Archaeopteryx, meaning "old wing", is a genus of bird-like dinosaurs, transitional between non-avian feathered dinosaurs and modern birds. The name derives from the ancient Greek ἀρχαῖος meaning "ancient", πτέρυξ, meaning "feather" or "wing". Between the late nineteenth century and the early twenty-first century, Archaeopteryx had been accepted by palaeontologists and popular reference books as the oldest known bird. Older potential avialans have since been identified, including Anchiornis and Aurornis. Archaeopteryx lived in the Late Jurassic around 150 million years ago, in what is now southern Germany during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Similar in size to a Eurasian magpie, with the largest individuals attaining the size of a raven, the largest species of Archaeopteryx could grow to about 0.5 m in length. Despite their small size, broad wings, inferred ability to fly or glide, Archaeopteryx had more in common with other small Mesozoic dinosaurs than with modern birds.
In particular, they shared the following features with the dromaeosaurids and troodontids: jaws with sharp teeth, three fingers with claws, a long bony tail, hyperextensible second toes and various features of the skeleton. These features make Archaeopteryx a clear candidate for a transitional fossil between non-avian dinosaurs and birds. Thus, Archaeopteryx plays an important role, not only in the study of the origin of birds, but in the study of dinosaurs, it was named from a single feather in 1861, though that feather would prove to be non-avian. That same year, the first complete specimen of Archaeopteryx was announced. Over the years, ten more fossils of Archaeopteryx have surfaced. Despite variation among these fossils, most experts regard all the remains that have been discovered as belonging to a single species, although this is still debated. Most of these eleven fossils include impressions of feathers; because these feathers are of an advanced form, these fossils are evidence that the evolution of feathers began before the Late Jurassic.
The type specimen of Archaeopteryx was discovered just two years after Charles Darwin published On the Origin of Species. Archaeopteryx seemed to confirm Darwin's theories and has since become a key piece of evidence for the origin of birds, the transitional fossils debate, confirmation of evolution. In March 2018, scientists reported that Archaeopteryx was capable of flight, but in a manner different from that of modern birds. Most of the specimens of Archaeopteryx that have been discovered come from the Solnhofen limestone in Bavaria, southern Germany, a lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils laid down during the early Tithonian stage of the Jurassic period 150.8–148.5 million years ago. Archaeopteryx was the size of a raven, with broad wings that were rounded at the ends and a long tail compared to its body length, it could reach up to 500 millimetres with an estimated mass of 0.8 to 1 kilogram. Archaeopteryx feathers, although less documented than its other features, were similar in structure to modern-day bird feathers.
Despite the presence of numerous avian features, Archaeopteryx had many non-avian theropod dinosaur characteristics. Unlike modern birds, Archaeopteryx had small teeth, as well as a long bony tail, features which Archaeopteryx shared with other dinosaurs of the time; because it displays features common to both birds and non-avian dinosaurs, Archaeopteryx has been considered a link between them. In the 1970s, John Ostrom, following Thomas Henry Huxley's lead in 1868, argued that birds evolved within theropod dinosaurs and Archaeopteryx was a critical piece of evidence for this argument. For instance, it has a long ascending process of the ankle bone, interdental plates, an obturator process of the ischium, long chevrons in the tail. In particular, Ostrom found that Archaeopteryx was remarkably similar to the theropod family Dromaeosauridae. Specimens of Archaeopteryx were most notable for their well-developed flight feathers, they were markedly asymmetrical and showed the structure of flight feathers in modern birds, with vanes given stability by a barb-barbule-barbicel arrangement.
The tail feathers were less asymmetrical, again in line with the situation in modern birds and had firm vanes. The thumb did not yet bear a separately movable tuft of stiff feathers; the body plumage of Archaeopteryx is less well documented and has only been properly researched in the well-preserved Berlin specimen. Thus, as more than one species seems to be involved, the research into the Berlin specimen's feathers does not hold true for the rest of the species of Archaeopteryx. In the Berlin specimen, there are "trousers" of well-developed feathers on the legs. In part they are firm and thus capable of supporting flight. A patch of pennaceous feathers is found running along its back, quite similar to the contour feathers of the body plumage of modern birds in being symmetrical and firm, although not as stiff as the flight-related feathers. Apart from that, the feather traces in the Berlin specimen are limited to a sort of "prot
Global Boundary Stratotype Section and Point
A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. Most, but not all, GSSPs are based on paleontological changes. Hence GSSPs are described in terms of transitions between different faunal stages, though far more faunal stages have been described than GSSPs; the GSSP definition effort commenced in 1977. As of 2012, 64 of the 101 stages that need a GSSP have been formally defined. A geologic section has to fulfill a set of criteria to be adapted as a GSSP by the ICS; the following list summarizes the criteria: A GSSP has to define the lower boundary of a geologic stage. The lower boundary has to be defined using a primary marker. There should be secondary markers; the horizon in which the marker appears should have minerals.
