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
Errivaspis is an extinct genus of pteraspid heterostracan agnathan vertebrate known from fossils at the Wayne Hereford Quarry, of Early Devonian England, of Podolia, Early Devonian Ukraine. It was described by Dr. Errol Ivor White as one of five form-variants of Pteraspis rostrata, i.e. "Pteraspis rostrata var. waynesis. In 1984, Alain Blieck moved var. waynesis into its own genus, which he named after Dr. White. Other researchers would mistakenly assume that Blieck synonymized the entire genus of Pteraspis into Errivaspis. Errivaspis had large dorsal plates and ventral plates, the linking branchial plate, as well as a cornual plate at the side, an orbital plate around the eye. A rostral plate formed a pointed ‘snout’, several small plates around the mouth, a dorsal spine pointing backwards; the posterior half of the body was covered with small scales. The caudal fin was fan-shaped. Michael J. Benton, "Vertebrate Palaeontology" 3rd Edition, p. 48 - 49
Goniatids, informally Goniatites, are ammonoid cephalopods that form the order Goniatitida, derived from the more primitive Agoniatitida during the Middle Devonian some 390 million years ago. Goniatites survived the Late Devonian extinction to flourish during the Carboniferous and Permian only to become extinct at the end of the Permian some 139 million years later. All goniatites possessed an external shell, divided internally into chambers filled with gas giving it buoyancy during the life of the animal. An open chamber at the front of the shell provided living space for the goniatitid animal, with access to open water through a ventral siphuncle; the general morphology and habit of goniatites was similar to that of their relatives the ammonites, being free swimming and possessing a head with two well developed eyes and arms. Goniatite shells are small to medium in size always less than 15 centimeters in diameter and smaller than 5 centimeters in diameter; the shell is always planispirally coiled, unlike those of Mesozoic ammonites in which some are trochoidal and aberrant.
Goniatitid shells vary in form from thinly discoidal to broadly globular and may be smooth or distinctly ornamented. Their shape suggests; the thin walls between the internal chambers of the shell are called the septa, as the goniatite grew it would move its body forward in the shell secreting septa behind it, thereby adding new chambers to the shell. The sutures are visible as a series of wavy lines on the surface of the shell; the sutures appear. The typical goniatitid has a suture with smooth saddles and lobes, which gives the name "goniatitic" to this particular suture pattern. In some the sutures have a distinctive "zigzag" pattern. Not all goniatitid ammonoides have goniatitic sutures. In some the sutures are ceratitic, in others ammonitic. Nor are goniatitic sutures limited to the Goniatidia; the sutures of nautiloids are by comparison somewhat simpler, being either straight or curved, whereas ammonoids showed suture patterns of increasing complexity. One explanation for this increasing extravagancy in suture pattern is that it leads to a higher strength of the shell.
Ecologically, goniatites were limited to environments of normal-marine salinity—as appears to be the case for all cephalopods throughout their history. Goniatites are much more abundant and speciose in sediments that represent called epicontinental seas than they are in those that represent the open ocean. Within these inland seas, goniatites' greatest abundance and diversity appears to have been achieved in deeper offshore and basinal environments rather than in nearshore environments. Known nearshore occurrences have been ascribed to wash-in of shells from offshore waters. Due to lack of strong evidence for any particular life mode, it remains unclear what resources goniatites were capitalizing on in these offshore environments. Only a few goniatites' full trophic apparatuses have been described, reports of stomach contents in these creatures' fossils remain questionable at best. However, goniatites lacked the calcified jaw apparatuses developed in ammonites. Goniatites are found in North America, North Africa and Australasia where they are used as index fossils in age determination and stratigraphic correlation.
However, they seem to occur in areas which at the time would have been tropical to subtropical. Any fossil-bearing limestone or shale from inland seas of the late Paleozoic tropics or subtropics is to yield some goniatites. In the USA, such rocks are found from Maine, New York, Virginia and in every state west to Nebraska and south to Texas and Alabama. Notable goniatite occurrences are found in certain limestones in western part of Ireland which are packed with beautifully preserved goniatite fossils, they are found in marine bands of the Carboniferous coal measures in Europe and in marine rocks of the Pennsylvanian period in Arkansas. Large numbers of goniatites occur in rocks from the Devonian period of Morocco. Miller and Schindewolf. Evolution of Complexity in Paleozoic Ammonoid Sutures, Supplementary Material
The Hunsrück Slate is a Lower Devonian lithostratigraphic unit, a type of rock strata, in the German regions of the Hunsrück and Taunus. It is a lagerstätte famous for exceptional preservation of a diverse fossil fauna assemblage; the Emsian stratigraphy of the southern Rhenish Massif can be divided into two lithological units: the older slates of the Hunsrück-Schiefer and the younger sandstones of the Singhofener Schichten. Stratigraphically below the Hunsrück Slates is the Taunus quartzite. All these metasedimentary rocks were deposited in the marine Rhenohercynian Basin, a back-arc basin south of the paleocontinent of Laurussia; the Hunsrück Slate comprises the Sauerthal-Schichten, Bornich-Schichten and Kaub-Schichten. These are 408–400 Mya old, making them part of the Latest Pragian to Early Emsian stages of the Devonian; the Hunsrück slate was a source for Rhenish slate over several centuries. Archaeological finds in West Germany show; the first documented case of mining in this area dates from the 14th century.
