小林 快次 - 第7回 ぼくの現場は、楽しいから。

小林 快次 - 第1回 はじめは気に入らなかった | 川上和人×小林快次「鳥類学者 無謀にも恐竜学者と語り合う」 (2018年8月1日・於神楽坂ラカグ) | 川上和人 , 小林快次 | 対談・インタビュー | 考える人 | 新潮社

小林 快次 - 古生物学者の小林快次先生がみんなの質問にこたえます!

Crocodylians are ectothermic animals, and their past distribution has been greatly influenced by changing climate since their Cretaceous origin. The Pliocene-Pleistocene witnessed a contraction of the crocodylian latitudinal ranges due to rapid cooling with superimposed pronounced orbital-scale climate oscillations. However, a chronologically-continuous record of the geographically marginal populations of crocodylians is yet to be provided for this time interval, and crocodylian response to such climatic changes is poorly known. This study describes a partial crocodylian skeleton from the Middle Pleistocene of Osaka, Japan, diagnosed as Toyotamaphimeia cf. machikanensis, on the basis of character comparisons, including ontogenetic skull shape change, and consideration of the reconstruction error in the holotype of T. The paleotemperature estimates for the crocodylian-bearing horizons indicate that late Early—Middle Pleistocene crocodylians in the Kinki district of Japan were living near their lower thermal limit. During the glacial periods, they might have moved to the southern extremity of Japan or locally became extinct from Japan, while re-expanding their range after the end of glacial periods. A total of 67 tracks 14 trackways [one didactylous, 13 tridactylous] and 12 isolated tracks belonging to four ichnomorphotypes were mapped on a single horizon. This indicates at least four different theropod trackmakers lived in the same area at the same time. This tracksite consists of laminated gray mudstone-yellowish brown siltstone couplets interbedded with eolian yellowish brown sandstone deposited on a distal floodplain. Abundant footprints with V-shaped profiles cross-section within in the vertical section indicate that dinosaurs repeatedly walked across in this area. Before the discovery of the tracks, the site was illegally excavated by fossil poachers, a widespread problem in the Gobi Desert. During excavation of the track horizon, a clenched, inclined Gallimimus foot skeleton was found in the mudstone, extended down 20 cm below the track-bearing sandstone layer. The occurrence of tracks closely associated with body fossils is unusual and taphonomically intriguing. It is possible that the foot skeleton represents an animal that died in its tracks. However, the depth of the foot in mud is probably too shallow for the animal to have been mired. Sedimentological and taphonomic evidence also suggests that the pes of Gallimimus may have passed straight through the track-bearing sandstone layer. The inclined right pes indicates that the body lay on its left side on the substrate. During decomposition in the mud, all digits were flexed but the distal phalanges were stuck and anchored in the stiff lower mud. Consequently, as more proximal phalanges were able to accommodate flexing, they were pulled away and dislocated from the anchored distal phalanges. Subsequent trampling by dinosaurs in the track-bearing sandstone would have further distorted the underlying foot. The Upper Cretaceous Nemegt Formation of Mongolia is rich in well-preserved dinosaurs and Ornithomimosauria is one of the most common taxa in the formation. Three ornithomimosaur taxa, Anserimimus planinychus, Deinocheirus mirificus, and Gallimimus bullatus, have been discovered from the formation so far. However, the recently discovered specimens suggest there is even greater morphological variation of ornithomimosaurs in the Nemegt Formation than are presently recognized. This study focuses on the structures of manual elements among Nemegt ornithomimosaurs and reveals their remarkable diversity. The manual structures of seven individuals, including aforementioned three known taxa and four new individuals, are morphologically distinct from each other. Numerical analyses on metacarpals, phalanges, and unguals also support high morphological diversity of the Nemegt ornithomimosaurs. The large diversity of manual morphology may be related to large variety of palaeoecological niches were prevailed in the Nemegt ecosystem. Ankylosaur braincase and endocranial morphologies are poorly known. Furthermore, cranial endocasts have been described for fewer than ten taxa so far. The complete inner ear morphology is known for only three species — Euoplocephalus tutus, Kunbarrasaurus ieversi, and Pawpawsaurus campbelli. Here, the first cranial endocast morphologies are presented for the Mongolian Cretaceous ankylosaurids Talarurus plicatospineus and Tarchia teresae. The study of paleoneurological features of these Mongolian taxa adds novel anatomical information to both species allowing the first comparison with ankylosaurids from North America. The development of a cerebellar flocculus that leaves an impression on the vestibular eminence — floccular recess — is observed in Euoplocephalus, Talarurus and T. Because this structure hasn't been identified in any nodosaurid so far, its presence in ankylosaurid cranial endocasts may represent a possible synapomorphy