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1.
Speculation regarding Tyrannosaurus in West Texas has been largely based upon a sub-adult tyrannosaurid maxilla from the Javelina Formation (Late Cretaceous–Maastrichtian) of Big Bend National Park. However, a very large anterior caudal vertebra, recently collected from the Javelina Formation, exhibits a morphology that can confidently be assigned to Tyrannosauridae and, because of its size, likely pertains to an adult Tyrannosaurus. The stratigraphic position of the specimen is closely bracketed by titanosaurid remains and further supports coexistence of these taxa. The stratigraphic position of the specimen possibly records one of the earliest occurrences of Tyrannosaurus. If so, Tyrannosaurus likely existed during roughly equivalent temporal intervals in disparate paleobiomes in both northern and southern late Maastrichtian faunal realms of North America. 相似文献
2.
Among titanosaurs, osteoderms are morphologically diverse and have been reported from deposits in South America, Africa, Madagascar, Eurasia and Oceania. In Brazil, titanosaur osteoderms are rare and have only been recorded from Bauru Basin sedimentary rocks. Here, we describe a keeled titanosaur osteoderm, which is the first occurrence of an osteoderm specimen in the São Luís Basin, Northeastern Brazil. This osteoderm is characterized by an external bulb, an internal root, and a very rugose cingulum limiting the external and internal surfaces. These characteristics are typical of Titanosauria dermal bones, and this specimen strengthens the idea that the armored sauropods were present during the early Late Cretaceous of Northeastern Brazil, extending their distribution in the northernmost portion of South America. 相似文献
3.
Transpressional tectonics are typically associated with restraining bends on major active strike-slip faults, resulting in uplift and steep terrain. This produces dynamic erosional and depositional conditions and difficulties for established lines of palaeoseismological investigation. Consequently, in these areas data are lacking to determine tectonic behaviour and future hazard potential along these important fault segments. The Big Bend of the San Andreas fault in the Transverse Ranges of southern California exemplifies these problems. However, landslides, probably seismically triggered, are widespread in the rugged terrain of the Big Bend. Fluvial reworking of these deposits rapidly produces geomorphic planes and lines that are markers for subsequent fault slip. The most useful are offset and abandoned stream channels, for these are relatively high precision markers for identifying individual faulting events. Palaeoseismological studies from the central Big Bend, involving 14C ages of charcoal fragments from trench exposures, illustrate these points and indicate that the past three faulting events, including the great 1857 earthquake, were relatively similar in scale, each producing offsets of about 7–7.5 m. The mean recurrence interval is 140–220 years. The pre-1857 event here may be the 1812 event documented south of the Big Bend or an event which took place probably between 1630 and 1690. Ground breakage in both events extended south of the Big Bend, unlike the 1857 event where rupture was skewed to the north. The preceding faulting event ruptured both to the north and south of the Big Bend and probably occurred between 1465 and 1495. All these events centred on the Big Bend and may be typical for this fault segment, suggesting that models of uniform long-term slip rates may not be applicable to the south-central San Andreas. A slip-rate estimate of 34–51 mm a− 1 for the central Big Bend, although uncertain, may also imply higher slip in the Big Bend and highlights difficulties in correlating slip-rates between sites with different tectonic settings. Slip rates on the San Andreas may increase within the broad compressional tectonics zone of the Big Bend, compared to the north and south where the plate boundary is a relatively linear and sub-parallel series of dominantly strike-slip faults. Partitioning slip within the Big Bend is inherently uncertain and insufficient suitably comparable data are available to sustain a uniform slip model, although such models are a common working assumption. 相似文献
4.
