface of the fossil feather that are identical to those that cause iridescence in modern bird feathers. Most of each apical barbule is preserved beneath a thin layer of sediment. The silvery sheen is generated by incoherent light diffraction between this sediment layer and melanosomes and, although related to the original iridescence of the feather, is not a feature of the feather itself. The reddish and greenish hues frequently exhibited by fossil feathers from the Messel Formation appear to be due to precipitates on the surface of individual melanosomes.KurzfassungBei einer Feder aus der eozänen Messel Formation von Deutschland wurde eine originale strukturelle Färbung aus dicht gepackten Melanosomen nachgewiesen, die modernen irridisierenden Federn ähnlich ist, die Dünnschichtdiffraktion zeigen. Das Fossil selbst zeigt in seinem derzeitigen Zustand einen silbrigen Glanz, aber es ist unklar, durch welchen Mechanismus dieser entsteht. Mit Hilfe von Rasterelektronenmikroskopie, Elektronenstrahlmikroanalyse und doppelt fokussierter Ionenfeinstrahlmikroskopie untersuchen wir die Herkunft der glänzenden Färbung, die an den apikalen Hakenstrahlen auftritt. Ionenfeinstrahlmikroskopie stellt eine leistungsfähige Methode zur Untersuchung dreidimensionaler Nanostrukturen in Fossilien dar. Ergebnisse dieser Untersuchungsmethode zeigen, dass sowohl die abgeflachten, apikalen Hakenstrahlen, als auch die einzelnen Schichten aus Strukturmelanosomen, die mit denen heutiger Vogelfedern nahezu identisch sind, annähernd unversehrt überliefert sind. Ein Großteil der apikalen Hakenstrahlen ist unter einer dünnen Sedimentschicht erhalten, die aufgrund der Interferenz mit den Melanosomen zu dem silber glänzenden Farbeffekt führt. Dieser Effekt wird durch die irridisierende Färbung der Feder verstärkt, trat allerdings nicht im Originalzustand auf. Dies deutet darauf hin, dass die rötliche und grünliche Färbung, die typisch für Federn aus Messel ist, aufgrund von Ablagerungen auf der Oberfläche der einzelnen Melanosome zustande kommt.

Insights into the Taxonomy and Systematics of North American Eocene Soft-Shelled Turtles from a Well-Preserved Specimen

ABSTRACT A nearly complete fossil soft-shelled turtle (Trionychidae) from the Eocene Washakie Formation of Wyoming is described and identified as Oliveremys uintaensis, comb. nov. Previously known only from a single shell specimen, O. uintaensis can now be diagnosed using both skull and shell characteristics, including callosified but unsculptured xiphiplastra. “Trionyx” tritor “T.” franciscae, “T.” nelsoni and “T.” scutumantiquum are identified as junior synonyms of O. uintaensis. Parsimony and Bayesian analyses place O. uintaensis and all of its junior synonyms along with multiple previously scored fossil trionychid taxa. Reinterpretation of three characters within the matrix, as well as the addition of fossil taxa, resulted in novel relationships. These relationships were not recovered when only extant trionychids were included in a reinterpreted matrix or when fossil taxa were added without reinterpretation. The results indicate that the addition of fossil taxa is sometimes necessary to detect changes caused by other revisions to the character matrix.

A new soft-shelled 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.