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The Kondo lattice, describing a matrix of local magnetic moments coupled via spin-exchange interactions to itinerant conduction electrons, is a prototype of strongly correlated quantum matter. Traditionally, Kondo lattices are realized in intermetallic compounds containing lanthanide or actinide. The complex electronic structure and limited tunability of both the electron density and exchange interactions in these bulk materials pose significant challenges to study Kondo lattice physics. Here, we report the realization of a synthetic Kondo lattice in AB-stacked MoTe2/WSe2 moiré bilayers, where the MoTe2 layer is tuned to a Mott insulating state, supporting a triangular moiré lattice of local moments, and the WSe2 layer is doped with itinerant conduction carriers. We observe heavy fermions with a large Fermi surface below the Kondo temperature. We also observe destruction of the heavy fermions by an external magnetic field with an abrupt decrease of the Fermi surface size and quasiparticle mass. We further demonstrate widely and continuously gate-tunable Kondo temperatures through either the itinerant carrier density or Kondo interaction. Our study opens the possibility of in-situ access to the rich phase diagram of the Kondo lattice with exotic quantum criticalities in a single device based on semiconductor moiré materials.

The deep structure of the continental collision between India and Asia and whether India's lower crust is underplated beneath Tibet or subducted into the mantle remain controversial. It is also unknown whether the active normal faults that facilitate orogen-parallel extension of Tibetan upper crust continue into the lower crust and upper mantle. Our receiver-function images collected parallel to the India-Tibet collision zone show the 20-km-thick Indian lower crust that underplates Tibet at 88.5-92°E beneath the Yarlung-Zangbo suture is essentially absent in the vicinity of the Cona-Sangri and Pumqu-Xainza grabens, demonstrating a clear link between upper-crustal and lower-crustal thinning. Satellite gravity data that covary with the thickness of Indian lower crust are consistent with the lower crust being only ∼30% eclogitized so gravitationally stable. Deep earthquakes coincide with Moho offsets and with lateral thinning of the Indian lower crust near the bottom of the partially eclogitized Indian lower crust, suggesting the Indian lower crust is locally foundering or stoping into the mantle. Loss of Indian lower crust by these means implies gravitational instability that can result from localized rapid eclogitization enabled by dehydration reactions in weakly hydrous mafic granulites or by volatile-rich asthenospheric upwelling directly beneath the two grabens. We propose that two competing processes, plateau formation by underplating and continental loss by foundering or stoping, are simultaneously operating beneath the collision zone.

The Sinacanthida ordo nov. and Mongolepidida are spine- and scale-based taxa whose remains encompass some of the earliest reported fossils of chondrichthyan fish. Investigation of fragmentary material from the Early Silurian Tataertag and Ymogantau Formations of the Tarim Basin (Xinjiang Uygur Autonomous Region, China) has revealed a diverse mongolepidid and sinacanthid fauna dominated by mongolepids and sinacanthids in association with abundant dermoskeletal elements of the endemic ‘armoured’ agnathans known as galeaspids.Micro-computed tomography, scanning electron microscopy and histological sections were used to identify seven mongolepid genera (including Tielikewatielepis sinensis gen. et sp. nov., Xiaohaizilepis liui gen. et sp. nov. and Taklamakanolepis asiaticus gen. et sp. nov.) together with a new chondrichthyan (Yuanolepis bachunensis gen. et sp. nov.) with scale crowns consisting of a mongolepid-type atubular dentine (lamellin). Unlike the more elaborate crown architecture of mongolepids, Yuanolepis gen. nov. exhibits a single row of crown elements consistent with the condition reported in stem chondrichthyans from the Lower Devonian (e.g. in Seretolepis, Parexus). The results corroborate previous work by recognising lamellin as the main component of sinacanthid spines and point to corresponding developmental patterns shared across the dermal skeleton of taxa with lamellin and more derived chondrichthyans (e.g. Doliodus, Kathemacanthus, Seretolepis and Parexus).The Tarim mongolepid fauna is inclusive of coeval taxa from the South China Block and accounts for over two-thirds of the species currently attributed to Mongolepidida. This demonstrates considerable overlap between the Tarim and South China components of the Lower Silurian Zhangjiajie Vertebrate Fauna.

