Primitive Mammals Research Articles

Cranial endocast of Anagale gobiensis (Anagalidae) and its implications for early brain evolution in Euarchontoglires

AbstractAnagalids are an extinct group of primitive mammals from the Asian Palaeogene thought to be possible basal members of Glires. Anagalid material is rare, with only a handful of crania known. Here we describe the first virtual endocast of an anagalid, based on the holotype of Anagale gobiensis (AMNH 26079; late Eocene, China), which allows for comparison with published endocasts from fossil members of modern euarchontogliran lineages (i.e. primates, rodents, lagomorphs). The endocast displays traits often observed in fossorial mammals, such as relatively small petrosal lobules and a low neocortical ratio, which would be consistent with previous inferences about use of subterranean food sources based on heavy dental wear. In fact, Anagale gobiensis has the lowest neocortical ratio yet recorded for a euarchontogliran. This species was olfaction‐driven, based on the relatively large olfactory bulbs and laterally expansive palaeocortex. The endocast supports previous inferences that relatively large olfactory bulbs, partial midbrain exposure and low encephalization quotient are ancestral for Euarchontoglires, although the likely fossorial adaptations of Anagale gobiensis may also partly explain these traits. While Anagale gobiensis is a primitive mammal in many aspects, some of its derived endocranial traits point towards a new, different trajectory of brain evolution within Euarchontoglires.

Mammalian dental diversity: an evolutionary template for regenerative dentistry

Discovery of odontogenic mechanisms essential for regenerating dental tissues and eventually developing a biomimetic artificial whole tooth for replacement is an ongoing aspiration for dental clinicians and researchers. Studying the diversity, development and evolutionary changes of mammalian dentitions, can provide key insights into the mechanisms of odontogenesis that can be harnessed for regenerative dental medicine. A myriad of influences is expected to have shaped the dentitions of mammals and our objective is to highlight the contributions of phylogeny, functional adaptation, and development to tooth shape. Innovations in tooth shape analysis will be discussed, such as in imaging methodologies and quantitative comparisons, molecular biology approaches to phylogeny and the ontogenetic basis of tooth form. Study of the inter and intra-species differences in tooth form as well as dental anomalies has provided clues toward the mechanisms of evolutionary change in dental form. Thus, phenotypic variation in tooth shape will also be discussed, including the role of development in creating tooth shape differences that evolutionary selection pressures may act upon. Functional adaptations have occurred in the context of the phylogenetic signal of primitive mammals, and predecessors to each phylogenetic branch, and examples will be discussed within members of the Order Carnivora, the Superfamily Suoidea and the Order Primates. The comparative study of mammalian tooth shape holds potential to inform dental research areas, such as etiopathogeneses of dental variation, and tooth shape anomalies, molecular mechanisms of tooth development and functional issues. Ultimately, insights from these research areas can be potentially translated for futuristic clinical applications like, regeneration of various tooth tissue layers and eventually full tooth replacement.

Different types of visual cells in the photoreceptor layer of the retinae of the treeshrew (Tupaia belangeri chinensis) as revealed by scanning microscopy.

The retinae of treeshrew have never been evaluated by scanning electron microscopic studies. This work described the visual cells in the photoreceptor layer of the retinae of treeshrew (Tupaia belangeri chinensis) living on the high plateau of Yunnan, China, via scanning electron microscopy. Results indicated five morphologically different types of cones, two of which contain oil droplets in their inner segments. To our knowledge, no prior studies have reported oil droplets in the visual cells of higher mammals, only in lower vertebrate and primitive mammals. In addition, this study revealed one type of degenerative visual cell without outer segments. The findings signal the needs for additional studies to understand the physiological functions and phylogenetic relationships of the diversity of visual cells in this group of mammal.

Species Distribution Model for the Asian Tapir and Vegetation Characteristics of Batang Gadis National Park, North Sumatra, Indonesia.

