Determine age of fossils. Top 10 Significant First Fossils.



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Determine age of fossils

Description[ edit ] Size compared with a human Anchiornis huxleyi was a small, bipedal theropod dinosaur with a triangular skull bearing several details in common with dromaeosaurids , troodontids , and primitive avialans. Like other early paravians, Anchiornis was small, about the size of a crow. Like all paravians, it was covered in feathers, though it also had scales on certain parts of the body. The wings, legs, and tail supported long but relatively narrow vaned feathers. Two types of simpler, downy plumaceous feathers covered the rest of the body, as in Sinornithosaurus: Long, simple feathers covered almost the entire head and neck, torso, upper legs, and the first half of the tail. The rest of the tail bore pennaceous tail feathers rectrices. Studies of Anchiornis specimens using laser fluorescence have revealed not only more details of the feathers, but also of the skin and muscle tissue. Taken together, this evidence has given scientists a nearly complete picture of Anchiornis anatomy. Additional studies indicate that Anchiornis had body plumage that consisted of short quills with long and independent, flexible barbs. These barbs stuck out from the quills at low angles on two opposing blades. This also gave each feather an overall forked shape and resulted in the theropod possessing a softer textured and "shaggier" appearing plumage than is seen in modern birds. The wing of Anchiornis was composed of 11 primary feathers and 10 secondary feathers. The primary feathers in Anchiornis were about as long as the secondaries, and formed a rounded wing. The wing feathers had curved but symmetrical central quills, with small and thin relative size, and rounded tips, all indicating poor aerodynamic ability. In the related dinosaurs Microraptor and Archaeopteryx , the longest wing feathers were closest to the tip of the wing, making the wings appear relatively long and pointed. However, in Anchiornis, the longest wing feathers were those nearest the wrist, making the wing broadest in the middle and tapering near the tip for a more rounded, less flight-adapted profile. In Anchiornis, this part of the wing was covered in covert feathers which smoothed the wing and covered the gaps between the larger primary and secondary feathers. However, unlike modern birds , the covert feathers of Anchiornis were not arranged in tracts or rows. In modern birds, the coverts usually cover only the upper portion of the wing, with most of the wing surface made up of uncovered flight feathers. In some Anchiornis fossils, on the other hand, several layers of covert feathers seem to extend down to cover most of the wing's surface, so that the wing is essentially made of multiple layers of feathers, rather than a layer of broad feathers with only their bases hidden by layers of coverts. This multi-layered wing arrangement might have helped strengthen the wing, considering that the primary and secondary feathers themselves were narrow and weak. Like the toes, the skin around the bottom of the fingers was covered in tiny, rounded scales. Unlike the toes, the flesh around the underside of the finger bones was twice as thick as the bones themselves and lacked distinct pads; instead, the fingers were straight and smooth without any major creases at the joints. Scales and skin around the fingers is very rarely preserved in fossils of early pennaraptorans , the only notable exceptions being Anchiornis and Caudipteryx , which had similar thick, scaly fingers associated with its wings. This has led many scientists to call Anchiornis a four-winged dinosaur , along with similar animals like Microraptor and Sapeornis. However, the extensive leg feathers indicate that this may be a vestigial trait, as running animals tend to have reduced, not increased, hair or feathers on their legs. The first toe, or hallux , was not reversed as in perching species. Also unlike Microraptor, the hindwing feathers were longest closer to the body, with the foot feathers being short and directed downward, almost perpendicular to the foot bones. The underside of the toes were formed into fleshy pads with distinct creases at the joints. The foot pads were covered in small, pebble-like scales. Scales were also present on the top of the feet but these are very hard to see in all known fossils. In , a team of scientists examined numerous points among the feathers of an extremely well-preserved Anchiornis specimen in the Beijing Museum of Natural History to survey the distribution of melanosomes, the pigment cells that give feathers their color. By studying the types of melanosomes and comparing them with those of modern birds, the scientists were able to map the specific colors and patterning present on this Anchiornis when it was alive. Though this technique had been used and described for isolated bird feathers and portions of other dinosaurs such as the tail of Sinosauropteryx , Anchiornis became the first Mesozoic dinosaur for which almost the entire life coloration was known note that the tail of this specimen was not