The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
An auk or alcid is a bird of the family Alcidae in the order Charadriiformes. The alcid family includes the murres, auklets and murrelets. Apart from the extinct great auk, all auks are notable for their ability to "fly" under water as well as in the air. Although they are excellent swimmers and divers, their walking appears clumsy. Several species have different common names in North America; the guillemots of Europe are referred to as murres in North America, if they occur in both continents, the little auk is referred to as the dovekie. Auks are superficially similar to penguins having black-and-white colours, upright posture and some of their habits, they are not related to penguins, but rather are believed to be an example of moderate convergent evolution. Auks are monomorphic. Extant auks range in size from the least auklet, at 85 g and 15 cm, to the thick-billed murre, at 1 kg and 45 cm. Due to their short wings, auks have to flap their wings quickly in order to fly. Although not to the extent of penguins, auks have sacrificed flight, mobility on land, in exchange for swimming ability.
This varies by subfamily, the Uria guillemots and murrelets being the most efficient under the water, whereas the puffins and auklets are better adapted for flying and walking. The feeding behaviour of auks is compared to that of penguins. In the region where auks live, their only seabird competition are cormorants. In areas where the two groups feed on the same prey, the auks tend to feed further offshore. Strong-swimming murres hunt faster schooling fish. Time depth recorders on auks have shown that they can dive as deep as 100 m in the case of Uria guillemots, 40 m for the Cepphus guillemots and 30 m for the auklets. Auks are pelagic birds, spending the majority of their adult life on the open sea and going ashore only for breeding, although some species — like the common guillemot — spend a great part of the year defending their nesting spot from others. Auks are monogamous, tend to form lifelong pairs, they lay a single egg, they are philopatric. Some species, such as the Uria guillemots, nest in large colonies on cliff edges.
All species except the Brachyramphus murrelets are colonial. Traditionally, the auks were believed to be one of the earliest distinct charadriiform lineages due to their characteristic morphology. However, genetic analyses have demonstrated that these peculiarities are the product of strong natural selection instead: as opposed to, for example, auks radically changed from a wading shorebird to a diving seabird lifestyle. Thus, the auks are no longer separated in their own suborder, but are considered part of the Lari suborder which otherwise contains gulls and similar birds. Judging from genetic data, their closest living relatives appear to be the skuas, with these two lineages separating about 30 million years ago. Alternatively, auks may have split off far earlier from the rest of the Lari and undergone strong morphological, but slow genetic evolution, which would require a high evolutionary pressure, coupled with a long lifespan and slow reproduction; the earliest unequivocal fossils of auks are from some 35 mya.
The genus Miocepphus, is the earliest known from good specimens. Two fragmentary fossils are assigned to the Alcidae, although this may not be correct: Hydrotherikornis and Petralca. Most extant genera are known to exist since the Late Early Pliocene. Miocene fossils have been found in both California and Maryland, but the greater diversity of fossils and tribes in the Pacific leads most scientists to conclude that it was there they first evolved, it is in the Miocene Pacific that the first fossils of extant genera are found. Early movement between the Pacific and the Atlantic happened to the south movements across the Arctic Ocean; the flightless subfamily Mancallinae, restricted to the Pacific coast of southern North America and became extinct in the Early Pleistocene, is sometimes includes in the family Alcidae under some definitions. One species, Miomancalla howardae, is the largest charadriiform of all time; the extant auks are broken up into 2 main groups: the high-billed puffins and auklets, as opposed to the more slender-billed murres and true auks, the murrelets and guillemots.
