News Article | November 21, 2016
On a promontory high above the sweeping grasslands of the Georgian steppe, a medieval church marks the spot where humans have come and gone along Silk Road trade routes for thousands of years. But 1.77 million years ago, this place was a crossroads for a different set of migrants. Among them were saber-toothed cats, Etruscan wolves, hyenas the size of lions—and early members of the human family. Here, primitive hominins poked their tiny heads into animal dens to scavenge abandoned kills, fileting meat from the bones of mammoths and wolves with crude stone tools and eating it raw. They stalked deer as the animals drank from an ancient lake and gathered hackberries and nuts from chestnut and walnut trees lining nearby rivers. Sometimes the hominins themselves became the prey, as gnaw marks from big cats or hyenas on their fossilized limb bones now testify. "Someone rang the dinner bell in gully one," says geologist Reid Ferring of the University of North Texas in Denton, part of an international team analyzing the site. "Humans and carnivores were eating each other." This is the famous site of Dmanisi, Georgia, which offers an unparalleled glimpse into a harsh early chapter in human evolution, when primitive members of our genus Homo struggled to survive in a new land far north of their ancestors' African home, braving winters without clothes or fire and competing with fierce carnivores for meat. The 4-hectare site has yielded closely packed, beautifully preserved fossils that are the oldest hominins known outside of Africa, including five skulls, about 50 skeletal bones, and an as-yet-unpublished pelvis unearthed 2 years ago. "There's no other place like it," says archaeologist Nick Toth of Indiana University in Bloomington. "It's just this mother lode for one moment in time." Until the discovery of the first jawbone at Dmanisi 25 years ago, researchers thought that the first hominins to leave Africa were classic H. erectus (also known as H. ergaster in Africa). These tall, relatively large-brained ancestors of modern humans arose about 1.9 million years ago and soon afterward invented a sophisticated new tool, the hand ax. They were thought to be the first people to migrate out of Africa, making it all the way to Java, at the far end of Asia, as early as 1.6 million years ago. But as the bones and tools from Dmanisi accumulate, a different picture of the earliest migrants is emerging. By now, the fossils have made it clear that these pioneers were startlingly primitive, with small bodies about 1.5 meters tall, simple tools, and brains one-third to one-half the size of modern humans'. Some paleontologists believe they provide a better glimpse of the early, primitive forms of H. erectus than fragmentary African fossils. "I think for the first time, by virtue of the Dmanisi hominins, we have a solid hypothesis for the origin of H. erectus," says Rick Potts, a paleoanthropologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C. This fall, paleontologists converged in Georgia for "Dmanisi and beyond," a conference held in Tbilisi and at the site itself from 20–24 September. There researchers celebrated 25 years of discoveries, inspected a half-dozen pits riddled with unexcavated fossils, and debated a geographic puzzle: How did these primitive hominins—or their ancestors—manage to trek at least 6000 kilometers from sub-Saharan Africa to the Caucasus Mountains? "What was it that allowed them to move out of Africa without fire, without very large brains? How did they survive?" asks paleoanthropologist Donald Johanson of Arizona State University in Tempe. They did not have it easy. To look at the teeth and jaws of the hominins at Dmanisi is to see a mouthful of pain, says Ann Margvelashvili, a postdoc in the lab of paleoanthropologist Marcia Ponce de León at the University of Zurich in Switzerland and the Georgian National Museum in Tbilisi. Margvelashvili found that compared with modern hunter-gatherers from Greenland and Australia, a teenager at Dmanisi had dental problems at a much younger age—a sign of generally poor health. The teen had cavities, dental crowding, and hypoplasia, a line indicating that enamel growth was halted at some point in childhood, probably because of malnutrition or disease. Another individual suffered from a serious dental infection