Search

In order to test for paleoenvironmental and paleoecological parameters important in dinosaur evolution, thirty-four fragments of dinosaur eggshell, paleosol carbonates from six localities, and calcite crystals from inside a dinosaur femur were collected from the Campanian to Maastrichtian Baruungoyot and Nemegt formations, Gobi Desert, Mongolia. The samples were examined for diagenesis using light microscopy, SEM, and cathodoluminescence, and each was analyzed for δ13C and δ18O values. Eggshell isotope values plot along two trends of enrichment, with paleosol carbonate nodule values plotting along locality specific trends. Convergence of the trends suggests similar initial conditions among localities. Permian-age detrital zircons in the fossiliferous sediment suggest that enriched eggshell and paleosol carbonate nodule δ13C values may have been caused by phreatic zone diagenetic alteration by waters with an aqueous bicarbonate component derived from interaction and dissolution of Permian calcareous marine host rocks. Our hypothetical model for eggshell diagenesis assumes a stable carbon- and oxygen-isotope domain space delimited by three end members: (1) apparently unaltered eggshell with primary microstructure, (2) non-luminescent eggshell with no preserved microstructure, and (3) luminescent eggshell with no preserved microstructure. The two end members showing no preservation of microstructure indicate different phases of diagenetic alteration in the presence of vadose and phreatic waters. None of the samples analyzed can be shown to be sufficiently unaltered for analysis using standard techniques. Biologically, eggshell is porous to facilitate the movement of gases while an embryo is developing within the egg. Geologically, that same property allows the flow of diagenetic ground waters, which modifies the primary isotopic signature of eggshell.

A braincase of the Cretaceous titanosaurian sauropod Malawisaurus dixeyi, complete except for the olfactory region, was CT scanned and a 3D rendering of the endocast and inner ear was generated. Cranial nerves appear in the same configuration as in other sauropods, including derived features that appear to characterize titanosaurians, specifically, an abducens nerve canal that passes lateral to the pituitary fossa rather than entering it. Furthermore, the hypoglossal nerve exits the skull via a single foramen, consistent with most titanosaurians, while other saurischians, including the basal titanosauriform, Giraffatitan, contain multiple rootlets. The size of the vestibular labyrinth is smaller than in Giraffatitan, but larger than in most derived titanosaurians. Similar to the condition found in Giraffatitan, the anterior semicircular canal is larger than the posterior semicircular canal. This contrasts with more derived titanosaurians that contain similarly sized anterior and posterior semicircular canals, congruent with the interpretation of Malawisaurus as a basal titanosaurian. Measurements of the humerus of Malawisaurus provide a body mass estimate of 4.7 metric tons. Comparison of body mass to radius of the semicircular canals of the vestibular labyrinth reveals that Malawisaurus fits the allometric relationship found in previous studies of extant mammals and Giraffatitan brancai. As in Giraffatitan, the anterior semicircular canal is significantly larger than is predicted by the allometric relationship suggesting greater sensitivity and slower movement of the head in the sagittal plane.

The forelimb elements of the leporid Serengetilagus praecapensis, from the famous Laetoli sites in Tanzania, occur in three stratigraphic levels. Most come from the Upper Laetolil Beds, the middle unit. Size frequency distributions of limb dimensions demonstrate one highly variable population with no clear trends through time. Statistical analyses cannot be used to support the presence of more than one species. Sexual dimorphism also is not apparent in the samples, but may have contributed to the variability in sizes. Anatomical traits of the forelimb ally Serengetilagus praecapensis with smaller, less cursorial leporids like the modern European rabbit Oryctolagus. Serengetilagus praecapensis has a predicted body mass in the range of 1.2–1.6 kg. Like some smaller modern rabbits, its forelimb suggests the capability for burrowing.

[This corrects the article DOI: 10.1371/journal.pone.0207935.].

