The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, the longest period of the Phanerozoic Eon; the Cretaceous Period is abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas; these oceans and seas were populated with now-extinct marine reptiles and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared; the Cretaceous ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk, found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from Latin creta; the Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use; as with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is defined, being placed at an iridium-rich layer found worldwide, believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico.
This layer has been dated at 66.043 Ma. A 140 Ma age for the Jurassic-Cretaceous boundary instead of the accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. From youngest to oldest, the subdivisions of the Cretaceous period are: Late Cretaceous Maastrichtian – Campanian – Santonian – Coniacian – Turonian – Cenomanian – Early Cretaceous Albian – Aptian – Barremian – Hauterivian – Valanginian – Berriasian – The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms; the Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type, formed under warm, shallow marine circumstances.
Due to the high sea level, there was extensive space for such sedimentation. Because of the young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for the Cretaceous, it consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast; the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not consolidated and the Chalk Group still consists of loose sediments in many places; the group has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is a marine system consisting of competent limestone beds or incompetent marls.
Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval; these shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. During th
The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō and ferō, was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern'system' names to be employed, reflects the fact that many coal beds were formed globally during that time; the Carboniferous is treated in North America as two geological periods, the earlier Mississippian and the Pennsylvanian. Terrestrial animal life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would evolve into amniotes, the first terrestrial vertebrates. Arthropods were very common, many were much larger than those of today. Vast swaths of forest covered the land, which would be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today.
The atmospheric content of oxygen reached its highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. The half of the period experienced glaciations, low sea level, mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change. In the United States the Carboniferous is broken into Mississippian and Pennsylvanian subperiods; the Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration. In Europe the Lower Carboniferous sub-system is known as the Dinantian, comprising the Tournaisian and Visean Series, dated at 362.5-332.9 Ma, the Upper Carboniferous sub-system is known as the Silesian, comprising the Namurian and Stephanian Series, dated at 332.9-298.9 Ma.
The Silesian is contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, the Westphalian as the Coal Measures and Pennant Sandstone; the International Commission on Stratigraphy faunal stages from youngest to oldest, together with some of their regional subdivisions, are: A global drop in sea level at the end of the Devonian reversed early in the Carboniferous. There was a drop in south polar temperatures; these conditions had little effect in the deep tropics, where lush swamps to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites hard; this sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America; this continental collision resulted in the Hercynian orogeny in Europe, the Alleghenian orogeny in North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, South China continents were still separated from Laurasia; the Late Carboniferous Pangaea was shaped like an "O." There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean. Average global temperatures in the Early Carboniferous Period were high: 20 °C.
However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C. Lack of growth rings of fossilized trees suggest a lack of seasons of a tropical climate. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are referred to as Permo-Carboniferous in age; the cooling and drying of the climate led to the Carboniferous Rainforest Collapse during the late Carboniferous. Tropical rainforests fragmented and were devastated by climate change. Carboniferous rocks in Europe and eastern North America consist of a repeated sequence of limestone, sandstone and coal beds. In North America, the early Carboniferous is marine
Graham Edward Budd is a British palaeontologist, Professor of palaeobiology at Uppsala University. Budd's research has focused on the anatomy and evolutionary significance of Palaeozoic arthropods and in the integration of palaeontology into evolutionary developmental biology, he has contributed to the theoretical understanding of the role of functional morphology in evolution. Together with Sören Jensen he reintroduced the concepts of crown groups to phylogenetics. Budd was awarded the Hodson Fund of the Palaeontological Association in 2002 and the President's Medal of the Palaeontological Association in 2015, he has edited Acta Zoologica together with Lennart Olsson. G. E. Budd. 2002. A palaeontological solution to the arthropod head problem. Nature 417: 271-275. G. E. Budd. 2006. On the origin and evolution of major morphological characters. Biological Reviews 81: 609-628. Arthropod head problem Graham Budd's web page at Uppsala University
Hallucigenia is a genus of Cambrian xenusiids known from articulated fossils in Burgess Shale-type deposits in Canada and China, from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study. Hallucigenia is now recognized as a "lobopodian worm", it is considered by some to represent an early ancestor of the living velvet worms, although other researchers favour a relationship closer to arthropods. Hallucigenia is a 0.5–3.5 cm long tubular organism with seven or eight pairs of slender legs, each terminating with a pair of claws. Above each leg is a rigid conical spine. The'head' and'tail' end of the organism are difficult to identify. Although some specimens display traces of a gut, the internal anatomy has not been formally described. Recent research suggests that the extended element is an elongated head with two simple eyes, a mouth with radial teeth, pharyngeal teeth within the front of the gut. Hallucigenia's spines are made up of one to four nested elements.