that damaged the jawbone and could have been the cause of death. Chipping and wear in several others suggested that they used their teeth as tools and to crack bones for marrow. And all the hominins' teeth were coated with plaque, the product of bacteria thriving in their mouths because of inflammation of the gums or the pH of their food or water. The dental mayhem put every one of them on "a road to toothlessness," Ponce de León says. They did, however, have tools to supplement their frail bodies. Crude ones—but lots of them. Researchers have found more than 15,000 stone flakes and cores, as well as more than 900 artifacts, in layers of sediments dating from 1.76 million to 1.85 million years ago. Even though H. erectus in East Africa had invented hand axes, part of the so-called Acheulean toolkit, by 1.76 million years ago, none have been found here at Dmanisi. Instead, the tools belong to the "Oldowan" or "Mode 1" toolkit—the first tools made by hominins, which include simple flakes for scraping and cutting and spherical choppers for pounding. The Oldowan tools at Dmanisi are crafted out of 50 different raw materials, which suggests the toolmakers weren't particularly selective. "They were not choosing their raw material—they were using everything," says archaeologist David Zhvania of the Georgian National Museum. That simple toolkit somehow enabled them to go global. "They were able to adjust their behavior to a wide variety of ecological situations," Potts says. Perhaps the key was the ability to butcher meat with these simple tools—if hominins could eat meat, they could survive in new habitats where they didn't know which plants were toxic. "Meat eating was a big, significant change," says paleoanthropologist Robert Foley of the University of Cambridge in the United Kingdom. Even with their puny stone flakes, "these guys were badass," competing for meat directly with large carnivores, Toth says. At the meeting, he pointed to piles of cobblestones near the entrance of an ancient gully, which suggest the hominins tried to fend off (or hunt) predators by stoning them. They set their own course as they left Africa. Researchers had long thought that H. erectus swept out of their native continent in the wake of African mammals they hunted and scavenged. But all of the roughly 17,000 animal bones analyzed so far at Dmanisi belong to Eurasian species, not African ones, according to biological anthropologist Martha Tappen of the University of Minnesota in Minneapolis. The only mammals not of Eurasian origin are the hominins—"striking" evidence the hominins were "behaving differently from other animals," Foley says. Perhaps venturing into new territory allowed the hominins to hunt prey that would not have known to fear and flee humans, suggests paleoanthropologist Robin Dennell of the University of Exeter in the United Kingdom. Tappen calls that an "intriguing new idea" but thinks it should be tested. Checking the types of animal bones at other early Homo fossil sites out of Africa could show whether the mix of prey species changed when hominins colonized a new site, supporting a "naïve prey" effect. Whatever impelled them, the migrants left behind a trail of tools that have enabled researchers to trace their steps out of Africa. There, the oldest stone tools, likely fashioned by the first members of early Homo, such as small-brained H. habilis, date reliably to 2.6 million years ago in Ethiopia (and, possibly, 3.3 million years in Kenya). New dates for stone tools and bones with cutmarks at Ain Boucherit, in the high plateau of northeastern Algeria, suggest that hominins had crossed the Sahara by 2.2 million years ago when it was wetter and green, according to archaeologist Mohamed Sahnouni of the National Centre for Research on Human Evolution in Burgos, Spain. His unpublished results, presented at the Dmanisi meeting, are the earliest evidence of a human presence in northern Africa. The next oldest tools are those from Dmanisi, at 1.85 million years old. The trail of stone tools then hopscotches to Asia, where Mode 1 toolkits show up by nearly 1.7 million years ago in China and 1.6 million in Java, with H. erectus fossils. "We pick up little fractions of a current" of ancient hominin movements, Foley says. The identity of the people who dropped these stone breadcrumbs is a mystery