taxon_rank protoavis
The skull is a bony structure that forms the head of the skeleton in most vertebrates . It supports the structures of the face and provides a protective cavity for the brain . The skull is composed of two parts : the cranium and the mandible . In the human these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone . The skull forms the anterior most portion of the skeleton and is a product of cephalisation  housing the brain , and several sensory structures such as the eyes , ears , nose , and mouth . In the human these sensory structures are part of the facial skeleton . Birds ( Aves ), also known as avian dinosaurs , are a ___MASK41___ of endothermic vertebrates , characterised by feathers , toothless beaked jaws , the laying of hard - shelled eggs , a high metabolic rate , a four - chambered heart , and a lightweight but strong skeleton . Birds live worldwide and range in size from the bee hummingbird to the ostrich . They rank as the class of tetrapods with the most living ___MASK59___ , at approximately ten thousand , with more than half of these being passerines , sometimes known as perching birds or , less accurately , as songbirds . Hummingbirds are birds from the Americas that constitute the ___MASK4___ Trochilidae . They are among the smallest of birds , most species measuring . Indeed , the smallest extant bird species is a hummingbird , the 5 - cm bee hummingbird weighing less than a U . S . penny ( 2 . 5 g ). Feathers are epidermal growths that ___MASK54___ the distinctive outer covering , or plumage , on birds . They are considered the most complex integumentary structures found in vertebrates , and indeed a premier example of a complex evolutionary novelty . They are among the characteristics that distinguish the extant birds from other living groups . The ostrich or common ostrich (" Struthio camelus ") is either one or two ___MASK59___ of large flightless birds native to Africa , the only living member ( s ) of the ___MASK81___ " Struthio ", which is in the ratite family . In 2014 , the Somali ostrich (" Struthio molybdophanes ") was recognized as a distinct ___MASK59___ . A ___MASK81___ ( genera ) is a taxonomic rank used in the biological classification of living and fossil organisms in biology . In the hierarchy of biological classification , ___MASK81___ comes above species and below family . In binomial nomenclature , the ___MASK81___ name forms the first part of the binomial species name for each species within the ___MASK81___ . Vertebrates comprise all ___MASK59___ of animals within the ___MASK21___ Vertebrata ( chordates with backbones ). Vertebrates represent the overwhelming majority of the phylum Chordata , with currently about 64 , 000 ___MASK59___ described . Vertebrates include the jawless fish and the jawed vertebrates , which include the cartilaginous fish ( sharks and rays ) and the bony fish . The Carnian ( less commonly , Karnian ) is the lowermost stage of the Upper Triassic ___MASK66___ ( or earliest age of the Late Triassic epoch ). It lasted from 237 to 228 . 4 million years ago ( Ma ). The Carnian is preceded by the Ladinian and is followed by the Norian . Its boundaries are not characterized by major extinctions or biotic turnovers , but a climatic event ( known as the Carnian Pluvial Event ) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations . Post is a city in and the county seat of Garza County , Texas , United States . The population was 5 , 376 at the 2010 census . The face is a central organ of sense and is also very central in the expression of emotion among humans and among numerous other ___MASK59___ . The face is normally found on the anterior (" frontal ", " rostral ") surface of the head of animals or humans , although not all animals have faces . The face is crucial for human identity , and damage such as scarring or developmental deformities have effects stretching beyond those of solely physical inconvenience . A passerine is any bird of the ___MASK84___ Passeriformes , which includes more than half of all bird ___MASK59___ . A notable feature of passerines compared to other orders of Aves is the arrangement of their toes , three pointing forward and one back , which facilitates perching . Sometimes known as perching birds or , less accurately , as songbirds , the passerines form one of the most diverse terrestrial vertebrate orders , with over 5 , 000 identified ___MASK59___ . It has roughly twice as many ___MASK59___ as the largest of the mammal orders , the Rodentia . It contains more than 110 families , the second - most of any ___MASK84___ of tetrapods ( after Squamata , the scaled reptiles ). The passerines contain several groups of brood parasites such as the viduas , cuckoo - finches , and the cowbirds . Most passerines are omnivorous , while the shrikes are carnivorous . Sankar Chatterjee is a paleontologist , and is the Paul W . Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University . He earned his Ph . D . from the University of Calcutta in 1970 and was a Post - doctoral Fellow at the Smithsonian Institution from 1977 - 1978 . Biology is a natural science concerned with the study of life and living organisms , including their structure , function , growth , evolution , distribution , identification and taxonomy . Modern biology is a vast and eclectic field , composed of many branches and subdisciplines . However , despite the broad scope of biology , there are certain general and unifying concepts within it that govern all study and research , consolidating it into single , coherent field . In general , biology recognizes the cell as the basic unit of life , genes as the basic unit of heredity , and evolution as the engine that propels the synthesis and creation of new ___MASK59___ . It is also understood today that all the organisms survive by consuming and transforming energy and by regulating their internal environment to maintain a stable and vital condition known as homeostasis . A bone is a rigid organ that constitutes part of the vertebrate skeleton . Bones support and protect the various organs of the body , produce red and white blood cells , store minerals , provide structure and support for the body , and enable mobility . Bones come in a ___MASK18___ of shapes and sizes and have a complex internal and external structure . They are lightweight yet strong and hard , and serve multiple functions . The Smithsonian Institution , established in 1846 " for the increase and diffusion of knowledge ," is a ___MASK41___ of museums and research centers administered by the Government of the United States . Originally organized as the " United States National Museum ," that name ceased to exist as an administrative entity in 1967 . Termed " the nation ' s attic " for its eclectic holdings of 138 million items , the Institution ' s nineteen museums , nine research centers , and zoo include historical and architectural landmarks , mostly located in the District of Columbia . Additional facilities are located in Arizona , Maryland , Massachusetts , New York City , Virginia , Texas , and Panama . More than 200 institutions and museums in 45 states , Puerto Rico , and Panama are Smithsonian Affiliates The Institution ' s thirty million annual visitors are admitted without charge . The institution ' s annual budget is around $ 1 . 2 billion with 2 / 3 coming from annual federal appropriations . Other funding comes from the Institution ' s endowment , private and corporate contributions , membership dues , and earned retail , concession , and licensing revenue . Institution publications include " Smithsonian " and " Air & Space " magazines . Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature , each in their own broad field of organisms . To an end - user who only deals with names of ___MASK59___ , with some awareness that ___MASK59___ are assignable to families , it may not be noticeable that there is more than one code , but beyond this basic level these are rather different in the way they work . Protoavis ( meaning `` first bird '' ) is a problematic taxon of archosaurian known from fragmentary remains from Late Triassic Norian stage deposits near Post , Texas . Much controversy remains over the animal , and there are many different interpretations of what Protoavis actually is . When it was first described , the fossils were described as being from a primitive bird which , if the identification is valid , would push back avian origins some 60 - 75 million years . The original describer of Protoavis texensis , Sankar Chatterjee of Texas Tech University , interpreted the type specimen to have come from a single animal , specifically a 35 cm tall bird that lived in what is now Texas , USA , around 210 million years ago . Though it existed far earlier than Archaeopteryx , its skeletal structure is allegedly more bird - like . Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull , suggesting a nocturnal or crepuscular lifestyle . Reconstructions usually depict it with feathers , as Chatterjee originally interpreted structures on the arm to be quill knobs , the attachment point for flight feathers found in some modern birds and non - avian dinosaurs . However , re - evaluation of the fossil material by subsequent authors such as Lawrence Witmer have been inconclusive regarding whether or not these structures are actual quill knobs . However , this description of Protoavis assumes that Protoavis has been correctly interpreted as a bird . Almost all palaeontologists doubt that Protoavis is a bird , or that all remains assigned to it even come from a single ___MASK59___ , because of the circumstances of its discovery and unconvincing avian synapomorphies in its fragmentary material . When they were found at the Tecovas and Bull Canyon Formations in the Texas panhandle in 1984 , in a sedimentary strata of a Triassic river delta , the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a flash flood . The heart is a muscular organ in humans and other animals , which pumps blood through the blood vessels of the circulatory system . Blood provides the body with oxygen and nutrients , as well as assists in the removal of metabolic wastes . The heart is located between the lungs , in the middle compartment of