The production continued with the Industrial Revolution at the end of the 1700s, but in 1846-49, the industry fell into crisis, resulting in poverty and misery in the mining areas. The economic upturn after the Franco-Prussian War of 1870-71 resulted in a renewed increase in slate production, where companies used more extensive pits. Production continued until the 1960s, when the competition from cheaper synthetic or imported slate resulted in production decline. Only a single pit in the Bundenbach region was worked in the 1990s. Since 1999, slate imports from Spain, Portugal and China caused the abandonment of local mining. Mining of Hunsrück slate was important for the discovery of fossils. Although not rare, fossils can only be found through extensive mining of slate. Many of the fine fossils exhibited in museums today were found by the slate miners; the first scientific publication on these fossils comes from Ferdinand von Roemer, who described starfish and crinoid fossils from Bundenbach.
German paleontologists such as R. Opitz, F. Broili, R. Judge, W. M. Lehmann studied many fossils between 1920 and 1959. Lehmann's death in 1959 and the decline of the slate industry caused a decline in fossil research. In 1970, Wilhelm Stürmer, a chemical physicist and radiologist at Siemens, developed a new method to examine the Hunsrück slate fossils using medium energy X-rays of 25-40 keV, he created high-resolution movies and stereoscopic images of unopened slates, which showed complex details of soft tissues that cannot be made visible with conventional methods. In the 1990s, Christoph Bartels and Günther Brassel have continued this work; the various fossil localities are quarries located south of the River Mosel and west of the Rhine in western Germany. The biota of the Hunsrück Slate are called "Bundenbach fossils" after the nearby German community of Bundenbach. More formally, the Hunsruck Slate is properly designated as a Konservat Lagerstätte due to the many fossils that exhibit preservation of soft tissues.
Hunsrück is one of the few marine Devonian Lagerstätte having soft tissue preservation, in many cases fossils are coated by a pyritic surface layer. Preservation of soft tissues as fossils requires rapid burial in an anoxic sedimentary layer where the decomposition of the organic matter is slowed; the pyritization found in Bundenbach fossils facilitated preservation and enhanced the inherent beauty of the fossils. Pyritization is rare in the fossil record, is believed to require not only rapid burial, but both burial in sediments low in organic matter, high in concentrations of sulfur and iron; such pyritization is prevalent in the lower Cambrian fossils from the Maotianshan shales of Chengjiang, the oldest Konservat Lagerstätte of Cambrian time. The best localities for exceptionally preserved fossils are in the communities of Bundenbach and Gemünden; the slates were quarried in the past for roofing tiles from small pits, of which over 600 are known. Today, only a single quarry remains open in the main fossiliferous region of Bundenbach.
There are areas of the Hunsrück Slates where fossils are neither well preserved, nor pyritized, indicating that there existed environments with shallow and oxygenated water. More than 260 animal species have been described from the Hunsrück Slate; the deposits occur in a strip some 15 km wide and 150 km long running from northwest to southeast. In the main depositional basins of Kaub and Gemünden, echinoderms are concentrated in the southwestern area around Bundenbach, with brachiopods predominating in the northeast; the presence of corals and trilobites with well-developed eyes and the rarity of plant fossils from the central basin areas suggest a shallow-water environment. Other animal fossils include sponges, brachiopods, ctenophores, cnidarians and worm trace fossils. Trilobites and echinoderms are abundant in some horizons. Crinoids and starfish are the predominant representatives of the echinoderms, although holothurians are represented. More than 60 species of crinoids are described from the Hunsrück Slate.
