Remains of the Baikal yak (Poehpagus mutus baikalensis N. Verestchagin, 1954) from Late Pleistocene localities of Southern Siberia

136 bones of the postcranial skeleton and a part of the skull of a female Baikal yak (Poephagus mutus baikalensis N. Verestcthagin, 1954), originating from 18 cave locations and open-type Paleolithic sites in Altai-Sayan, Transbaikalia and Central Mongolia were examined. The material includes 38 metacarpals and 9 metatarsals of the yak. Morphometric differences in the structure of the postcranial skeleton of the yak and the bison (Bison priscus Bojanus, 1827) were revealed. The body size of the Baikal yak significantly exceeded that of the wild Tibetan yak (Poephagus mutus Przewalski, 1883). The largest representatives of P. m. baikalensis inhabited the Altai Mountains. In most of the sites, located in the mid-mountain landscapes of Southern Siberia (with absolute heights of 500–700 m), only a few remains of the Baikal yak were found, accounting for 0.01% to 1–2% of the number of megafauna remains. Most likely, herds of yaks did not live here permanently, but appeared only sporadically, during seasonal migrations. In higher mountainous areas (from 1000–1500 m) of Gorny Altai and Khangai Mountains in Central Mongolia, the proportion of the remains of the Baikal yak increases significantly – up to 16–22%. Like the contemporary P. mutus, the Pleistocene yak found its ecological optimum in the high-mountainous parts of ridges and mountain plateaus, dominated by cold, dry mountain-steppe landscapes with herb-grass vegetation and a small amount of snow. During the periods of cryochrones, the area of P. m. baikalensis apparently expanded significantly, incorporating the adjacent foothill territories. During the periods of thermochrones, it was most likely limited to the high-mountainous areas of the mountain uplifts of Southern Siberia.

Exquisite air sac histological traces in a hyperpneumatized nanoid sauropod dinosaur from South America

This study reports the occurrence of pneumosteum (osteohistological structure related to an avian-like air sac system) in a nanoid (5.7-m-long) saltasaurid titanosaur from Upper Cretaceous Brazil. We corroborate the hypothesis of the presence of an air sac system in titanosaurians based upon vertebral features identified through external observation and computed tomography. This is the fifth non-avian dinosaur taxon in which histological traces of air sacs have been found. We provided a detailed description of pneumatic structures from external osteology and CT scan data as a parameter for comparison with other taxa. The camellate pattern found in the vertebral centrum (ce) of this taxon and other titanosaurs shows distinct architectures. This might indicate whether cervical or lung diverticula pneumatized different elements. A cotylar internal plate of bone tissue sustains radial camellae (rad) in a condition similar to Alamosaurus and Saltasaurus. Moreover, circumferential chambers (cc) near the cotyle might be an example of convergence between diplodocoids and titanosaurs. Finally, we also register for the first time pneumatic foramina (fo) and fossae connecting camellate structures inside the neural canal in Titanosauria and the second published case in non-avian dinosaurs. The extreme pneumaticity observed in this nanoid titanosaur contrasts with previous assumptions that this feature correlates with the evolution of gigantic sizes in sauropodomorphs. This study reinforces that even small-bodied sauropod clades could present a hyperpneumatized postcranial skeleton, a character inherited from their large-bodied ancestors.

Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile

Armoured dinosaurs are well known for forms that evolved specialized tail weapons: paired tail spikes in stegosaurs, and heavy tail clubs in advanced ankylosaurs1. Armoured dinosaurs from southern Gondwana are rare and enigmatic, but likely include the earliest branches of Ankylosauria2-4. Here, we describe a mostly complete, semiarticulated skeleton of a small (about 2m) armoured dinosaur from the late Cretaceous of Magallanes in southernmost Chile, a region biogeographically related to West Antarctica5. Stegouros elengassen gen. et sp. nov. evolved a large tail weapon unlike any dinosaur: A flat, frond-like structure formed by 7 pairs of laterally projecting osteoderms encasing the distal half of the tail. Stegouros shows ankylosaurian cranial characters, but a largely primitive postcranial skeleton, with some stegosaur-like characters. Phylogenetic analyses placed Stegouros in Ankylosauria, and specifically related to Kunbarrasaurus from Australia6 and Antarctopelta from Antarctica7, forming a clade of Gondwanan ankylosaurs that split earliest from all other ankylosaurs. Large osteoderms and specialized tail vertebrae in Antarctopelta suggest it had a tail weapon similar to Stegouros. We propose a new clade, the Parankylosauria, to include the first ancestor of Stegouros but not Ankylosaurus, and all descendants of that ancestor.