New sauropod dinosaur material is described from Jones Ranch, Early Cretaceous of Texas (USA). Originally described as Paluxysaurus jonesi, the material from Jones Ranch has recently been referred to Sauroposeidon proteles. Elements newly prepared from dense concretionary matrix include the sacrum, ilium and proximal portion of the tail. Reconstructions of the skull and sacrum plus pelvic girdles are presented. ‘Paluxysaurus jonesi’ (=S. proteles) is a blunt-faced sauropod that was originally regarded as closely related to Brachiosaurus. Portions of the sacrum are now exposed and show that it is nearly complete, missing only parts of the first sacral (S1). The anterior sacrals are firmly fused, however, a newly discovered opisthocoelous last sacral (S6) remains unfused. A complete sequence of proximal caudal vertebrae shows a rapid transition from anteroposteriorly short and mediolaterally broad centra anteriorly, to more elongate cylindrical centra posteriorly. All proximal caudals have slightly amphicoelous centra. Some middle anterior caudals have a shallow longitudinal groove on the ventral surface of the centrum. Specimens from Jones Ranch exhibit characters of the sacrum and tail that clearly corroborate placement of ‘P. jonesi’ (Sauroposeidon proteles) as a somphospondylan titanosauriform.

Here we report the occurrence of Terminonaris represented by three specimens recovered from the early middle Cenomanian (96 Ma) Woodbine Formation of Lewisville Lake, Denton County, Texas. Crocodyl...

Timing and magnitude of surface uplift are key to understanding the impact of crustal deformation and topographic growth on atmospheric circulation, environmental conditions, and surface processes. Uplift of the East African Plateau is linked to mantle processes, but paleoaltimetry data are too scarce to constrain plateau evolution and subsequent vertical motions associated with rifting. Here, we assess the paleotopographic implications of a beaked whale fossil (Ziphiidae) from the Turkana region of Kenya found 740 km inland from the present-day coastline of the Indian Ocean at an elevation of 620 m. The specimen is similar to 17 My old and represents the oldest derived beaked whale known, consistent with molecular estimates of the emergence of modern straptoothed whales (Mesoplodon). The whale traveled from the Indian Ocean inland along an eastward-directed drainage system controlled by the Cretaceous Anza Graben and was stranded slightly above sea level. Surface uplift from near sea level coincides with paleoclimatic change from a humid environment to highly variable and much drier conditions, which altered biotic communities and drove evolution in east Africa, including that of primates.

Two articulated skeletons of an ornithopod dinosaur from the Early Cretaceous of Texas form the basis for description of a new species of Tenontosaurus. The new ornithopod, Tenontosaurus dossi sp. nov., is a sister species to Tenontosaurus tilletti Ostrom found in Montana and Wyoming. Specimens of the new species are temporally older than those of T. tilletti, and in most cases of unequivocal polarity they are more primitive. The Texas species is clearly the most primitive iguanodontian, and thus shares many primitive characters with the weakly supported clade Hypsilophodontidae. The specimens from Texas represent unscavenged carcasses entombed in a brackish-water lagoonal or estuarine sands.

A 12.6 million year old forest assemblage of leaves, twigs, and rare fruit is preserved in the Ngorora Formation of central Kenya. The assemblage is autochtonous, preserved in airfall tuff and represents well the diversity, heterogeneity and richness of the original forest. The herbaceous component, not usually preserved in paleobotanical assemblages, is present. Nearest neighbor analysis and mapping of the vertical distribution of plant organs indicates that leaves and twigs are preserved near the parent plant and that there is no apparent size, weight, or species bias in deposition of these remains. Leaves occur isolated, in clusters, or attached to branches, and fell directly to the ground as a result of ashfall, most falling very soon after ashfall commenced. The absence of upright trunks and large stems is probably due to post-depositional weathering which may also be responsible for the absence of a leaf litter layer. However, leaf litter may have been absent at the time of ash deposition.

Pterosaurs are rare components of Texas Cretaceous faunas. The best known is Quetzalcoatlus northropi, from the Javelina Formation (Maastrichtian) of Big Bend National Park, with a wingspan of some 11-12 m (Lawson, 1975; Langston, 1986; Busbey and Lehmann, 1989). Texas pterosaur specimens of less spectacular proportions include a pteranodontid partial humerus (USNM 13804) from the Eagle Ford Formation (late Cenomanian-late Turonian) of Austin (Gilmore, 1935; Bennett, 1989) and a first wing phalanx of a pterodactyloid from the Buda Formation (Cenomanian) of Hays County (Langston, 1974; Lawson, 1975). Pterosaur bones were also recorded at localities near Forestburg, Montague County (Zangerl and Denison, 1950), in the Antlers Formation (Winkler et al., 1990), although these specimens are undiagnostic hollow bone fragments.

