A primitive sarcopterygian fish with an eyestalk

The discovery of two Early Devonian osteichthyan (bony fish) fossils has challenged established ideas about the origin of osteichthyans and their divergence into actinopterygians (teleosts and their relatives) and sarcopterygians (tetrapods, coelacanths, lungfishes and related groups). Psarolepis from China and an unnamed braincase from Australia combine derived sarcopterygian and actinopterygian characters with primitive features previously restricted to non-osteichthyans, suggesting that early osteichthyan evolution may have involved substantial parallellism between sarcopterygians and actinopterygians. But interpretation of these fossils has been hampered by poor phylogenetic resolution. Here we describe a basal sarcopterygian fish, Achoania gen, et sp. nov., that fills the morphological gap between Psarolepis and higher sarcoptergyians. We also report the presence of eyestalk attachments in both Achoania and Psarolepis, showing that this supposedly non-osteichthyan feature occurs in basal sarcopterygians as well as the actinoptergyian-like Australian braincase.     

A primitive fish close to the common ancestor of tetrapods and lungfish

The relationship of the three living groups of sarcopterygians or lobe-finned fish (tetrapods, lungfish and coelacanths) has been a matter of debate. Although opinions still differ, most recent phylogenies suggest that tetrapods are more closely related to lungfish than to coelacanths. However, no previously known fossil taxon exhibits a concrete character combination approximating the condition expected in the last common ancestor of tetrapods and lungfish -- and it is still poorly understood how early sarcopterygians diverged into the tetrapod lineage (Tetrapodomorpha) and the lungfish lineage (Dipnomorpha). Here we describe a fossil sarcopterygian fish, Styloichthys changae gen. et sp. nov., that possesses an eyestalk and which exhibits the character combination expected in a stem group close to the last common ancestor of tetrapods and lungfish. Styloichthys from the Lower Devonian of China bridges the morphological gap between stem-group sarcopterygians (Psarolepis and Achoania) and basal tetrapodomorphs/basal dipnomorphs. It provides information that will help in the study of the relationship of early sarcopterygians, and which will also help to resolve the tetrapod-lungfish divergence into a documented sequence of character acquisition.     

A Devonian tetrapod-like fish and the evolution of the tetrapod body plan

The relationship of limbed vertebrates (tetrapods) to lobe-finned fish (sarcopterygians) is well established, but the origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes. Here we report the discovery of a well-preserved species of fossil sarcopterygian fish from the Late Devonian of Arctic Canada that represents an intermediate between fish with fins and tetrapods with limbs, and provides unique insights into how and in what order important tetrapod characters arose. Although the body scales, fin rays, lower jaw and palate are comparable to those in more primitive sarcopterygians, the new species also has a shortened skull roof, a modified ear region, a mobile neck, a functional wrist joint, and other features that presage tetrapod conditions. The morphological features and geological setting of this new animal are suggestive of life in shallow-water, marginal and subaerial habitats.     

A Cretaceous terrestrial snake with robust hindlimbs and a sacrum

It has commonly been thought that snakes underwent progressive loss of their limbs by gradual diminution of their use. However, recent developmental and palaeontological discoveries suggest a more complex scenario of limb reduction, still poorly documented in the fossil record. Here we report a fossil snake with a sacrum supporting a pelvic girdle and robust, functional legs outside the ribcage. The new fossil, from the Upper Cretaceous period of Patagonia, fills an important gap in the evolutionary progression towards limblessness because other known fossil snakes with developed hindlimbs, the marine Haasiophis, Pachyrhachis and Eupodophis, lack a sacral region. Phylogenetic analysis shows that the new fossil is the most primitive (basal) snake known and that all other limbed fossil snakes are closer to the more advanced macrostomatan snakes, a group including boas, pythons and colubroids. The new fossil retains several features associated with a subterranean or surface dwelling life that are also present in primitive extant snake lineages, supporting the hypothesis of a terrestrial rather than marine origin of snakes.     