Postcranial osteology of Beipiaosaurus inexpectus (Theropoda: Therizinosauria)

Beipiaosaurus inexpectus, from the Lower Cretaceous Yixian Formation (Sihetun locality, near Beipiao), Liaoning, China, is a key taxon for understanding the early evolution of therizinosaurians. Since initial publication in 1999, only the cranial elements of this taxon have been described in detail. Here we present a detailed description of the postcranial skeletal anatomy of the holotype specimen of B. inexpectus, including two never before described dorsal vertebrae from the anterior half of the series. Based on these observations, and comparisons with the postcranial skeleton of therizinosaurian taxa named since the most recent diagnosis, we revised the diagnostic features for B. inexpectus adding three new possible autapomorphies (PII-3 shorter than PIII-4, subequal length of the pre- and postacetabular portions of the ilium, and equidimensional pubic peduncle of ilium). Additionally, we also propose three possible synapomorphies for more inclusive taxa (Therizinosauroidea and Therizinosauridae) and discuss implications for evolutionary trends within Therizinosauria. The newly acquired data from the postcranial osteology of the holotype specimen of B. inexpectus sheds light on our understanding of postcranial skeletal evolution and identification of therizinosaurians.

Osteological materials from Chechnya and Ingushetia in the collections of the MSU Research Institute and Museum of Anthropology

The article revises osteological collections from Chechnya and Ingushetia in the Anuchin Research Institute and Museum of Anthropology of the Lomonosov Moscow State University. Materials and methods. We worked mainly with the archival records of the Museum of Anthropology and the Institute of Archaeology RAS, and directly with the museum items (skulls). The collections from Chechnya and Ingushetia originated mostly from excavations conducted by E.I. Krupnov and his students – R.M. Munchaev and V.I. Markovin in the 1930s and 1950-1960s. In addition to these materials, there are three skulls brought to the museum by V.F. Miller at the end of the 19th century, and two skulls donated to the museum by V.V. Bunak in the first half of the XX century. Results. Some inconsistencies in archaeological dates were revealed between the archival records, information in the 1986 catalog and in the scientific excavation reports. In cases when this was revealed, the revised archaeological dates were presented. The most remarkable was the situation with the Bamut cemetery. Among 7 skulls, listed in all archival documents of the Museum of Anthropology as late medieval, one skull was found to be Eneolithic. Conclusion. Osteological materials from Chechnya and Ingushetia of the Museum of Anthropology collections amount 29 storage units (29 skulls and 1 incomplete postcranial skeleton) and cover a wide chronological range from the Eneolithic to the Late Middle Ages. The craniological data for most of these materials were published by A.G. Gadzhiev and V.P. Alekseev.

A new, remarkably preserved, enantiornithine bird from the Upper Cretaceous Qiupa Formation of Henan (central China) and convergent evolution between enantiornithines and modern birds

A new enantiornithine bird is described on the basis of a well preserved partial skeleton from the Upper Cretaceous Qiupa Formation of Henan Province (central China). It provides new evidence about the osteology of Late Cretaceous enantiornithines, which are mainly known from isolated bones; in contrast, Early Cretaceous forms are often represented by complete skeletons. While the postcranial skeleton shows the usual distinctive characters of enantiornithines, the skull displays several features, including confluence of the antorbital fenestra and the orbit and loss of the postorbital, evolved convergently with modern birds. Although some enantiornithines retained primitive cranial morphologies into the latest Cretaceous Period, at least one lineage evolved cranial modifications that parallel those in modern birds.

