A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
The oilbird, locally known as the guácharo, is a bird species found in the northern areas of South America including the island of Trinidad. It is the only species in the family Steatornithidae. Nesting in colonies in caves, oilbirds are nocturnal feeders on the fruits of the oil palm and tropical laurels, they are the only nocturnal flying fruit-eating birds in the world. They forage with specially adapted eyesight; however they navigate by echolocation in the same way as one of the few birds to do so. They produce a high-pitched clicking sound of around 2 kHz, audible to humans. Oilbirds are related to the nightjars and placed with these in the order Caprimulgiformes. However, the nightjars and their relatives are insectivores while the oilbird is a specialist fructivore, it is sufficiently distinctive to be placed in a family and suborder of its own; some research indicates that it should be considered a distinct order. The caripensis of the binomial name means "of Caripe", Steatornis means "fat bird", in reference to the fatness of the chicks.
The oilbird is called a tayo in Spanish, both terms being of indigenous origin. In Trinidad it was sometimes called diablotin referring to its loud cries, which have been likened to those of tortured men; the common name "oilbird" comes from the fact that in the past chicks were captured and boiled down in order to make oil. The fossil record of the family suggests that they were once more distributed around the globe; the first fossil oilbird was described by Storrs Olson in 1987 from a fossil found in the Green River Formation in Wyoming. The species, Prefica nivea was not adapted to hovering flight or living in caves, unlike the oilbird; some of the same families and genera of plants the present day oilbird feeds on have been found in the Green River Formation, suggesting that prehistoric species may have eaten the same fruit and spread the same seeds. Another species from the Upper Eocene has been discovered in France; this is a slim bird at 40 -- 49 cm, with a wing span of 95 cm. It has a flattened, powerfully hooked, bill surrounded by deep chestnut rictal bristles up to 5 centimetres long.
The adult weighs 350–475 g but the chicks can weigh more, at up to 600 grams, when their parents feed them a good deal of fruit before they fly. The feathers of the oilbird are soft like those of many nightbirds, but not as soft as those of owls or nightjars, as they do not need to be silent like predatory species; the oilbird is reddish-brown with white spots on the nape and wings. Lower parts are cinnamon-buff with white diamond-shaped spots edged in black, these spots start small towards the throat and get larger towards the back; the stiff tail feathers are a rich brown spotted with white on either side. The feet are small and useless, other than for clinging to vertical surfaces; the long wings have evolved to make it capable of hovering and twisting flight, which enables it to navigate through restricted areas of its caves. For example, the wings have deep wingtip slotting, like New World vultures, to reduce the stalling speed, the wings have a low aspect ratio and low wing-loading, all to make the oilbird capable of flying at low speeds.
The eyes of oilbirds are adapted to nocturnal foraging. The eyes are small, but the pupils are large, allowing the highest light-gathering capacity of any bird; the retina is dominated by rod cells, 1,000,000 rods per mm2, the highest density of any vertebrate eye, which are organised in layers, an arrangement unique among birds but shared by deep-sea fish. They have low numbers of cone cells, the whole arrangement would allow them to capture more light in low light conditions but have poor vision in daylight. Although they have specially adapted vision to forage by sight, they are among the few birds known to supplement sight by echolocation in sufficiently poor light conditions, using a series of sharp audible clicks for this purpose; the only other birds known to do this are some species of swift. In addition to clicks used for echolocation oilbirds produce a variety of harsh screams while in their caves. Entering a cave with a light provokes these raucous calls; the oilbird ranges from Guyana and the island of Trinidad to Venezuela, Ecuador, Peru and Brazil.
They range from sea-level to 3,400 m. The species has specific habitat requirements, needing both caves to breed in and roost in and forest containing fruiting trees. Where suitable caves are absent oilbirds will roost and breed in narrow gorges and grottos with suitable rock shelves. One such colony in Ecuador held a colony of a hundred birds in a canyon with ledges protected by vegetation; some smaller caves and gorges are used only for roosting. While it was once thought that oildbirds always or nearly always roosted in caves, canyons or gullies, researchers placing GPS trackers on non-breeding birds found that they roost in trees in the forest as well as in caves, it is a seasonal migrant across some of its range, moving from its breeding caves in search of fruit trees. It has occurred as a rare vagrant to Costa Rica and Aruba; the Guácharo Cave, in the mountainous Caripe district of northern Monagas, Venezuela, is where Alexander von Humboldt first studied the species. Oilbirds are nocturnal.