The Asian tapir is a primitive mammal whose habitat is heavily fragmented due to human activities. Studies on the Asian tapirs in Sumatra are very few, thereby basic information for developing tapir conservation programmes is limited. This study aimed to develop the species distribution model to map the potential distribution of tapirs in Batang Gadis National Park (BGNP), investigate the characteristic of tapir habitat, and identify tapir feed plants around BGNP. The model was developed using the Maximum Entropy (Maxent) approach, based on the existing information on tapir occurrence in BGNP and environmental variables. Vegetation characteristics in different land cover (primary forests, secondary forests, and open fields) were investigated using the strip transect method. This study found that zonal classification, temperature and precipitation have the greatest percentage contribution to the model. The model estimated that around 24.45% of BGNP areas are suitable for tapir habitat, and tapirs distribute near community gardens. Our results also showed that plant diversity at study sites was categorised as moderate-high. About 23 plant species dominated by the Moraceae family were identified as feed plants for tapirs. In developing tapir conservation programmes, BGNP management needs to consider tapir distribution that is closed to community gardens. We propose BGNP to enrich feed plants in open fields of the wilderness and traditional zones; reduce the canopy cover in the wilderness and utilisation zones to stimulate the growth of feed plants; facilitate local people to live harmoniously with tapirs; involve local communities in tapir conservation programmes; encourage local communities to plant non-palatable crops for tapirs; and provide a compensation scheme.

The evolution of factor XI and the kallikrein-kinin system.

Factor XI (FXI) is the zymogen of a plasma protease (FXIa) that contributes to hemostasis by activating factor IX (FIX). In the original cascade model of coagulation, FXI is converted to FXIa by factor XIIa (FXIIa), a component, along with prekallikrein and high-molecular-weight kininogen (HK), of the plasma kallikrein-kinin system (KKS). More recent coagulation models emphasize thrombin as a FXI activator, bypassing the need for FXIIa and the KKS. We took an evolutionary approach to better understand the relationship of FXI to the KKS and thrombin generation. BLAST searches were conducted for FXI, FXII, prekallikrein, and HK using genomes for multiple vertebrate species. The analysis shows the KKS appeared in lobe-finned fish, the ancestors of all land vertebrates. FXI arose later from a duplication of the prekallikrein gene early in mammalian evolution. Features of FXI that facilitate efficient FIX activation are present in all living mammals, including primitive egg-laying monotremes, and may represent enhancement of FIX-activating activity inherent in prekallikrein. FXI activation by thrombin is a more recent acquisition, appearing in placental mammals. These findings suggest FXI activation by FXIIa may be more important to hemostasis in primitive mammals than in placental mammals. FXI activation by thrombin places FXI partially under control of the vitamin K-dependent coagulation mechanism, reducing the importance of the KKS in blood coagulation. This would explain why humans with FXI deficiency have a bleeding abnormality, whereas those lacking components of the KKS do not.

The white-eared opossum failed to understand the parallel strings task: studying a primitive mammal under natural conditions.

The present study aimed to investigate if the white-eared opossum under natural conditions is capable of spontaneously solving the parallel string task. The experimental study with this primitive mammal was carried out on fifteen naïve animals of both sexes in northeastern Brazil. The parallel strings task was arranged in apparatuses with a vertical and a horizontal arrangement. A food reward (a slice of banana) was connected at the extremity of one string. A total of 505 videos were recorded using trap cameras. Despite the observed interest in obtaining the bait, the number of attempts to reach it and the use of the strings as support (trying to directly reach the bait in the vertical apparatus), the individuals were unable to pull any of the strings, suggesting that they could not understand the problem. The present study points to the relevance of using the species Didelphis albiventris and other species from this family (e.g., D. virginiana) to broaden our knowledge about the cognitive capacity of mammalian species. In addition, the opossums might represent an advisable path to better understand the evolution of cognition in this group.