with unknown paleobiological implications. The Nemegt locality is one of the most famous dinosaur localities in Mongolia ever since the site was discovered in 1946. It yields abundant dinosaur skeletons however, little attention had been given to dinosaur footprints at the locality. The only Nemegt dinosaur footprint study focused on descriptions of the footprints, gave only a few taxonomic implications, and provided no comparison with other dinosaur tracksites. This study reports newly recorded dinosaur footprints hadrosaurs, sauropods, and theropods at the Nemegt locality during the Nemegt Educational Expedition of 2016. A single footprint-bearing horizon that extends several kilometres was examined within the Nemegt Formation to determine the ichno-taxonomic assemblage of the Nemegt dinosaurs. A significant difference was identified between taxonomic compositions based on skeletal remains and ichno-taxonomic compositions based on footprints. Although the vast majority of the skeletal elements collected in the area belong to theropods, the footprints suggest that the Nemegt locality was dominated by herbivorous dinosaurs. This suggests that the previously inferred Tarbosaurus dominant taxonomic composition at the Nemegt locality is a result of a preservational bias. The size distribution of the newly studied footprints suggest that the Nemegt hadrosaurs had an adult-dominant and multigenerational population structure. Comparisons with dinosaur tracksites at the Cantwell Alaska, USA and Tremp Spain formations show that the population structure and body sizes of the Nemegt hadrosaurs were similar to those of the high-latitude Cantwell hadrosaurs. It suggests that the Nemegt area was more open and had higher plant productivity than the Tremp area. The North American fossil record of dinosaur eggshells for the Cretaceous is primarily restricted to formations of the middle Albian-Cenomanian and uppermost Campanian-Maastrichtian stages, with a large gap in the record for intermediate stages. Here we describe a dinosaur eggshell assemblage from a formation that represents an intermediate and poorly fossiliferous stage of the Upper Cretaceous, the Santonian Milk River Formation of southern Alberta, Canada. The Milk River eggshell assemblage contains five eggshell taxa: Continuoolithus, Porituberoolithus, Prismatoolithus, Spheroolithus, and Triprismatoolithus. These ootaxa are most similar to those reported from younger Campanian-Maastrichtian formations of the northern Western Interior than they are to ootaxa reported from older middle Cretaceous formations i. , predominantly Macroelongatoolithus. Characteristics of the Milk River ootaxa indicate that they are ascribable to at least one ornithopod and four small theropod species. The taxonomic affinity of the eggshell assemblage is consistent with the dinosaur fauna known based on isolated teeth and fragmentary skeletal remains from the formation, although most ornithischians and large theropods are not represented by eggshell. Relative to the Milk River Formation eggshell, similar oospecies occurring in younger Cretaceous deposits tend to be somewhat thicker, which may reflect an increase in body size of various dinosaur lineages during the Late Cretaceous. Crown Copyright C 2017 Published by Elsevier Ltd. The late Cenozoic fossil record of alligators in East Asia is crucial in understanding the origin and past distribution of Asian alligators that are now represented by a single species, Alligator sinensis. This study reports a partial skeleton of A. sinensis from the Late Pliocene approximately 3. It demonstrates the oldest record of A. sinensis and wider distribution of this species in the past. Tectonic and geographic history of East Asia suggests that alligators presumably dispersed into Japan before 25 Ma or after 10 Ma, yet finally were wiped out from Japan due to the semi-isolated condition of the Japanese island arc and the deteriorated climate during the Plio-Pleistocene. Derived members of the enigmatic mammalian order Desmostylia have molars comprising appressed columns whose morphology does not render their function in feeding simple to discern. Here we describe a new genus and species, Ounalashkastylus tomidai, more derived than Cornwallius but less derived than Desmostylus and Vanderhoofius, which develop a hypertrophied medial eminence on the dentary ontogenetically. Tooth morphology, vaulted palate and the medial eminence, which can rise to the level of the occlusal surface of M-2, suggest that derived desmostylids clenched their teeth strongly while employing suction during feeding, most likely on marine and coastal plants. The horned dinosaur Centrosaurus apertus from the Belly River Group Campanian is represented by multiple articulated skulls and skeletons, and is particularly notable for its occurrence in dozens of large-scale monodominant bonebeds, which have been found in the Dinosaur Park Formation across southern Alberta and Saskatchewan. Here we present a detailed taphonomic analysis of the first large-scale Centrosaurus apertus bonebed McPheeters bonebed from the Oldman Formation of southeastern Alberta. The