The history of life on Earth during the past 600 million years is marked by numerous episodes of dinosaurs extinction. Indeed, most of the species that have ever lived are now extinct. Many of these became extinct because they evolved into other species, so that biological diversity was maintained or increased, and viewed in this light extinction is a normal part of the evolution of life. However, there have been episodes on a global scale during which biological diversity has decreased markedly through large numbers of species becoming extinct over intervals of just a few million years. These episodes are referred to as 'mass extinctions', to distinguish them from the normal extinctions which occur through the evolution of new species.
The two most significant mass extinction events in the Earth's history occurred at the end of the Permian Period (i.e. the end of the Palaeozoic Era) and at the end of the Cretaceous Period (i.e. the end of the Mesozoic Era). The first of these was the more severe, leading to the extinction of 54% of all families of marine animals and up to 96% of all marine species. Many major groups of marine invertebrates completely disappeared (tabulate and rugose corals, trilobites, eurypterids, conulariids, fusulinid foraminifera, goniatitic ammonoids, and some groups of echinoderms) or declined dramatically in diversity (brachiopods, bryozoans, gastropods, etc.). The effects of the extinction on land organisms are less clear. The end Cretaceous extinction was nowhere near as devastating but has attracted a great deal of interest because it eliminated the dinosaurs. Also becoming extinct at the same time were the large marine reptiles such as plesiosaurs, and various marine invertebrates including ammonoids and certain other groups of molluscs and protozoans inhabiting mainly tropical seas.
At the present time, no single cause for mass extinctions can be identified. In searching for a possible cause, attention must be focussed on phenomena of global scale that can lead to dramatic changes in the physical environment. Such phenomena may include falls in sea level, global cooling, periods of greatly increased volcanic activity, or meteorite impact with the Earth. A world-wide fall in sea level could lead to extinction of some marine organisms through loss of shallow water habitats on continental shelves. The consequent reduction in habitat area would lead to increased competition amongst species and decreased population sizes. Global cooling would most affect faunas inhabiting warm, shallow seas, especially reef-dwelling organisms (as occurred in the end-Cretaceous extinctions), or those inhabiting land areas in the tropics. Other faunas would be less affected, because deeper water marine faunas are generally adapted to cooler conditions, and terrestrial faunas in temperate or polar regions are adapted to seasonal climatic changes. The fact that some extinction events have coincided with major glaciations lends support to global cooling as one cause for mass extinctions. Massive volcanism leading to the injection into the atmosphere of large amounts of dust or ash could cause mass extinctions either by poisoning with toxic substances, or by global cooling due to a reduction in solar radiation reaching the Earth. Meteorite impact as a possible cause for extinctions has received considerable publicity in recent years. In addition to the obvious localised effect, such an impact could have a global influence through the generation of atmospheric dust leading to darkness, cooling and contamination by toxic substances. Support for meteorite impact as a cause for the end-Cretaceous mass extinctions in particular is derived from a widespread iridium anomaly in rocks deposited at this time.
Saturday, July 31, 2010
Friday, July 30, 2010
Dinosaurs Fossils and the Scientific Process
What can fossils tell us?
Fossils are one of the most important sources of information about the Earth's past. They can tell us the age of the rocks in which they are found, what the environment was like when the fossilised organisms were alive, and even how the organisms functioned. They can also tell us about Earth movements, such as mountain building, about the former positions of continents (ancient geography), and about the evolution of life on Earth.
How are fossils recovered from rocks?
This segment explains how fossils are found within rocks, and the various ways in which they are recovered and prepared for scientific study.
Reconstructing dinosaurs fossils.
This segment shows how the fragmentary remains of fossils (particularly vertebrate fossils) are used to reconstruct the skeleton and body of the entire organism, so as to determine its appearance and way of life. Such reconstructions commonly undergo dramatic modification through the years, as ideas on how ancient organisms lived change.
This segment deals with what fossils are, the various ways in which they are preserved in rocks, the distinction between body fossils and trace fossils, and what pseudo fossils are.
Early views on the nature of fossils.