The marker has to have regional and global correlation in outcrops of the same age The marker should be independent of facies. The outcrop has to have an adequate thickness Sedimentation has to be continuous without any changes in facies The outcrop should be unaffected by tectonic and sedimentary movements, metamorphism The outcrop has to be accessible to research and free to access; this includes that the outcrop has to be located where it can be visited has to be kept in good condition, in accessible terrain, extensive enough to allow repeated sampling and open to researchers of all nationalities. The Precambrian-Cambrian boundary GSSP at Fortune Head, Newfoundland is a typical GSSP, it is set aside as a nature preserve. A continuous section is available from beds that are Precambrian into beds that are Cambrian; the boundary is set at the first appearance of a complex trace fossil Treptichnus pedum, found worldwide. The Fortune Head GSSP is unlikely to be built over. Nonetheless, Treptichnus pedum is less than ideal as a marker fossil as it is not found in every Cambrian sequence, it is not assured that it is found at the same level in every exposure.
In fact, further eroding its value as a boundary marker, it has since been identified in strata 4m below the GSSP! However, no other fossil is known. There is no radiometrically datable bed at the boundary at Fortune Head, but there is one above the boundary in similar beds nearby; these factors have led some geologists to suggest. Once a GSSP boundary has been agreed upon, a "golden spike" is driven into the geologic section to mark the precise boundary for future geologists; the first stratigraphic boundary was defined in 1977 by identifying the Silurian-Devonian boundary with a bronze plaque at a locality called Klonk, northeast of the village of Suchomasty in the Czech Republic. GSSPs are sometimes referred to as Golden Spikes; because defining a GSSP depends on finding well-preserved geologic sections and identifying key events, this task becomes more difficult as one goes farther back in time. Before 630 million years ago, boundaries on the geologic timescale are defined by reference to fixed dates, known as "Global Standard Stratigraphic Ages".
Body form European Mammal Neogene Fauna Geologic time scale New Zealand geologic time scale List of GSSPs North American Land Mammal Age Type locality Hedberg, H. D. International stratigraphic guide: A guide to stratigraphic classification and procedure, New York, John Wiley and Sons, 1976 International Stratigraphic Chart from the International Commission on Stratigraphy GSSP table with pages on each ratified GSSP from the ICS Subcommission for Stratigraphic Information USA National Park Service Washington State University Web Geological Time Machine Eon or Aeon, Math Words - An alphabetical index The Global Boundary Stratotype Section and Point: overview Chart of The Global Boundary Stratotype Sections and Points: chart Table of Global Boundary Stratotype Sections and Points with links to summary pages for each one: chart GSSPs and Continental drift 3D views Geotime chart displaying geologic time periods compared to the fossil record - Deals with chronology and classifications for laymen
Gargoyleosaurus is one of the earliest ankylosaurs known from reasonably complete fossil remains. Its skull measures 29 centimetres in length, its total body length is an estimated 3 to 4 metres, it may have weighed as much as 1 tonne. The holotype was discovered at the Bone Cabin Quarry West locality, in Albany County, Wyoming in exposures of the Upper Jurassic Morrison Formation; the type species, G. parkpinorum was described by Ken Carpenter et al. in 1998. A mounted skeletal reconstruction of Gargoyleosaurus parkpinorum can be seen at the Denver Museum of Nature and Science. Gargoyleosaurus was present in stratigraphic zone 2 of the Morrison Formation; the holotype specimen of Gargoyleosaurus parkpinorum was collected by Western Paleontology Labs in 1996 and is held in the collections of the Denver Museum of Nature and Science, Colorado. Besides the holotype, two other partial skeletons are known; the holotype consists of most of a partial postcranial skeleton. The specimen was described as Gargoyleosaurus parkpini by Carpenter and Cloward in 1998 renamed G. parkpinorum by Carpenter et al. in 2001, in accordance with ICZN art.
31.1.2A. Much of the skull and skeleton has been recovered, the taxon displays cranial sculpturing, including pronounced deltoid quadratojugal and squamosal bosses; the taxon is further characterized by a narrow rostrum, the presence of seven conical teeth in each premaxilla, an incomplete osseous nasal septum, a linerarly arranged nasal cavity, the absence of an osseus secondary palate, and, as regards osteoderms, two sets of co-ossified cervical plates and a number of elongate conical spines. Vickaryous et al. place Gargoyleosaurus parkpinorum within the Family Ankylosauridae of the Ankylosauria and are in agreement with most previous phylogenetic hypotheses, which place the genus as the sister group to all other ankylosaurids. These studies however, only utilized the skull, whereas many of the distinctive features of the family Polacanthidae are in the postcranial skeleton. Timeline of ankylosaur research Carpenter, K. Miles, C. and Cloward, K.. "Skull of a Jurassic ankylosaur." Nature 393: 782-783.