The discovery of Entelognathus revealed the presence of maxilla, premaxilla, and dentary, supposedly diagnostic osteichthyan bones, in a Silurian placoderm. However, the relationship between these marginal jaw bones and the gnathal plates of conventional placoderms, thought to represent the inner dental arcade, remains uncertain. Here we report a second Silurian maxillate placoderm, which bridges the gnathal and maxillate conditions. We propose that the maxilla, premaxilla, and dentary are homologous to the gnathal plates of placoderms and that all belong to the same dental arcade. The gnathal-maxillate transformation occurred concurrently in upper and lower jaws, predating the addition of infradentary bones to the lower jaw.

In classic orogenic models, the mountain range is underlain by a deep crustal root. Here we present the crustal and upper mantle structures along two receiver function profiles across Qilian, an orogen experiencing recent growth at the northern margin of the Tibetan plateau. Opposite to an expected crustal root beneath the orogen, the Moho beneath Qilian is arch-like, shallower beneath the center and deepens by up to 10 km beneath its southern and northern boundaries. Additional velocity interfaces sub-parallel to the Moho are observed in the lower crust of the basins south of Qilian, which we interpret as the top of a mechanically strong lower crust thrusting several tens of kilometers underneath Qilian. In the north, the small lateral offset between the surface and mantle traces of the thrust system reveals a steep boundary, indicating that the North China cratonic crust acts as a strong resistance to the northward growth of the plateau, forcing the development of the left-lateral strike-slip Haiyuan fault south of the northern Qilian suture. The young Qilian orogen thus has been rising and growing progressively from the boundaries to the center, squeezed up by more rigid tectonic blocks in the north and south.

Copyright: © 2017 Choo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited., Our understanding of early gnathostome evolution has been hampered by a generally scant fossil record beyond the Devonian. Recent discoveries from the late Silurian Xiaoxiang Fauna of Yunnan, China, have yielded significant new information, including the earliest articulated osteichthyan fossils from the Ludlow-aged Kuanti Formation. Here we describe the partial postcranium of a new primitive bony fish from the Kuanti Formation that represents the second known taxon of pre-Devonian osteichthyan revealing articulated remains. The new form, Sparalepis tingi gen. et sp. nov., displays similarities with Guiyu and Psarolepis, including a spine-bearing pectoral girdle and a placoderm-like dermal pelvic girdle, a structure only recently identified in early osteichthyans. The squamation with particularly thick rhombic scales shares an overall morphological similarity to that of Psarolepis. However, the anterior flank scales of Sparalepis possess an unusual interlocking system of ventral bulges embraced by dorsal concavities on the outer surfaces. A phylogenetic analysis resolves Sparalepis within a previously recovered cluster of stem-sarcopterygians including Guiyu, Psarolepis and Achoania. The high diversity of osteichthyans from the Ludlow of Yunnan strongly contrasts with other Silurian vertebrate assemblages, suggesting that the South China block may have been an early center of diversification for early gnathostomes, well before the advent of the Devonian “Age of Fishes”.

A 409-million-year-old predatory fish provides unique insights into the early evolution of modern lobe-finned fishes., Crown or modern sarcopterygians (coelacanths, lungfishes, and tetrapods) differ substantially from stem sarcopterygians, such as Guiyu and Psarolepis, and a lack of transitional fossil taxa limits our understanding of the origin of the crown group. The Onychodontiformes, an enigmatic Devonian predatory fish group, seems to have characteristics of both stem and crown sarcopterygians but is difficult to place because of insufficient anatomical information. We describe the new skull material of Qingmenodus, a Pragian (~409-million-year-old) onychodont from China, using high-resolution computed tomography to image internal structures of the braincase. In addition to its remarkable similarities with stem sarcopterygians in the ethmosphenoid portion, Qingmenodus exhibits coelacanth-like neurocranial features in the otic region. A phylogenetic analysis based on a revised data set unambiguously assigns onychodonts to crown sarcopterygians as stem coelacanths. Qingmenodus thus bridges the morphological gap between stem sarcopterygians and coelacanths and helps to illuminate the early evolution and diversification of crown sarcopterygians.