The oldest articulated chondrichthyan from the Early Devonian period

Chondrichthyans (including living sharks, skates, rays and chimaeras) have a fossil record of scales and dermal denticles perhaps dating back to the Late Ordovician period, about 455 million years ago. Their fossil tooth record extends to the earliest Devonian period, almost 418 million years ago, whereas the oldest known articulated shark remains date from the Early Devonian period, about 394 million years ago. Here we report the discovery of an articulated shark that is almost 409 million years old from the Early Devonian (early Emsian) period of New Brunswick, Canada. The specimen, identified as Doliodus problematicus (Woodward), sheds light on the earliest chondrichthyans and their interrelationships with basal jawed vertebrates. This species has been truly problematic. Previously known only from isolated teeth, it has been identified as an acanthodian and a chondrichthyan. This specimen is the oldest shark showing the tooth families in situ, and preserves one of the oldest chondrichthyan braincases. More notably, it shows the presence of paired pectoral fin-spines, previously unknown in cartilaginous fishes.     

The pectoral fin of Panderichthys and the origin of digits

One of the identifying characteristics of tetrapods (limbed vertebrates) is the presence of fingers and toes. Whereas the proximal part of the tetrapod limb skeleton can easily be homologized with the paired fin skeletons of sarcopterygian (lobe-finned) fish, there has been much debate about the origin of digits. Early hypotheses interpreted digits as derivatives of fin radials, but during the 1990s the idea gained acceptance that digits are evolutionary novelties without direct equivalents in fish fin skeletons. This was partly based on developmental genetic data, but also substantially on the pectoral fin skeleton of the elpistostegid (transitional fish/tetrapod) Panderichthys, which appeared to lack distal digit-like radials. Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like 'ulnare' of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more tetrapod-like than that found in Tiktaalik and, in combination with new data about fin development in basal actinopterygians, sharks and lungfish, makes a strong case for fingers not being a novelty of tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish.     

The most primitive osteichthyan braincase?

Most living vertebrates, from teleosts to tetrapods, are osteichthyans (bony fishes), but the origin of this major group is poorly understood. The actinopterygians (ray-finned bony fishes) are the most successful living vertebrates in terms of diversity. They appear in the fossil record in the Late Silurian but are poorly known before the Late Devonian. Here we report the discovery of the oldest and most primitive actinopterygian-like osteichthyan braincase known, from 400-million-year-old limestone in southeastern Australia. This specimen displays previously unknown primitive conditions, in particular, an opening for a cartilaginous eyestalk. It provides an important and unique counterpart to the similarly aged and recently described Psarolepis from China and Vietnam. The contrasting features of these specimens, and the unusual anatomy of the new specimen in particular, provide new insights into anatomical conditions close to the evolutionary radiation of all modern osteichthyan groups.     

Lamprey-like gills in a gnathostome-related Devonian jawless vertebrate

So far, the Palaeozoic fossil jawless vertebrates have not provided any direct evidence for the organization of the gills, apart from vague impressions--supposedly left by gill filaments--on the bony surface of the gill chamber in certain armoured forms or 'ostracoderms' (for example, osteostracans and heterostracans). The latter are currently regarded as more closely related to the living jawed vertebrates (crown gnathostomes) than to the living jawless vertebrates (hagfish and lampreys, or cyclostomes). Here we report the first direct evidence for the position of the gill filaments--possibly supported by gill rays--enclosed by gill pouches in a 370-million year (Myr)-old jawless vertebrate, Endeiolepis, from the Late Devonian fossil fish site of Miguasha, Quebec, Canada. This extinct jawless fish has much the same gill organization as living lampreys, although it possesses an unusually large number of gill pouches--a condition unlike that in any extant vertebrates and that raises questions about gill development. Endeiolepis is currently regarded as a close relative of anaspids, a group of 410-430-Myr-old 'ostracoderms'. Assuming that current vertebrate phylogeny is correct, this discovery demonstrates that pouches enclosing the gills are primitive for vertebrates, but have been subsequently lost in jawed vertebrates.     