Carpenter, K. The Armored Dinosaurs. Pp. 454–483. Indiana University Press, Bloomington. Vickaryous and Weishampel. "Ankylosauria". in The Dinosauria, Weishampel, D. B. Dodson, P. and Osmólska, H. editors. University of California Press. Killbourne, B. and Carpenter, K.. "Redescription of Gargoyleosaurus parkpinorum, a polacanthid ankylosaur from the Upper Jurassic of Albany County, Wyoming". Neues Jahrbuch für Geologie und Paläontologie, 237, 111-160. Gargoyleosaurus from the Natural History Museum
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with powerful limbs, they are known to have first appeared in the early Jurassic Period, persisted until the end of the Cretaceous Period. They have been found on every continent; the first dinosaur discovered in Antarctica was the ankylosaurian Antarctopelta, fossils of which were recovered from Ross Island in 1986. Ankylosauria was first named by Henry Fairfield Osborn in 1923. In the Linnaean classification system, the group is considered either a suborder or an infraorder, it is contained within the group Thyreophora, which includes the stegosaurs, armored dinosaurs known for their combination of plates and spikes. They sported a small brain size in proportion to their body, second only to the Saurischian sauropods, they were rather slow moving because of the shortness of the limbs combined with being incapable of running.
Their top speed was less than 10 km/hour. All ankylosaurians had armor over much of their bodies scutes and nodules, with large spines in some cases; the scutes, or plates, are rectangular to oval objects organized in transverse rows with keels on the upper surface. Smaller nodules and plates filled in the open spaces between large plates. In all three groups, the first two rows of plates tend to form a sort of half-ring around the neck; the skull has armor plastered on to it, including a distinctive piece on the outside-rear of the lower jaw. Ankylosaurs were built low to the ground one foot off the ground surface, they had triangular teeth that were loosely packed, similar to stegosaurs. The large hyoid bones left in skeletons indicates that they had flexible tongues, they had a large, side secondary palate. This means that they could breathe unlike crocodiles, their expanded gut region suggests the use of fermentation to digest their food, using symbiotic bacteria and gut flora. Their diet consisted of ferns and angiosperms.
Mallon et al. examined herbivore coexistence on the island continent of Laramidia during the Late Cretaceous. It was concluded that ankylosaurs were restricted to feeding on vegetation at, or below, the height of 1 meter. Possible neonate-sized ankylosaur fossils have been documented in the scientific literature. Ankylosauria is split into two families: Nodosauridae and Ankylosauridae. A third family, the Polacanthidae, is sometimes used, but is more found to be a sub-group of one of the primary families; the first formal definition of Ankylosauria as a clade, a group containing all species of a certain evolutionary branch, was given in 1997 by Carpenter. He defined the group as all dinosaurs closer to Ankylosaurus than to Stegosaurus; this definition is followed by most paleontologists today. This "stem-based" definition means that the primitive armored dinosaur Scelidosaurus, closer to ankylosaurids than to stegosaurids, is technically a member of Ankylosauria. Upon the discovery of Bienosaurus, Dong Zhiming erected the family Scelidosauridae for both of these primitive ankylosaurs.
In 2001, Carpenter proposed a new group uniting Scelidosaurus, Ankylosauridae and Polacanthidae, with Minmi, to the exclusion of Stegosaurus. However, many taxonomists find; this group traditionally includes Nodosaurus and Sauropelta. The nodosauridae had longer snouts than their ankylosaurid cousins, they did not sport the archetypal'clubs' at the ends of their tails. Nodosaurids had muscular shoulders and a specialized knob of bone on each shoulder blade called the acromial process, it served as an attachment site for the muscles. These spines would be used for self-defense against predators, they had wide, flaring hips and thick limbs. They had smaller, narrow beaks than the ankylosaurids, which allowed them to be selective over what plant matter they grazed on. Most nodosaurid finds are from North America. Major differences distinguishing the ankylosaurids from the nodosaurids is that the ankylosaurids had bony clubs at the end of their tails, domed snouts in front of the eyes, large squamosal plates projecting from the top and bottom of each side of the skull, all of which nodosaurids lacked.