McPheeters bonebed rivals the richest bonebeds in the Dinosaur Park Formation in terms of bone density and size, and the complete disarticulation of elements. The bonebed occurs in an overbank facies and is dominated by small bone clasts, suggesting that only low energy water current contributed to the formation of the bonebed before its final burial event. Patterns of taphonomic modification suggest that bones experienced little weathering, breakage, or scavenging. In turn, these conclusions are compatible with an overall interpretation of rapid burial in humid conditions after the disarticulation of elements. These taphonomic features are virtually identical to those seen in the well-documented bonebeds of this species in the Dinosaur Park Formation, which are interpreted to represent mass death events caused by seasonal tropical storms and associated large-scale flooding. Late Cretaceous dinosaur species typically have small geographic and stratigraphic ranges defined by the extent of single geological formations. The new bonebed extends the distribution of Centrosaurus apertus to the upper Oldman Formation, which is interpreted as more inland than the coastally influenced Dinosaur Park Formation, and suggests that mass death events related to seasonal tropical storms occurred over a broader geographic area and in a greater range of paleoenvironments than previously documented. The Ganzhou area of Jiangxi Province, southern China is becoming one of the most productive oviraptorosaurian localities in the world. A new oviraptorid dinosaur was unearthed from the uppermost Upper Cretaceous Nanxiong Formation of Ganzhou area. It is characterized by an anterodorsally sloping occiput and quadrate a feature shared with Citipati , a circular supratemporal fenestra that is much smaller than the lower temporal fenestra, and a dentary in which the dorsal margin above the external mandibular fenestra is strongly concave ventrally. The position of the anteroventral corner of the external naris in relation to the posterodorsal corner of the antorbital fenestra provides new insight into the craniofacial evolution of oviraptorosaurid dinosaurs. A phylogenetic analysis recovers the new taxon as closely related to the Mongolian Citipati. Six oviraptorid dinosaurs from the Nanxiong Formation Ganzhou and Nanxiong are distributed within three clades of the family. Each of the three clades from the Nanxiong Formation has close relatives in Inner Mongolia and Mongolia, and in both places each clade may have had a specific diet or occupied a different ecological niche. Oviraptorid dinosaurs were geographically widespread across Asia in the latest Cretaceous and were an important component of terrestrial ecosystems during this time. The holotype of Deinocheirus mirificus was collected by the 1965 Polish-Mongolian Palaeontological Expedition at Altan Uul III in the southern Gobi of Mongolia 1. Because the holotype consists mostly of giant forelimbs 2. 4 min length with scapulocoracoids 2 , for almost 50 years Deinocheirus has remained one of the most mysterious dinosaurs. The mosaic of ornithomimosaur and nonornithomimosaur characters in the holotype has made it difficult to resolve the phylogenetic status of Deinocheirus 3,4. Here we describe two new specimens of Deinocheirus that were discovered in the Nemegt Formation of Altan Uul IV in 2006 and Bugiin Tsav in 2009. Cladistic analysis indicates that Deinocheirus is the largest member of the Ornithomimosauria; however, it has many unique skeletal features unknown in other ornithomimosaurs, indicating that Deinocheirus was a heavily built, non-cursorial animal with an elongate snout, a deep jaw, tall neural spines, a pygostyle, a U-shaped furcula, an expanded pelvis for strong muscle attachments, a relatively short hind limb and broad-tipped pedal unguals. Ecomorphological features in the skull, more than a thousand gastroliths, and stomach contents fish remains suggest that Deinocheirus was a megaomnivore that lived in mesic environments. Background: Osteohistological examinations of fossil vertebrates have utilized a number of proxies, such as counts and spacing of lines of arrested growth LAGs and osteocyte lacunar densities OLD , in order to make inferences related to skeletochronology and mass-specific growth rates. However, many of these studies rely on samplings of isolated bones from single individuals. These analyses do not take individual variation into account, and as a result may lead to misleading inferences of the physiology of extinct organisms. This study uses a multi-element, multi-individual sampling of ornithomimid dinosaurs to test the amount of individual variation in the aforementioned osteohistological indicators. Based on these results we also assess the conclusions of previous studies that tested paleohistological hypotheses using isolated elements. Results: LAG number was found to be consistent within the hind limb bones of each individual, with the exception of the fibula, which preserves one additional LAG. Considerable differences in LAG spacing were found between elements of the sampled individuals, with larger variation found