that has only deepened with study of the Dmanisi fossils. The excavation team has classified all the hominins at the Georgia site as H. erectus, but they are so primitive and variable that researchers debate whether they belong in H. erectus, H. habilis, a separate species, H. georgicus—or a mix of all three, who may have inhabited the site at slightly different dates. A new reanalysis of the Dmanisi skulls presented at the meeting added fuel to this debate by underscoring just how primitive most of the skulls were. Using a statistics-based technique to compare their shape and size with the skulls of many other hominins, Harvard University paleoanthropologist Philip Rightmire found that only one of the Dmanisi skulls—at 730 cubic centimeters—fits "comfortably within the confines of H. erectus." The others—particularly the smallest at 546 cc—cluster more closely with H. habilis in size. Nor did the Dmanisi hominins walk just like modern humans. A new analysis of cross sections of three toe bones found that the cortical bone—the dense outer layer—wasn't buttressed in the same way as it is in the toes of modern humans. When these hominins "toed off," the forces on their toes must have been distributed differently. They may have walked a bit more like chimps, perhaps pushing off the outside edge of their foot more, says Tea Jashashvili of the University of Southern California in Los Angeles and the Georgian National Museum. "If there are so many primitive traits, why are they calling it H. erectus?" asks Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York City. "People are avoiding the question of what H. erectus is. Every time new stuff comes up, they're enlarging the taxon to fit new stuff in." Foley ventures: "I haven't the slightest idea of what H. erectus means." Indeed, H. erectus now includes the 1-million-year-old type specimen from Trinil on the island of Java as well as fossils from South Africa, East Africa, Georgia, Europe, and China that span roughly 300,000 to 1.9 million years. "They're putting everything into H. erectus over huge geographical distances, essentially spread throughout the whole world, and over a vast number of years," Johanson says. Yet no other species matches the Dmanisi specimens better, Rightmire says. For example, the shapes of their dental palate and skulls match those of H. erectus, not H. habilis. And the variation in skull size and facial shape is no greater than in other species, including both modern humans or chimps, says Ponce de León—especially when the growth of the jaw and face over a lifetime are considered. Though the fossils' small stature and brains might fit best with H. habilis, their relatively long legs and modern body proportions place them in H. erectus, says David Lordkipanidze, general director of the Georgian National Museum and head of the Dmanisi team. "We can't forget that these are not just heads rolling around, dispersing around the globe," Potts adds. Like Rightmire, he thinks the fossils represent an early, primitive form of H. erectus, which had evolved from a H. habilis–like ancestor and still bore some primitive features shared with H. habilis. Regardless of the Dmanisi people's precise identity, researchers studying them agree that the wealth of fossils and artifacts coming from the site offer rare evidence for a critical moment in the human saga. They show that it didn't take a technological revolution or a particularly big brain to cross continents. And they suggest an origin story for first migrants all across Asia: Perhaps some members of the group of primitive H. erectus that gave rise to the Dmanisi people also pushed farther east, where their offspring evolved into later, bigger-brained H. erectus on Java (at the same time as H. erectus in Africa was independently evolving bigger brains and bodies). "For me, Dmanisi could be the ancestor for H. erectus in Java," says paleoanthropologist Yousuke Kaifu of the National Museum of Nature and Science in Tokyo. In spite of the remaining mysteries about the ancient people who died on this windy promontory, they have already taught researchers lessons that extend far beyond Georgia. And for that, Lordkipanidze is grateful. At the end of a barbecue in the camp house here, he raised a glass of wine and offered a toast: "I want to thank the people who died here," he said.
