Ichnotaxonomic Review of Large Ornithopod Dinosaur Tracks: Temporal and Geographic Implications

BackgroundLarge ornithopod tracks are known from the Upper Jurassic to the uppermost Cretaceous rocks of all continents but Antarctica. They include the tracks historically called Iguanodon footprints, iguanodontid footprints, hadrosaur/hadrosaurid footprints, and other large ornithopod tracks that have been used to define ichnotaxa. More than 40 ichnospecies based on large ornithopod tracks have been defined, but the validity of many of them is questionable.Conclusions/SignificanceThe monospecific ichnogenus Iguanodontipus (I. burreyi) is characterized by a small, rounded heel and elongate, narrow digit impressions. Its distribution is limited to the Berriasian-Valanginian of Europe. Caririchnium consists of four ichnospecies (C. magnificum [type ichnospecies], C. kortmeyeri, C. billsarjeanti and C. lotus) with a large, rounded heel and short, wide digit impressions. This ichnogenus ranges from the Berriasian-Hauterivian to the Aptian-Albian of South America, North America, Asia and Europe. Finally, Hadrosauropodus (three ichnospecies: H. langstoni [type ichnospecies], H. leonardii and H. kyoungsookimi) shows a large, bilobed heel and short, wide digit impressions. It is known from the Aptian-Albian to the Maastrichtian of North America, Asia and Europe. The ichnofamily Iguanodontipodidae includes large iguanodontian tracks characterized mainly by mesaxonic, tridactyl and subsymmetrical pes tracks that are as wide as (or wider than) long and have one pad impression in each digit and one in the heel. Its distribution is confidently limited to the Cretaceous of Europe, Asia, North America and South America.     

New triconodontids (Mammalia) from the Lower Cretaceous Shahai and Fuxin formations, northeastern China

The first triconodontids from Asia have been discovered from the Lower Cretaceous (Aptian to Albian) Shahai and Fuxin formations in Liaoning Province, northeastern China: Meiconodon lii gen. and sp. nov. and M. setoguchii gen. and sp. nov. M. lii is characterized by molariform teeth with a developed cusp d, an m3 with taller cusp a, an m4 with three primary cusps of subequal height, the posteriorly decreasing transverse width of the m4, and a considerably reduced m5. M. setoguchii is slightly larger than M. lii, and characterized by a sharp labial cingulum on the m4, and a less developed cusp d on the molariform teeth than M. lii. The extensive interlocking system between molariforms, posteriorly recumbent primary molariform cusps, and their great degree of asymmetry in occlusal view with rounded labial faces and more angulate lingual faces in lateral view, indicate that Meiconodon belongs to the triconodontid subfamily Alticonodontinae. These new taxa are the first record of Triconodontidae from Asia, and of Alticonodontinae outside North America, suggesting the occurrence of mammalian faunal exchange between North America and Asia during or before the Aptian-Albian.     

Reanalysis of Wupus agilis (Early Cretaceous) of Chongqing,China as a Large Avian Trace: Differentiating between Large Bird and Small Non-Avian Theropod Tracks

Trace fossils provide the only records of Early Cretaceous birds from many parts of the world. The identification of traces from large avian track-makers is made difficult given their overall similarity in size and tridactyly in comparison with traces of small non-avian theropods. Reanalysis of Wupus agilis from the Early Cretaceous (Aptian-Albian) Jiaguan Formation, one of a small but growing number of known avian-pterosaur track assemblages, of southeast China determines that these are the traces of a large avian track-maker, analogous to extant herons. Wupus, originally identified as the trace of a small non-avian theropod track-maker, is therefore similar in both footprint and trackway characteristics to the Early Cretaceous (Albian) large avian trace Limiavipes curriei from western Canada, and Wupus is reassigned to the ichnofamily Limiavipedidae. The reanalysis of Wupus reveals that it and Limiavipes are distinct from similar traces of small to medium-sized non-avian theropods (Irenichnites, Columbosauripus, Magnoavipes) based on their relatively large footprint length to pace length ratio and higher mean footprint splay, and that Wupus shares enough characters with Limiavipes to be reassigned to the ichnofamily Limiavipedidae. The ability to discern traces of large avians from those of small non-avian theropods provides more data on the diversity of Early Cretaceous birds. This analysis reveals that, despite the current lack of body fossils, large wading birds were globally distributed in both Laurasia and Gondwana during the Early Cretaceous.     