Morphological study of larynx, trachea, and lungs of Didelphis marsupialis (LINNAEUS, 1758)

Background and Aim:From a biomedical point of view, the value of marsupials as a model of primitive mammals is indisputable. Among its species, the possum is a model that allows the study of the ontogeny of different organic systems, as well as their physiological aspects. The relevance of anatomical, functional, evolutionary, and phylogenetic study of marsupials for the development of comparative morphology is extensively documented in the literature. However, there are still many aspects to be further evaluated, as the anatomy and histology of the respiratory tract of this species. The aim of this study was to describe the morphology of the larynx, trachea, and lungs of Didelphis marsupialis.Materials and Methods:Five adult male animals were donated to the Comparative Animal Anatomy Laboratory – LAAC/CCAA-UFMA, for morphological studies. Specimens were washed in running water to perform biometrics. Then, they were fixed with 10% formaldehyde solution. After the fixation period, the specimens were positioned in dorsal decubitus position, for dissection of the respiratory system organs, by opening the ventral region of the neck and thoracic cavity, with subsequent removal of the pectoral muscles, ribs, and sternum. For histological analysis, fragments of 1 cm2 of the larynx (epiglottis and thyroid cartilages), trachea, and lungs were collected and fixed in 10% formaldehyde solution. Right after fixation, the fragments were dehydrated in increasing concentrations of ethyl alcohol (70, 80, 95, and 100%), diaphanized in xylene, embedded in paraffin, and sectioned into thin slices of 5 μm using a microtome. Sections were stained using the hematoxylin and eosin technique.Results:Anatomically, the larynx starts right after the pharynx. It consisted of four cartilages: Epiglottis, cricoid, thyroid, and arytenoid. The trachea was made of dorsally incomplete cartilaginous rings. At the entrance of the thoracic cavity, it bifurcated into the left and right main bronchus. The left lung was smaller than the right lung, with two lobes (cranial and caudal). The right lung presents the cranial, middle, caudal, and accessory lobes. Histologically, the epiglottis consisted of elastic cartilage and is covered by a non-keratinized stratified squamous epithelium. Thyroid cartilage is made of hyaline cartilage covered by smooth muscle. The trachea presents hyaline cartilage, with ciliated pseudo-stratified epithelium, serous glands, isogenic groups of chondrocytes, and perichondrium. The lung consisted of bronchi, bronchioles, and alveoli, also presenting blood vessels and arteries.Conclusion:Morphologically, the larynx, trachea, and lungs of D. marsupialis were similar to those of the other Didelphids described in the literature.

Platypus Induced Pluripotent Stem Cells: The Unique Pluripotency Signature of a Monotreme

The platypus (Ornithorhynchus anatinus) is an egg-laying monotreme mammal whose ancestors diverged ∼166 million years ago from the evolutionary pathway that eventually gave rise to both marsupial and eutherian mammals. Consequently, its genome is an extraordinary amalgam of both ancestral reptilian and derived mammalian features. To gain insight into the evolution of mammalian pluripotency, we have generated induced pluripotent stem cells from the platypus (piPSCs). Deep sequencing of the piPSC transcriptome revealed that piPSCs robustly express the core eutherian pluripotency factors POU5F1/OCT4, SOX2, and NANOG. Given the more extensive role of SOX3 over SOX2 in avian pluripotency, our data indicate that between 315 and 166 million years ago, primitive mammals replaced the role of SOX3 in the vertebrate pluripotency network with SOX2. DAX1/NR0B1 is not expressed in piPSCs and an analysis of the platypus DAX1 promoter revealed the absence of a proximal SOX2-binding DNA motif known to be critical for DAX1 expression in eutherian pluripotent stem cells, suggesting that the acquisition of SOX2 responsiveness by DAX1 has facilitated its recruitment into the pluripotency network of eutherians. Using the RNAseq data, we were also able to demonstrate that in both fibroblasts and piPSCs, the expression ratio of X chromosomes to autosomes (X1-5 X1-5:AA) is approximately equal to 1, indicating that there is no upregulation of X-linked genes. Finally, the RNAseq data also allowed us to explore the process of X-linked gene inactivation in the platypus, where we determined that for any given gene, there is no preference for silencing of the maternal or paternal allele; that is, within a population of cells, the silencing of X-linked genes is not imprinted.