News Article | November 19, 2015
Endocasts of the skulls of a hobbit (left) and a modern human (right). Research by Dean Falk of Florida State University and colleagues has suggested features of the hobbit's skull more closely resembled that of a normal human than a microcepha More An ancient, 3-foot-tall (0.9 meters) human whose diminutive stature has earned it the nickname "hobbit" has puzzled evolutionary scientists since its little bones were discovered on the Indonesian island of Flores. Some have suggested the individual was a Homo sapien with some miniaturizing disorder. Now, teeth from the hobbit suggest it belonged to a unique species rather than a modern human with a growth disorder. The new research also suggests hobbits may share a direct ancestor with modern humans. The 18,000-year-old fossil remains of the hobbit were discovered in 2003. Since then, scientists have suggested that the hobbit, which had a brain about the size of a grapefruit, was a unique branch of the human lineage Homo, dubbed Homo floresiensis. However, other researchers have argued the hobbit was really a modern human with microcephaly, a condition that leads to an abnormally small head, a small body and some mental retardation. [Real-Life Hobbit: See Photos of Homo floresiensis] To learn more about the hobbit, scientists have now performed the first comprehensive analysis of the ancient human's teeth. The researchers compared the 40 known hobbit teeth with those from 490 modern humans from Asia, Oceania, Africa and Europe, as well as from a variety of extinct hominins, such as Homo habilis, which is suspected to be among the first makers of stone tools. (Hominins consist of humans and their relatives dating after the split from the chimpanzee lineage.) The researchers found hobbit teeth were as small as those from short modern humans. However, other features of these teeth looked completely dissimilar from those of modern humans. The hobbit teeth displayed a unique mosaic of primitive traits seen in early hominins mixed with more-advanced traits seen in later hominins, the researchers said. For instance, the canine and premolar teeth looked primitive, whereas the molar teeth looked advanced, or as if they had emerged later in the evolution of Homo sapiens, the scientists said. These findings contradict earlier claims that hobbits possessed teeth entirely like those of modern humans. The results also suggest hobbits were not just modern humans with severe abnormalities, the researchers said. The researchers found that the hobbit's primitive dental features are most similar to specimens of Homo erectus, the earliest undisputed ancestor of modern humans, from the Indonesian island of Java. However, H. erectus was about as tall as modern humans. The scientists suggest that on isolated islands, the ancestors of the hobbit underwent dramatic dwarfism, with their bodies shrinking from about 5.4 feet (1.65 m) to 3.6 feet (1.1 m), and brains dwindling from about 52 cubic inches (860 cubic centimeters) to 26 cubic inches (426 cubic cm). "For me, this work will turn the tide about the question of evolutionary origin of H. floresiensis," study lead author Yousuke Kaifu, a paleoanthropologist at Japan's National Museum of Nature and Science in Tokyo, told Live Science. While the human lineage generally evolved larger bodies and brains over time, the hobbit suggests that isolation on islands could substantially reverse this evolutionary trend, Kaifu said. The scientists detailed their findings online Nov. 18 in the journal PLOS ONE. Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Hidaka H.,Hiroshima University |
Yoneda S.,National Museum of Nature and Science
Geochimica et Cosmochimica Acta | Year: 2011
Barium isotopic compositions of chemical leachates from six carbonaceous chondrites, Orgueil (CI), Mighei (CM2), Murray (CM2), Efremovka (CV3), Kainsaz (CO3), and Karoonda (CK4), were determined using thermal ionization mass spectrometry in order to assess the chemical evolution in the early solar system. The Ba isotopic data from most of the leachates show variable 135Ba excesses correlated with 137Ba excesses, suggesting the presence and heterogeneity of additional nucleosynthetic components for s- and r-processes in the solar system. The isotopic deviations observed in this study were generally small (-1<ε<+1) except in the case of the acid residues of CI and CM meteorites. Large deviations of 135Ba (ε=-13.5 to -5.0) and 137Ba (ε=-6.2∼-1.2) observed in the acid residues from one CI and two CM meteorites show significant evidence for the enrichment of s-process isotopes derived from presolar grains. Two models were proposed to estimate the 135Cs isotopic abundances by subtraction of the s- and r-isotopic components from the total Ba isotopic abundances in the three CM meteorites, Mighei, Murchison (measured in a previous study), and Murray. The data points show individual linear trends between 135Cs/136Ba ratios and 135Ba isotopic deviations for the three samples. Considering the different trends observed in the three CM meteorites, the Ba isotopic composition of the CM meteorite parent body was heterogeneous at its formation. Chronological information is unclear in the data for Murchison and Murray because of large analytical uncertainties imposed by error propagation. Only the Mighei meteorite data indicate the possible existence of presently extinct 135Cs (135Cs/133Cs=(2.7±1.6)×10-4) in the early solar system. Another explanation of the data for the three CM meteorite is mixing of at least three components with different Ba isotopic compositions, although this is model-dependent. © 2011 Elsevier Ltd.