The 438-370-million-year-old galeaspids, diversified armoured jawless vertebrates ('ostracoderms') from China and northern Vietnam, were assumed to have a benthic feeding habit in a coastal, marine environment. Here, we describe two new genera of galeaspid fishes, Platylomaspis gen. nov. and Nanningaspis gen. nov. from the Middle Palaeozoic of China. The two new forms are characterized by a rostral process and strikingly broad ventral rim, and clustered with Gumuaspis to form a new family, Gumuaspidae, which represents the most primitive clade of Polybranchiaspiformes. They extend the earliest occurrence of Polybranchiaspiformes backward about 19 million years, and expand its geographical distribution from southern China and northern Vietnam to the Tarim Basin, northwestern China. The new taxa exhibit many morphological convergences with modern rays, and might specify a new kind of lifestyle of galeaspids, the half burrowing habit. Probably benefiting from the new lifestyle, the Gumuaspidae has become the longest lasting galeaspid family. The new findings demonstrated that the demersal galeaspids had developed three different kinds of lifestyles: semi-infaunal benthic (half buried), epibenthic, and suprabenthic (nektonic) habits to accommodate to differentiated ecological niches, and reached the peak of their diversity by the Pragian of the Early Devonian.

The evolutionary history of osteichthyans (bony fishes plus tetrapods) extends back to the Ludlow epoch of the Silurian period. However, these Silurian forms have been documented exclusively by fragmentary fossils. Here we report the discovery of an exceptionally preserved primitive fish from the Ludlow of Yunnan, China, that represents the oldest near-complete gnathostome (jawed vertebrate). The postcranial skeleton of this fish includes a primitive pectoral girdle and median fin spine as in non-osteichthyan gnathostomes, but a derived macromeric squamation as in crown osteichthyans, and substantiates the unexpected mix of postcranial features in basal sarcopterygians, previously restored from the disarticulated remains of Psarolepis. As the oldest articulated sarcopterygian, the new taxon offers insights into the origin and early divergence of osteichthyans, and indicates that the minimum date for the actinopterygian-sarcopterygian split was no later than 419 million years ago.

An apparent absence of Silurian fishes more than half-a-metre in length has been viewed as evidence that gnathostomes were restricted in size and diversity prior to the Devonian. Here we describe the largest pre-Devonian vertebrate (Megamastax amblyodus gen. et sp. nov.), a predatory marine osteichthyan from the Silurian Kuanti Formation (late Ludlow, ~423 million years ago) of Yunnan, China, with an estimated length of about 1 meter. The unusual dentition of the new form suggests a durophagous diet which, combined with its large size, indicates a considerable degree of trophic specialisation among early osteichthyans. The lack of large Silurian vertebrates has recently been used as constraint in palaeoatmospheric modelling, with purported lower oxygen levels imposing a physiological size limit. Regardless of the exact causal relationship between oxygen availability and evolutionary success, this finding refutes the assumption that pre-Emsian vertebrates were restricted to small body sizes.

The gnathostome (jawed vertebrate) crown group comprises two extant clades with contrasting character complements. Notably, Chondrichthyes (cartilaginous fish) lack the large dermal bones that characterize Osteichthyes (bony fish and tetrapods). The polarities of these differences, and the morphology of the last common ancestor of crown gnathostomes, are the subject of continuing debate. Here we describe a three-dimensionally preserved 419-million-year-old placoderm fish from the Silurian of China that represents the first stem gnathostome with dermal marginal jaw bones (premaxilla, maxilla and dentary), features previously restricted to Osteichthyes. A phylogenetic analysis places the new form near the top of the gnathostome stem group but does not fully resolve its relationships to other placoderms. The analysis also assigns all acanthodians to the chondrichthyan stem group. These results suggest that the last common ancestor of Chondrichthyes and Osteichthyes had a macromeric dermal skeleton, and provide a new framework for studying crown gnathostome divergence.