During the day the birds leave at night to find fruit outside the cave. It was once thought tha
Fowl are birds belonging to one of two biological orders, namely the gamefowl or landfowl and the waterfowl. Studies of anatomical and molecular similarities suggest these two groups are close evolutionary relatives; this clade is supported by morphological and DNA sequence data as well as retrotransposon presence/absence data. As opposed to "fowl", "poultry" is a term for any kind of domesticated bird or bird captive-raised for meat, eggs, or feathers. In colloquial speech, the term "fowl" is used near-synonymously with "poultry," and many languages do not distinguish between "poultry" and "fowl". Nonetheless, the fact that the Galliformes and Anseriformes most form a monophyletic group makes a distinction between "fowl" and "poultry" warranted; the historic difference is due to the Germanic/Latin split word pairs characteristic of Middle English. Many birds that are eaten by humans are fowl, including poultry such as chickens or turkeys, game birds such as pheasants or partridges, other wildfowl like guineafowl or peafowl, waterfowl such as ducks or geese.
While they are quite diverse ecologically and in an adaptation to their different lifestyles morphologically and ethologically, some features still unite water- and landfowl. Many of these, are plesiomorphic for Neornithes as a whole, are shared with paleognaths. Galloanserae are prolific. By comparison, birds of prey and pigeons lay more than two eggs. While most living birds are monogamous, at least for a breeding season, many Galloanserae are notoriously polygynous or polygamous. To ornithologists, this is well known in dabbling ducks, where the males band together to "gang rape" unwilling females; the general public is most familiar with the polygynous habits of domestic chickens, where one or two roosters are kept with a whole flock of females. Hybridization is frequent in the Galloanserae, genera, not known to produce viable hybrids in birds, can be brought to interbreed with comparative ease. Guineafowl have produced hybrids with domestic fowl and Indian peafowl, to which they are not closely related as Galliformes go.
This is an important factor complicating mtDNA sequence-based research on their relationships. The mallards of North America, for example, are mostly derived from some males which arrived from Siberia, settled down, mated with American black duck ancestors. See Gamebird hybrids. Galloanserae young are remarkably precocious. Anseriform young are able to swim and dive a few hours after hatching, the hatchlings of mound-builders are feathered and able to fly for prolonged distances as soon as they emerge from the nest mound. From the limited fossils that have to date been recovered, the conclusion that the Galloanserae were widespread—the predominant group of modern birds—by the end of the Cretaceous is accepted nowadays. Fossils such as Vegavis indicate that modern waterfowl, albeit belonging to a now-extinct lineage, were contemporaries of the nonavian dinosaurs. While the dominant aviformes of the mesozoic, the enantiornithes, all died out with the dinosaurs, the galloanserae survived to become the first successful group of modern birds after the dinosaurs died out.
As opposed to the morphologically conservative Galliformes, the Anseriformes have adapted to filter-feeding and are characterized by a large number of autapomorphies related to this lifestyle. The advanced feeding systems of the Anseriformes, together with similarities of the early anseriform Presbyornis to shorebirds, had prompted some scientists to ally Anseriformes with Charadriiformes, instead. However, as strong support for the Galloanserae has emerged in subsequent studies, the fowl clade continues to be accepted as a genuine evolutionary lineage by the vast majority of scientists. Benson, D.: Presbyornis isoni and other late Paleocene birds from North Dakota. Smithsonian Contributions to Paleobiology 69: 253-266. Chubb, A.: New nuclear evidence for the oldest divergence among neognath birds: the phylogenetic utility of ZENK. Molecular Phylogenetics and Evolution 30: 140-151 Feduccia, A.: The Origin and Evolution of Birds, Second Edition. Yale University Press, New Haven. Kriegs, Jan Ole.
BMC Evolutionary Biology 7: 190. Kulikova, Irina V.. V.. D.. J.. Auk 122: 949-965. DOI: 10.1642/0004-80381222.0. CO. Erratum: Auk 122: 1309. DOI: 10.1642/0004-80381222.0. CO. G.. E. & Monroe, B. L.: A classification of the living birds of the world based on DNA-DNA hybridization studies. Auk 105: 409-423. "Fowl". Collier
The Holocene is the current geological epoch. It began 11,650 cal years before present, after the last glacial period, which concluded with the Holocene glacial retreat; the Holocene and the preceding Pleistocene together form the Quaternary period. The Holocene has been identified with the current warm period, known as MIS 1, it is considered by some to be an interglacial period within the Pleistocene Epoch. The Holocene has seen the growth and impacts of the human species worldwide, including all its written history, development of major civilizations, overall significant transition toward urban living in the present. Human impacts on modern-era Earth and its ecosystems may be considered of global significance for future evolution of living species, including synchronous lithospheric evidence, or more hydrospheric and atmospheric evidence of human impacts. In July 2018, the International Union of Geological Sciences split the Holocene epoch into three distinct subsections, Greenlandian and Meghalayan, as proposed by International Commission on Stratigraphy.