Atoposaurid crocodyliforms from the Khorat Group of Thailand: first record of <Emphasis Type="Italic">Theriosuchus</Emphasis> from Southeast Asia

We describe a partial crocodilian skull from the Mesozoic non-marine sediments of the Khorat Plateau Sao Khua Formation (Berriasian-Barremian) in northeastern Thailand and assign it to Theriosuchus grandinaris sp. nov. An isolated dentary from the Phu Kradung Formation (latest Jurassic–Early Cretaceous) is also tentatively assigned to the genus Theriosuchus, and an isolated tooth from the Khok Kruat Formation (Aptian-Albian) may belong to this genus. The Thai fossils represent the first unambiguous evidence of presence of Theriosuchus outside Europe. Its occurrence in Thailand increases the known diversity of neosuchian crocodyliforms from Southeast Asia and suggests that Atoposauridae had a wide geographical distribution from the Late Jurassic to the Early Cretaceous.     

Tithonian-Berriasian foraminiferal faunas from the Torinosu-type calcareous blocks of the southern Kanto Mountains, Japan: their implications for post-accretionary tectonics of Jurassic to Cretaceous terranes

The Torinosu-type limestones, having many lithologic characters showing their original deposition on shallow shelves, are widely distributed in the Jurassic to Cretaceous terranes of Japan. The foraminiferal faunas from the Jurassic to the lowermost Cretaceous of Japan were first revealed in the calcareous blocks of the southern Kanto Mountains. Distinguished microfaunas consist of 39 species including many marker species of the Upper Jurassic to Lower Cretaceous in Europe, West Asia, and North Africa such as Melathrokerion spirialis, Charentia evoluta, Freixialina planispiralis, Nautiloculina oolithica, Everticyclammina cf. virguliana, Haplophragmium lutzei and Pseudocyclammina lituus. These faunas suggest a Tithonian to Berriasian age of Torinosu-type limestones. They are contained in four tectonostratigraphic units (Kamiyozawa, Hikawa and Gozenyama Formations; Ogouchi Group) continuously accreted from Middle Jurassic to Late Cretaceous. The younger deposition age of Torinosu-type limestones than the accretion age (Bajocian to Bathonian) in the Kamiyozawa Formation and their older age than the accretion age of the Ogouchi Group (late Albian to middle Maastrichtian) are important to date the post-accretionary tectonics of Jurassic to Cretaceous terranes of Japan and to explain the emplacement process of Torinosu-type limestones.     

Nuurcala obesa sp. n. (Blattida,Caloblattinidae) from the Lower Cretaceous Yixian Formation in?Liaoning?Province,China

Nuurcala obesa sp. n., in the cockroach family Caloblattinidae, is described from the Lower Cretaceous Yixian Formation (Liaoning Province, China) based on a combination of differential characters of fore- and hind wing venation, colouration and body structures. Systematically, Nuurcala (Vršanský, 2003), known from the Cretaceous sediments of Bon Tsagaan and Khurilt, Mongolia, is closely related to other genera of Caloblattinidae known from the Jurassic and Cretaceous localities in other parts of Asia.     

A new troodontid theropod dinosaur from the lower Cretaceous of Utah

Background

The theropod dinosaur family Troodontidae is known from the Upper Jurassic, Lower Cretaceous, and Upper Cretaceous of Asia and from the Upper Jurassic and Upper Cretaceous of North America. Before now no undisputed troodontids from North America have been reported from the Early Cretaceous.

Methodology/Principal Findings

Herein we describe a theropod maxilla from the Lower Cretaceous Cedar Mountain Formation of Utah and perform a phylogenetic analysis to determine its phylogenetic position. The specimen is distinctive enough to assign to a new genus and species, Geminiraptor suarezarum. Phylogenetic analysis places G. suarezarum within Troodontidae in an unresolved polytomy with Mei, Byronosaurus, Sinornithoides, Sinusonasus, and Troodon + (Saurornithoides + Zanabazar). Geminiraptor suarezarum uniquely exhibits extreme pneumatic inflation of the maxilla internal to the antorbital fossa such that the anterior maxilla has a triangular cross-section. Unlike troodontids more closely related to Troodon, G. suarezarum exhibits bony septa between the dental alveoli and a promaxillary foramen that is visible in lateral view.

Conclusions/Significance

This is the first report of a North American troodontid from the Lower Cretaceous. It therefore contributes to a fuller understanding of troodontid biogeography through time. It also adds to the known dinosaurian fauna of the Cedar Mountain Formation.     