INDEPTH geophysical and geological observations imply that a partially molten midcrustal layer exists beneath southern Tibet. This partially molten layer has been produced by crustal thickening and behaves as a fluid on the time scale of Himalayan deformation. It is confined on the south by the structurally imbricated Indian crust underlying the Tethyan and High Himalaya and is underlain, apparently, by a stiff Indian mantle lid. The results suggest that during Neogene time the underthrusting Indian crust has acted as a plunger, displacing the molten middle crust to the north while at the same time contributing to this layer by melting and ductile flow. Viewed broadly, the Neogene evolution of the Himalaya is essentially a record of the southward extrusion of the partially molten middle crust underlying southern Tibet.

Recent discoveries of advanced fish-like stem-tetrapods (for example, Panderichthys and Tiktaalik) have greatly improved our knowledge of the fin-to-limb transition. However, a paucity of fossil data from primitive finned tetrapods prevents profound understanding of the acquisition sequence of tetrapod characters. Here we report a new stem-tetrapod (Tungsenia paradoxa gen. et sp. nov.) from the Lower Devonian (Pragian, ∼409 million years ago) of China, which extends the earliest record of tetrapods by some 10 million years. Sharing many primitive features with stem-lungfishes, the new taxon further fills in the morphological gap between tetrapods and lungfishes. The X-ray tomography study of the skull depicts the plesiomorphic condition of the brain in the tetrapods. The enlargement of the cerebral hemispheres and the possible presence of the pars tuberalis in this stem-tetrapod indicate that some important brain modifications related to terrestrial life had occurred at the beginning of the tetrapod evolution, much earlier than previously thought.

Coelacanths are known for their evolutionary conservatism, and the body plan seen in Latimeria can be traced to late Middle Devonian Diplocercides, Holopterygius and presumably Euporosteus. However, the group's early history is unclear because of an incomplete fossil record. Until now, the only Early Devonian coelacanth is an isolated dentary (Eoactinistia) from Australia, whose position within the coelacanths is unknown. Here we report the earliest known coelacanth skull (Euporosteus yunnanensis sp. nov.) from the Early Devonian (late Pragian) of Yunnan, China. Resolved by maximum parsimony, maximum likelihood and Bayesian analyses as crownward of Diplocercides or as its sister taxon, the new form extends the chronological range of anatomically modern coelacanths by about 17 Myr. The finding lends support to the possibility that Eoactinistia is also an anatomically modern coelacanth, and provides a more refined reference point for studying the rapid early diversification and subsequent evolutionary conservatism of the coelacanths.

Ray-finned bony fish (ranging from cod to guppies) and lobe-finned bony fish (lungfish, coelacanths and the ancestors of the land vertebrates) were clearly once close relatives, but a large morphological gulf still separates fossils of both groups dating from times when they looked much more similar than they do now. A fossil of a primitive lobe-finned fish that combines many features found in both groups has now been discovered in the Yumman fossil beds in China, and this new species offers a bridgehead between the two distinct lines of fishy descent. A primitive fossil species of lobe-finned fish combines many histological features found in both ray-finned bony fishes and lobe-finned bony fishes. Osteichthyans, or bony vertebrates, include actinopterygians (teleosts and their relatives) and sarcopterygians (coelacanths, lungfishes and tetrapods). Despite features found in basal actinopterygians (for example, Dialipina and Ligulalepis)1,2,3 and basal sarcopterygians (for example, Psarolepis and Achoania)4,5, the morphological gap between the two lineages remains wide and how sarcopterygians developed a dermal surface covering known as cosmine (composed of a pore–canal network and a single layer of odontodes and enamel) is still poorly known6,7,8,9,10. Here we describe a primitive fossil fish, Meemannia eos gen. et sp. nov., that possesses an actinopterygian-like skull roof and a cosmine-like dermal surface combining a pore–canal network (found in various fossil sarcopterygians) with superimposed layers of odontodes and enamel (previously known in actinopterygians and some acanthodians11,12,13). This 405-million-year-old fish from the Lower Devonian of Yunnan (China) demonstrates that cosmine in many fossil sarcopterygians arose step by step through the acquisition of a pore–canal network followed by the subsequently developed ability to resorb previous generations of odontodes and enamel. Meemannia provides key characters for studying deep osteichthyan phylogeny and indicates a possible morphotype for the common ancestor of actinopterygians and sarcopterygians.