The boundary stratotype of Meghalayan is a speleothem in Mawmluh cave in India, the global auxiliary stratotype is an ice core from Mount Logan in Canada. The name Holocene comes from the Ancient Greek words ὅλος and καινός, meaning "entirely recent", it is accepted by the International Commission on Stratigraphy that the Holocene started 11,650 cal years BP. The Subcommission on Quaternary Stratigraphy quotes Gibbard and van Kolfschoten in Gradstein Ogg and Smith in stating the term'Recent' as an alternative to Holocene is invalid and should not be used and observe that the term Flandrian, derived from marine transgression sediments on the Flanders coast of Belgium has been used as a synonym for Holocene by authors who consider the last 10,000 years should have the same stage-status as previous interglacial events and thus be included in the Pleistocene; the International Commission on Stratigraphy, considers the Holocene an epoch following the Pleistocene and the last glacial period. Local names for the last glacial period include the Wisconsinan in North America, the Weichselian in Europe, the Devensian in Britain, the Llanquihue in Chile and the Otiran in New Zealand.
The Holocene can be subdivided into five time intervals, or chronozones, based on climatic fluctuations: Preboreal, Atlantic and Subatlantic. Note: "ka" means "kilo-annum" Before Present, i.e. 1,000 years before 1950 The Blytt–Sernander classification of climatic periods defined by plant remains in peat mosses, is being explored. Geologists working in different regions are studying sea levels, peat bogs and ice core samples by a variety of methods, with a view toward further verifying and refining the Blytt–Sernander sequence, they find a general correspondence across Eurasia and North America, though the method was once thought to be of no interest. The scheme was defined for Northern Europe, but the climate changes were claimed to occur more widely; the periods of the scheme include a few of the final pre-Holocene oscillations of the last glacial period and classify climates of more recent prehistory. Paleontologists have not defined any faunal stages for the Holocene. If subdivision is necessary, periods of human technological development, such as the Mesolithic and Bronze Age, are used.
However, the time periods referenced by these terms vary with the emergence of those technologies in different parts of the world. Climatically, the Holocene may be divided evenly into the Neoglacial periods. According to some scholars, a third division, the Anthropocene, has now begun; the International Commission on Stratigraphy Subcommission on Quaternary Stratigraphy’s working group on the'Anthropocene' note this term is used to denote the present time interval in which many geologically significant conditions and processes have been profoundly altered by human activities. The'Anthropocene' is not a formally defined geological unit. Continental motions due to plate tectonics are less than a kilometre over a span of only 10,000 years. However, ice melt caused world sea levels to rise about 35 m in the early part of the Holocene. In addition, many areas above about 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as 180 m due to post-glacial rebound over the late Pleistocene and Holocene, are still rising today.
The sea level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea. Holocene marine fossils are known, from Vermont and Michigan. Other than higher-latitude temporary marine incursions associated with glacial depression, Holocene fossils are found in lakebed and cave deposits. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any tectonic uplift of non-glacial origin. Post-glacial rebound in the Scandinavia region resulted in the formation of the Baltic Sea; the region continues to rise, still causing weak earthquakes across Northern Europe. The equivalent event in North America was the rebound of Hudson Bay, as it shrank from its larger, immediate post-glacial Tyrrell Sea phase, to near its present boundaries. Climate has been stable over the Holocene. Ice core
Palaeognathae, or paleognaths, is one of the two living clades of birds – the other being Neognathae. Together, these two clades form the clade Neornithes. Palaeognathae contains five extant branches of flightless lineages, termed ratites, one flying lineage, the Neotropic tinamous. There are 47 species of tinamous, 5 of kiwis, 3 of cassowaries, 1 of emus, 2 of rheas and 2 of ostrich. Recent research has indicated that paleognaths are monophyletic but the traditional taxonomic split between flightless and flighted forms is incorrect. There are three extinct groups, the Lithornithiformes, the Dinornithiformes and the Aepyornithiformes, that are undisputed members of Palaeognathae. There are other extinct birds which have been allied with the Palaeognathae by at least one author, but their affinities are a matter of dispute; the word Paleognath is derived from the ancient Greek for "old jaws" in reference to the skeletal anatomy of the palate, described as more primitive and reptilian than that in other birds.