in elements of the foot compared with the femur, fibula, and tibia. Osteocyte lacunar density ranged between 29000 and 42000 osteocyte lacunae per mm 3 , and was found to vary more between hind limb bones of an individual and within bones, than between the average values of individuals. Conclusions: The variation between hind limb elements in LAG number and LAG spacing suggests that direct comparisons of these elements may be misleading, and that LAG spacing is not a reliable proxy for mass-specific growth rates of an individual. Sampling of multiple bones should be performed as an internal check of model-based LAG retro-calculation and growth equations. The observation that osteocyte lacunar density varies more between individual bone elements than between average individual values suggests that the choice of sampled element can greatly influence the result, and care should be taken to not bias interpretations of the physiology of fossil tetrapods. The discovery of a new tracksite of mostly hadrosaurid dinosaur footprints, made by a herd living in an ancient high-latitude continental ecosystem, provides insight into the herd structure and behavior of northern polar dinosaurs and perspective on populations of large-bodied herbivores in an Arctic greenhouse world. This tracksite occurs in the Upper Cretaceous Cantwell Formation in the Alaska Range Denali National Park, Alaska, United States , and it is the largest tracksite known from this far north. Preservation of the tracksite is exceptional: most tracks, regardless of size, contain skin impressions and they co-occur with well-preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects. Statistical analyses of the tracks show that individuals of four different age classes of hadrosaurids lived together in a large social group. Our research results independently corroborate the growth curve for hadrosaurids proposed by paleohistologists that suggests that these dinosaurs experienced a period of rapid growth early in their life history. Therizinosauria are an unusual group of theropod dinosaurs, found mostly in the Cretaceous deposits in Mongolia, China and western USA. The basal forms of this group are represented by incomplete or disarticulated material. Here, we report a nearly complete, articulated skeleton of a new basal therizinosaur from the Early Cretaceous Yixian Formation of Jianchang County, western part of Liaoning Province, which sheds light on our understanding of anatomy of basal therizinosaurs. This new dinosaur shows some typical therizinosaur features, such as neural spines of the anterior caudal vertebrae that possess anterior and posterior alae, a rectangular buttress on the ventrolateral side of the proximal end of metacarpal I, and appressed metatarsal shafts. Our phylogenetic analysis suggests that it is a basal therizinosaur sister taxon to Therizinosauroidea because it bears many basal therizinosaur characters in the dentition, pelvis and hind limbs. The new therizinosaur described here has unique tooth and jaw characters such as the offsetting of the tooth row by a shelf and dentary teeth with labially concave and lingually convex dentary teeth, similar to ornithopods and ceratopsians. Bonebeds can provide a wealth of anatomical, taphonomic, and ontogenetic information about the specimens preserved within them, and can provide evidence for inferred behavior. The material described here represents the first known bonebed of ornithomimids in North America, and the fourth record of an ornithomimosaur bonebed in the world. Partial skeletons representing three individuals are preserved in this assemblage, each comprising primarily portions of the posterior postcrania pelvis, hind limbs and tail. All three individuals are morphologically similar, although one is larger in overall size. Given the stratigraphic position of the site, and the morphology of the postcrania, the preserved material represents a taxon from the clade containing Ornithomimus and Struthiomimus. Pedal ungual morphology is examined and found to be too variable to be useful in distinguishing these species taxonomically. This site provides additional evidence of gregarious behavior in ornithomimids and the first probable record of that behavior in North American forms. An unnamed nonmarine sedimentary package of rocks in southeastern Alaska in Wrangell-St. Elias National Park and Preserve has provided the first evidence of dinosaurs for this vast region. The rock unit is contained within the Wrangellia Terrane and exposures are of limited geographic extent. The rock unit is considered to be latest Cretaceous age. Sections are overwhelmingly dominated by extraformational conglomerates. Fine- to medium-grained light coloured sandstones are common and medium grey shales occur as minor components of the sections. Megafloral specimens indicate an abundance of horsetails, ferns and gymnosperm wood. Rather than two-dimensional impressions, most ferns are preserved in three dimensions, suggesting rapid burial. The abundance of charcoal in these rocks suggests that this area during deposition was also prone to ecological disturbance. Field parties found