Bones in the fossil record sometimes exhibit unusual structures that can be attributed to pathologies, taphonomic alterations, or morphological variation. The goal of this work is to describe three bone abnormalities present in the type specimen of Bonitasaura salgadoi from the Cretaceous of north Patagonia, Argentina. The studied material corresponds to a left femur, a left metatarsal III, and a right prezygapophysis of a mid-caudal vertebra. Macroscopic and/or histological examinations were conducted, and a discussion concerning the origin of each abnormality is provided. The results of this study suggest that the anomalous structures are pathologies. In the femur, an osteoblastic tumor was identified by the presence of a large outgrowth of ovoid appearance with a spiculated microstructural pattern. The metatarsal III shows an enthesophyte (or bone spur) based on its location, shape and growth in parallel to the long axis of the bone element. Finally, the abnormal tissue observed in the prezygapophysis of the caudal vertebra was determined to be an infection by the presence of reactive new bone associated with a local widening of the subperiosteal margin and a sinus of drainage. This is the first report of multiple pathologies in a single specimen of a titanosaur, and it provides new insights about paleopathologies in sauropod dinosaurs. 相似文献
5.
There are 24 known localities for skeletal remains of sauropod dinosaurs in the republics of Central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan). Sauropod remains are very rare at all these localities and represented usually only by isolated teeth. Only narrow-crowned teeth are known from the Cretaceous of Central Asia. The oldest record of such teeth is from the Aptian Sultanbobo Formation of Uzbekistan. Exposures of the Turonian Bissekty Formation at the most productive vertebrate locality in the region, Dzharakuduk in Uzbekistan, has yielded many isolated teeth and a few skeletal remains that can be attributed to a non-lithostrotian titanosaur. Similar narrow-crowned, cylindrical teeth from Cenomanian-to Coniacian-age strata in the Kyzylkum Desert, Uzbekistan, may belong to a closely related taxon. Another taxon, with teeth that are pentagonal in cross-section, is known from the Santonian Yalovach and Bostobe formations of Tajikistan and western Kazakhstan, respectively. A femur reported from the Santonian Syuksyuk Formation of southern Kazakhstan possibly belongs to a lithostrotian titanosaur. The change in tooth structure at the Coniacian–Santonian boundary in the region possibly suggests replacement of non-lithostrotian titanosaurs by lithostrotians. The titanosaur from the Bissekty Formation is similar to Dongyangosaurus sinensis from the Cenomanian–Turonian of Zhejiang (China) in the extensive pneumatization of the neural arch on the anterior caudal vertebrae with several fossae. It also resembles Baotianmansaurus henanensis from the Cenomanian of Henan (China) in the possession of very short anterior caudal centra. These three taxa possibly represent an as yet formally unrecognized endemic clade of Asian non-lithostrotian titanosaurs. 相似文献
6.
7.
Here we describe a new record of a sauropod dinosaur from the Lower Cretaceous (Hauterivian–Barremian) Rio Piranhas Formation, Sousa Basin, NE Brazil. Dinosaur fossil bones from this deposit were unknown until now. Thus, the discovery of a sauropod fibula from this locality is highly significant. Our discovery represents an indeterminate titanosaur and the earliest stratigraphic occurrence of this group in central Gondwana. When compared to chronocorrelate titanosaur trackmakers of this geological unit, this fossil specimen appears substantially smaller. Histological analysis of the fibula suggests that this is a relatively young individual (approximately 40–50% adult body size) that had passed its most rapid phase of early juvenile growth, but had not yet attained somatic maturity. Thus, the fibula recovered is from a young individual rather than from a small-bodied adult titanosaur. 相似文献
8.
9.
Isolated left prefrontal, left squamosal and atlas of titanosaur dinosaurs are described and compared. They come from the Late Cretaceous Serra da Galga Member of the Marília Formation at the Serra do Veadinho region, Peirópolis (Uberaba County, Minas Gerais State, Brazil). Due to the sparse cranial elements of titanosaurs already known from Brazil, these specimens are noticeable to be presented. In addition, the atlas vertebra is described for the first time for Brazilian titanosaurs. The morphology of the cranial bones closely resembles lithostratian titanosaurs, such as Rapetosaurus, rather than basal titanosaurs. The atlas is similar to that of other titanosaurs, suggesting that the anatomy of this element seems to be more conservative than other vertebral elements, in which vertebral laminae play an important rule in titanosaur taxonomy. 相似文献
10.