The spine surface of Hallucigenia sparsa is covered in an ornament of minute triangular'scales', while the spine surface of Hallucigenia hongmeia is a net-like texture of microscopic circular openings, which can be interpreted as the remains of Papillae. Hallucigenia possessed Annulations running down the length of its trunk, much like modern Onychophora, they may have had hair-like setae lining their fine anterior appendages for use in filter feeding. Hallucigenia was described by Walcott as a species of the polychaete worm Canadia. In his 1977 redescription of the organism, Simon Conway Morris recognized the animal as something quite distinct, establishing the new genus. No specimen was available that showed both rows of legs, as such Conway Morris reconstructed the animal walking on its spines, with its single row of legs interpreted as tentacles on the animal's back. A dark stain at one end of the animal was interpreted as a featureless head. Only the forward tentacles could reach to the'head', meaning that a mouth on the head would have to be fed by passing food along the line of tentacles.
Conway Morris suggested. This raised questions, such as how it would walk on the stiff legs, but it was accepted as the best available interpretation. An alternative interpretation considered Hallucigenia to be an appendage of a larger, unknown animal. There had been precedent for this, as Anomalocaris had been identified as three separate creatures before being identified as a single huge 1-metre-long creature. Given the uncertainty of its taxonomy, Hallucigenia was tentatively placed within the phylum Lobopodia, a catch-all taxon containing numerous odd "worms with legs". In 1991, Lars Ramskold and Hou Xianguang, working with additional specimens of a "hallucigenid", from the lower Cambrian Maotianshan shales of China, reinterpreted Hallucigenia as an Onychophoran, they inverted it, interpreting the tentacles, which they believe to be paired, as walking structures and the spines as protective. Further preparation of fossil specimens showed that the'second legs' were buried at an angle to the plane along which the rock had split, could be revealed by removing the overlying sediment.
Ramskold and Hou believe that the blob-like'head' is a stain that appears in many specimens, not a preserved portion of the anatomy. This stain may be an artefact of decomposition. Hallucigenia is unquestionably a panarthropod, has long been interpreted as a stem-group onychophoran – a position that has now found support from phylogenetic analysis. A key character demonstrating this affinity is the cone-in-cone construction of Hallucigenia claws, a feature shared only with modern onychophorans. Hallucigenia exhibits certain characters inherited from the ancestral ecdysozoan, but lost in the modern onychophorans – in particular its distinctive foregut armature. Below is a cladogram for Hallucigenia according to al.. 2015. In 2002, Desmond Collins informally suggested that new Hallucigenia fossils from the Burgess Shale showed male and female forms, one with "a rigid trunk, robust neck and a globular head" and the other thinner, with a small head. Further species are represented from the Chengjiang.
Hallucigenia was first described from the Burgess Shale in southeastern British Canada. 109 specimens of Hallucigenia are known from the Greater Phyllopod bed, where they comprise 0.3% of the community. Hallucigenia forms a minor component of Chinese lagerstätten. Isolated hallucigeniid spines, are distributed in a range of Cambrian deposits, preserved both as carbonaceous and mineralized fossils. Smith, Martin R.. "Hallucigenia's onychophoran-like claws and the case for Tactopoda". Nature. 514: 363–6. Bibcode:2014Natur.514..363S. Doi:10.1038/nature13576. PMID 25132546. Lay summary – ScienceDaily. "Hallucigenia sparsa". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011. Http://www.nmnh.si.edu/paleo/shale/phallu.htm - https://web.archive.org/web/20040506033303/http://www.arrakis.es/~owenwang/articulos/pasados.htm http://www.yvonnenavarro.com/hallug.htm
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints; the rock unit is a black shale and crops out at a number of localities near the town of Field in Yoho National Park and the Kicking Horse Pass. Another outcrop is in Kootenay National Park 42 km to the south; the Burgess Shale was discovered by palaeontologist Charles Walcott on 30 August 1909, towards the end of the season's fieldwork. He returned in 1910 with his sons and wife, establishing a quarry on the flanks of Fossil Ridge; the significance of soft-bodied preservation, the range of organisms he recognised as new to science, led him to return to the quarry every year until 1924. At that point, aged 74, he had amassed over 65,000 specimens. Describing the fossils was a vast task, pursued by Walcott until his death in 1927.