First Paleoichnological Evidence for Baby–Riding in Early Mammals

It is not yet known how old parental care in mammals is. One fossil trackway ascribed to Ameghinichnus patagonicus of a mouse-sized primitive mammal from the Middle Jurassic of Patagonia, Argentina, of almost 170 Ma, shows deviation from the usual bilateral symmetry of posture and motion: the left forelimb digits were dragging in the swing phase, and the tail was bent to the right and dragged over the right footprints. However, the footprints are evenly spaced, indicating that the animal was not limping. The opposition of the tail and the forelimb dragging marks could possibly be explained by a heavy load carried on the left side. This hypothesis is supported by experiments on laboratory rats. A plausible load for Ameghinichnus track-maker could be babies riding on a milk-producing mother, as they do in extant opossums and many other mammals. Baby-riding is a missed possible feature of basal mammals, which potentially integrates evolutionary acquisition of profound mammalian features, such as milk-feeding, endothermy, hairs, and limb parasagittalism.

The biogeography and ecology of Sri Lankan mammals point to conservation priorities

All mammals originated on the supercontinent of Pangaea in the Mesozoic era during the “Age of Reptiles.” However, the crown ancestors of contemporary mammals did not flourish until major environmental and biotic changes had occurred. An asteroid collided with earth at the end of the Cretaceous Period (the K-Pg boundary event) wiping out non-flying dinosaurs and primitive mammals. It was followed by large-scale volcanism, a spike in atmospheric oxygen and the proliferation of flowering plants. New niches became available for the ancestors of today’s mammals to fill. Evidence suggesting whether the ancestors of the Sri Lankan and Indian mammals originated on the tectonically marooned Indian plate before crashing into Asia or on the Laurasian supercontinent is inconclusive. Modern Sri Lankan mammals show their greatest affinity with those of southern India, and were more diverse in the Pleistocene when rhinoceros, hippopotamus, wild dogs, gaur and lions enriched the island’s landscapes. Native Sri Lankan land-based mammals are diversified into about 108 unique taxa (among 91 species and 53 genera), differentiated as phenotypic adaptations to sharply contrasting environments among seven major phyto-climatic zones. Endemic subspecies are distributed fairly equally across different phyto-climatic zones (n=24 to 29), except in the highlands where they are fewer (n=14) having evolved rapidly to species and genera among the insectivores and rodents whose reproductive rates are high. Conversely, greater numbers of endemic species (n=13) and genera (n=3) occur in the highlands than in the other zones (2-6 endemic species, no endemic genera). The prevalence of endemism is inversely related to body size or vagility. This suggests a greater probability of genetic exchange among distant populations of large bodied mobile mammals within Sri Lanka, as well as with Indian fauna during periods of land bridges in the Pleistocene. Most (8 of 13) endangered and critically endangered endemic mammals occur in the wet montane regions that offer the least Protected Areas (PAs). More than 85% of PAs occur in the extensive dry zone about half of which is not suited for water dependent mammals whose distributions are restricted to alluvial forests (less than 1% of PAs). Historically, the national cost of conservation has been low and therefore politically palatable. Current conservation urgently requires a major change in management policy combined with realistic investment to prevent extinctions of many endemic mammals and other unique Sri Lankan biota.