Many types of fishes have been described from the Hunsruck slate. Several genera of placoderm armoured fish have been recorded, including some preserved in three dimensions. Agnathan jawless fishes are the most preserved vertebrates the flattened Drepanaspis, notable for its upwards-facing mouth, the streamlined Pteraspis. Spines from acanthodii spiny sharks and a single sarcopterygian lobe-fin specimen are known. List of fossil sites
Late Devonian extinction
The Late Devonian extinction was one of five major extinction events in the history of life on Earth. A major extinction, the Kellwasser event, occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, about 376–360 million years ago. Overall, 19% of all families and 50% of all genera became extinct. A second, distinct mass extinction, the Hangenberg event, closed the Devonian period. Although it is clear that there was a massive loss of biodiversity in the Late Devonian, the timespan of this event is uncertain, with estimates ranging from 500,000 to 25 million years, extending from the mid-Givetian to the end-Famennian. Nor is it clear whether there were two sharp mass extinctions or a series of smaller extinctions, though the latest research suggests multiple causes and a series of distinct extinction pulses during an interval of some three million years; some consider the extinction to be as many as seven distinct events, spread over about 25 million years, with notable extinctions at the ends of the Givetian and Famennian stages.
By the Late Devonian, the land had been colonized by insects. In the oceans were massive reefs built by corals and stromatoporoids. Euramerica and Gondwana were beginning to converge into; the extinction seems to have only affected marine life. Hard-hit groups include brachiopods and reef-building organisms; the causes of these extinctions are unclear. Leading hypotheses include changes in sea level and ocean anoxia triggered by global cooling or oceanic volcanism; the impact of a comet or another extraterrestrial body has been suggested, such as the Siljan Ring event in Sweden. Some statistical analysis suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions; this might have been caused by invasions of cosmopolitan species, rather than by any single event. Jawed vertebrates seem to have been unaffected by the loss of reefs or other aspects of the Kellwasser event, while agnathans were in decline long before the end of the Frasnian. During the Late Devonian, the continents were arranged differently from today, with a supercontinent, covering much of the Southern Hemisphere.
The continent of Siberia occupied the Northern Hemisphere, while an equatorial continent, was drifting towards Gondwana, closing the Iapetus Ocean. The Caledonian mountains were growing across what is now the Scottish Highlands and Scandinavia, while the Appalachians rose over America; the biota was very different. Plants, on land in forms similar to mosses and lichens since the Ordovician, had just developed roots and water transport systems that allowed them to survive away from places that were wet—and built huge forests on the highlands. Several different clades had developed a shrubby or tree-like habit by the Late Givetian, including the cladoxylalean ferns, lepidosigillarioid lycopsids, aneurophyte and archaeopterid progymnosperms. Fish were undergoing a huge radiation, the first tetrapods, such as Tiktaalik, were beginning to evolve leg-like structures. Extinction rates appear to have been higher than the background rate, for an extended interval covering the last 20–25 million years of the Devonian.
During this time, about eight to ten distinct events can be seen, of which two stand out as severe. The Kellwasser event was preceded by a longer period of prolonged biodiversity loss; the fossil record of the first 15 million years of the Carboniferous period which followed is void of terrestrial animal fossils related to losses during the end-Devonian Hangenberg event. This period is known as Romer's gap; the Kellwasser event, named for its locus typicus, the Kellwassertal in Lower Saxony, Germany, is the term given to the extinction pulse that occurred near the Frasnian–Famennian boundary. Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, the first event to be detected based on marine invertebrate record. There may in fact have been two spaced events here, as shown by the presence of two distinct anoxic shale layers; the Hangenberg event is found on or just below the Devonian–Carboniferous boundary and marks the last spike in the period of extinction.
It is marked by an overlying sandstone deposit. Unlike the Kellwasser event, the Hangenberg event affected both terrestrial habitats; the extinction events were accompanied by widespread oceanic anoxia. This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil in the USA; the Kellwasser event and most other Later Devonian pulses affected the marine community, had a greater effect on shallow warm-water organisms than on cool-water organisms. The most important group to be affected by the Kellwasser event were the reef-builders of the great Devonian reef-systems, including the stromatoporoids, the rugose and tabulate corals. Reefs of the Devonian were dominated by sponges and calcifying bacteria, producing structures such as oncolites and stromatolites; the collapse of the reef system was so stark that bigger reef-building by new families of carbonate-secreting organisms, the modern scleractinian or "stony" corals, did not recover until the Mesozoic era.