Lowermost occurrence of ostracod Cypridea species in East Asia and implications for the non-marine Jurassic/Cretaceous boundary

Cypridea Bosquet, 1852 is a non-marine ostracod genus of the Superfamily Cypridoidea, and the extinct Family Cyprideidae, which achieved high diversity in the Early Cretaceous. This genus plays an important role in the subdivision and correlation of strata, as well as in paleogeographic and paleoclimatic studies. Cypridea species are remarkably abundant and diverse, and are extensively distributed across East Asia. However, the lowermost occurrence of Cypridea species (LOOC) in East Asia is still being debated, varying from the Upper Jurassic to Lower Cretaceous. Here, we aim to conduct a preliminary investigation of the Cypridea-bearing strata of East Asia (China, Mongolia, Korea and Japan), and attempt to update the strata correlation, based on new progress of the ostracod correlations, as well as the progress of other research methods on the relative Jurassic/Cretaceous (J/K) strata of these areas. Results show that the LOOCs in most basins of East Asia are documented in Lower Cretaceous (～Berriasian) strata. However, Cypridea species are extremely rare near the J/K boundary interval but flourish until Valanginian–Hauterivian in most basins of East Asia. Therefore, we propose that the LOOC in each corresponding basin of East Asia can be used as an auxiliary marker of the non-marine J/K boundary. Cypridea species may have travelled first from Africa (Kimmeridgian) to Europe (J/K period), and then East Asia (Early Cretaceous), which resulted in the LOOC in East Asia later than in the other continents.     

A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America,and the Biogeography of Neoceratopsia

The fossil record for neoceratopsian (horned) dinosaurs in the Lower Cretaceous of North America primarily comprises isolated teeth and postcrania of limited taxonomic resolution, hampering previous efforts to reconstruct the early evolution of this group in North America. An associated cranium and lower jaw from the Cloverly Formation (?middle–late Albian, between 104 and 109 million years old) of southern Montana is designated as the holotype for Aquilops americanus gen. et sp. nov. Aquilops americanus is distinguished by several autapomorphies, including a strongly hooked rostral bone with a midline boss and an elongate and sharply pointed antorbital fossa. The skull in the only known specimen is comparatively small, measuring 84 mm between the tips of the rostral and jugal. The taxon is interpreted as a basal neoceratopsian closely related to Early Cretaceous Asian taxa, such as Liaoceratops and Auroraceratops. Biogeographically, A. americanus probably originated via a dispersal from Asia into North America; the exact route of this dispersal is ambiguous, although a Beringian rather than European route seems more likely in light of the absence of ceratopsians in the Early Cretaceous of Europe. Other amniote clades show similar biogeographic patterns, supporting an intercontinental migratory event between Asia and North America during the late Early Cretaceous. The temporal and geographic distribution of Upper Cretaceous neoceratopsians (leptoceratopsids and ceratopsoids) suggests at least intermittent connections between North America and Asia through the early Late Cretaceous, likely followed by an interval of isolation and finally reconnection during the latest Cretaceous.     

A new iguanodontian dinosaur from the Khok Kruat Formation (Early Cretaceous,Aptian) of northeastern Thailand

A new taxon of ornithopod dinosaur is described as Siamodon nimngami nov. gen, nov. sep., on the basis of a well-preserved maxilla from the Khok Kruat Formation (Aptian) of northeastern Thailand. An isolated tooth and a braincase are referred to this taxon, and the status of other ornithopod specimens from Thailand and Laos is discussed. S. nimngami nov. gen, nov. sep. is considered as an advanced iguanodontian, apparently close to Probactrosaurus, from which it differs by various characters of the maxilla. Siamodon is an addition to the already long list of advanced iguanodontian taxa from the late Early Cretaceous of Asia. The diversity and abundance of these forms may suggest that advanced iguanodontians first appeared in Asia, before spreading to other parts of the world.     

The evolution of the lepidosaurian lower temporal bar: new perspectives from the Late Cretaceous of South China

Until recently, it was considered axiomatic that the skull of lizards and snakes arose from that of a diapsid ancestor by loss of the lower temporal bar. The presence of the bar in the living New Zealand Tuatara, Sphenodon, was thus considered primitive, corroborating its status as a ‘living fossil’. A combination of new fossils and rigorous phylogeny has demonstrated unequivocally that the absence of the bar is the primitive lepidosaurian condition, prompting questions as to its function. Here we describe new material of Tianyusaurus, a remarkable lizard from the Late Cretaceous of China that is paradoxical in having a complete lower temporal bar and a fixed quadrate. New material from Jiangxi Province is more complete and less distorted than the original holotype. Tianyusaurus is shown to be a member of the Boreoteiioidea, a successful clade of large herbivorous lizards that were dispersed through eastern Asia, Europe and North America in the Late Cretaceous, but disappeared in the end-Cretaceous extinction. A unique combination of characters suggests that Tianyusaurus took food items requiring a large gape.     