A new species of great ape from the late Miocene epoch in Ethiopia

With the discovery of Ardipithecus, Orrorin and Sahelanthropus, our knowledge of hominid evolution before the emergence of Pliocene species of Australopithecus has significantly increased, extending the hominid fossil record back to at least 6 million years (Myr) ago. However, because of the dearth of fossil hominoid remains in sub-Saharan Africa spanning the period 12-7 Myr ago, nothing is known of the actual timing and mode of divergence of the African ape and hominid lineages. Most genomic-based studies suggest a late divergence date-5-6 Myr ago and 6-8 Myr ago for the human-chimp and human-gorilla splits, respectively-and some palaeontological and molecular analyses hypothesize a Eurasian origin of the African ape and hominid clade. We report here the discovery and recognition of a new species of great ape, Chororapithecus abyssinicus, from the 10-10.5-Myr-old deposits of the Chorora Formation at the southern margin of the Afar rift. To the best of our knowledge, these are the first fossils of a large-bodied Miocene ape from the African continent north of Kenya. They exhibit a gorilla-sized dentition that combines distinct shearing crests with thick enamel on its 'functional' side cusps. Visualization of the enamel-dentine junction by micro-computed tomography reveals shearing crest features that partly resemble the modern gorilla condition. These features represent genetically based structural modifications probably associated with an initial adaptation to a comparatively fibrous diet. The relatively flat cuspal enamel-dentine junction and thick enamel, however, suggest a concurrent adaptation to hard and/or abrasive food items. The combined evidence suggests that Chororapithecus may be a basal member of the gorilla clade, and that the latter exhibited some amount of adaptive and phyletic diversity at around 10-11 Myr ago.     

面向STEP-NC自由曲面特征的加工操作方法智能决策

为提升复杂零件工艺规划的集成化和智能化,提出一种基于混合算法面向STEP-NC自由曲面特征的加工操作方法智能决策方法.首先,构建了面向STEP-NC自由曲面特征的加工操作方法决策BP神经网络模型.然后,基于自适应视野策略、自适应步长策略和混沌算法给出了改进的人工鱼群算法,并与BP神经网络相融合设计了用于STEP-NC自由曲面特征加工操作方法决策的混合算法.并利用归一化的零件加工信息实现了STEP-NC自由曲面特征的加工操作方法高效智能决策.最后,通过实例验证了该方法的有效性和可行性.     

Using the fossil record to estimate the age of the last common ancestor of extant primates

Divergence times estimated from molecular data often considerably predate the earliest known fossil representatives of the groups studied. For the order Primates, molecular data calibrated with various external fossil dates uniformly suggest a mid-Cretaceous divergence from other placental mammals, some 90 million years (Myr) ago, whereas the oldest known fossil primates are from the basal Eocene epoch (54-55 Myr ago). The common ancestor of primates should be earlier than the oldest known fossils, but adequate quantification is needed to interpret possible discrepancies between molecular and palaeontological estimates. Here we present a new statistical method, based on an estimate of species preservation derived from a model of the diversification pattern, that suggests a Cretaceous last common ancestor of primates, approximately 81.5 Myr ago, close to the initial divergence time inferred from molecular data. It also suggests that no more than 7% of all primate species that have ever existed are known from fossils. The approach unites all the available palaeontological methods of timing evolutionary events: the fossil record, extant species and clade diversification models.     

Significance of enamel thickness in hominoid evolution

Enamel thickness has assumed unique importance in the debate about the hominid status of Ramapithecus, despite the fact that there is little agreement about the meaning of 'thick enamel' or the significance of enamel thickness for hominoid taxonomy. My aim here is to evaluate the usefulness of enamel thickness and microstructure as characteristics for determining the relationships of the later Miocene hominoids, based both on a quantitative study of enamel thickness in extant hominoids and four species of later Miocene Sivapithecus (including 'Ramapithecus') and on scanning electron microscope analysis of enamel microstructure. Four categories of enamel thickness are defined metrically here and have been related to enamel microstructure and developmental rates. Thin fast-formed (pattern 3) enamel represents the ancestral condition in hominoids; it increased developmentally to thick pattern 3 enamel in the great ape and human clade and that condition is primitively retained in Homo and in the fossil hominoid Sivapithecus (including 'Ramapithecus'). Enamel thickness has been secondarily reduced in the African apes and also, although at a different rate and extent, in the orang-utan. Thick enamel, previously the most important characteristic in arguments about the earliest hominid, does not therefore identify a hominid.     

Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins.

