Dinosaurs are so called “Ancient” creatures. They have lived on planet earth 350 million years ago (Dino 2008). Dinosaurs were one of several kinds of prehistoric reptiles that lived during the Mesozoic Era, the “Age of Reptiles”. Dinosaurs were land-dwelling reptiles that walked with an erect stance. Their unique hip structure caused their legs to stick out from under their bodies, and not sprawl out from the side (like other reptiles). When dinosaurs first evolved from more primitive archosaurs, they were bipedal (walked on two legs).
Much later, some dinosaur groups returned to a four-legged stance, having hind legs much larger than their front legs. The dinosaurs dominated the Earth for over 165 million years, but mysteriously went extinct 65 million years ago. Dinosaurs suddenly became extinct about 65 million years ago, at the end of the Cretaceous period, which was a time of high volcanic and tectonic activity. There are a lot of theories why the extinction occurred. The most widely accepted theory is that an asteroid impact caused major climactic changes which the dinosaurs couldn’t adapt to (Dino 2006).
They say Dinosaurs did not disappeared completely, that they have evolved into birds due to changes in climate in different periods that allowed them to evolve. And the stages of their transformation are recorded in the fossil record. There are recent discoveries that shown scientists how dinosaurs recycled many of their features that have been originally designed for other purpose. Once the “avian dinosaurs” were launched, they quickly evolved in ways that can help them to fly even better, shrinking themselves several times in body size and many more.
They say that changes in the tectonic plates of the Earth plays a role in the evolution of the Dinosaurs. There are fossils found that there are some similarities between the dinosaurs and the animals today (Dino 2008). A Study of fossil bones shows that Dinosaurs put on a rapid growth spurt after hatching, unlike modern reptiles which grow slowly at a constant rate. According to a research by Kevin Padian and colleagues at the University of California at Berkeley, birds stayed small abbreviating this early growth phase although they were almost certainly descended from dinosaurs.
Some older specimens of Archaeopteryx are even twice of those dated for flight but they became smaller and smaller. The relative elongation of forelimbs associated in the shortening of the early growth phase of the Archaeopteryx, which would have been advantageous to the inception of flight (Henderson 2001). The most famous fossil of Archaeopteryx was found in 1861 in Germany, two years after the publication of Charles Darwin’s “Origin of Species”. The fossil was a crow-size creature with big legs, a bony tail and a mouthful of teeth.
Scientists studied for decades, the aerodynamics of archaeopteryx to determine whether it really could fly. Based on the studies, Archaeopteryx could probably fly but not well. “It is an unusual animal”, said the paleontologist Angela Milner of London’s Natural History Museum. “It’s like a dinosaur skeleton with feathers”, but in a study released by a multinational group of experts including Milner, new evidences were presented that bolstered the case that the creature was a capable flier.
They used modern X-ray scanning, Milner and her colleagues found out that some parts of the brain of the Archaeopteryx is concerned with flight controls and that the brain does not look like a living reptile (Gugliotta 2004). It has so much like the same sense of balance and sharp vision found in today’s birds. It senses were a bit more primitive than its modern evolutionary descendants, the pigeon-size Archaeopteryx was certainly well equipped to navigate over land and forests looking for distant prey. They say that Archaeopteryx was the earliest known bird (Perlman 2004),
Since 1990’s, a number of feathered dinosaurs were found that provide clear evidence of the close relationship between the dinosaurs and birds. Most of the fossil found was in Northeastern China. The feathered dinosaurs that were discovered so far include Beipiaosaurus, Caudipteryx, Dilong, Microraptor, Protarchaeopteryx, Shuvuuia, Sinornithosaurus, and Sinosauropteryx; and dinosaur-like birds like Confuciusornis; all of which were found in Northern China (Dino 2006). Microraptor has long asymmetric flight feathers on its hands and feet.
In the last decade, fossils were found in China that led the scientists to conclude that the dinosaur spread its legs out laterally and maintained its wings in a tandem pattern, like a dragonfly. According to scientists, ancestors of modern birds were built like biplanes. Microraptor was not capable of taking off from the ground and that it was only a moderate glider which was indicated in the scientists’ evidence. They said that the dinosaur was probably one of the earliest flying animals and the precursor to all bird flight.
This is the first study to attempt to quantify the possible flight performance of this strange ‘four-winged’ dinosaur since it was described in 2003, However, whether Microraptor was on the main line of evolution that led to powered flapping flight or was a side experiment is currently hotly debated among researchers, as is the hypothesis that avian powered developed thought a gliding stage” said Angela Milner (Ja 2007). The fossil of Beipiaosaurus was found in May 27, 1999 in China. It is a genus of therizinosauroid theropod dinosaur.