evidence of a small theropod and ornithopods. A single theropod pes impression is approximately 9 cm long and 7 cm wide. Attribution to the Theropoda was based on the sinusoidal shape of the impression of the middle digit. An ornithopod impression, identified by clearly blunt and rounded digit impressions, is approximately 22 cm long and 26 cm wide. All impressions are under tracks. Previously described feathered dinosaurs reveal a fascinating record of feather evolution, although substantial phylogenetic gaps remain. Here we report the occurrence of feathers in ornithomimosaurs, a clade of non-maniraptoran theropods for which fossilized feathers were previously unknown. The Ornithomimus specimens, recovered from Upper Cretaceous deposits of Alberta, Canada, provide new insights into dinosaur plumage and the origin of the avian wing. Individuals from different growth stages reveal the presence of a filamentous feather covering throughout life and winglike structures on the forelimbs of adults. The appearance of winglike structures in older animals indicates that they may have evolved in association with reproductive behaviors. These specimens show that primordial wings originated earlier than previously thought, among non-maniraptoran theropods. The Zhutian and Dafeng formations Upper Cretaceous of the Heyuan Basin in northeastern Guangdong Province, China, have produced thousands of dinosaur eggs. Macromorphological features egg diameter, egg shape, outer surface texture, and shell thickness of 461 eggs were analyzed using non-destructive techniques and subjected to statistical analyses in order to assess their diversity and taxonomic affinities. Three types 1, 2 and 3 of eggs were discerned based on shape and outer surface morphology. Type 1 eggs are spherical to ellipsoidal in shape and have a rough surface. Three subtypes Type 1-A-1, 1-A-2, and 1-B are apparent from scatter plots and cluster analyses of egg diameters and shell thickness. Type 2 eggs are elongate with linear ornamentation on the surface, and are comparable to eggs that belong to the oofamily Elongatoolithidae. Type 3 eggs are elongate with a smooth surface, and are assigned to the oofamily Prismatoolithidae. Macromorphological features of the various egg types suggest that Type 1 could have been laid by ornithischian, sauropod or therizinosaur dinosaurs, Type 2 by oviraptorids, and Type 3 by troodontids. This study represents the first comprehensive statistical analysis of macrofeatures of dinosaur eggs, and reveals taxonomic diversity in the dinosaurs that were laying eggs in the Upper Cretaceous Heyuan area heretofore unrecognized in skeletal remains. A partial skeleton of the ornithomimid dinosaur, discovered from the Late Cretaceous Qiupa Formation of Luanchuan County, Tantou Basin, Henan Province, China, is described here and assigned to a new genus and species, Qiupalong henanensis, with unique features a notch on the lateral surface of the lateral posterior process of the proximal end of tibia and a small pit at the contact between astragalus and calcaneum. A phylogenetic analysis in this study suggests that it is a derived ornithomimid and form a monophyly with North American ornithomimids Struthiomimus altus and Ornithomimus edmontonicus , sharing two characters straight pubic shaft and large acute angle between pubic shaft and boot. Some characters small anterior process of the pubic boot and curved pedal unguals are seen in basal ornithomimosaurs as well, but these features in Q. Qiupalong is the first definitive ornithomimid from outside of the Gobi Desert and is the southern-most occurrence of Late Cretaceous ornithomimid from eastern Asia, demonstrating southern extension of ornithomimid distribution in Asia. Here, we examine 145 dinosaur eggshells from a new fossil locality in the Qiupa Formation Upper Cretaceous of the Luanchuan area in western Henan Province, China. The eggshells display elongatoolithid macro- and microstructures, including ridges and nodes on the outer surface, two ultrastructural layers, and an undulatory boundary between the mammillary and continuous layers. A phylogenic analysis shows that the Luanchuan eggshells belong to the ooclade Elongatoolithidae. Within Elongatoolithidae, the thickness ratio of the mammillary layer to the entire eggshell, and the porosity of the Luanchuan eggshells are comparable to the oogenera Macroolithus and Elongatoolithus. There is no direct evidence for the taxonomic identity of the Luanchuan eggshells; however, they were likely laid by oviraptorids based on their phylogenetic position and their similarities with known oviraptorid eggs. The Upper Cretaceous Cantwell Formation in Denali National Park and Preserve DENA , Alaska, contains an unparalleled fossil avian biodiversity. The Cantwell Formation, thousands of metres thick, was deposited near its current latitude and is exposed throughout much of DENA and elsewhere in the central Alaska Range. The Formation comprises a lower, dominantly fluvial sedimentary unit and an upper, mostly volcanic unit. Sedimentation of the lower unit was mainly in alluvial fan, braided and meandering stream, and