This segment is an account of past and alternative views on the origin and nature of fossils, such as the notion that they were the result of so-called 'plastic forces' or 'formative virtues' acting within the earth, or the belief that they are the remains of organisms that perished in the Biblical Flood.
Source from : http://museumvictoria.com.au/dinosaurs/sciprocess.html
Thursday, July 29, 2010
Here are some clipart images I've found that are free for personal use. I've left them Black and White. Feel free to add colors or use part of an image.
In order of pictures: Allosaurus, Brachiosaurus, Brachylophosaurus, Camarasaurus, Ceratosaurus, Chasmosaurus
Will Chinese Dino Feathers Reveal Their Secrets?
Dinosaurs must have been some color or another, but what? So far, artists and paleontologists could only guess, but recent discoveries in Mongolia may start to answer the question. Mark Norell and Michael Novacek of the AMNH have found dinosaurs fossil feathers that clearly show bands of dark and light that millions of years ago had some color. Perhaps they were only black and white, but they may have been red and yellow or blue and orange.
Sometime in the fall of 2001, we may start to find out what the real colors were.
How is this possible? The answer is in pigments and bacteria.
We know from the remains of modern birds, that pigments of certain colors leave specific chemical "traces" (tiny, microscopic bits of chemicals) when bacteria "digest" them. There are also chemical "traces" in fossils. A red pigment leaves a different trace than a blue pigment or a green pigment.
By studying the chemical traces in fossilized feathers, Dr. Norell hopes to discover some of their secrets! Stay tuned!
Dinosaurs Extinction and commercial dinosaurs fossils hunters are a big concern!
A group of extraordinary paleontologists agreed on a couple of things: 2000 was a slow year in paleontology, commercial fossil hunters are causing problems, molecular biology is very important to paleontology, the Cambrian/Pre-Cambrian boundary is the hot thing to study, and 30% of all living animals may be extinct by the end of the century.
Michael J. Novacek, Senior Vice President and Provost, Curator, Division of Paleontology at the AMNH; Mark A. Norell, Chairman and Curator, Division of Paleontology; Andrew H. Knoll, Curator of Paleobotanical Collections Harvard Univeristy; and Warren D. Allmon, Director, Paleontological Research Institution all gathered at a little table in the American Museum of Natural History (AMNH) near a display of fossils while about two dozen reporters sipped orange juice and ate granola with berries. Despite the fact that reporters got more breakfast than they did, these fine scientists explained what's been going on in paleontology for the past year.
The biggest dinosaur news, of course, were some new papers in Nature about new bird (avian) fossils found in China that helped to fill in our knowledge of the evolution of birds: especially one about Apsaravis ukhaana, a Mesozoic ornithurine bird. There was also a huge new dinosaur discovered in Argentina, and a now infamous "forgery" of a Chinese bird fossil.
On the dinosaur front once again, Dr. Mark Norell pointed out that so many new dinosaurs have been found in so many countries -- China, Africa, Venezuela and more -- that we will have to revise our idea of when certain famous dinosaurs lived. It was once thought that some sauropods only lived during one era, but as more digging is done, paleontologists find fossils like Ceratopsians, for example, that cross the Triassic and Jurassic.
Drs. Novacek and Knoll both agreed that commercial fossil hunters are creating problems. For the first time ever, paleontologists must take security measures at their dig sites to prevent fossils from being stolen. In addition, several auctions for dinosaurs fossils encouraged people to dig them up without proper care and documentation just to make money. If amateur paleontolgists followed good procedures, the information about what surrounds the fossils would not be lost to science.
Dr. Knoll explained that paleobiology is becoming very important and useful. There are new techniques for studying microscopic evidence that surrounds or is a part of fossils. This evidence lets scientists correlate theories about evolution with much better evidence (biochemical responses to environment, especially) that tells us things about extinct animals that are not obvious from just looking at their shape. Apparently, some of this evidence will make us reconsider just how animals evolved! Also, the biochemical evidence shows that the world was not always the same: the atmosphere and climate in the time of the dinosaurs may have been so different from out own that it would have been impossible for people to exist back then.
