Mahito Watabe

A new enantiornithine bird from the Late Cretaceous of the Gobi Desert

Synopsis We report on a new species of enantiornithine bird from the Late Cretaceous of the Mongolian Gobi Desert, which adds to the meager record of birds from the latest part of the Mesozoic in this region. The exceptional, three‐dimensional bones of the new fossil increase the known anatomical diversity of enantiornithine birds, providing information about previously unreported morphologies such as a pneumatised furcula. Several synapomorphies nest the new bird within an enantiornithine clade of proficient fliers, but the anatomy and proportions of its flight apparatus imply significant aerodynamic restrictions. The combination of phylogeny and our functional interpretation suggests that this new fossil bird is a representative of a flightless lineage. This discovery thus provides the first evidence of a trend towards more limited flying capabilities among Enantiornithes, a group of Cretaceous birds otherwise believed to be represented by competent fliers.

Fine structure of bone in dinosaurs, birds and mammals.

After observation of detailed structural evidence for the origin of birds from dinosaurs, and in light of evidence that dinosaur bone tissue resembles the histology in mammals, the histology of bone has become one of the focal points in discussions of the physiology of dinosaurs and Mesozoic birds. Most of this microstructural information has focused on features related to the vascular organization and the amount of remodelled bone around vascular canals. However, the finer structures have received less attention, although differences in such structures have been observed among modern vertebrates. Here we present evidence that canaliculi—the submicrometre-sized channels that interconnect bone cells and vascular canals—and the collagen fibre bundles in bone are differently organized among certain dinosaur lineages. Ornithomimid dinosaurs are more like birds than mammals in these features. In canalicular structure, and to some extent in fibre bundle arrangement, ornithischian dinosaurs are more like mammals. These differences in both canalicular and lamellar structure are probably linked to differences in the process and rate of bone formation.

Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia

ABSTRACT A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugjn Tsav locality in the Mongolian Gobi Desert is described. With a total length of 290 mm, the present specimen represents one of the smallest skulls known for this species. Not surprisingly, it shows various characteristics common to juvenile tyrannosaurids, such as the rostral margin of the maxillary fenestra not reaching that of the external antorbital fenestra and the postorbital lacking the cornual process. The nasal bears a small lacrimal process, which disappears in adults. Lacking some of the morphological characteristics that are adapted for bearing great feeding forces in adult individuals, this juvenile specimen suggests that T. bataar would have changed its dietary niches during ontogeny. The numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same as those in adults, suggesting that they do not change onto genetically in T. bataar and thus are not consistent with the hypothesis that the numbers of alveoli decreases ontogenetically in tyrannosaurids.

The paleoenvironments of Tugrikin-shireh (Gobi Desert, Mongolia) and aspects of the taphonomy and paleoecology of Protoceratops (Dinosauria: Ornithishichia)

Tugrikin-shireh, south-central Gobi Desert, Mongolia, consists of about 1.5 km of westand northwest-facing exposures that produce a rich vertebrate fauna dominated by the ornithischian dinosaur Protoceratops. The sandstones of Tugrik are thick-bedded (2-9 m) and are distinguished by large-scale (10s to 100s of meters in cross-section), high-angle (28-34 ?) trough-cross stratification. The axes of the cross stratification dip east-northeast. These and other sedimentary features indicate eolian deposition, driven by westerly winds. At Tugrik, bedding planes as well as inferred slip faces, are dominated by a complex calciteand iron-oxide-cemented ichnofauna. At least three different trace fossil types are preserved. A biologically active ecosystem is reflected by the vertebrate body fossil and invertebrate trace fossil assemblages. Protoceratops specimens are commonly found articulated and semi-articulated, and oriented parallel to the maximum dip direction of the sediments in which they are entombed. Limbs are commonly contracted and necks are pulled back, in poses indicative of dessication. In some cases, death probably occurred by suffocation during sand storms, but in other cases, by less dramatic processes. Turgik may constitute the basinward continuation of a nearby braid plain-to-eolian suite of depositional environments. Penecontemporaneous deposits in northern China reveal similar suites of environments, suggesting a uniform depositional response in the region to Late Cretaceous climates.

A pygostyle from a non-avian theropod

The independent evolution of a bird-like tail has been discovered in an oviraptorosaur.

Function and evolution of ankylosaur dermal armor

Ankylosaurs have spike-, plate-, and club-shaped osteoderms probably used as defensive and/or offensive weapons. Previous studies have proposed the evolution and function of small ankylosaur osteoderms, but histological variations in their defensive weapons are little known. Here, we provide comparisons of the internal structures in defensive weapons of ankylosaurs, which shed light on understanding their evolutionary history and function. Histological features of spikes, plates, and clubs are similar to those of small osteoderms in having thin compact bone, thick cancellous bone with large vascular canals, and abundant collagen fibers. A previous study demonstrated that each of the three groups of ankylosaurs (the Polacanthidae, Nodosauridae, and Ankylosauridae) have distinct arrangements of collagen fibers in small osteoderms. This study shows that spikes and clubs of ankylosaurs maintain the same characteristic features for each group despite the differences in shapes and sizes. These histological similarities suggest that various types of osteoderms in ankylosaurs retained the thin compact bone and abundant fiber structures of the small osteoderms during their evolution. Polacanthid spikes show thin compact bone, with less collagen fibers than in spikes of nodosaurids and spikes and clubs of ankylosaurids. Also, ankylosaurid plates with hollow bases are very thin in morphology and show thin compact bone. These results imply that the bone strengths of polacanthid spikes and ankylosaurid plates are lower than spikes and clubs of other ankylosaurs, indicating that they may be used more probably as display and/or thermoregulation rather than as weapons. It is thus probable that ankylosaur armor in general played more than just a defensive role.