Further taxa to be starkly affected include the brachiopods, ammonites and acritarchs
Pteraspis is an extinct genus of pteraspidid heterostracan agnathan vertebrate that lived in the Pragian epoch of the Devonian period in what is now Britain and Belgium. Like other heterostracan fishes, Pteraspis had a protective armored plating covering the front of its body. Though lacking fins other than its lobed tail, it is thought to have been a good swimmer thanks to stiff, wing-like protrusions derived from the armoured plates over its gills. This, along with the horn-like rostrum, made Pteraspis streamlined in shape. Pteraspis had some stiff spikes on its back an additional form of protection against predators, it is thought to have fed from shoals of plankton just under the ocean surface, is found in association with marine fossils. Pteraspis grew to a length of 20 centimeters. Parker, Steve. Dinosaurus: the complete guide to dinosaurs. Firefly Books Inc, 2003. Pg. 59
Ammonoids are an extinct group of marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs referred to as ammonites, are more related to living coleoids than they are to shelled nautiloids such as the living Nautilus species; the earliest ammonites appear during the Devonian, the last species died out in the Cretaceous–Paleogene extinction event. Ammonites are excellent index fossils, it is possible to link the rock layer in which a particular species or genus is found to specific geologic time periods, their fossil shells take the form of planispirals, although there were some helically spiraled and nonspiraled forms. The name "ammonite", from which the scientific term is derived, was inspired by the spiral shape of their fossilized shells, which somewhat resemble coiled rams' horns. Pliny the Elder called fossils of these animals ammonis cornua because the Egyptian god Ammon was depicted wearing ram's horns; the name of an ammonite genus ends in -ceras, Greek for "horn".
Ammonites can be distinguished by their septa, the dividing walls that separate the chambers in the phragmocone, by the nature of their sutures where the septa joint the outer shell wall, in general by their siphuncles. Ammonoid septa characteristically have bulges and indentations and are to varying degrees convex from the front, distinguishing them from nautiloid septa which are simple concave dish-shaped structures; the topology of the septa around the rim, results in the various suture patterns found. Three major types of suture patterns are found in the Ammonoidea: Goniatitic - numerous undivided lobes and saddles; this pattern is characteristic of the Paleozoic ammonoids. Ceratitic - lobes have subdivided tips, giving them a saw-toothed appearance, rounded undivided saddles; this suture pattern is characteristic of Triassic ammonoids and appears again in the Cretaceous "pseudoceratites". Ammonitic - lobes and saddles are much subdivided. Ammonoids of this type are the most important species from a biostratigraphical point of view.
This suture type is characteristic of Jurassic and Cretaceous ammonoids, but extends back all the way to the Permian. The siphuncle in most ammonoids is a narrow tubular structure that runs along the shell's outer rim, known as the venter, connecting the chambers of the phragmocone to the body or living chamber; this distinguishes them from living nautiloides and typical Nautilida, in which the siphuncle runs through the center of each chamber. However the earliest nautiloids from the Late Cambrian and Ordovician had ventral siphuncles like ammonites, although proportionally larger and more internally structured; the word "siphuncle" comes from the New Latin siphunculus, meaning "little siphon". Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian and became extinct at the close of the Cretaceous along with the dinosaurs; the classification of ammonoids is based in part on the ornamentation and structure of the septa comprising their shells' gas chambers.
While nearly all nautiloids show curving sutures, the ammonoid suture line is variably folded, forming saddles and lobes. The Ammonoidea can be divided into six orders, listed here starting with the most primitive and going to the more derived: Agoniatitida, Lower Devonian - Middle Devonian Clymeniida, Upper Devonian Goniatitida, Middle Devonian - Upper Permian Prolecanitida, Upper Devonian - Upper Triassic Ceratitida, Upper Permian - Upper Triassic Ammonitida, Lower Jurassic - Upper CretaceousIn some classifications, these are left as suborders, included in only three orders: Goniatitida and Ammonitida; the Treatise on Invertebrate Paleontology divides the Ammonoidea, regarded as an order, into eight suborders, the Anarcestina, Clymeniina and Prolecanitina from the Paleozoic. In subsequent taxonomies, these are sometimes regarded as orders within the subclass Ammonoidea; because ammonites and their close relatives are extinct, little is known about their way of life. Their soft body parts are rarely preserved in any detail.
Nonetheless, much has been worked out by examining ammonoid shells and by using models of these shells in water tanks. Many ammonoids lived in the open water of ancient seas, rather than at the sea bottom, because their fossils are found in rocks laid down under conditions where no bottom-dwelling life is found. Many of them are thought to have been good swimmers, with flattened, discus-shaped, streamlined shells, although some ammonoids were less effective swimmers and were to have been slow-swimming bottom-dwellers. Synchrotron analysis of an aptychophoran ammonite revealed remains of isopod and mollusc larvae in its buccal cavity, indicating at least this kind of ammonite fed on plankton, they may have avoided predation by squirting ink, much like modern cephalopods. The soft body of the creature occupied the largest segments of the shell at the end of the coil; the smaller earlier segments were walled off and the animal could maintain its buoyancy by filling them with gas. Thus, the smaller sections of the coil would have floated ab