What career should young paleontologists choose? Dr. Allman recommend the study of the Cambrian and Pre-Cambrian boundary (about 5,700,000 years ago). While there are no dinosaurs back then, there are amazingly well preserved fossils including whole embryos! Many of these are just being found around the world. Using the tools of developmental biology, there is much to be learned about how early evolution took place.
Once considered to be sort of outsiders, Paleontologists are now consulted by modern conservationists to help understand how animal and plant species are becoming extinct. Paleontology has studied dinosaurs extinction for almost 2 centuries, but conservationists are only beginning to understand how the destruction of the rain forests in South America or pollution in the United States may resemble events that happened at the K/T (Cretaceous/Triassic) extinction.
They have a scary message. Within the next 50 to 100 years, nearly 30% of the life forms (animals and plants) now alive on earth may become extinct! This is because human beings so dominate this planet that they have stopped being careful of what they do and how it affects other living beings. Humans are using up all the land area that other animals used to live in. People use it to build houses or grow food, but the other animals have no place else to go.
They've all promised to come back next February to tell us what's new. We only hope that they get some breakfast before then.
Few subjects in the Earth sciences are as fascinating to the public as dinosaurs. The study of dinosaurs stretches our imaginations, gives us new perspectives on time and space, and invites us to discover worlds very different from our modern Earth.
From a scientific viewpoint, however, the study of dinosaurs is important both for understanding the causes of past major dinosaurs extinctions of land animals and for understanding the changes in biological diversity caused by previous geological and climatic changes of the Earth. These changes are still occurring today. A wealth of new information about dinosaurs has been learned over the past 30 years, and science's old ideas of dinosaurs as slow, clumsy beasts have been totally turned around. This pamphlet contains answers to some frequently asked questions about dinosaurs, with current ideas and evidence to correct some long-lived popular misconceptions. Although much has been discovered recently about dinosaurs, there is still a great deal more to learn about our planet and its ancient inhabitants.
# When did the first dinosaurs appear on Earth?
# Are all fossil animals dinosaurs?
# Did people and dinosaurs live at the same time?
# Where did dinosaurs live?
# Did all the dinosaurs live together, and at the same time?
# How are dinosaurs named?
# What was the biggest dinosaur? What was the smallest?
# How many types of dinosaurs are known?
# Were dinosaurs warm-blooded?
# How long could a dinosaur live?
# What did dinosaurs eat?
# How fast could dinosaurs walk or run?
# Did dinosaurs communicate?
# Why did some dinosaurs grow so big?
# Which was the smartest dinosaur?
# What colors were dinosaurs?
# Were dinosaurs social animals?
# When did dinosaurs become extinct?
# Why did the dinosaurs die out?
# Where can I find more information about dinosaurs?
Source from Great Site: http://pubs.usgs.gov/gip/dinosaurs/
She possesses a set of fearsome jaws, is in spectacular condition for her age and would make a striking addition to any drawing room – provided you have one big enough to contain her 33ft-long set of dinosaurs fossilised bones.
Anyone with a seriously large wallet could soon be able to buy this rare, partially complete fossilised skeleton of an Allosaurus, a large carnivorous dinosaur that lived about 150 million years ago and is sometimes referred to as the T. rex of the Jurassic Period – T. rex itself lived much later during a period known as the Cretaceous Period.
The female Allosaurus, discovered in a dinosaurs fossil graveyard in the US state of Wyoming, is one of the prime exhibits going on sale later this year at the French headquarters of Sotheby's in Paris. She is expected to attract huge interest from the growing number of wealthy fossil collectors keen to snap up one of the rarest of dinosaur finds.
Another item on sale is a flying carnivorous reptile with a 35-inch wingspan called Dorygnathus banthesis, displayed in the original black matrix rock it was found in when it was unearthed in 1932 from a site in Holzmaden, Germany. Sotheby's estimates that the oval-skulled pterosaur will fetch €160,000-€250,000 (£145,000-£247,000).