Cloning, expression analysis, and antibacterial propertiesof three serum amyloid A in common carp (Cyprinus carpio)

Three serum amyloid A (SAA) genes were identified from the common carp (Cyprinus carpio) by PCR and RT-PCR. Considering both direction and sequence similarity with mammal's orthologs, they were named CcSAA3a, CcSAA3b and CcSAA1. CcSAA3b and CcSAA1 are adjacent on contig LHQP01017858, suggesting that the prototype of or the simplest SAA multigene family have occurred in common carp. A phylogenetic analysis of the SAAs indicated that the fish SAAs were closer to those of invertebrates and Ornithorhynchus anatinus, a primitive mammal, than to mammalian SAAs. Quantitative real-time RT-PCR results displayed different expression profiles of three CcSAAs. The CcSAA3a was detected in all tested tissues, and was most abundant in the muscle; CcSAA3b was predominately expressed in the intestine and liver, and CcSAA1 in the skin. The expression level of CcSAA3a was higher than that of CcSAA3b and CcSAA1 in most tissues. Stimulation with Aeromonas hydrophila dramatically induced the expression of the three CcSAAs in all examined tissues, especially in the liver. Like Epinephelus coioides SAA, all of three rCcSAA fusion proteins could bind to both Gram-negative bacteria (A. hydrophila and E. coli) and Gram-positive bacterium (S. aureus), playing a role in the identification of bacteria. However, only rCcSAA3a showed significantly anti-A. hydrophila and anti-E. coli in vitro antibacterial activity assays. These results suggested that the three CcSAAs were in functional differentiation and play significant roles in the innate immunity of common carp.

Observations on Fur Development in Echidna (Monotremata, Mammalia) Indicate that Spines Precede Hairs in Ontogeny

In the primitive mammal echidna, the initial 2-3 generations of skin appendages produced from birth forms spines and only later true hairs appear. Microscopy on preserved museum specimens reveals that the morphogenesis of spines and hairs is similar but that a larger dermal papilla is formed in spines. The growing shaft comprises a medulla surrounded by a cortex and by an external cuticle. A thick inner root sheath made of cornified cells surrounds the growing shaft inside the spine canal that eventually exits with a pointed tip. Hairs develop later with the same modality of spines but have a smaller papilla and give rise to a fur coat among spines. Therefore the integument of developing echidnas initially produces spines from large dermal papillae but the reduction in size of the papillae later determines the formation of hairs. Although the morphogenesis of spines and hairs can represent a case of specialization in this species, the primitive mammalian characteristics of echidnas has also inspired new speculations on the evolution of the mammalian hair from mammalian-like reptiles with a spiny coat. The resemblance in the morphogenesis between spines and hairs has suggested some hypothesis on hair evolution, in particular that hairs might be derived from the reduction of protective large spines present in ancient mammalian-like reptiles possibly derived from the reduction of pre-existing pointed scales. The hypothesis suggests that spines became reduced and internalized in the skin forming hairs.

Morphology of the nasal capsule of primates--with special reference to Daubentonia and Homo.

Primitive mammals are considered macrosmatic. They have very large and complicated nasal capsules, nasal cavities with extensive olfactory epithelia, and relatively large olfactory bulbs. The complicated structures of the nasal capsule follow a relatively conservative "bauplan," which is normally easy to see in earlier fetal stages; especially in altricial taxa it differentiates well into postnatal life. As anteriormost part of the chondrocranium, the nasal capsule is at first cartilaginous. Most of it ossifies endochondrally, but "appositional bone" ("Zuwachsknochen") is also common. Many fetal structures become resorbed. Together, all surviving bone structures form the ethmoid bone, but cartilages of the external nose and of the vomeronasal complex can persist throughout life. We describe in detail the anatomy of Daubentonia madagascariensis based on a fetal stage (41 mm HL) and an adult skull was analyzed by µCT. We found that the nasal capsule of this species is by far the most complicated one of all extant Primates. We also describe older fetuses of Homo sapiens (35 and 63 mm HL) as representative of a derived primate. The most significant feature of man--and probably of all anthropoids--is the complete loss of the recessus frontoturbinalis and its associated structures. It can be demonstrated that the evolutionary reductions within the primate nasal capsule mainly affect those structures associated with olfaction, whereas cartilages that are important for the biomechanics of the facial skull of the fetus persist.