preserved. The crown feathers were mainly rufous with a gray base and front, and the face had rufous speckles among predominantly black head feathers. The forewing and hindwing feathers were white with black tips. The coverts shorter feathers covering the bases of the long wing feathers were gray, contrasting the mainly white main wings. The larger coverts of the wing were also white with gray or black tips, forming rows of darker dots along mid-wing. These took the form of dark stripes or even rows of dots on the outer wing primary feather coverts but a more uneven array of speckles on the inner wing secondary coverts. The shanks of the legs were gray other than the long hindwing feathers, and the feet and toes were black. In contrast to the study, only gray-black type melanosomes were found. Even when the crown feathers were examined, none of the rounder, rufous-type melanosomes were seen. The scientists who conducted this second study suggested several possible explanations for this discrepancy. First, the different preservation of melanosomes or different investigative techniques might have influenced the results of the original study. Second, because the Beijing Museum specimen was smaller, it is possible that the rufous color was replaced as these animals aged. Third, it is possible that there were regional differences or even different species of Anchiornis which had different color patterns in their plumage. These rocks have been difficult to date, but most studies have concluded that they belong to the Tiaojishan Formation of rocks dated to the late Jurassic period Oxfordian age , It is an articulated skeleton missing the skull, part of the tail, and the right forelimb. The name Anchiornis huxleyi was chosen by Xu and colleagues in honor of Thomas Henry Huxley , an early proponent of biological evolution , and one of the first to propose a close evolutionary relationship between birds and dinosaurs. The generic name Anchiornis comes from combining the Ancient Greek words for "nearby" and "bird", because it was interpreted as important in filling a gap in the transition between the body plans of birds and dinosaurs. According to the farmer, this second specimen had been found nearby in the area of Daxishan, also from Tiaojishan Formation rocks of about the same age as the first Anchiornis. Two scientists visited the site in order to compare the new fossil with the rock types found there, and were able to confirm that the new specimen probably did come from the area the farmer described. They were able to dig up several fish fossils and a third Anchiornis fossil. The farmer's fossil underwent study which was published on September 24, , in the journal Nature. It is larger and much more complete than the first specimen, and preserved long wing feathers on the hands, arms, legs and feet, showing that it was a four-winged dinosaur similar to Microraptor. Martyniuk, , based on the color pattern of the Beijing specimen. While only a few specimens have been described in detail, many more have been identified and are held in both private collections and museums. One of these, a nearly complete skeleton missing the tail, also preserving extensive feather remains, was reported in This fossil also showed evidence that Anchiornis had a feathered crest on its head, and was used to determine the animal's life coloration. This fossil, a nearly complete skeleton, was prepared and studied by scientists at the Geology Park and identified as an Anchiornis. It was then used for a scanning electron microscope study of Anchiornis feather microstructure. The study also examined the well-preserved melanosomes of the feathers to determine their color. The scientists involved in the study found that the coloration found for this specimen was different than the color reported for BMNHC PH, and they noted that the BMNHC specimen may not in fact be Anchiornis, as it was described before similar species from the same formation had been discovered. While this specimen has yet to be fully described, it was photographed for a article in National Geographic and was used in a study of Anchiornis covert feathers and wing anatomy the following year. Determine age of fossils

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4 Comments

  1. Among the primitive apterygotes, only the collembolans springtails have been found as fossils in the Devonian Period about A large muscular foot spreads beneath the body. The minerals in the sediment gradually replace the organism while retaining its shape.

  2. Radiometric dating has shown that the earliest known stromatolites are over 3. The sizes of the specimens range from that of a blue jay to that of a large chicken.

  3. Ghedoghedo Hylonomus lyelli, which lived million years ago during the late Carboniferous period, is the first known reptile to exist. Being the oldest-known fossil ancestor to placental mammals , Juramaia serves as fossil evidence of the date when the eutherian group diverged from other mammals. Like wooden pegs instead of screws, hand-cut dovetail joints on the sides of drawers indicate older, prefactory assembly methods.

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