Origin and evolution of the powdery mildews (Ascomycota,Erysiphales)

Molecular phylogeny suggests a close relationship of Asteraceae to the early evolution of Golovinomyces. The family Asteraceae, with a geographic origin in South America, expanded into the Northern Hemisphere, where it may have been infected by an ancestor of Golovinomyces, thus starting a close host–parasite relationship. Using this event as a calibration point, we designed molecular clocks for powdery mildews using the 28S rDNA D1/D2 and internal transcribed spacer (ITS) regions. According to these clocks, the powdery mildews originated in the Late Cretaceous and the first radiation of the major lineages occurred at the Cretaceous/Paleogene boundary. Ancestral powdery mildews may have first radiated on broad-leaved deciduous trees in the high latitudes of the Northern Hemisphere, and continued further speciation whilst migrating to southward during the world cooling in the Paleogene and Neogene periods. The cradle of four herb infecting genera, viz. Blumeria, Golovinomyces, Leveillula, and Neoërysiphe may be within the area extending from Central/West Asia to the Mediterranean.     

A New Hadrosauroid Dinosaur from the Early Late Cretaceous of Shanxi Province,China

Background

The origin of hadrosaurid dinosaurs is far from clear, mainly due to the paucity of their early Late Cretaceous close relatives. Compared to numerous Early Cretaceous basal hadrosauroids, which are mainly from Eastern Asia, only six early Late Cretaceous (pre-Campanian) basal hadrosauroids have been found: three from Asia and three from North America.

Methodology/Principal Findings

Here we describe a new hadrosauroid dinosaur, Yunganglong datongensis gen. et sp. nov., from the early Late Cretaceous Zhumapu Formation of Shanxi Province in northern China. The new taxon is represented by an associated but disarticulated partial adult skeleton including the caudodorsal part of the skull. Cladistic analysis and comparative studies show that Yunganglong represents one of the most basal Late Cretaceous hadrosauroids and is diagnosed by a unique combination of features in its skull and femur.

Conclusions/Significance

The discovery of Yunganglong adds another record of basal Hadrosauroidea in the early Late Cretaceous, and helps to elucidate the origin and evolution of Hadrosauridae.     

A second hadrosauroid dinosaur from the early Late Cretaceous of Zuoyun,Shanxi Province,China

A second basal hadrosauroid dinosaur, Zuoyunlong huangi gen. et sp. nov., is reported from the early Late Cretaceous Zhumapu Formation in Zuoyun County, Shanxi Province, northern China. Zuoyunlong preserves a partial right ilium and ischium and is unique in having a very short postacetabular process 50% as long as the iliac central plate. Our cladistic analysis recovers Zuoyunlong as the most basal Late Cretaceous hadrosauroid, with a sister taxon relationship with Probactrosaurus from the late Early Cretaceous of Inner Mongolia. Including Zuoyunlong, four Cenomanian basal hadrosauroids have been recorded, and the two taxa in North America (Eolambia and Protohadros) represent the earliest known hadrosauroids outside of Asia. In the light of the proposed phylogenetic topology and biogeographic data, the discovery of Zuoyunlong indicates that the first dispersal of hadrosauroids from Asia to North America probably happened around the boundary between the Early and Late Cretaceous.     

The origin and early evolution of metatherian mammals: the Cretaceous record

Metatherians, which comprise marsupials and their closest fossil relatives, were one of the most dominant clades of mammals during the Cretaceous and are the most diverse clade of living mammals after Placentalia. Our understanding of this group has increased greatly over the past 20 years, with the discovery of new specimens and the application of new analytical tools. Here we provide a review of the phylogenetic relationships of metatherians with respect to other mammals, discuss the taxonomic definition and diagnosis of Metatheria, outline the Cretaceous history of major metatherian clades, describe the paleobiology, biogeography, and macroevolution of Cretaceous metatherians, and provide a physical and climatic background of Cretaceous metatherian faunas. Metatherians are a clade of boreosphendian mammals that must have originated by the Late Jurassic, but the first unequivocal metatherian fossil is from the Early Cretaceous of Asia. Metatherians have the distinctive tightly interlocking occlusal molar pattern of tribosphenic mammals, but differ from Eutheria in their dental formula and tooth replacement pattern, which may be related to the metatherian reproductive process which includes an extended period of lactation followed by birth of extremely altricial young. Metatherians were widespread over Laurasia during the Cretaceous, with members present in Asia, Europe, and North America by the early Late Cretaceous. In particular, they were taxonomically and morphologically diverse and relatively abundant in the Late Cretaceous of western North America, where they have been used to examine patterns of biogeography, macroevolution, diversification, and extinction through the Late Cretaceous and across the Cretaceous-Paleogene (K-Pg) boundary. Metatherian diversification patterns suggest that they were not strongly affected by a Cretaceous Terrestrial Revolution, but they clearly underwent a severe extinction across the K-Pg boundary.     