the chest . In humans , other mammals , and birds , the heart is divided into four chambers : upper left and right atria ; and lower left and right ventricles . Commonly the right atrium and ventricle are referred together as the " right heart " and their left counterparts as the " left heart ". Fish in contrast have two chambers , an atrium and a ventricle , while reptiles have three chambers . In a healthy heart blood flows one way through the heart due to heart valves , which prevent backflow . The heart is enclosed in a protective sac , the pericardium , which also contains a small amount of fluid . The wall of the heart is made up of three layers : epicardium , myocardium , and endocardium . The heart pumps blood with a rhythm determined by a ___MASK41___ of pacemaking cells in the sinoatrial node . These generate a current that causes contraction of the heart , traveling through the atrioventricular node and along the conduction system of the heart . The heart receives blood low in oxygen from the systemic circulation , which enters the right atrium from the superior and inferior venae cavae and passes to the right ventricle . From here it is pumped into the pulmonary circulation , through the lungs where it receives oxygen and gives off carbon dioxide . Oxygenated blood then returns to the left atrium , passes through the left ventricle and is pumped out through the aorta to the systemic circulation  where the oxygen is used and metabolized to carbon dioxide . The heart beats at a resting rate close to 72 beats per minute . Exercise temporarily increases the rate , but lowers resting heart rate in the long term , and is good for heart health . Cardiovascular diseases ( CVD ) are the most common cause of death globally as of 2008 , accounting for 30 % of deaths . Of these more than three quarters are a result of coronary artery disease and stroke . Risk factors include : smoking , being overweight , little exercise , high cholesterol , high blood pressure , and poorly controlled diabetes , among others . Cardiovascular diseases frequently have no symptoms or may cause chest pain or shortness of breath . Diagnosis of heart disease is often done by the taking of a medical history , listening to the heart - sounds with a stethoscope , ECG , and ultrasound . Specialists who focus on diseases of the heart are called cardiologists , although many specialties of medicine may be involved in treatment . The Triassic is a geologic period and system which spans 50 . 9 million years from the end of the Permian Period million years ago ( Mya ), to the beginning of the Jurassic Period Mya . The Triassic is the first period of the Mesozoic Era . Both the start and end of the period are marked by major extinction events . The Triassic was named in 1834 by Friedrich von Alberti , after the three distinct rock layers (" tri " meaning " three ") that are found throughout Germany and northwestern Europe  red beds , capped by marine limestone , followed by a ___MASK66___ of terrestrial mud - and sandstones  called the " Trias ". Eyes are organs of the visual system . They provide organisms vision , the ability to process visual detail , as well as enabling several photo response functions that are independent of vision . Eyes detect light and convert it into electro - chemical impulses in neurons . In higher organisms , the eye is a complex optical system which collects light from the surrounding environment , regulates its intensity through a diaphragm , focuses it through an adjustable assembly of lenses to ___MASK54___ an image , converts this image into a set of electrical signals , and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain . Eyes with resolving power have come in ten fundamentally different forms , and 96 % of animal ___MASK59___ possess a complex optical system . Image - resolving eyes are present in molluscs , chordates and arthropods . The Late Triassic is the third and final of three epochs of the Triassic Period in the geologic timescale . The Triassic - Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth . The corresponding ___MASK66___ is known as the Upper Triassic . In Europe the epoch was called the Keuper , after a German lithostratigraphic group ( a sequence of rock strata ) that has a roughly corresponding age . The Late Triassic spans the time between Ma and Ma ( million years ago ). The Late Triassic is divided into the Carnian , Norian and Rhaetian ages . Modern humans (" Homo sapiens ", primarily ssp . " Homo sapiens sapiens ") are the only extant members of Hominina ___MASK12___ ( or human ___MASK12___ ), a ___MASK95___ of the ___MASK12___ Hominini belonging to the ___MASK4___ of great apes . They are characterized by erect posture and bipedal locomotion ; manual dexterity and increased tool use , compared to other animals ; and a general trend toward larger , more complex brains and societies . The bee hummingbird , zunzuncito or Helena hummingbird (" Mellisuga helenae ") is a ___MASK59___ of hummingbird . Dinosaurs are a diverse ___MASK41___ of animals of the clade Dinosauria that first appeared during the Triassic . Although the exact origin and timing of the evolution of dinosaurs is the subject of active research , the current scientific consensus places their origin between 231 and 243 million years ago . They became the dominant terrestrial vertebrates after the Triassic  Jurassic extinction event 201 million years ago . Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous  Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago . Archaeopteryx , sometimes referred to by its German name (" original bird " or " first bird "), is a ___MASK81___ of bird - like dinosaurs that is transitional between non - avian feathered dinosaurs and modern birds . The name derives from the ancient Greek (" archaos ") meaning " ancient ", and (" ptéryx "), meaning " feather " or " wing ". Between the late nineteenth century and the early twenty - first century , " Archaeopteryx " had been generally accepted by palaeontologists and popular reference books as the oldest known bird ( member of the group Avialae ). Older potential avialans have since been identified , including " Anchiornis ", " Xiaotingia ", and " Aurornis ". The ___MASK34___ Tetrapoda ( Ancient Greek s tetrapods , " four - footed "), or the tetrapods , comprises the first four - limbed vertebrates and their descendants , including the living and extinct amphibians , birds , mammals , reptiles and some ancient , exclusively aquatic creatures such as the Acanthostega . Tetrapods evolved from the lobe - finned fishes around 390 million years ago in the middle Devonian Period , with modern tetrapod groups having appeared by the late Devonian , 367 . 5 million years ago . The specific aquatic ancestors of the tetrapods , and the process by which land colonization occurred , remain unclear , and are areas of active research and debate among palaeontologists at present . A songbird is a bird belonging to the clade Passeri of the perching birds ( Passeriformes ). Another name that is sometimes seen as a scientific or vernacular name is Oscines , from Latin " oscen ", " a songbird ". This ___MASK41___ contains some 4 , 000 ___MASK59___ found all over the world , in which the vocal organ typically is developed in such a way as to produce a diverse and elaborate bird song . A feathered dinosaur is any ___MASK59___ of dinosaur possessing feathers . For over 150 years , since scientific research began on dinosaurs in the early 1800s , dinosaurs were generally believed to be related to the reptile ___MASK4___ ; the word " dinosaur ", coined in 1842 by paleontologist Richard Owen , comes from the Greek for " formidable lizard ". This view began to shift during the so - called dinosaur renaissance in scientific research in the late 1960s , and by the mid - 1990s significant evidence had emerged that dinosaurs are much more closely related to birds . In fact , birds are now believed to have descended directly from the theropod group of dinosaurs , and are thus classified as dinosaurs themselves , meaning that any modern bird can be considered a feathered dinosaur , since all modern birds possess feathers ( with the exception of a few artificially selected chickens ). Anchiornis is a ___MASK81___ of small , feathered , eumaniraptoran dinosaurs . The ___MASK81___ " Anchiornis " contains only the type species " Anchiornis huxleyi ". It was named in honor of Thomas Henry Huxley , an early proponent of biological evolution , and one of the first to propose a close evolutionary relationship between birds and dinosaurs . The generic name " Anchiornis " means " near bird ", and its describers cited it as important in filling a gap in the transition between the body plans of birds and dinosaurs . In biology , a taxon ( plural taxa ; back - formation from " taxonomy ") is a ___MASK41___ of one or more populations of an organism or organisms seen by taxonomists to form a unit . Although neither is required , a taxon is usually known by a particular name and given a particular ranking , especially if and when it is accepted or becomes established . It is not uncommon , however , for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion . If a taxon is given a formal scientific name , its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping . A head is the part of an organism which usually comprises the eyes , ears , nose and mouth , each of which aid in various sensory functions such as sight , hearing , smell , and taste . Some very simple animals may not have a head , but many bilaterally symmetric forms do . Heads develop in animals by an evolutionary trend known as cephalization . In bilaterally symmetrical animals , nervous tissues concentrate at the anterior region , forming structures responsible for information processing . Through biological evolution , sense organs and feeding structures also concentrate into the anterior region ; these collectively ___MASK54___ the head . A county seat is an administrative center , seat of government , or capital city of a county or civil parish . The term is used in the United States , Canada , Romania , China and Taiwan . In the United ___MASK26___ and Ireland , county towns have a similar function .