Vertebrates from the Comanche Series (Lower Cretaceous) in central Texas occur in the superposed Twin Mountains, Glen Rose, and Paluxy formations. Stratigraphie position and relationship to marine units are more clearly defined for the central Texas localities than for the classic mammal-producing sites in the Antlers Formation of north-central Texas. The diverse terrestrial to marine faunas include new records for the ray Rhinobatos, a ptychodont (cf. Hylaeobatis ornata), and the salmoniform Enchodus. Anurans, salamanders, lacertilians, and mammals representing early forms relevant to the emergence of extant higher taxa are present but fragmentary. Crocodilians are represented by at least three taxa and theropods by more than three. Eight species of mammals have been named from the Comanche Series, with perhaps as many as four other unnamed species represented. Paleoenvironments appear to control the distribution of taxa: dinosaurs are found in coastal settings and are abundant in some terrestri...

Living placental and marsupial mammals (therians) use distinctive tooth-replacement patterns that have not yet been traced back fully to their time of divergence in the Early Cretaceous (>100 Myr ago). Slaughteria eruptens, a small 110 Myr old fossil mammal from Texas, USA, is near the base of that divergence. Using ultra-high-resolution X-ray CT analysis we demonstrate that Slaughteria preserves an unrecognized pattern of tooth replacement with simple posterior premolars replacing molariform precursors. Differing from both placentals that have a more complex posterior adult premolar, and from marsupials, in which only one premolar is replaced, Slaughteria provides the first direct evidence of a tooth-replacement pattern that is plausible for the common ancestor of all therians. By our interpretation Slaughteria has only one adult molar in place and contains two mental foramina in the jaw, thus changing characters that are critical to reconstruction of mammalian relationships and to species discrimination and interpretations of diversity for Early Cretaceous mammals.

Interdune deposits in the Navajo Sandstone of Arizona are identified as the source of most fossils known from the formation. They provide information on terrestrial life in a poorly known interval of the North American Jurassic. The biota includes sphenophytes, ostracodes, and four species of vertebrates, including a skeleton of the geologically youngest tritylodontid synapsid from western North America. Fossils and sedimentary rock localized in interdunes indicate areas of greater available moisture, and therefore greater carrying capacity, than surrounding dune deposits that compose the bulk of the formation. Environmental conditions in interdunes favor fossil preservation and thus provide a focus for future studies. The diversity and adaptations of fossils from Navajo interdunes support models of climatic amelioration during sand-sea evolution when wet interdunes were deposited.

Winkler, D. A., 1983. Paleoecology of an early Eocene mammalian fauna from paleosols in the Clarks Fork Basin, northwestern Wyoming (U.S.A.). Palaeogeogr., Palaeoclimmatol., Palaeoecol., 43: 261--298. The paleoecology and depositional history of an early Eocene vertebrate assemblage dominated by small mammals is analyzed at a richly fossiliferous locality in the Willwood Formation, northwestern Wyoming. Systematic surface sampling using a quadrat net, screen washing, and quarrying of fresh sediment show that all vertebrate material in these fluvial deposits is contained in dark gray mudstones representing the A horizons of paleosols. Seven such paleosols occur in 22 m of stratigraphic section. The fauna includes 34 species of mammals, and also birds, reptiles, amphibians, fishes and gastropods. All vertebrate fossil material is fragmented, but it shows no evidence of transportation or current sorting. Surface weathering and possibly carnivore activity are responsible for the fragmentation and for an overabundance of dense and compact skeletal elements. Detailed surface collections were made to obtain multiple samples from the different bone beds (paleosols). Principle component analysis shows that differences in the type and abundance of fossils from the various collecting areas are related to differences between contained bone beds, not differences along single bone beds. One paleosol has a red B horizon and six have an orange B horizon. The gray-over-red colored paleosol is faunally distinct from gray-over-orange paleosols. It contains the only specimens of two large, archaic mammals, and no very small mammalian taxa. Cluster analysis on the occurrence of vertebrate taxa is used to define subsets of the fauna that may represent animals living in different habitats. Separate clusters are formed by a group of the most common terrestrial herbivorous mammals and the crocodilian Allognathosuchus, and by a group of small, possibly arboreal herbivores and carnivores. The relative abundance of each mammalian species was initially calculated from a sample representing a minimum of 300 individual animals collected from the surface. The surface sample is dominated by mammals that are medium-sized for the fauna. Screen washing yields a greater relative abundance of very small mammals than was found on the surface. This indicates that the surface sample is biased against small forms. Corrected relative abundances based on both surface and washing samples show that the fauna is dominated numerically by very small mammals (one multituberculate species and several insectivores). Screen washing of fresh matrix is the best means of sampling a locality for paleoecological purposes.