The tribal arrangement was based on analyses of morphology and ecology. MtDNA cytochrome b sequence and allozyme studies confirm these findings except that the Synthliboramphus murrelets should be split into a distinct tribe, as they appear more related to the Alcini – in any case, assumption of a closer relationship between the former and the true guillemots was only weakly supported by earlier studies. Of the genera there are only a few species in each; this is a product of the rather small geographic range of the family, the periods of glacial advance and retreat that have
Neoaves is a clade that consists of all modern birds with the exception of Paleognathae and Galloanserae. 95% of the 10,000 known species of modern birds belong to the Neoaves. The early diversification of the various neoavian groups occurred rapidly around the Cretaceous–Paleogene extinction event, attempts to resolve their relationships with each other have resulted in much controversy. One hypothesis for the phylogeny of modern birds was presented by Prum, R. O. et al. The following cladogram illustrates the proposed relationships, with some taxon names following Yury, T. et al. and Kimball et al. 2013
The oystercatchers are a group of waders forming the family Haematopodidae, which has a single genus, Haematopus. They are found on coasts worldwide apart from the polar regions and some tropical regions of Africa and South East Asia; the exception to this is the Eurasian oystercatcher and the South Island oystercatcher, both of which breed inland, far inland in some cases. In the past there has been a great deal of confusion as to the species limits, with discrete populations of all black oystercatchers being afforded specific status but pied oystercatchers being considered one single species; the name oystercatcher was coined by Mark Catesby in 1731 as a common name for the North American species H. palliatus, described as eating oysters. Yarrell in 1843 established this as the preferred term, replacing the older name sea sea-pie; the genus name Haematopus comes from the Greek haima αἳμα blood, pous πούς foot. The different species of oystercatcher show little variation in appearance, they range from 39–50 cm in length and 72–91 cm in wingspan.
The Eurasian oystercatcher is the lightest on average, at 526 g, while the sooty oystercatcher is the heaviest, at 819 g. The plumage of all species is either all-black, or black on white underneath; the variable oystercatcher is exceptional in being either all-black or pied. They are large and noisy plover-like birds, with massive long orange or red bills used for smashing or prying open molluscs; the bill shape varies according to the diet. Those birds with blade-like bill tips pry open or smash mollusc shells, those with pointed bill tips tend to probe for annelid worms, they show sexual dimorphism, with females being longer-billed and heavier than males. The diet of oystercatchers varies with location. Species occurring inland feed upon earthworms and insect larvae; the diet of coastal oystercatchers is more varied, although dependent upon coast type. Other prey items include echinoderms and crabs. Nearly all species of oystercatcher are monogamous, although there are reports of polygamy in the Eurasian oystercatcher.
They are territorial during the breeding season. There is strong mate and site fidelity in the species that have been studied, with one record of a pair defending the same site for 20 years. A single nesting attempt is made per breeding season, timed over the summer months; the nests of oystercatchers are simple affairs, scrapes in the ground which may be lined, placed in a spot with good visibility. The eggs of oystercatchers are spotted and cryptic. Between one and four eggs are laid, with three being typical in the Northern Hemisphere and two in the south. Incubation is shared but not proportionally, females tend to take more incubation and males engage in more territory defence. Incubation varies by lasting between 24 -- 39 days. Oystercatchers are known to practice "egg dumping." Like the cuckoo, they sometimes lay their eggs in the nests of other species such as seagulls, abandoning them to be raised by those birds. The Canary Islands oystercatcher became extinct during the 20th century; the Chatham oystercatcher is endemic to the Chatham Islands of New Zealand but is listed as endangered by the IUCN, while both the African and Eurasian oystercatchers are considered near threatened.
There has been conflict with commercial shellfish farmers, but studies have found that the impact of oystercatchers is much smaller than that of shore crabs. One fossil species is known: Haematopus sulcatus from the early Pliocene of Florida. ARKive – images and movies of the oystercatcher Oystercatcher videos on the Internet Bird Collection LIVE webcam at the seashore in Namsos, Norway 2013
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era; as with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish. Multi-cellular life began to appear on land in the form of small, bryophyte-like and vascular plants that grew beside lakes and coastlines, terrestrial arthropods are first found on land during the Silurian. However, terrestrial life would not diversify and affect the landscape until the Devonian; the Silurian system was first identified by British geologist Roderick Murchison, examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s.
He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, from the Latin name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, the germ of the modern geological time scale; as it was first identified, the "Silurian" series when traced farther afield came to overlap Sedgwick's "Cambrian" sequence, provoking furious disagreements that ended the friendship. Charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was "Gotlandian" after the strata of the Baltic island of Gotland; the French geologist Joachim Barrande, building on Murchison's work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge.