Gross A.,ETH Zurich |
Hosoya T.,National Museum of Nature and Science |
Queloz V.,ETH Zurich
Molecular Ecology | Year: 2014
Understanding the genetic diversity and structure of invasive pathogens in source and in introduced areas is crucial to the revelation of hidden biological features of an organism, to the reconstruction of the course of invasions and to the establishment of effective control measures. Hymenoscyphus pseudoalbidus (anamorph: Chalara fraxinea) is an invasive and highly destructive fungal pathogen found on common ash Fraxinus excelsior in Europe and is native to East Asia. To gain insights into its dispersal mechanisms and history of invasion, we used microsatellite markers and characterized the genetic structure and diversity of H. pseudoalbidus populations at three spatial levels: (i) between Europe and Japan, (ii) in Europe and (iii) at the epidemic's front in Switzerland. Phylogenetic and network analysis demonstrated that individuals from both regions are conspecific. However, populations from Japan harboured a higher genetic diversity and were genetically differentiated from European ones. No evident population structure was found among the 1208 European strains using Bayesian and multivariate clustering analysis. Only the distribution of genetic diversity in space, pairwise population differentiation (GST) and the spatial analysis of principal components revealed a faint geographical pattern around Europe. A significant allele deficiency in most European populations pointed to a recent genetic bottleneck, whereas no pattern of isolation by distance was found. Our data suggest that H. pseudoalbidus was introduced just once by at least two individuals. The potential source region of H. pseudoalbidus is vast, and further investigations are required for a more accurate localization of the source population. © 2014 John Wiley & Sons Ltd.
News Article | December 3, 2015
Before baleen whales developed their iconic bristled filter-feeding structures, they relied on their pointy teeth and a suctioning method to nab and gulp down prey, a new study finds. The findings are based on the fossilized remains of a newfound species of early baleen whale. Paleontologists Jim Goedert and Bruce Crowley, both researchers at the Burke Museum at the University of Washington in Seattle, discovered the fossilized whale off the northern tip of Washington's Olympic Peninsula. At 30 million to 33 million years old, the newly identified species of whale is one of the oldest and smallest known baleen whales to swim around Earth's oceans, said Felix Marx, a postdoctoral fellow at the National Museum of Nature and Science of Japan and the study's lead researcher. [Whale Album: Photos Reveal Giants of the Deep] The whale measured just over 6.5 feet (2 meters) long, making it much smaller than today's smallest baleen whale, the 21-foot-long (6.4 m) pygmy right whale, and almost 14 times smaller than the 90-foot-long (27.5 m) blue whale, the largest modern baleen whale. Moreover, the newfound whale skeleton has 17 preserved teeth — a finding that reveals information about how these early whales hunted and fed, Marx said. He and his colleagues named the new species Fucaia buelli after the Strait of Juan de Fuca, where they found the whale, and Carl Buell, an illustrator known for drawing living and extinct marine animals. "Instead, they filter small animals directly from the water using a series of comblike baleen plates suspended from their upper jaws," Marx told Live Science in an email. But the baleen whales' ancestors — including F. buelli — did have teeth, raising the question of how baleen whales lost their teeth without losing the ability to hunt and feed during the transition to baleen-only feeding. Some studies suggest that ancient whales had teeth and then developed baleen before losing their teeth. "However, Fucaia now shows that the transition was probably more complex," Marx said. "The teeth of Fucaia are so large that they line the entire upper jaw, and thus simply leave no room for baleen. Wear on the teeth also shows that the upper and lower teeth sheared against each other as the mouth opened and closed; thus, any baleen that might have been present would constantly have been caught between the teeth." Even without baleen plates, F. buelli would have been a successful hunter, Marx said. The researchers suggested that the whale used its teeth and a suctioning technique to capture prey, or at least it caught prey with its teeth, and then sucked it to the back of its mouth to swallow it. "Suction feeding is common among living marine mammals, and seen in many [living] toothed whales and dolphins, as well as the gray whale," Marx said. Two key features suggest that F. buelli used this suctioning to filter food from the water, he said. First, the fossils indicate that the whale had large gums, which could have helped the creature seal off the sides of its mouth when its jaws were slightly opened. "The effect of this would be to reduce the size of the mouth opening, and thus to concentrate the flow created by suction at the tip of the snout," Marx said. [Marine Marvels: Spectacular Photos of Sea Creatures] Secondly, living whales create suction in their mouths by using strong muscles to pull the tongue and throat backward and downward. Fossil evidence suggests that some of these muscles were well developed in F. buelli, Marx said. This suctioning technique could have eased the transition from toothy to baleen-only whales, he said. "As whales evolved better suction, they were able to catch smaller prey than teeth alone could handle but, at the same time, needed a more efficient way to expel the water sucked in with the food," Marx said. "This need is perfectly matched by baleen, which developed from the already enlarged gums and provided an easy way to expel excess water while, at the same time, retaining the prey inside the mouth." The new study is an exciting "solid paper," said Jorge Velez-Juarbe, a curator of marine mammals at the Natural History Museum of Los Angeles County who was not involved in the new study.