A modern human-like sequence of dental development, as a proxy for the pace of life history, is regarded as one of the diagnostic hallmarks of our own genus Homo. Brain size, age at first reproduction, lifespan and other life-history traits correlate tightly with dental development. Here we report differences in enamel growth that show the earliest fossils attributed to Homo do not resemble modern humans in their development. We used daily incremental markings in enamel to calculate rates of enamel formation in 13 fossil hominins and identified differences in this key determinant of tooth formation time. Neither australopiths nor fossils currently attributed to early Homo shared the slow trajectory of enamel growth typical of modern humans; rather, both resembled modern and fossil African apes. We then reconstructed tooth formation times in australopiths, in the approximately 1.5-Myr-old Homo erectus skeleton from Nariokotome, Kenya, and in another Homo erectus specimen, Sangiran S7-37 from Java. These times were shorter than those in modern humans. It therefore seems likely that truly modern dental development emerged relatively late in human evolution.     

Skull of the large non-macrostomatan snake Yurlunggur from the Australian Oligo-Miocene

Understanding the origin and early evolution of snakes from lizards depends on accurate morphological knowledge of the skull in basal lineages, but fossil specimens of archaic snakes have been rare, and either fragmentary or difficult to study as a result of compression by enclosing sediments. A number of Cenozoic fossil snakes from Australia have vertebral morphology diagnostic of an extinct group, Madtsoiidae, that was widespread in Gondwana from mid-Cretaceous (Cenomanian) to Eocene times, and also reached Europe in the late Cretaceous period. Despite this long history, only about half the skull is known from the best-known species Wonambi naracoortensis, and the few known cranial elements of other species have added little further evidence for phylogenetic relationships. Conflicting hypotheses have been proposed for their relationships and evolutionary significance, either as basal ophidians with many ancestral (varanoid- or mosasaur-like) features, or advanced (macrostomatan) alethinophidians of little relevance to snake origins. Here I report two partial skeletons referred to Yurlunggur, from the late Oligocene and early Miocene of northern Australia, which together represent almost the complete skull and mandible. The exceptionally preserved skulls provide new evidence linking Yurlunggur with Wonambi and other madtsoiids, falsifying predictions of the macrostomatan hypothesis, and supporting the exclusion of Madtsoiidae from the clade including all extant snakes.     

搪瓷用钢抗鳞爆性能研究进展

搪瓷制品鳞爆缺陷已经成为国内外研究重点。为提高搪瓷用钢的抗鳞爆性能,非常有必要了解搪瓷层的鳞爆机理。综述了国内外研究鳞爆机理以及氢扩散影响因素的现状。     

A eudicot from the Early Cretaceous of China

The current molecular systematics of angiosperms recognizes the basal angiosperms and five major angiosperm lineages: the Chloranthaceae, the magnoliids, the monocots, Ceratophyllum and the eudicots, which consist of the basal eudicots and the core eudicots. The eudicots form the majority of the angiosperms in the world today. The flowering plants are of exceptional evolutionary interest because of their diversity of over 250,000 species and their abundance as the dominant vegetation in most terrestrial ecosystems, but little is known of their very early history. In this report we document an early presence of eudicots during the Early Cretaceous Period. Diagnostic characters of the eudicot fossil Leefructus gen. nov. include simple and deeply trilobate leaves clustered at the nodes in threes or fours, basal palinactinodromous primary venation, pinnate secondary venation, and a long axillary reproductive axis terminating in a flattened receptacle bearing five long, narrow pseudo-syncarpous carpels. These morphological characters suggest that its affinities are with the Ranunculaceae, a basal eudicot family. The fossil co-occurs with Archaefructus sinensis and Hyrcantha decussata whereas Archaefructus liaoningensis comes from more ancient sediments. Multiple radiometric dates of the Lower Cretaceous Yixian Formation place the bed yielding this fossil at 122.6-125.8 million years old. The earliest fossil records of eudicots are 127 to 125 million years old, on the basis of pollen. Thus, Leefructus gen. nov. suggests that the basal eudicots were already present and diverse by the latest Barremian and earliest Aptian.     