Increased homeothermy during reproduction in a basal placental mammal

Homeothermic endothermy, the maintenance of a high and stable body temperature (Tb) using heat produced by elevated metabolism, is energetically expensive. There is increasing evidence that the earliest endotherms were heterotherms that, rather than maintaining strict homeothermy, allowed Tb to fluctuate with large variations between active and rest-phase Tb. The high level of homeothermy observed in modern mammals is therefore likely to have evolved from an ancestral heterothermic state. One of the hypotheses for the evolution of endothermy is that homeothermy allows for greater energetic output during reproduction (parental care model). We tested this hypothesis by measuring metabolic rates over a range of ambient temperatures in both reproductive and non-reproductive greater hedgehog tenrecs (Setifer setosus), a physiologically primitive mammal from Madagascar. Tenrecs have some of the lowest metabolic rates and highest levels of Tb variability of any mammal and are therefore good models of the ancestral eutherian state. During pregnancy and lactation, there was an increase in metabolism and Tb below the thermoneutral zone, accompanied by a decrease in Tb variability. The lower critical limit of the thermoneutral zone was estimated at ~25°C. However, whereas increases in resting metabolism were substantial below 20°C (up to 150% higher during reproduction), daytime rest-phase ambient temperatures at the study site rarely reached equivalent low levels. Thus, S. setosus provide an example for how relatively low-cost increases in homeothermy could have led to substantial increases in fitness by allowing for the faster production of young. The mechanisms necessary for increases in thermogenesis during reproduction would have further benefited the development of homeothermy in mammals.

Impact of the Konio pathway in the thalamocortical visual system: a modeling study

In the early visual system, regarding the detection of a visual event, motion information is pre-processed in the Magnocellular pathway, while it has been shown that the Koniocellular pathway [1] also plays an important role, providing a global analysis about such a kind of information processing. However, the functional interplay between these two parallel pathways remains partially understood. Previous works have attacked this question by studying the signals produced by the corresponding ganglion cells [1] and their elaboration at further steps [2], rather than proposing to model the underlying mechanisms at a mesoscopic level, i.e., focusing on the functional aspects of such dual processing. Neurobiological studies dedicated to the thalamocortical stage of the early visual system provide knowledge on particular characteristics of the system, namely: 1) the variety of cell types in the retina [2], inducing different pathways, 2) the variety of thalamocortical projections through focused vs diffuse efferences to the cortex [3], from core vs matrix (specific vs non-specific) thalamic nuclei, and 3) the variety of kinds of connectivity between thalamic, cortical and collicular areas (i.e., feedforward, feedback, shortcuts, driver and modulator information flows [4]). To figure out the impact of these multi-scale characteristics, we propose here a systemic approach at the structure level. To this end, we have developed a reduced bio-inspired distributed asynchronous model of the primitive mammal visual system, considering only motion event detection. This computational model is fed with natural image sequences, and is implemented as a large size distributed calculation [5] with thousands of computation units per structure. Thanks to the dual analysis integrating local and larger image cues, we test the system for the detection of specific dynamical patterns (which could be interpreted as, e.g., threats or targets). Our simulations aim at showing that these multi-scale interactions help improving the speed and/or quality of such critical tasks, including target selection and tracking. We expect this approach to propose an innovative answer to the interplay issues quoted here, generalizable to other visuo-motor functions. This also provides a platform that could be used as a testbed for new hypotheses. Further information flows to be included could correspond to the Parvocellular pathway (and its related functions). Other structures such as the pulvinar, or higher cortical areas, would also allow us to explore even more developed mechanisms and behaviors [3,6].

Genomic Evidence Supported Teeshrew is Closely Related to Primates

The evidence of the latest whole genome sequencing data supported that treeshrews are neither Insectivora nor primate mammals, but they are closely related to primates, and clarified the ongoing controversy regarding the phylogenetic position of tree shrews. It can be said with certainty that treeshrews are small primitive mammals which belong to the Order Scandentia in Euarchontoglires, with a close relationship to primates.