If neither of these beasts takes your fancy, then how about a complete skeleton of a fish-eating Plesiosaurus, a type of primitive marine lizard that lived about 190 million years ago?
It was dug out from a limestone outcrop in Blockley, Gloucestershire, in the early 1990s. Sotheby's says that the 6ft 7in by 9ft 10in skeleton is the best-preserved specimen of a Plesiosaurus to date, meaning it could easily go for more than £300,000. For those who do not like the idea of taking a fearsome carnivore home with them, there is the alternative of bagging a pair of petrified crabs buried suddenly near Vicenza in Italy 45 million years ago.
Alternatively, there is a fossilised palm leaf and accompanying fishes dating from the Eocene Period some 50 million years ago, about 15 million years after the dinosaurs went extinct but before mammals had fully risen to take their place as the dominant, large terrestrial lifeforms.
"Whether you look at them as artistic masterpieces or wonders of nature, dinosaur skeletons, fossils and minerals retrace the saga of evolution, especially that of mighty terrestrial and marine mammals that are now extinct," said Professor Eric Mickeler, a palaeontologist and the expert consultant on the Sotheby's sale.
Whatever the motives of those wanting to own such magnificent specimens, it is clear that collecting and dealing in fossil relics of a prehistoric age is big business, according to Lorraine Cornish, a senior conservator at the Natural History Museum in London, who is involved in the museum's purchases of dinosaurs fossils.
"We try not to buy on the commercial market. For a start we have limited funds, but we also don't particularly want to encourage the sale of fossils that may be dug up without the details of the find being recorded, which would mean the loss of important scientific information," Mrs Cornish said.
"But we have to accept that dealing in fossils is a reality. Some very wealthy people are passionate about the fossils they collect and they want the best, just like some people want the best works of art," she added.
One of the prime fossil exhibits in the Natural History Museum in London is a heavy-clawed dinosaur called Baryonyx walkeri which was unearthed in a clay pit near Dorking in Surrey.
One of its distinctive claws was found sticking out of the ground by William Walker, a local amateur collector, in 1983.
Mr Walker took the claw to the museum, whose experts organised a proper excavation. In return, Mr Walker received replica claws and had the species named after him.
"We try to develop really close relationships with amateur fossil collectors. In that way, if they find something they are likely to bring it and show it to us first," Mrs Cornish said.
In Britain it is perfectly legal to collect and deal in fossils of dinosaurs or other prehistoric animals provided that certain guidelines are met, such as securing the approval of the landowner and getting particular permission from official authorities if the collecting area falls within a designated Site of Special Scientific Interest, which are often established to protect the best fossil deposits.
Although there is no legislation specifically designed with fossils in mind, guidelines dictate that detailed records of the find should be kept and the excavation should be done with sufficient care.
One important site for amphibian fossils near North Berwick, for instance, was entirely removed illegally in a matter of hours by a collector using a mechanical digger.
Some of the most important finds have been made by amateur and professional fossil collectors. One such collector, Stan Wood, unearthed the earliest known fossil reptile near Bathgate in West Lothian.
The eight-inch-long fossil, known as "Lizzie", was later sold to the National Museums of Scotland for £180,000 – considerably less than Mr Wood could have received if he had sold it to foreign collectors, according to Matt Dale, an Edinburgh fossil dealer who now runs Mr Wood's fossil business.
Source from great site: http://www.independent.co.uk
Wednesday, July 28, 2010
An ancient ‘crime scene’ in Utah has revealed evidence of a dinosaur in the act of preying on a small mammal.
A 77-million-year-old dinosaur claw mark and scratched-out digging traces were discovered next to a series of mammal burrows in Dixie National Forest by Edward Simpson, a geologist at Kutztown University in Pennsylvania, and his colleagues.
“It appears a dinosaur was digging down and trapping rodent-like mammals in a similar way to coyotes hunting around prairie dog burrows today,” New Scientist quoted Simpson as saying.
The size and curvature of the claw indicates that it was a maniraptoran theropod - carnivorous dinosaurs including velociraptors and the ancestors of modern birds among their ranks.
The traces were preserved when sand was suddenly dumped onto the burrows during a flood.