A ceratopsian dinosaur from China and the early evolution of Ceratopsia

Ceratopsians (horned dinosaurs) represent one of the last and the most diverse radiations of non-avian dinosaurs. Although recent systematic work unanimously supports a basal division of Ceratopsia into parrot-like psittacosaurids and frilled neoceratopsians, the early evolution of the group remains poorly understood, mainly owing to its incomplete early fossil record. Here we describe a primitive ceratopsian from China. Cladistic analysis posits this new species as the most basal neoceratopsian. This new taxon demonstrates that some neoceratopsian characters evolved in a more incremental fashion than previously known and also implies mosaic evolution of characters early in ceratopsian history.     

网络技术环境下远程教学课件的开发与制作

结合在网络环境下开发《组织学与胚胎学》远程教学课件的实战经验,指出必须根据教学环境和课程特点,搜集足够的相关素材,选择合适的课件开发工具,利用计算机技术和网络技术,按一定的步骤,才能开发出一个结构合理、操作简便、交互性强、适用于网络教学的好课件。同时指出远程教学课件的普遍使用也对高校教学人员提出了更高和更新的要求。     

A deep-bodied ginglymodian fish from the Middle Triassic of eastern Yunnan Province, China, and the phylogeny of lower neopterygians

The Ginglymodi are a group of ray-finned fishes that make up one of three major subdivisions of the infraclass Neopterygii.Ex- tant ginglymodians are represented by gars,which inhabit freshwater environments of North and Central America and Cuba.Here, we report the discovery of well-preserved fossils of a new ginglymodian,Kyphosichthys grandei gen.et sp.nov.,from the Middle Triassic(Anisian)marine deposits(Guanling Formation)in Luoping,eastern Yunnan Province,China.The discovery documents the first known fossil record of highly deep-bodied ginglymodians,adding new information on the early morphological diversity of this group.The studies of functional morphology of extant deep-bodied fishes indicate that Kyphosichthys is not a fast swim- mer but has a good performance in precise maneuvering,representing a morphological adaptation to structurally complex habitats (e.g.thick macrophyte beds,rocky areas,or coral reefs),which differs from the other members of this group.A cladistic analysis with the new fish taxon included supports the hypothesis that the Ginglymodi are more closely related to the Halecomorphi than to the Teleostei.Represented by Felberia,Kyphosichthys,and Dapedium,a highly deep and short fish body type has inde- pendently evolved at least three times in the stem-group neopterygians,ginglymodians,and basal teleosts within the lower neop- terygians of the Triassic.     

Cloning the interferon regulatory factor I gene in lungfish （Protopterus annectens） and its molecular evolution among sarcopterygians

Sarcopterygians is an important vertebrate clade that includes crossopterygians and tetrapods. Crossopterygians are lobe-finned fish that include lungfish and coelacanths. Tetrapods include amphibians, reptiles, avians and mammals. To compare the interferon regulatory factor 1 (irf-1) gene structure and to explore phylogenetic relationships among sarcopterygians, we cloned the cDNA sequence of irf-1 from lungfish and compared it with irf-1 orthologs in other sarcopterygian species. The lungfish is a primitive sarcopterygian that occupies a very important position in vertebrate phylogeny. Interferon regulatory factors (IRFs) are a family of proteins involved in innate immunity. To date, 11 IRF family members have been reported. All IRFs share homology in the first 115 amino acids, which encompasses a DNA binding domain containing a characteristic repeat of 5 tryptophan residues separated by 10–18 amino acids. IRF-1 and IRF-2 were the first members of this family to be reported and they have a very important role in innate immunity. However, studies of the irf-1 and irf-2 genes are mostly confined to mammals; very few non-mammalian irf-1 genes have been reported. Consistent with the irf-1 gene sequences already published, the first 345 nucleotides of lungfish irf-1 are highly conserved. At the carboxyl terminal a C-terminal transactivating region motif and an interferon associated domain (IAD2) were identified. 417 million years separate the present from the closest common ancestor of lungfish and tetrapods; however, the irf-1 genes among sarcopterygians are highly conserved and have very obvious phylogenetic relationships. Also the interrelationship tree of sarcopterygians, based on IRF-1 amino acid sequences, is identical with trees produced using other data, such as morphological characteristics or mitochondrial gene sequences.