He divided the Silurian rocks of Bohemia into eight stages. His interpretation was questioned in 1854 by Edward Forbes, the stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils; the Llandovery Epoch lasted from 443.8 ± 1.5 to 433.4 ± 2.8 mya, is subdivided into three stages: the Rhuddanian, lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years ago, the Telychian. The epoch is named for the town of Llandovery in Wales; the Wenlock, which lasted from 433.4 ± 1.5 to 427.4 ± 2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in England. During the Wenlock, the oldest-known tracheophytes of the genus Cooksonia, appear; the complexity of later Gondwana plants like Baragwanathia, which resembled a modern clubmoss, indicates a much longer history for vascular plants, extending into the early Silurian or Ordovician.
The first terrestrial animals appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, the Ludfordian stage. It is named for the town of Ludlow in England; the Přídolí, lasting from 423 ± 1.5 to 419.2 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area. In North America a different suite of regional stages is sometimes used: Cayugan Lockportian Tonawandan Ontarian Alexandrian In Estonia the following suite of regional stages is used: Ohessaare stage Kaugatuma stage Kuressaare stage Paadla stage Rootsiküla stage Jaagarahu stage Jaani stage Adavere stage Raikküla stage Juuru stage With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe.
The high sea levels of the Silurian and the flat land resulted in a number of island chains, thus a rich diversity of environmental settings. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late-Ordovician glaciation; the southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity; the continents of Avalonia and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. When the proto-Europe coll
Seabirds are birds that are adapted to life within the marine environment. While seabirds vary in lifestyle and physiology, they exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations; the first seabirds evolved in the Cretaceous period, modern seabird families emerged in the Paleogene. In general, seabirds live longer and have fewer young than other birds do, but they invest a great deal of time in their young. Most species nest in colonies. Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases, they feed both at the ocean's surface and below it, feed on each other. Seabirds can be pelagic, coastal, or in some cases spend a part of the year away from the sea entirely. Seabirds and humans have a long history together: they have provided food to hunters, guided fishermen to fishing stocks and led sailors to land. Many species are threatened by human activities, conservation efforts are under way.
There exists no single definition of which groups and species are seabirds, most definitions are in some way arbitrary. In the words of two seabird scientists, "The one common characteristic that all seabirds share is that they feed in saltwater. However, by convention all of the Sphenisciformes and Procellariiformes, all of the Pelecaniformes except the darters, some of the Charadriiformes are classified as seabirds; the phalaropes are included as well, since although they are waders, two of the three species are oceanic for nine months of the year, crossing the equator to feed pelagically. Loons and grebes, which nest on lakes but winter at sea, are categorized as water birds, not seabirds. Although there are a number of sea ducks in the family Anatidae that are marine in the winter, by convention they are excluded from the seabird grouping. Many waders and herons are highly marine, living on the sea's edge, but are not treated as seabirds. Sea eagles and other fish-eating birds of prey are typically excluded, however tied to marine environments they may be.
Seabirds, by virtue of living in a geologically depositional environment, are well represented in the fossil record. They are first known to occur in the Cretaceous period, the earliest being the Hesperornithiformes, like Hesperornis regalis, a flightless loon-like seabird that could dive in a fashion similar to grebes and loons but had a beak filled with sharp teeth. Flying Cretaceous seabirds do not exceed wingspans of two meters. While Hesperornis is not thought to have left descendants, the earliest modern seabirds occurred in the Cretaceous, with a species called Tytthostonyx glauconiticus, which seems allied to the Procellariiformes and Pelecaniformes. In the Paleogene both pterosaurs and marine reptiles became extinct, allowing seabirds to expand ecologically; these post-extinction seas were dominated by early Procellariidae, giant penguins and two extinct families, the Pelagornithidae and the Plotopteridae. Modern genera began their wide radiation in the Miocene, although the genus Puffinus might date back to the Oligocene.