The traditional ankylosaurids are from in the Cretaceous. They had much wider bodies and have been discovered with bony eyelids; the large clubs at the end of their tails may have been used in sexual selection. This family included Ankylosaurus and Pinacosaurus; the clubs were made of several plates of bone that were permeated by soft tissue, allowing them to absorb thousands of pounds of force. Their beaks were larger and broader than the nodosaurids, indicating that these ankylosaurs were generalists in their diet; the family Polacanthidae was named by George Reber Wieland in 1911 to refer to a group of ankylosaurs that seemed to him to be intermediate between the ankylosaurids and nodosaurids. This grouping was ignored by most researchers until the late 1990s, when it was used as a subfamily by Kirkland for a natural group recovered by his 1998 analysi
The Aalenian is a subdivision of the Middle Jurassic epoch/series of the geologic timescale that extends from about 174.1 Ma to about 170.3 Ma. It was succeeded by the Bajocian; the Aalenian takes its name from the town of Aalen, some 70 km east of Stuttgart in Germany. The town lies at the northeastern end of the Swabian Jura; the name Aalenian was introduced in scientific literature by Swiss geologist Karl Mayer-Eymar in 1864. The base of the Aalenian is defined as the place in the stratigraphic column where the ammonite genus Leioceras first appears; the global reference profile is located 500 meters north of the village of Fuentelsaz in the Spanish province of Guadalajara. The top of the Aalenian is at the first appearance of ammonite genus Hyperlioceras. In the Tethys domain, the Aalenian contains four ammonite biozones: zone of Graphoceras concavum zone of Brasilia bradfordensis zone of Ludwigia murchisonae zone of Leioceras opalinum Gradstein, F. M.. G. & Smith, A. G.. Cresta, S.. L.. R.. J.. A..
L.. J.. Mayer-Eymar, K.. 1 Tabelle, Zürich. Sepkoski, J.. GeoWhen Database - Aalenian Lower Jurassic timescale, at the website of the subcommission for stratigraphic information of the ICS Stratigraphic chart of the Upper and Lower Jurassic, at the website of Norges Network of offshore records of geology and stratigraphy
Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy. Absolute dating provides a numerical age or range in contrast with relative dating which places events in order without any measure of the age between events. In archaeology, absolute dating is based on the physical and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials with known dates. Techniques include tree rings in timbers, radiocarbon dating of wood or bones, trapped-charge dating methods such as thermoluminescence dating of glazed ceramics. Coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year.
In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from young to systems such as uranium–lead dating that allow acquisition of absolute ages for some of the oldest rocks on earth. Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes. Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age. For example, techniques based on isotopes with half lives in the thousands of years, such as carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments. One of the most used and well-known absolute dating techniques is carbon-14 dating, used to date organic remains.
This is a radiometric technique. Cosmic radiation entering the earth’s atmosphere produces carbon-14, plants take in carbon-14 as they fix carbon dioxide. Carbon-14 moves up the food chain as predators eat other animals. With death, the uptake of carbon-14 stops, it takes 5,730 years for half the carbon-14 to change to nitrogen. After another 5,730 years only one-quarter of the original carbon-14 will remain. After yet another 5,730 years only one-eighth will be left. By measuring the carbon-14 in organic material, scientists can determine the date of death of the organic matter in an artifact or ecofact; the short half-life of carbon-14, 5,730 years, makes dating reliable only up to about 50,000 years. The technique cannot pinpoint the date of an archeological site better than historic records, but is effective for precise dates when calibrated with other dating techniques such as tree-ring dating. An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem.
It is possible in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record. Thus dating that particular tree does not indicate when the fire burned or the structure was built. For this reason, many archaeologists prefer to use samples from short-lived plants for radiocarbon dating; the development of accelerator mass spectrometry dating, which allows a date to be obtained from a small sample, has been useful in this regard. Other radiometric dating techniques are available for earlier periods. One of the most used is potassium–argon dating. Potassium-40 is a radioactive isotope of potassium that decays into argon-40; the half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.
Argon, a noble gas, is not incorporated into such samples except when produced in situ through radioactive decay. The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice. K–Ar dating was used to calibrate the geomagnetic polarity time scale. Thermoluminescence testing dates items to the last time they were heated; this technique is based on the principle. This process frees electrons within minerals. Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light; this light can be measured to determine the last time. Radiation levels do not remain constant over time. Fluctuating levels can skew results – for example, if an item went through several high radiation eras, thermoluminescence will return an older date for the item. Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.
Because of these and other factors, Thermoluminescence is at the most about 15% accurate. It cannot be used to date a site on its own. However, it can be used to confirm the antiquity of an item. Optically stimulated luminescence dating constrains the time at which sediment was last exposed to light. During sediment transport, exposure to s