The fossil was established in Liaoning Province, China. It has been dated to the Middle Cretaceous period, about 125 million years ago. A significant number of fossilized bones for this species were recovered, including: cranial fragments, a mandible, three cervical vertebrae, four dorsal vertebrae, a caudal vertebra, the scapula and scapulacoracoid, a integral forelimb, and a complete pelvis with hind limb. It was measured 2. 2 meters (7. 3 ft) in period and . 88 meters (2. 9 ft) tall at the hip. It is among the largest known feathered dinosaurs.
Its weight is estimated as about 85 kilograms (187 lbs. ). Beipiaosaurus has a toothless beak with cheek teeth. The feet of Beipiaosaurus have reduced inner toes, showing that the derived therizinosaurid condition may have evolved from a three-toed therizinosauroid ancestor. Its head was large and it has some features similar to the related oviraptorosaurs. The fossil’s skin impressions indicate its body was covered by downy feather-like fibers, which are similar to those of Sinosauropteryx, but longer, and are oriented perpendicular to the arm.
The feathers of Beipiaosaurus represent intermediate stage between Sinosauropteryx and more advance birds as suggested by Xu et al because only theropod dinosaurs are so far known to have been feathered, this discovery is further evidence that therizinosaurs were indeed theropods (Beip 2007). Caudipteryx is one of the few non-avian dinosaurs for which feathery impressions are known. Its specimen was first mistakenly for a Protarchaeopteryx specimen. Its name implies that it had a special assemblage of feathers on its tail, possibly for ornamental purposes.
There are bands of dark and light on the tail feathers. These may be remnants of the animal’s pigmentation, something that is hardly ever preserved. Caudipteryx had very short forelimbs and symmetrical feathers, meaning that it did not fly. It legs were long, perhaps for running and/or wading. A recent study has suggested that it was capable of perching (Tuciarione 1998). Caudipteryx shows filaments more closely related to the feathers of birds, although it is unlikely that this dinosaur could fly (Townsend 1998).
The first dinosaur found with feathers was called Sinosauropteryx prima, which means ‘first Chinese dragon feather’. Its skeleton was surrounded by a halo of feathers. Sinosauropteryx’s very simple feathers were almost hair-like and probably first evolved to insulate small, warm-blooded dinosaurs from cold and heat. Sinosauropteryx could not fly (Chine 2002). It lived in the early Cretaceous. The fossil was remarkably preserved despite that the skull was crushed and the bones of the hands and feet were scattered.
The fossil was discovered by a farmer and fossil hunter from Northeast China named Li Yumin. “For me, this fossil represents to our present time what the first Archaeopteryx find was for Huxley and Darwin, and it will finally prove that feathers or proto-feathers are indeed an archosaurian/dinosaurian trait and present in many theropods nondirectly related to Archaeopteryx. We are narrowing the gaps on our knowledge on the origin of feathers, the concept of birds as dinosaurs (or dinosaurs as birds) and the possible relation of insulation and metabolism in the Dinosaurian.
The puzzle will become a little clearer as more research is done and more discoveries come to light” said Phillip Currie in a Society of Vertebrate Paleontology meetings (Smith 2008). Sinornithosaurus have lived in the early Cretaceous. Sinornithosaurus had a broad range of feathers including downy, insulating fluff over most of its body and longer display feathers on its arms, tail and head. Some of its long feathers had barbules and hooklets that bound together a feather’s barbs and gave the feather greater strength, flexibility and surface area.
It is possible that such feathers helped dinosaurs like Sinornithosaurus and Velociraptor to balance, or may even have boosted them when leaping into the air after prey. At least two specimens of Sinornithosaurus have been found at Liaoning (Chine 2002). The first specimen of Sinornithosaurus was know as “Dave” which was well preserved image of these animals, modern feathers and all. It was about 4 ft long (Martiniuk 2003). It is remarkably similar to early birds postcranially.
The shoulder girdle shows that terrestrial dromaeosaurids had attained the prerequisites for powered, flapping flight, supporting the idea that bird flight originated from the ground up. Protarchaeopteryx was a small feathered bird-like dinosaur. It is considered to be more primitive than Archaeopteryx because it was a little more like the non-avian theropods. The best preserved fossil was found showing feathers attached to the front leg and tail. Its feathers are symmetrical, indicating that it may not have been able to fly.
Its fossil was discovered in the year 1996, preserved in a fine-grained stone. It lay to rest the arguments regarding dinosaurs having feathers. The discussion has shifted to the type of feathers that dinosaurs has and when did the flight feathers evolved. Although it has close resemble to Archaeopteryx, they lack the precise form of true birds, particularly the length of wing and design of individual feathers. Because of this fossil, scientists believe that the fossil was true dinosaurs, that it is the ancestor of first birds (Qiang 1997).