The highest diversity of seabirds existed during the Late Miocene and the Pliocene. At the end of the latter, the oceanic food web had undergone a period of upheaval due to extinction of considerable numbers of marine species. Seabirds have made numerous adaptations to feeding in the sea. Wing morphology has been shaped by the niche an individual species or family has evolved, so that looking at a wing's shape and loading can tell a scientist about its life feeding behaviour. Longer wings and low wing loading are typical of more pelagic species, while diving species have shorter wings. Species such as the wandering albatross, which forage over huge areas of sea, have a reduced capacity for powered flight and are dependent on a type of gliding called dynamic soaring as well as slope soaring. Seabirds almost always have webbed feet, to aid movement on the surface as well as assisting diving in some species; the Procellariiformes are unusual among birds in having a strong sense of smell, used to find distributed food in a vast ocean, to locate their colonies.
Salt glands are used by seabirds to deal with the salt they ingest by drinking and feeding, to help them osmoregulate. The excretions from these glands are pure sodium chloride. With the exception of the cormorants and some terns, in common with most other birds, all seabirds have waterproof plumage. However, compared to land birds, they have far more feathers protecting their bodies; this dense plumage is better able to protect the bird from getting wet, cold is kept out by a dense layer of down feathers. The cormorants possess a layer of unique feathers that retain a smaller layer of air but otherwise soak up water; this allows them to swim without fighting the buoyancy that retai
Neognaths are birds within the subclass Neornithes of the class Aves. The Neognathae include all living birds. There are nearly 10,000 species of neognaths; the earliest fossils are known from the end of the Cretaceous but molecular clocks suggest that neognaths originated sometime in the first half of the Late Cretaceous about 90 million year ago. Since they have undergone adaptive radiation producing the diversity of form and behavior that we see today, it includes the order Passeriformes, the largest clade of land vertebrates, containing some 60% of living birds and being more than twice as speciose as rodents and about five times as speciose as Chiroptera, which are the largest clades of mammals. There are some small orders birds of unclear relationships like the puzzling hoatzin; the neognaths have fused metacarpals, an elongate third finger, 13 or fewer vertebrae. They differ from the Palaeognathae in features like the structure of their jawbones. "Neognathae" means "new jaws", but it seems that the "more ancient" paleognath jaws are among the few apomorphic features of the Palaeognaths, meaning that the respective jaw structure of these groups is not informative in terms of comparative evolution.
The Neognathae were long ranked as a superorder subdivided into orders. Attempts to organise this group further, as in the Conspectus of Charles Lucien Bonaparte, were never accepted by a significant majority of ornithologists; until the 1980s, there was little subdivision of the Aves in general, less of phylogenetic merit. Since the availability of massive amounts of new data from fossils and molecular sequences allowed scientists to refine the classification. With new groups of neognath orders being verified, the taxonomic rank of the group needed to shift. Most researchers have now employed the unranked taxa of phylogenetic nomenclature; the Neognathae are now universally accepted to subdivide into two lineages, the "fowl" clade Galloanseres and the Neoaves. The subdivisions of the latter are still not well resolved, but several monophyletic lineages have been proposed, such as the Mirandornithes, Cypselomorphae and Coronaves. Although groups such as the former two are robustly supported, this cannot be said for the Metaves and Coronaves division for which there is no material evidence at present, while the Mesozoic record of Neognathae is at present utterly devoid of birds that should have been present if these proposed clades were real.
The orders are arranged in a sequence. It differs from the used Clements taxonomy as well as from the Sibley-Ahlquist taxonomy, combining those elements from each that more modern research agrees with while updating those that are refuted. Most of the changes affect those "higher landbirds". Feduccia defined the clade Neognathia as birds whose palatal mobility increased due to the following modifications: Loss of the Basipterygoid articulation with the cranium. Development of a pterygoid/palatine joint. Reduction of the vomer, such that it does not reach caudally to the pterygoid, or is lost entirely. Neognathae cladogram of modern bird relationships based on Prum, R. O. et al. with some clade names after Kimball et al.. 2013. Claramunt, S.. "A new time tree reveals Earth history's imprint on the evolution of modern birds". Sci Adv. 1: e1501005. Doi:10.1126/sciadv.1501005. PMC 4730849. PMID 26824065. Mindell, David P. & Brown, Joseph W.: The Tree of Life Web Project - Neornithes. Version of 2005-DEC-14.
Retrieved 2008-JAN-08. Mindell, David P.. Version of 2005-DEC-14. Retrieved 2008-JAN-08. Tree of Life: Neoaves Tree of Life: Galloanserae