On the systematic position of the Early Cretaceous fern genus “Athyrium”

The oldest fossils assigned to Athyrium (mostly based on the sorus morphology) comprise fronds and spores from the Lower Cretaceous of Northeast Asia. However, most molecular dating suggests that extant Athyrium diverged from its sister genus during the Eocene or later, implying that the Cretaceous fossils probably belong to another polypodiaceous taxon. By examining the sorus morphology of extant genera related to the family Athyriaceae, we found that the primary diagnostic feature for assigning the Cretaceous fossils to Athyrium, i.e., the sorus shape, is common to the entire extant family, or plesiomorphic for the genus. As the fronds are more commonly preserved than the reproductive parts, we compared the fossil frond morphology with those of living taxa of the family that is divided into two types. The Cretaceous fossil we examined here bears the frond’s costal groove characters on adaxial side, which is more closely related to that of the Deparia-clade instead of the clade including Athyrium and other genera of the family. The observation is further confirmed by the cladistic analysis using morphological characters. The systematic position of the Early Cretaceous “Athyrium” was resolved as a stem member of the total Athyriaceae using a tip-dating approach with the Fossilized Birth-Death model in a Bayesian framework. Our study suggests that Early Cretaceous fossils previously assigned to Athyrium require taxonomic revision.     

First fossil record of the genus Nageia (Podocarpaceae) in south China and its phytogeographic implications

The first fossil record of the genus Nageia Gaertner from the Tertiary of southern China is reported. Nageia hainanensis sp. nov. is described from the Eocene Changchang Formation of Hainan Island. The extant species of Nageia are widely distributed in southeastern Asia, from northeastern India to southeastern China and southern Japan, and southward through Indochina to the Malay Archipelago and New Guinea. The fossil evidence of Nageia has been discovered from the Lower Cretaceous of the Far East of Russia and Japan. The distribution of both modern and fossil species of Nageia indicates that this genus could have originated in the northeastern part of Asia in the Early Cretaceous and spread to south China at least in the Eocene. Discovery of Nageia fossil record in south China provides important evidence for the geological and phytogeographic history of the genus.     

A new basal hadrosauroid dinosaur from the Late Cretaceous of Uzbekistan and the early radiation of duck-billed dinosaurs

Levnesovia transoxiana gen. et sp. nov., from the Late Cretaceous (Middle–Late Turonian) of Uzbekistan, is the oldest well-documented taxon referable to Hadrosauroidea sensu Godefroit et al. It differs from a somewhat younger and closely related Bactrosaurus from Inner Mongolia (China) by a tall sagittal crest on the parietals and the absence of club-shaped dorsal neural spines in adult specimens. Levnesovia, Bactrosaurus and possibly Gilmoreosaurus represent the earliest radiation of Hadrosauroidea, which took place during the Cenomanian–Turonian and possibly in North America. The second, Santonian-age radiation of Hadrosauroidea included Aralosaurus, Hadrosauridae and lineages leading to Tanius (Campanian) and Telmatosaurus (Maastrichtian). Hadrosauridae appears to be monophyletic, but Hadrosaurinae and Lambeosaurinae originated in North America and Asia, respectively.     

The first well-preserved Early Cretaceous brachiosaurid dinosaur in Asia

A new genus and species of brachiosaurid sauropods, Qiaowanlong kangxii gen. et sp. nov., is reported, representing the first well-preserved Early Cretaceous brachiosaurid in Asia and expanding the distribution of brachiosaurids undoubtedly into the Asian continent. The new taxon was recovered from the late Early Cretaceous Xinminpu Group of Yujingzi Basin in northwestern Gansu Province, China, and is represented by a series of eight mid-cervical vertebrae, a right pelvic girdle and some unidentified bones. The existence of deeply excavated cervical neural spines and a rising transition in the neural spine height among mid-cervical vertebrae clearly show the affinity of Qiaowanlong as a member of brachiosaurids. Among brachiosaurids, Qiaowanlong shares a derived feature with the North American Early Cretaceous brachiosaurid Sauroposeidon: the lack of cranial centrodiapophyseal lamina. However, Qiaowanlong is unique in possessing a suite of features, such as a low central length/cotyle height ratio, bifurcated cervical neural spines and a much reduced ischium. The discovery of Qiaowanlong and other new material indicates a diverse and abundant sauropod assemblage in China during the Early Cretaceous.