Protarchaeopteryx has forelimbs that show the important part of the avian does not evolve for flight but for seizing prey. It has long arms, huge hands and sharp claws to capture prey. Protarchaeopteryx is the most poorly known theropod in the Northeastern China. It is not modified as Caudipteryx, but it some shared new features including the skull form and short tail. It suggests that they could be closely related. Like the ancestral dinosaur Sinosauropteryx and Caudipteryx, Protarchaeopteryx have powerfully developed hind limbs (Trea 2005).
According to Ji Quiang, director of the National Geographic Museum in Beijing, who worked on the fossils, “They represent a missing link between dinosaurs and birds which we had expected to find,”. This suggests that perhaps the fossils’ resemblance to birds could be a case of convergent evolution and that their feathers evolved for insulation, not flight, indicating a warm-blooded physiology. It appeared ten million years later. One explanation is that both species evolved from a common ancestor, but one evolved faster than the other (Qiang 1997).
Shuvuuia is best known as member of the Alvarezsaur group of dinosaurs, possibly because it is the only alvarezsaurid scientists currently have skull material from. Once considered primitive flightless birds, Shuvuuia and its kin are now considered to belong to a group of dinosaurs known as the Maniraptorids, which includes Deinonychosaurs, such as Velociraptor, Therizinosaurs, like Therizinosaurus, and Oviraptorids , like Incisivosaurus, as well as true birds, which are now considered to be specialized flying dinosaurs.
Like an ostrich or emu, Shuvuuia’s forelimbs were too short for it to use for flying, but they were very strong, and at the end of each arm was a single large, hooked claw. What this claw was used for and how Shuvuuia used it in its daily lifestyle has been the subject of much debate, but it is most likely that Shuvuuia was an insectivore, and used its claws to tear open tree bark or termite mounds to find insects (Bongey 2004). Birds is thought to have begun in the Jurassic Period, with the earliest birds derived from theropod dinosaurs, in which, Archaeopterxy is from the late Jurassic Period.
But still, Archaeopteryx is not commonly considered to have been a true bird. Macroevolution theory states that modern birds are simply feathered dinosaurs. This means the scales of reptiles slowly evolved into feathers. A dated showcase for evolution – Archaeopteryx – was discovered soon after the publication of Darwin’s infamous book in 1859. Other fossil specimens of Archaeopteryx were later discovered, but they all had feathers and wings, with no indication of how the front legs gradually evolved into wings.
More importantly, the flight feathers of this creature are fully developed with no indication as to how they allegedly evolved from scales. After many decades of finding no fossils that would make the connection between birds and dinosaurs (Archaeopteryx being a contentious exception), secular scientists have now discovered fossils that provide a critical connection. But the “feathered dinosaur” fossils could be viewed as discoveries of convenience, much like the 1996 discovery of “microfossils” on the famous Mars meteorite conveniently made at a time that NASA needed government funding (Feat 2005).
Evolution generally occurs at a scale far too slow to be witnessed by humans. However, bird species are currently going extinct at a far greater rate than any possible speciation or other generation of new species. The disappearance of a population, subspecies, or species represents the permanent loss of a range of genes. Another concern with evolutionary implications is a suspected increase in hybridization. This may arise from human alteration of habitats enabling related allopatric species to overlap. Forest fragmentation can create extensive open areas, connecting previously isolated patches of open habitat.
Populations that were isolated for sufficient time to diverge significantly, but not sufficient to be incapable of producing fertile offspring may now be interbreeding so broadly that the integrity of the original species may be compromised. For example, the many hybrid hummingbirds found in northwest South America may represent a threat to the conservation of the distinct species involved (Fjeldsa 1990). The extinction of the non-avian dinosaurs is one of the most intriguing problems in paleontology. Only since the 1980s has the nature of this extinction become apparent.
The theory first proposed by Walter Alvarez linked the extinction event at the end of the Cretaceous period to a bolides impact about 65. 5 Ma, based on a sudden change in Iridium levels in fossilized layers. The bulk of the evidence now indicates that a 10-kilometer-wide bolides hit the Yucatan Peninsula 65 Ma, creating the 170 km wide Chicxulub Crater, and caused the extinction. Scientists are still disputing whether dinosaurs were in steady decline or still thriving before the meteor struck. Although the speed of extinction cannot be deduced from the fossil record alone, the latest models suggest the extinction was extremely rapid.
It appears to have been caused by heat caused by the meteorite impact and the matter ejected from the crater re-entering the Earth’s atmosphere around the world. Other theories link the extinction with increased volcanic activity, decreasing oxygen level in the atmosphere and dropping temperatures. Other groups as well as the dinosaurs went extinct at the same time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most kinds of birds, and many groups of mammals, became extinct (Dino 2006).