雅鲁藏布江是东构造结的核心区域,为研究雅鲁藏布江大拐弯流域现今隆升发育现状,本文基于ArcGIS平台,对雅鲁藏布江下游大拐弯流域的ASTER-DEM30 m面积-高程积分值（Hypsometry Index,简称HI法,是一种基于数字高程模型来获取流域演化特征及其构造活动响应指标的方法）进行计算,并结合构造、岩性、气候、第四系以及河流等基础资料探讨该地区隆升差异。结果表明:HI>0.43的隆升区主要集中在大拐弯缝合带以外的区域且分布与各断块中的三级夷平面具有较好的耦合性;而HI>0.60拉萨断隆隆升区分布范围最大,加拉白垒断隆分布最小,仅在大拐弯小范围分布;HI < 0.43的侵蚀下切区,处于河流的一二级谷肩位置以及河流发育较为成熟的区域;林芝-派镇段区域内HI < 0.35,以侵蚀下切为主。由以上得出:区内构造挤压作用依然存在,而气候、河流以及断裂带密度的影响是在构造背景下产生的,随着时间推移以上因素会逐渐抑制构造抬升作用,并且对侵蚀的促进作用在不同区域内表现不同;当构造作用发挥主要作用时,断块以隆升作用为主,HI>0.43;气候作用的影响使加拉白垒与南迦巴瓦峰处于隆升停滞,HI < 0.43;林芝段HI < 0.35说明在气候、河流发育以及断裂带密度的影响下会加大侵蚀的力度使得区域内以侵蚀下切为主,未有抬升迹象。整体上,在构造、气候、河流发育及断裂带密度综合影响下,隆升作用由雅鲁藏布江流域下游外部向内部逐渐减弱,而局部区域上的差异是由影响因素发挥作用的差异决定的。 相似文献
11.
A new species of hybodontid shark is described for the Lower Cretaceous of Brazil. The type specimen is derived from pre-Aptian strata of Malhada Vermelha Formation, Lima Campos Basin (Ceará State, northeastern Brazil), with referred material from the Missão Velha Formation of Araripe Basin, northeastern Brazil. The new taxon differs from other Planohybodus species by the presence of a stronger tooth ornamentation characterized by simple, usually non-branching cristae that nearly reach the apex of the main cusp as well as distinctly divergent lateral cusplets. In addition, certain North-American specimens formerly attributed to Hybodus are identified as Planohybodus. The new species presented herein, in addition to the North-American remains, represents an important contribution to the knowledge of the distribution of Planohybodus, expanding the geographic range of the genus to South and North America in the Late Jurassic and Early Cretaceous. 相似文献
12.
Diego Brandoni Raúl I. Vezzosi 《Boreas: An International Journal of Quaternary Research》2019,48(4):879-890
The aim of this contribution is to describe a femur (MCRS 199) assigned to Nothrotheriops sp. from the Late Pleistocene of Santa Fe Province (Argentina), and discuss the implications of this find in the context of the dispersal of ground sloths during the Great American Biotic Interchange. The specimen MCRS 199 is smaller than the femora referred to the North American species Nothrotheriops texanus and Nothrotheriops shastensis but shares several features with these species: (i) shape and position of the greater trochanter, (ii) development of the lesser trochanter, (iii) presence of connection between the third trochanter and the ectepicondyle, (iv) distal third of the femur wider, with ML/DW index of 1.93, and (v) location and relationship of the distal condyles. These similarities allow us to assign MCRS 199 to Nothrotheriops sp. The record of Nothrotheriops sp. from Santa Fe Province chronologically coincides with the earliest records of Nothrotheriops shastensis suggesting a broad geographical distribution of Nothrotheriops during the Late Pleistocene, ranging from 33–36°N (e.g. states of California and Arizona, USA) to 31°S (northern Salado River, Santa Fe Province, Argentina). Thus, Nothrotheriops have dispersed from North America (where Nothrotheriops has early records, Calabrian–Middle Pleistocene) to South America where localities bearing Nothrotheriops are Late Pleistocene in age. In addition, once in South America and probably during the Middle Pleistocene, Nothrotheriops probably gave rise to its sister taxon, Nothrotherium, with records from the Middle Pleistocene (e.g. 223 ka BP, northeastern Brazil) to the Late Pleistocene (e.g. 15 ka BP). 相似文献
13.