An exquisitely preserved troodontid theropod with new information on the palatal structure from the Upper Cretaceous of Mongolia

Troodontidae is a clade of small-bodied theropod dinosaurs. A new troodontid, Gobivenator mongoliensis gen. et sp. nov., is described based on the most complete skeleton of a Late Cretaceous member of this clade presently known, from the Campanian Djadokhta Formation in the central Gobi Desert. G. mongoliensis is different from other troodontids in possessing a pointed anterior end of the fused parietal and a fossa on the surangular in front of the posterior surangular foramen. The skull was superbly preserved in the specimen and provides detailed information of the entire configuration of the palate in Troodontidae. Overall morphology of the palate in Gobivenator resembles those of dromaeosaurids and Archaeopteryx, showing an apparent trend of elongation of the pterygoid process of the palatine and reduction of the pterygopalatine suture toward the basal Avialae. The palatal configuration suggests that the skull of Gobivenator would have been akinetic but had already acquired prerequisites for later evolution of cranial kinesis in birds, such as the loss of the epipterygoid and reduction in contact areas among bones.

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

New information on scavenging and selective feeding behaviour of tyrannosaurids

Feeding traces for carnivorous theropod dinosaurs are typically rare but can provide important evidence of prey choice and mode of feeding. Here we report a humerus of the hadrosaurine Saurolophus which was heavily damaged from feeding attributed to the giant tyrannosaurine Tarbosaurus. The bone shows multiple bites made in three distinctive styles termed “punctures”, “drag marks” and “bite-and-drag marks”. The distribution of these bites suggest that the animal was actively selecting which biting style to use based on which part of the bone was being engaged. The lack of damage to the rest of the otherwise complete and articulated hadrosaur strongly implies that this was a scavenging event, the first reported for a tyrannosaurid, and not feeding at a kill site.

Hyaenodon chunkhtensis and the hyaenodontid fauna from the upper Eocene Ergilin Dzo Formation of Mongolia

Hyaenodon Laizer and Parieu, 1838 is one of the most speciose genera of the Hyaenodontidae (Mammalia; Creodonta) and is widely distributed in the late middle Eocene to Oligocene of North America (Mellett, 1977; Gunnell, 1998), in the late Eocene to Oligocene of Europe (Lange-Badré, 1979; Schmidt-Kittler, 1987), and in the late middle Eocene to early Miocene of Asia (Russell and Zhai, 1987; Lange-Badré and Dashzeveg, 1989; Huang et al., 2001; Wang et al., 2005). Hyaenodon chunkhtensis Dashzeveg, 1985 is one of the six smallest species of Hyaenodon and is the smallest among the Asian species of Hyaenodon (Lavrov and Emry, 1998). So far, H. chunkhtensis had been reported only from the lower Oligocene Hsanda Gol ‘svita’ at the Shunkht locality of southern Mongolia (Dashzeveg, 1985). The upper Eocene Ergilin Dzo Formation of southeastern Mongolia has been famous for yielding many vertebrate fossils including several species of Hyaenodon (Matthew and Granger, 1923; Belyayeva et al., 1974; Dashzeveg, 1974, 1993; Yanovskaya et al., 1977). The mammals of this formation are the type fauna of the Ergilian (late Eocene) Asian Land Mammal Age (Russell and Zhai, 1987; McKenna and Bell, 1997; Meng and McKenna, 1998). Although in this formation several species of hyaenodontid creodonts have been reported (Matthew and Granger, 1925; Gromova, 1952; Dashzeveg, 1964, 1985; Lange-Badré and Dashzeveg, 1989; Lavrov, 1999), the number of taxa and generic and species names of the hyaenodontids from the formation are confused (Russell and Zhai, 1987; Polly, 1993; Wang et al., 2005; Morlo and Nagel, 2006; Egi et al., 2007). In this short article, we report H. chunkhtensis from the Ergilin Dzo Formation at the Khoer Dzan locality and briefly review the hyaenodontid fauna of the formation to clarify its current status. The specimen described here is a left mandible with p4–m3 discovered by the Hayashibara Museum of Natural Sciences and Mongolian Paleontological Center Joint Paleontological Expedition in 2004 (Tsubamoto, Watabe et al., 2006). The specimen was found by surface prospecting at a lower part of a slope of the locality, so that the precise stratigraphic horizon of the specimen within the formation cannot be determined. This discovery adds one more species to the hyaenodontid fauna of the formation. Institutional Abbreviations—AMNH, American Museum of Natural History, New York, USA; BDMAS, Biological Department of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia; HMNS, Hayashibara Museum of Natural Sciences, Okayama, Japan; MPC, Mongolian Paleontological Center, Ulaanbaatar, Mongolia; MPC-M, mammalian fossil collections stored in MPC; PIN, Paleontological Institute, Russian Academy of Sciences, Moscow, Russia; PSS and PST, Paleontology and Stratigraphy Section, Geological Institute, Ulaanbaatar, Mongolia; SHG, specimens from the Shand Gol locality of central Mongolia stored in Vienna Museum, Vienna ( Wien), Austria. Anatomical Abbreviations—c, lower canine; M/m, upper/ lower molar; P/p, upper/lower premolar.