Symmetrical gaits and center of mass mechanics in small-bodied, primitive mammals

Widely accepted relationships between gaits (footfall patterns) and center of mass mechanics have been formulated from observations for cursorial mammals. However, sparse data on smaller or more generalized forms suggest a fundamentally different relationship. This study explores locomotor dynamics in one eutherian and five metatherian (marsupials) mammals—all small-bodied (<2kg) with generalized body plans that utilize symmetrical gaits. Across our sample, trials conforming to vaulting mechanics occurred least frequently (<10% of all trials) while bouncing mechanics was obtained most commonly (60%); the remaining trials represented mixed mechanics. Contrary to the common situation in large mammals, there was no evidence for discrete gait switching within symmetrical gaits as speed increased. This was in part due to the common practice of grounded running. The adaptive advantage of different patterns of center-of-mass motion and their putative energy savings remain questionable in small-bodied mammals.

Primates

Primates

Depositional evolution of the Early Cretaceous Sihetun Lake and implications for regional climatic and volcanic history in western Liaoning, NE China

Numerous well-known fossils of the Jehol Biota, including early birds, feathered theropods, primitive mammals, and putative early angiosperms, have been discovered in lacustrine deposits (Lake Sihetun) of the Lower Cretaceous Yixian Formation of western Liaoning province, NE China. Based on extensive field investigations and four high-resolution excavations, we document in detail the spatio-temporal changes of sedimentary facies, facies associations and limnic community relicts, reconstruct the depositional history, and discuss the significance of these deposits regarding the regional climatic and volcanic history. Four phases are recognized in the history of Lake Sihetun. They are: (1) a phase of fluctuating but gradually rising water level indicated by subaerial and shallow-water lacustrine deposits, (2) a lake with beach–nearshore facies along the marginal areas and suspension-dominated lake floor facies in central areas, (3) a lake phase with a lake floor dominated by hyperpycnal flows, and (4) progradation of a fan delta. Two distinct depositional conditions are observed: stratified and unstratified lake intervals. The former occurred mainly during the second phase and produced clay-poor and clay-rich laminae, whereas the latter developed during the other three phases, and were dominated by deposition of subaqueous sedimentary density flows. These alternations of depositional conditions in offshore lacustrine deposits suggest that the Yixian Formation may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions. Resurgent volcanism is inferred to have become stronger during the late phase of lake development based on distribution of deposits characterizing the unstratified lake interval and volcanic rocks of the overlying Upper Lava unit, a higher content of primary pyroclastic fragments, and evidence of strong syndepositional disturbance.

The Triune Brain: Limbic Mind Mind Plastic, Emotional Mind

Problem statement: The theory discussed is revealing, as compared to studies on the human brain, the fact that he has inherited the str ucture and organization of three fundamental types of reptiles, ancient or primitive mammals and mammals, or recent evolved. What is very disconcerting is that nature has been able to connect with each othe r and establish a sort of communication between them. Approach: The objective was to focus the study on chemical s ubstances that regulate the activity of nerve cells, neurons. We can define neu romodulators or modulators of behavior because their intervention more or less obvious influence o ur own actions. The method under consideration is the TMS, transcranial magnetic stimulation, a nonin vasive technique of Neurostimulation and neuromodulation which is based on a type of electro magnetic induction of an electric field. Results: This property of TMS allows us to understand the pr ecise moment when a brain region contributes to a certain task, to map the functional connectivity be tween different brain regions, to identify the caus al relationships involved far treated between brain, c ognition and behavior. Conclusion: It 'as certain that the thoughts and experience change the configuratio n of our brain connections, but so can the induced systems, based on the same principle, capable of al tering particularly for therapeutic, rehabilitative or educational, the brain matter on the basis of premi ses of the so-called phenomenon called Hebbian learning based on chemical changes in the cells and synapses known as long-term potentiation.