Kristin Saltonstall 《Estuaries and Coasts》2003,26(2):444-451
Over the past century, the distribution and abundance ofPhragmites australis (common reed) has dramatically increased in both freshwater and brackish wetlands throughout North America. It has been hypothesized that the increased competitive ability ofPhragmites could be the result of an introduction of a more aggressive genotype. Sequence data from 2 noncoding regions of the chloroplast genome show that, historically, 11 native haplotypes were found across North America and population-structuring distinguishing samples from the Atlantic Coast, Midwest, West, and Gulf Coast regions of the continent was evident. Today a single genetically-distinct haplotype dominates the Atlantic Coast and is also found across the continent in lower frequencies; this type is common in Europe and Asia and has most likely been introduced to North America. Comparisons of modern populations with historic samples show that along the Atlantic Coast, this cosmopolitan type has replaced native haplotypes and it is invading new sites throughout the rest of the country. In the Midwest and West, native populations are still common but introduced populations are found along roadsides throughout the area. Gulf Coast populations are dominated by another population type that is genetically distinct from all other North American population types. 相似文献
14.
Alexander B. Kuzmichev 《Tectonophysics》2009,463(1-4):86-108
The South Anyui suture is a major tectonic boundary in NE Asia, believed to represent the remains of an ocean basin which separated Siberia from North America in Jurassic time. Its history also figures prominently in the Mesozoic reconstruction of the Arctic and the origin and evolution of the Amerasia basin. Three types of proposed trends of the South Anyui suture are evaluated. 1) The suture ends near the Kolyma River mouth where it meets the rotational transform. The paper, however, proves that the suture continues further westward up to Big Lyakhov Is. Consequently, a simple geometric rotational model for Amerasia basin origin must be rejected. 2) The suture trends from Big Lyakhov to the Anjou islands. The Anjou islands geology is examined, and it is concluded that the suture could not go through them. Hence, all proposed versions of the rotational hypothesis of the Amerasia basin opening are claimed to be invalid. 3) A proposed Taimyrian connection of the suture is examined, and it is concluded that this model must be rejected as well. The failure of all previously suggested models for the suture extent through the New Siberian islands and Laptev Sea means that in Early Mesozoic there was no oceanic basin that separated the New Siberian–Chukotka terrane from Siberia. Thus Siberia and North America formed a continuous continent in Jurassic time. This paper presents evidence that the South Anyui suture has instead turned back from Big Lyakhov island and followed a sinuous path designated as the Chroma Loop before connecting with the Kolyma Loop suture. On this model the South Anyui suture can be interpreted as a small segment of extensive boundary which separated the Amerasia Jurassic margin and terranes accreted to it from the Pacific. The modern boundary around the North Pacific is also quite sinuous. It was suggested that in Jurassic time it was straighter and the Amerasia ocean was originated as a common back-arc basin. Finally a new two-pole parallelogram hypothesis for the Amerasia basin opening is suggested and the approaches to its verification are outlined. 相似文献
15.
A symphyseal region of the fused dentaries of a caenagnathid theropod is described from the Upper Cretaceous Nemegt Formation at the Bugin Tsav locality in the Mongolian Gobi Desert. In contrast to the high diversity of Caenagnathidae in the upper Campanian to Maastrichtian in North America, only specimens of a single caenagnathid, Elmisaurus raurus, have been reported in the coeval strata in Asia. Although dentaries are commonly-found bones in the fossil record of Caenagnathidae, the present specimen is the first discovery of caenagnathid dentaries from the upper Campanian to Maastrichtian in Asia. The Nemegt Formation is unique for its diverse oviraptorosaurian fauna that includes both Caenagnathidae and Oviraptoridae as well as the non-caenagnathoid Avimimus portentosus. Hypothesized coexistence of eolian and fluvial environments in the Gobi Basin during the deposition of the Nemegt Formation might explain such co-occurrence of Caenagnathidae and Oviraptoridae. 相似文献
16.