News Article | November 21, 2015
Ancient tiny people known as hobbits, a product of the so-called “island effect,” evolved from large-bodied Homo erectus hailing from Asia, as a pioneering review of their teeth recently showed. The new study suggests that a look at the Homo floresiensis, whose remains were discovered in Indonesian island Flores, offers the possibility of a bit of hobbit in humans today. Early modern humans might have interbred with Homo erectus from Asia at a small scale. The hobbit shrank because of the effects of “insular dwarfism,” where a population evolves given smaller isolated islands and fewer available resources in their limited-range surroundings. The team, led by project leader Yousuke Kaifu of Tokyo’s National Museum of Nature and Science, compared the hobbits’ teeth with those of 490 Homo sapiens people along with different ancient and already extinct humans. The toothy findings showed that these ancient humans’ pearly whites are both primitive and modern, and reflect hobbit-related human lineage – distinct from Africa’s, which had evolved in Asia and had spread to other areas. The teeth and skull of the hobbit closely resembled those of Java Man, a member of Asian Homo erectus. This means that in a relatively short span of time, the hobbit shrank from around five feet to just over three feet. Their brains also turned smaller by more than half, from around 1.8 pounds to a little over 0.8 pound. The hobbits were estimated to have been around for a while, as indicated by stone tools as old as a million years ago on the island, and to have gone extinct about 13,000 years past. "I think it is quite possible that they met with early modern humans, who expanded from Africa into Australia around 50,000 years ago," speculated Kaifu. From there on, the story of the hobbit is shrouded in mystery, whether they were wiped out by disease or mass killings or they were integrated in the Homo sapiens population. The ancient humans’ teeth continue to puzzle experts, including anthropologist Dr. María Martinón-Torres from University College London. For instance, the molars appeared to have only four cusps compared to five cusps in most primitive humans. Martinón-Torres added that these ancient human species are entirely different from anything she has studied yet they cannot be considered merely as a scaled-down version of humans. For Kaifu, the study will reverse the trend about the question of evolutionary origin of Homo floresiensis while the hobbit becomes an example of how island isolation could dramatically change the evolutionary process. The research was published on Nov. 18 in the journal PLOS One.
Hayashi T.,National Museum of Nature and Science
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011
The almost monospecific assemblages of planktonic diatoms that occurred in ancient lakes during the middle Brunhes Chron are an important research issue for lake ecosystems because their existence implies that the famous paradox of the plankton was no paradox at that time. To investigate their cause, I examined the assemblage structure and diversity of planktonic diatoms in the Paleo-Kathmandu Lake at Nepal Himalaya over the past 600. kyr. The assemblage structure changes frequently after 300. ka but remains nearly stable before then. Additionally, planktonic species show a relatively high average diversity after 300. ka but show an extremely low average before then. Those abnormal ecological conditions before 300. ka reflect the formation of almost monospecific planktonic diatom assemblages of Cyclotella kathmanduensis and Puncticulata versiformis. The assemblage structure and species diversity of the planktonic diatoms were controlled by lake-level fluctuations (especially lake-level declines) as ecological disturbances. After 300. ka, fluctuations in lake levels occur in about 20. ka intervals, which probably helped to sustain diverse planktonic diatom assemblages. In contrast, much longer intervals occurred between lake-level fluctuations before 300. ka, and these were of a frequency that was too low to sustain diverse planktonic diatom assemblages. This may have allowed C. kathmanduensis and P. versiformis to form monospecific assemblages. © 2010 Elsevier B.V.