INDEPTH seismic reflection profiling shows that the decollement beneath which Indian lithosphere underthrusts the Himalaya extends at least 225 kilometers north of the Himalayan deformation front to a depth of approximately 50 kilometers. Prominent reflections appear at depths of 15 to 18 kilometers near where the decollement reflector apparently terminates. These reflections extend north of the Zangbo suture to the Damxung graben of the Tibet Plateau. Some of these reflections have locally anomalous amplitudes (bright spots) and coincident negative polarities implying that they are produced by fluids in the crust. The presence of geothermal activity and high heat flow in the regions of these reflections and the tectonic setting suggest that the bright spots mark granitic magmas derived by partial melting of the tectonically thickened crust.

Seismic data from central Tibet have been combined to image the subsurface structure and understand the evolution of the collision of India and Eurasia. The 410- and 660-kilometer mantle discontinuities are sharply defined, implying a lack of a subducting slab beneath the plateau. The discontinuities appear slightly deeper beneath northern Tibet, implying that the average temperature of the mantle above the transition zone is about 300°C hotter in the north than in the south. There is a prominent south-dipping converter in the uppermost mantle beneath northern Tibet that might represent the top of the Eurasian mantle lithosphere underthrusting the northern margin of the plateau.

THE Himalaya and adjacent Tibetan plateau, constituting Earth's largest region of elevated topography and anomalously thick crust, formed as a consequence of Cenozoic collision between India and Asia—itself considered the archetypal continent–continent collision1–3. Here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling. Our ∼100-km-long profile, acquired in the Tethyan Himalaya, shows a mid-crustal reflection that prob-ably marks the active thrust fault along which the Indian plate is underthrusting southern Tibet; upper-crustal reflections with geo-metries suggestive of large-scale structural imbrication of the upper crust; and Moho reflections from the base of the double-normal-thickness crust underlying the region. These results lend substantial support to the view that crustal thickening beneath southernmost Tibet was accomplished by wholesale underthrusting of Indian continental crust beneath the structurally imbricated upper crust comprising the Tethyan Himalaya.

Earthquake data collected by the INDEPTH-II Passive-Source Experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern Tibet. North of the Zangbo suture, beneath the southern Lhasa block, a midcrustal low-velocity zone is revealed by inversion of receiver functions, Rayleigh-wave phase velocities, and modeling of the radial component of teleseismic P-waveforms. Conversely, to the south beneath the Tethyan Himalaya, no low-velocity zone was observed. The presence of the midcrustal low-velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern Yadong-Gulu rift and possibly much of southern Tibet.

The earliest tetrapods (vertebrates with limbs rather than paired fins) date from the Late Devonian Period (370–354 million years ago)1,2 — nine genera have been described, all of which are from the Euramerican supercontinent that comprises Europe, north America and Greenland, apart from a single Gondwanan genus, Metaxygnathus, from Australia3,4,5. Here we report the discovery of the first Devonian tetrapod from Asia, a finding that substantially extends the geographical range of these animals and raises new questions about their dispersal. These forms seem to have achieved worldwide distribution and great taxonomic diversity within a relatively short time.

Three-component wide-angle seismic data acquired in southern Tibet during Project INDEPTH show strong P-to-S converted reflections from reflectors that are aligned at a depth of approximately 15 kilometers beneath the northern Yadong-Gulu rift. These converted reflections are locally higher in amplitude than the corresponding P-wave reflections. Modeling of reflection mode conversion as a function of incidence angle indicates that this condition obtains for a reflector that is a solid over fluid interface; it is not typical of a solid-solid interface. The likely candidates for a fluid trapped within the crystalline crust of southern Tibet are granitic magma and water (brine).