Walcott, led by scientific opinion at the time, attempted to categorise all fossils into living taxa, as a result, the fossils were regarded as little more than curiosities at the time. It was not until 1962 that a first-hand reinvestigation of the fossils was attempted, by Alberto Simonetta; this led scientists to recognise that Walcott had scratched the surface of information available in the Burgess Shale, made it clear that the organisms did not fit comfortably into modern groups. Excavations were resumed at the Walcott Quarry by the Geological Survey of Canada under the persuasion of trilobite expert Harry Blackmore Whittington, a new quarry, the Raymond, was established about 20 metres higher up Fossil Ridge. Whittington, with the help of research students Derek Briggs and Simon Conway Morris of the University of Cambridge, began a thorough reassessment of the Burgess Shale, revealed that the fauna represented were much more diverse and unusual than Walcott had recognized. Indeed, many of the animals present had bizarre anatomical features and only the slightest resemblance to other known animals.
Examples include Opabinia, with five eyes and a snout like a vacuum cleaner hose and Hallucigenia, reconstructed upside down, walking on bilaterally symmetrical spines. With Parks Canada and UNESCO recognising the significance of the Burgess Shale, collecting fossils became politically more difficult from the mid-1970s. Collections continued to be made by the Royal Ontario Museum; the curator of invertebrate palaeontology, Desmond Collins, identified a number of additional outcrops, stratigraphically both higher and lower than the original Walcott quarry. These localities continue to yield new organisms faster. Stephen Jay Gould's book Wonderful Life, published in 1989, brought the Burgess Shale fossils to the public's attention. Gould suggests that the extraordinary diversity of the fossils indicates that life forms at the time were much more disparate in body form than those that survive today, that many of the unique lineages were evolutionary experiments that became extinct. Gould's interpretation of the diversity of Cambrian fauna relied on Simon Conway Morris's reinterpretation of Charles Walcott's original publications.
However, Conway Morris disagreed with Gould's conclusions, arguing that all the Cambrian fauna could be classified into modern day phyla. The Burgess Shale has attracted the interest of paleoclimatologists who want to study and predict long-term future changes in Earth's climate. According to Peter Ward and Donald Brownlee in the 2003 book The Life and Death of Planet Earth, climatologists study the fossil records in the Burgess Shale to understand the climate of the Cambrian explosion, use it to predict what Earth's climate would look like 500 million years in the future when a warming and expanding Sun combined with declining CO2 and oxygen levels heat the Earth toward temperatures not seen since the Archean Eon 3 billion years ago, before the first plants and animals appeared, therefore understand how and when the last living things will die out. See Future of the Earth. After the Burgess Shale site was registered as a World Heritage Site in 1980, it was included in the Canadian Rocky Mountain Parks WHS designation in 1984.
In February 2014, the discovery was announced of another Burgess Shale outcrop in Kootenay National Park to the south. In just 15 days of field collecting in 2013, 50 animal species were unearthed at the new site; the fossil-bearing deposits of the Burgess Shale correlate to the Stephen Formation, a collection of calcareous dark mudstones, about 508 million years old. The beds were deposited at the base of a cliff about 160 m tall, below the depth agitated by waves during storms; this vertical cliff was composed of the calcareous reefs of the Cathedral Formation, which formed shortly before the deposition of the Burgess Shale. The precise formation mechanism is not known for certain, but the most accepted hypothesis suggests that the edge of the Cathedral Formation reef became detached from the rest of the reef and being transported some distance — kilometers — away from the reef edge. Reactivation of faults at the base of the formation led to its disintegration from about 509 million years ago.
This would have left a steep cliff, the bottom of which would be protected from tectonic decompression because the limestone of the Cathedral Formation is difficult to compress. This protection explains why fossils preserved further from the Cathedral Formation are impossible to work with — tectonic squeezing of the beds has produced a vertical cleavage that fractures the rocks, so they split perpendicular to the fossils; the Walcott quarry
Priapulida, sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility, because their general shape and their extensible spiny introvert may recall the shape of a penis, they live in comparatively shallow waters up to 90 metres deep. Some species show a remarkable tolerance for hydrogen anoxia, they can be quite abundant in some areas. In an Alaskan bay as many as 85 adult individuals of Priapulus caudatus per square meter has been recorded, while the density of its larvae can be as high as 58,000 per square meter. Together with Echiura and Sipuncula, they were once placed in the taxon Gephyrea, but consistent morphological and molecular evidence supports their belonging to Ecdysozoa, which includes arthropods and nematodes. Fossil findings show that the mouth design of the stem-arthropod Pambdelurion is identical with that of priapulids, indicating that their mouth is an original trait inherited from the last common ancestor of both priapulids and arthropods if modern arthropods no longer possess it.