lacustrine environments, with possible marginal-marine influence at times. Pollen data suggest that these sedimentary rocks are late Campanian or early Maastrichtian in age; thus the Cantwell Formation is correlative with other well-known dinosaur localities in Alaska. Bird tracks are preserved in multiple locations along a 40-km transect in DENA in fluvial and lacustrine deposits. Some bird tracks are found in association with dinosaur tracks and others are found on beds interbedded with dinosaur track-bearing layers. The Cantwell Formation contains footprints assigned to several ichnotaxa found in either Asia or North America based on such morphological criteria as the presence or absence of a hallux, print size and shape, and angle of divarication: Aquatilavipes swiboldae, Ignotornis mcconnelli, Magnoavipes denaliensis sp. The presence of a mixed Asian and North American ichnofauna suggests that at least some birds used Alaska as a bridge between Asia and North America. This diverse assemblage of avian traces, combined with the known fossil bone record and invertebrate trace fossil record, demonstrates that the northern Late Cretaceous polar region contained significant biodiversity. In 2008, a new basal neoceratopsian was discovered in the Tando beds Albian of Tando Basin in South Korea. It represents the first ceratopsian dinosaur in the Korean peninsula and is assigned to Koreaceratops hwaseongensis gen. Autapomorphies of Koreaceratops include very tall neural spines over five times higher than the associated centra in the distal caudals, and a unique astragalus divided into two fossae by a prominent craniocaudal ridge on the proximal surface. A phylogenetic analysis indicates that Koreaceratops is positioned between Archaeoceratops and all more derived neoceratopsians, and the elongation of caudal neural spines was an important derived character in non-ceratopsid neoceratopsians. The very tall caudal neural spines in Koreaceratops, Montanoceratops, Udanoceratops, Protoceratops, and Bagaceratops appear to be homoplasious, suggesting an independent adaptation, possibly for swimming. Skeletal evidence suggests that obligate quadrupedalism occurred gradually in neoceratopsians progressing from bipedal through facultative quadrupedalism, to complete quadrupedalism in Coronosauria. A new dinosaur Chuxiongosaurus lufengensis gen. is erected based on a nearly complete skull. The taxon is characterized by the lacrimal perpendicular to the ventral margin of the upper jaw, which is similar to that of Thecodontosaurus; a depression present on the dorsal profile of the snout behind the naris; the rostral profile of the maxilla slopes continuously towards the rostral tip; and the presence of 25 dentary teeth. It also displays prosauropod characters such as a relatively long skull, the slope of the maxillary rostral profile, and teeth that do not have basically constricted crowns. The new specimen is more basal than Anchisaurus and represents the first basal sauropod dinosaur from the Early Jurassic of China. New material of dsungaripterid pterosaurs from the Early Cretaceous of Tatal, western Mongolia, allows the diagnoses of Dsungaripteridae and Noripterus to be amended. All pterosaurs found at Tatal belong to Dsungaripteridae either Dsungaripterus or Noripterus. The name Phobetor is a junior synonym of Noripterus. The differing shapes of the anterior tips of skulls, differing tooth morphologies and the coexistence of both Dsungaripterus and Noripterus may imply that they occupied distinct ecological niches. We report on the first record of a pterosaur from Alaska. This record consists of a single manus track from the lower part of the Upper Cretaceous Cantwell Formation in Denali National Park, Alaska, United States, making this the northernmost occurrence for this group of reptiles. The specimen is from deposits that record a low-lying floodplain with small lakes and ponds, dissected by small channels that fed a larger tributary stream on an active fan lobe. The dominant vegetation was comprised of conifers with an understory of ferns and horsetails. We provide a description of the holotype skull Of the unusual oviraptorosaur Incisivosaurus gauthieri. Previous phylogenetic analyses have placed this taxon firmly within Oviraptorosauria near the base of the clade; however, until now only a cursory description of this important specimen was available. The presence of many primitive characteristics e. , maxillary and dentary teeth as well as an extended palate and rostrum indicates that the observed similarities between avians and derived oviraptorids are convergences rather than shared derived characters. In addition, we clarify previous descriptions of several ambiguous anatomical features, most notably of the palate. We also employ computed tomographic CT analysis, which allows for a more complete description of the braincase and the reconstruction of an endocranial endocast. CT imagery reveals features that were before unobtainable, such as the presence of a replacement tooth behind the large rodentiform incisor in the premaxilla. This arrangement indicates that although the inci.