The teeth in 51 individuals of the red fox, Vulpes vulpes , from the Upper Peninsula of Michigan were measured to quantify dental variation and correlation in this species. Upper and lower first molars tend to be the least variable in the toothrow; the canines, incisors, and posteriormost molars tend to be more variable. Variability of the cheek teeth is uncorrelated with sequence of tooth eruption, but rather appears to be inversely related to occlusal complexity, with teeth in the carnassial region being the least variable. Correlations and partial correlations of tooth length were calculated for all pairs of upper and lower teeth. Surprisingly, the tooth pairs that are most highly correlated are in the premolar series where no tooth-to-tooth occlusion is possible. Reduced variability near occluding carnassials in each toothrow is presumably related to the functional importance of precise occlusion, but this is not reflected in the pattern of correlations and partial correlations.

Major groups of modern mammals have their origins in the Mesozoic Era, yet the mammalian fossil record is generally poor for that time interval. Fundamental morphological changes that led to modern mammals are often represented by small samples of isolated teeth. Fortunately, functional wear facets on teeth allow prediction of the morphology of occluding teeth that may be unrepresented by fossils. A major step in mammalian evolution occurred in the Early Cretaceous with the evolution of tribosphenic molars, which characterize marsupials and placentals, the two most abundant and diverse extant groups of mammals. A tooth from the Early Cretaceous (110 million years before present) of Texas tests previous predictions (based on lower molars) of the morphology of upper molars in early tribosphenic dentitions. The lingual cusp (protocone) is primitively without shear facets, as expected, but the cheek side of the tooth is derived (advanced) in having distinctive cusps along the margin. The tooth, although distressingly inadequate to define many features of the organism, demonstrates unexpected morphological diversity at a strategic stage of mammalian evolution and falsifies previous claims of the earliest occurrence of true marsupials.

The upper Couch Formation is part of the lower of two formations composing the Ogallala Group in Blanco and Yellowhouse canyons in northwestern Texas. An eolian origin for the upper Couch Formation is indicated by its mean grain size, pedogenic carbonate nodules, massive bedding, and blanketlike morphology. The unit conforms poorly to the usual eolian depositional models; it resulted from a combination of the processes involved in loess and sand-sheet formation. Grassland or savanna vegetation probably existed over the area and aided in sediment trapping. Vertebrates are unusual in eolian units, but the adaptations and mode of preservation of those in the upper Couch Formation also support an eolian interpretation. This and other widespread silty sand sheets in the Ogallala indicate major fluctuations in depositional style, possibly climatically controlled. Lateral continuity and preservation of vertebrates give silty sand sheets great potential as correlation tools.

Deposition of the basal fluvial sediments of the Miocene-Pliocene Ogallala Formation in western Texas and eastern New Mexico was controlled by topography on the underlying erosional surface. Paleovalley-fill facies consist of gravelly and sandy braided-stream deposits interbedded with and overlain by eolian sediments deposited as sand sheets and loess. Uplands on the pre-Ogallala erosional surface are overlain primarily by similar eolian sediments. Calcic paleosols, consisting mostly of glaebules and rhizoconcretions of CaCO/sub 3/, occur throughout the eolian facies. Massive to laminated and locally pisolitic, brecciated, and recemented pedogenic calcretes occur primarily near or at the top of the Ogallala Formation. Eolian facies preserve numerous superposed calcretes and calcic paleosols, reflecting slow episodic aggradation on a savannah or grassland under arid to subhumid climatic conditions. The change from fluvial to mostly eolian sedimentation probably resulted from diversion of streams that deposited fluvial sediments of the Ogallala Formation to form the Pecos and Canadian rivers. Source areas for eolian sediments may initially have been flood plains of Ogallala braided streams and later the flood plains of the newly formed Pecos and Canadian rivers. 38 references.