Among Ecdysozoa, their nearest relatives are Kinorhyncha and Loricifera, with which they constitute the Scalidophora clade named after the spines covering the introvert. They feed on slow-moving invertebrates, such as polychaete worms. Priapulid-like fossils are known at least as far back as the Middle Cambrian, they were major predators of the Cambrian period. However, crown-group priapulids cannot be recognized until the Carboniferous. About 20 extant species of priapulid worms are known, half of them being of meiobenthic size. Priapulids are cylindrical worm-like animals, ranging from 0.2–0.3 to 39 centimetres long, with a median anterior mouth quite devoid of any armature or tentacles. The body is divided into a main trunk or abdomen and a somewhat swollen proboscis region ornamented with longitudinal ridges; the body is ringed and has circles of spines, which are continued into the protrusible pharynx. Some species may have a tail or a pair of caudal appendages; the body has a chitinous cuticle, moulted as the animal grows.
There is a wide body-cavity, which has no connection with the renal or reproductive organs, so it is not a coelom. There are no vascular or respiratory systems, but the body cavity does contain phagocytic amoebocytes and cells containing the respiratory pigment haemerythrin; the alimentary canal is straight, consisting of an eversible pharynx, an intestine, a short rectum. The pharynx is lined by teeth; the anus is terminal, although in Priapulus one or two hollow ventral diverticula of the body-wall stretch out behind it. The nervous system consists of a nerve ring around the pharynx and a prominent cord running the length of the body with ganglia and longitudinal and transversal neurites consistent with an orthogonal organisation; the nervous system retains a basiepidermal configuration with a connection with the ectoderm, forming part of the body wall. There are no specialized sense organs, but there are sensory nerve endings in the body on the proboscis; the priapulids are gonochoristic, having two separate sexes Their male and female organs are associated with the excretory protonephridia.
They comprise a pair of branching tufts, each of which opens to the exterior on one side of the anus. The tips of these tufts enclose a flame-cell like those found in flatworms and other animals, these function as excretory organs; as the animals mature, diverticula arise on the tubes of these organs, which develop either spermatozoa or ova. These sex cells pass out through the ducts; the perigenital area of the genus Tubiluchus exhibit sexual dimorphism. Priapulid development has been reappraised because early studies reported abnormal development caused by high temperature of embryo culture. For the species Priapulus caudatus, the 80 µm egg undergoes a total and radial cleavage following a symmetrical and subequal pattern. Development is remarkably slow, with the first cleavage taking place 15 hours after fertilization, gastrulation after several days and hatching of the first'lorica' larvae after 15 to 20 days; the species Meiopriapulus fijiensis have direct development. In current systematics, they are described as protostomes, despite having a deuterostomic development.
Because the group is so ancient, it is assumed the deuterostome condition which appears to be ancestral for bilaterians have been maintained. Stem-group priapulids are known from the Middle Cambrian Burgess Shale, where their soft-part anatomy is preserved in conjunction with their gut contents – allowing a reconstruction of their diets. In addition, isolated microfossils are widespread in Cambrian deposits, allowing the distribution of priapulids – and individual species – to be tracked through Cambrian oceans. Trace fossils that are morphologically identical to modern priapulid burrows mark the start of the Cambrian period, suggesting that priapulids, or at least close anatomical relatives, evolved around this time. Crown-group priapulid body fossils are first known from the Carboniferous. Uncertain relationship "Class" PalaeoscolecidaStem-group Priapulida Class †Archaeopriapulida Family †Ottoiidae Genus †Ancalagon Genus †Fieldia Genus †Lecythioscopa Genus †Ottoia Genus †Scolecofurca Genus †Selkirkia Family †Louisellidae Genus †Anningvermis Genus †Corynetis Genus †LouisellaPhylum Priapulida Class Priapulimorpha Order Priapulimorphida Family Priapulidae G
Dinocaridida is a proposed extinct taxon of fossil arthropod-like marine animals found, with one exception, in the Cambrian and Ordovician. It is subdivided into the opabiniids; the name of this group comes from Greek, "deinos" and "caris", meaning "terror shrimp" or "terror crab", due to their crustacean-like appearance and the hypotheses suggesting that members of this class were amongst the dominating and most diverse apex predators of their time. Dinocaridids are bilaterally symmetrical, with a non-mineralized cuticle and a body divided into two major tagmata, or body-sections; the frontal section have two claws found just in front of the mouth, located on these creatures' underside. The body will possess each with its own gill branch and swimming lobe, it is thought that these lobes moved in an up-and-down motion to propel the animal forward in a fashion similar to the cuttlefish. The placement of Dinocaridida is uncertain: they appear to be a stem group to arthropods. In some recent works they are grouped with other enigmatic forms in the phylum Lobopodia.
The group is geographically widespread, has been reported from Cambrian strata in Canada and Russia, as well as the Ordovician of Morocco and Devonian of Germany