However, a chronologically-continuous record of the geographically marginal populations of crocodylians is yet to be provided for this time interval, and crocodylian response to such climatic changes is poorly known. 『』(2019年)• — 最新版恐竜の世界 uptodatedinos [もっとも賢い恐竜] 中生代を通してもっとも頭がよかった恐竜といわれるトロオドン類。

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川上 恐竜は6600万年前に絶滅しなければ、地球に巨大な隕石が落ちなければ、どこまで大きくなったと思われます? 小林 う~ん、限界は既にきていたんじゃないかな。

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ある研究者が頭足類(イカやタコなど)の墨の化石を研究していて、その研究のなかでメラニン色素を作る細胞小器官「メラノソーム」を見つけました。

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そのうち噂が聞こえてきまして。

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A partial skeleton of the ornithomimid dinosaur, discovered from the Late Cretaceous Qiupa Formation of Luanchuan County, Tantou Basin, Henan Province, China, is described here and assigned to a new genus and species, Qiupalong henanensis, with unique features a notch on the lateral surface of the lateral posterior process of the proximal end of tibia and a small pit at the contact between astragalus and calcaneum. そして、人間の時間的感覚ではその危機感を把握することができません。

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でも、僕はまだ、海へ進出した恐竜の化石が見つかっていないだけなんじゃないかとも思うんです。

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A phylogenetic analysis indicates that Koreaceratops is positioned between Archaeoceratops and all more derived neoceratopsians, and the elongation of caudal neural spines was an important derived character in non-ceratopsid neoceratopsians. A significant difference was identified between taxonomic compositions based on skeletal remains and ichno-taxonomic compositions based on footprints. , predominantly Macroelongatoolithus. 先ほどの「不安定さ」の話にもつながりますが、こうした「ある」「ない」の議論が僕ら研究者の間で過熱していくことで、恐竜研究は進歩します。

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一方で、その彼らの眼のおかげで、恐竜化石が見つかっている面があるのだ。

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大学は、ワイオミング大学地質学地球物理学科卒業でした。

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アンモナイト愛好家のお父さんがいるとしよう。

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(おわり) とは 何かについて考え、それが「わかる」とはどういうことでしょうか。

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目が大きければ、もっと見えたかもしれませんが、見えすぎるかもしれないですね。

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