Bone Structural, Biomechanical and Histomorphometric Characteristics of the Postcranial Skeleton of the Marsh Rice Rat (Oryzomys palustris)

INTRODUCTIONThe rice rat (Oryzomys palustris) is a non-conventional laboratory rodent species used to model some human bone disorders. However, no studies have been conducted to characterize the postcranial skeleton. Therefore, we aimed to investigate age- and gender-related features of the appendicular skeleton of this species.METHODSWe used femurs and tibiae from 94 rats of both genders aged 4-28 wks. Bone mineral content (BMC), bone mineral density (BMD), and biomechanical properties were determined in femurs. In addition, bone histomorphometry of tibiae was conducted to assess bone cells activities and bone turnover over time.RESULTSBodyweight, bone length, total metaphysis BMC/BMD, cortical BMC/BMD, cortical thickness, and cortical area progressively augmented with age. Whereas the increase in these parameters plateaued at age 16-22 wks in female rats, they continued to rise to age 28 wks in male rats. Furthermore, bone strength parameters increased with age, with few differences between genders. We also observed a rapid decrease in longitudinal growth between ages 4-16 wks. Whereas young rats had a greater bone formation rate and bone turnover, older rice rats had greater bone volume and trabecular thickness, with no differences between genders.CONCLUSIONS1) Sexual dimorphism in the rice rat becomes grossly evident at age 16 wks; 2) the age-related increases in bone mass, structural cortical parameters, and in some biomechanical property parameters plateau at an older age in male than in female rats; and 3) bone growth and remodeling significantly decreased with age indistinctive of the gender.

Desmodilliscus braueri crania compared to Pachyuromys duprasi (Desmodilliscini, Gerbillinae, Rodentia)

Molecular phylogenies support the monophyly of Desmodilliscus braueri and Pachyuromys duprasi as a clade basally split from all other gerbillines. While this monophyly supports their placement in a single tribe (Desmodilliscini), no morphological synapomorphies exist among desmodilliscines. This study compares the scale-independent cranial shapes of these two species using geometric morphometrics to determine how they differ and/or converge. Tribal synapomorphies, should they exist, may appear as interspecifically invariable cranial regions. No such invariable cranial regions were detected. The two species significantly differed in cranial size and shape. A small part of shape variation was allometric, with a weak unique allometric effect. No sexual size nor shape dimorphism was found. The sister taxa greatly differed in almost all cranial features, with Pachyuromys (when compared to Desmodilliscus) having a larger-sized cranium, with a larger bulla and suprameatal triangle, a more posteriorly placed palatine foramina, and more anteriorly shifted (and reduced) rostral cranial structures, due to being crowded by the hypertrophied bulla. Cranial variation patterns are consistent with the literature. The extreme morphological divergence among these species is explained by the distant divergence time and ecological differences. Absence of cranial shape synapomorphies does not preclude synapomorphies in other craniodental morphological features (e.g., detailed morphology of the dentition and cranial foramina) or in other morphological structures, such as the postcranial skeleton.

New morphological data on the rare sigmodontine Mindomys hammondi (Rodentia, Cricetidae), an arboreal oryzomyine from north-western Andean montane forests

The monotypic rodent Mindomys Weksler, Percequillo & Voss, 2006 (Cricetidae, Sigmodontinae) is one of the rarest members of the speciose tribe Oryzomyini. As this species is restricted to the Chocó forests of the western Andean slope in northern Ecuador, our knowledge is based on a few specimens collected decades ago. Here we add the first data on some aspects of external anatomy (cheiridia examined in fresh, ears, rhinarium), genital anatomy (penis), soft anatomy (palate, stomach, caecum) and postcranial skeleton retrieved from a full adult male, recently trapped in Reserva Drácula, Carchi, Ecuador. Several features of this specimen, paradoxically the first to be added to Ecuadorian mammal collections, reinforce the view that Mindomys is an arboreal sigmodontine.