Momma K.,National Museum of Nature and Science
Journal of Physics Condensed Matter | Year: 2014
A review on silica clathrate compounds, which are variants of pure silica zeolites with relatively small voids, is presented. Zeolites have found many uses in industrial and domestic settings as materials for catalysis, separations, adsorption, ion exchange, drug delivery, and other applications. Zeolites with pure silica frameworks have attracted particular interest because of their high thermal stability, well-characterized framework structures, and simple chemical compositions. Recent advances in new synthetic routes have extended the structural diversity of pure silica zeolite frameworks. Thermochemical analyses and computational simulations have provided a basis for applications of these materials and the syntheses of new types of pure silica zeolites. High-pressure and high-temperature experiments have also revealed diverse responses of these framework structures to pressure, temperature, and various guest species. This paper summarizes the framework topologies, synthetic processes, energetics, physical properties, and some applications of silica clathrate compounds. © 2014 IOP Publishing Ltd.
Momma K.,National Museum of Nature and Science
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2014
A review on silica clathrate compounds, which are variants of pure silica zeolites with relatively small voids, is presented. Zeolites have found many uses in industrial and domestic settings as materials for catalysis, separations, adsorption, ion exchange, drug delivery, and other applications. Zeolites with pure silica frameworks have attracted particular interest because of their high thermal stability, well-characterized framework structures, and simple chemical compositions. Recent advances in new synthetic routes have extended the structural diversity of pure silica zeolite frameworks. Thermochemical analyses and computational simulations have provided a basis for applications of these materials and the syntheses of new types of pure silica zeolites. High-pressure and high-temperature experiments have also revealed diverse responses of these framework structures to pressure, temperature, and various guest species. This paper summarizes the framework topologies, synthetic processes, energetics, physical properties, and some applications of silica clathrate compounds.
Reconstructions of the axial muscle insertions in the occipital region of dinosaurs: Evaluations of past hypotheses on marginocephalia and tyrannosauridae using the extant phylogenetic bracket approach
Tsuihiji T.,National Museum of Nature and Science
Anatomical Record | Year: 2010
The insertions of the cervical axial musculature on the occiput in marginocephalian and tyrannosaurid dinosaurs have been reconstructed in several studies with a view to their functional implications. Most of the past reconstructions on marginocephalians, however, relied on the anatomy of just one clade of reptiles, Lepidosauria, and lack phylogenetic justification. In this study, these past reconstructions were evaluated using the Extant Phylogenetic Bracket approach based on the anatomy of various extant diapsids. Many muscle insertions reconstructed in this study were substantially different from those in the past studies, demonstrating the importance of phylogenetically justified inferences based on the conditions of Aves and Crocodylia for reconstructing the anatomy of non-avian dinosaurs. The present reconstructions show that axial muscle insertions were generally enlarged in derived marginocephalians, apparently correlated with expansion of their parietosquamosal shelf/frill. Several muscle insertions on the occiput in tyrannosaurids reconstructed in this study using the Extant Phylogenetic Bracket approach were also rather different from recent reconstructions based on the same, phylogenetic and parsimony-based method. Such differences are mainly due to differences in initial identifications of muscle insertion areas or different hypotheses on muscle homologies in extant diapsids. This result emphasizes the importance of accurate and detailed observations on the anatomy of extant animals as the basis for paleobiological inferences such as anatomical reconstructions and functional analyses. © 2010 Wiley-Liss, Inc.