The new caprinoidean rudist bivalve Cobbanicaprina bighornensis gen. nov., sp. nov. is described from the upper middle Cenomanian of Big Horn County, Montana, USA. Cobbanicaprina gen. nov. is closely related to Mexicaprina and differs from that form in the absence of an external ligamental groove. The presence of Cobbanicaprina gen. nov. in the middle Cenomanian indicates that the Caprinuloideidae did not become extinct at the top of the Albian and persisted into the Cenomanian. The presence of this specimen so far north in the Western Interior Seaway is attributed to a dried-out individual specimen having been transported post-mortem by currents. 相似文献
17.
A new species of cladid crinoid, Hylodecrinus cymrus, is described from the Pembroke Limestone Group (Mississippian, Tournaisian, Courceyan) of West Angle Bay in south Pembrokeshire, Wales. It has a medium bowl‐shaped aboral cup, with strong ridges extending across the basals and radials forming pits at the plate corners. It is most similar to the late Tournaisian H. carinatus (Hall, 1861) of North America but differs in having less strongly cuneate brachials that are longer than wide with more subtle carinae on the aboral side. This specimen represents the first report of this genus from Europe, which most probably migrated from North America. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
18.
In Mexico, just 54% of the reported Pleistocene Bison material has been identified to species. Current paleontological research in northwestern Oaxaca, southern Mexico, has allowed collection of several specimens of Bison antiquus that are part of the Viko Vijin Local Fauna. B. antiquus had a very wide geographic distribution, from lowlands to mountainous landscapes of North and Central America. The B. antiquus record from southern Mexico links their former records from central Mexico and middle Central America and confirms this wide geographic distribution. The univariate mesowear score of the B. antiquus specimens from Oaxaca is in the lower extreme of grazers and the upper end of mixed-feeders, suggesting that they had a less abrasive diet than the modern plains Bison, as has been observed in other samples of this species from diverse parts of North America. The presence of B. antiquus in the Viko Vijin L. F. constrains the age of this fossil assemblage within a range from 60 Ka to 11.7 Ka. 相似文献
19.
Grant D. Zazula Derek G. Turner Brent C. Ward Jeffrey Bond 《Quaternary Science Reviews》2011,30(19-20):2355-2360
Western camel (C. hesternus) fossils are rare from Eastern Beringia, thus there is little available information on their chronology, paleoecology, and biogeography in this region. In August of 2010, a partial proximal phalanx of a western camel was recovered from a sedimentary exposure along the White River, in the formerly glaciated terrain of southwest Yukon, northwest Canada. The fossil specimen was recovered in situ from sediments that are correlated by stratigraphic, tephra and radiocarbon data to the Marine Isotope Stage (MIS) 5 interglacial period (Sangamonian). Associated paleoenvironmental data indicates that this western camel inhabited a shrub tundra ecosystem that did not include spruce trees or boreal forest during a relatively cold interval between MIS 5e and 5a. This is the oldest reliably dated western camel fossil from Eastern Beringia and supports the model of range expansion for this species to the high latitudes of northwest North America during the last interglacial (sensu lato). 相似文献
20.
Mammoths in our midst: The proboscideans of Anza-Borrego Desert State Park®, Southern California,USA
Anza-Borrego Desert State Park® (ABDSP) has an exceptional proboscidean fossil record. The remains of Gomphotheriidae and Elephantidae span over 10 Ma and encompass over eighty productive sites. The most numerous of the proboscideans are the mammoths. Significant specimens include one of the youngest Gomphotherium and the most complete skeleton of Mammuthus meridionalis in North America.Over 6 km of fossiliferous sediments spans the Miocene–Pliocene and Pliocene–Pleistocene boundaries and provides a continuous record of changing environments. Over 550 taxa of aquatic and terrestrial plants, marine and lacustrine invertebrates, and marine, fresh water and terrestrial vertebrates are represented. Present are both Asian and South American immigrant mammals. M. meridionalis and M. columbi (=M. imperator) regionally co-existed here. A specimen from the Diablo Formation extends the temporal range of Gomphotherium in North America nearly one million years into the middle Blancan. 相似文献