Paleognathous birds retain some basal morphological characters but are by no means living fossils as their genomes continued to evolve at the DNA level under selective pressure at rates comparable to the Neognathae branch of living birds, though there is some controversy about the precise relationship between them and the other birds. There are several other scientific controversies about their evolution. No unambiguously paleognathous fossil birds are known until the Cenozoic, but there have been many reports of putative paleognathes, it has long been inferred that they may have evolved in the Cretaceous. Given the northern hemisphere location of the morphologically most basal fossil forms, a Laurasian origin for the group can be inferred; the present entirely Gondwanan distribution would have resulted from multiple colonisations of the southern landmasses by flying forms that subsequently evolved flightlessness, in many cases, gigantism. One study of molecular and paleontological data found that modern bird orders, including the paleognathous ones, began diverging from one another in the Early Cretaceous.
Benton summarized this and other molecular studies as implying that paleognaths should have arisen 110 to 120 million years ago in the Early Cretaceous. He points out, that there is no fossil record until 70 million years ago, leaving a 45 million year gap, he asks whether the paleognath fossils will be found one day, or whether the estimated rates of molecular evolution are too slow, that bird evolution accelerated during an adaptive radiation after the Cretaceous–Paleogene boundary. Other authors questioned the monophyly of the Palaeognathae on various grounds, suggesting that they could be a hodgepodge of unrelated birds that have come to be grouped together because they are coincidentally flightless. Unrelated birds might have developed ratite-like anatomies multiple times around the world through convergent evolution. McDowell asserted that the similarities in the palate anatomy of paleognathes might be neoteny, or retained embryonic features, he noted that there were other feature of the skull, such as the retention of sutures into adulthood, that were like those of juvenile birds.
Thus the characteristic palate was a frozen stage that many carinate bird embryos passed through during development. The retention of early developmental stages may have been a mechanism by which various birds became flightless and came to look similar to one another. Hope reviewed all known bird fossils from the Mesozoic looking for evidence of the origin of the evolutionary radiation of the Neornithes; that radiation would signal that the paleognaths had diverged. She notes five Early Cretaceous taxa, she finds that none of them can be assigned as such. However, she does find evidence that the Neognathae and, therefore the Palaeognathae had diverged no than the Early Campanian age of the Cretaceous period. Vegavis is a fossil bird from the Albian period of Early Cretaceous Antarctica. Vegavis is most related to true ducks; because all phylogenetic analyses predict that ducks diverged after paleognathes, this is evidence that paleognathes had arisen well before that time. An exceptionally preserved specimen of the extinct flying paleognathe Lithornis was published by Leonard et al. in 2005.
It is an articulated and nearly complete fossil from the early Eocene of Denmark, thought to have the best preserved lithornithiform skull found. The authors concluded that Lithornis was a close sister taxon to tinamous, rather than ostriches, that the lithorniforms + tinamous were the most basal paleognaths, they concluded that all ratites, were monophyletic, descending from one common ancestor that became flightless. They interpret the paleognath-like Limenavis, from Early Cretaceous Patagonia, as possible evidence of a Cretaceous and monophyletic origin for paleognathes. An ambitious genomic analysis of the living birds was performed in 2007, it contradicted Leonard et al.. It found that tinamous are not primitive among the most advanced; this requires multiple events of flightlessness within the paleognathes and refutes the Gondwana vicariance hypothesis. The st
The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, its base, are somewhat in flux; the period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells; as a result, our understanding of the Cambrian biology surpasses that of some periods. The Cambrian marked a profound change in life on Earth. Complex, multicellular organisms became more common in the millions of years preceding the Cambrian, but it was not until this period that mineralized—hence fossilized—organisms became common; the rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates. Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia; the seas were warm, polar ice was absent for much of the period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified; the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia and Newfoundland, in the western USA.
The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, in Spain. The Cambrian Period was followed by the Ordovician Period; the Cambrian is divided into ten ages. Only three series and six stages are named and have a GSSP; because the international stratigraphic subdivision is not yet complete, many local subdivisions are still used. In some of these subdivisions the Cambrian is divided into three series with locally differing names – the Early Cambrian, Middle Cambrian and Furongian. Rocks of these epochs are referred to as belonging to Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian; each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance: *Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was held to represent the first appearance of complex life, represented by trilobites; the recognition of small shelly fossils before the first trilobites, Ediacara biota earlier, led to calls for a more defined base to the Cambrian period. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, it is the T. pedum ichnofossil assemblage, now formally used to correlate the base of the Cambrian. This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate.
A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, to the disappearance of distinctive Ediacaran fossils. There are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata — which w