The find is published in Geology.
Source from Great Website:http://www.thehindu.com/sci-tech/article534831.ece
Small Australian dinosaurs endured around six months of darkness each year during the Early Cretaceous, with freezing temperatures and huge predators.
So the diminutive dinosaurs took refuge underground, according to a new study.
The findings, which will be presented at next month's Geological Society of America annual meeting in Portland, reveal how dinosaurs and certain other animals developed strategies for surviving harsh environments and predation.
Predator tracks near burrows in Australia indicate 1,700-pound carnivorous dinosaurs hunted diminutive 22-pounders, which had to think fast.
"What defense did they have other than running? How about staying out of sight in burrows?" Anthony Martin told Discovery News.
Martin, a senior lecturer in environmental studies at Emory University and an honorary research associate at Melbourne's Monash University, outlined his discoveries in a paper that will be published in the October issue of Cretaceous Research. They represent at least three years of work.
In 2006, he identified the 95-million-year-old skeletal remains of a small adult dinosaur and two juveniles in a fossilized burrow in southwestern Montana.
The species is now called Oryctodromeus cubicularis, meaning "digging runner of the lair." That same year he also found tracks for a carnivorous dinosaur in Victoria, Australia, where a theropod (two-footed dino) claw and a few related bones have been uncovered.
In 2007, while hiking in Victoria, Australia, Martin spotted three dinosaur burrows etched into a 105-million-year-old outcrop that's about six-feet long and one-foot in diameter. At least one of the burrows descends into a spiral and ends in an enlarged chamber.
"The burrows show a behavior that was probably related to surviving a polar winter, but also could have served as protection against large predators, such as the large theropod dinosaurs," he said, adding that Australia's big Allosaurus-like dinosaurs "must have had some physiological adaptations that helped them to survive cold, dark winters."
Average annual temperature in Early Cretaceous Victoria was likely less than 41 degrees Fahrenheit, "which means that wintertime temperatures were well below freezing, plus it was dark for five to six months of the year," he explained.
Patricia Vickers-Rich, chair of paleontology at Monash University, said of the Australian burrows, "We have wondered for some time what these structures were and when Tony found burrows with dinosaur bones in them in Montana, he became suspicious that these structures in southern Victoria were of a similar nature."
More recently, Martin has found insect and crayfish fossil burrows in Victoria that date back to the same period. The crayfish burrows are the oldest known for Australia. Mammal and turtle fossils suggest these animals might also have retreated into underground chambers.
Taken together, he said, the "dinosaur burrows and tracks, as well as crayfish and insect burrows, give us new insights on animals' adaptations to polar environments during the time of the dinosaurs."
In the long run, however, that adaptability wasn't enough to save the down under dinosaurs.
"Dinosaurs were a very successful group for more than 160 million years, but they still eventually went extinct for various reasons, so it's not surprising that even the best adapted ones, including burrowers, just wouldn't necessarily make it through every environmental change," he said.
Birds, such as puffins, swallows, kingfishers and some owls, do burrow, he added, but there's no evidence they are the direct descendants of the burrowing dinosaur lineages.
A miniature version of Tyrannosaurus rex is throwing a bone to paleontologists interested in how the king of dinosaurs evolved.
The newly discovered species, called Raptorex kriegsteini, lived tens of millions of years before T. rex and shares many similar features, suggesting it could be a direct ancestor of T. rex, researchers report online September 17 in Science. Raptorex possessed a Tyrannosaurus body plan -- with a large head, strong legs and jaws, and puny forelimbs -- which reveals that traits once thought particular to large predators could have been useful to smaller animals who had them as well.
"It was the common perception that the arms got smaller as the animals grew bigger," says study author Paul Sereno of the University of Chicago. "No one had any idea there was something like Raptorex lurking around."
The findings are based on a nearly complete 125-million-year-old fossil unearthed in China. Though it doesn't represent a full adult, Sereno says the fused bones indicate that this Raptorex was almost full-grown. At full size, Raptorex would have been about 90 times lighter than T. rex.
Despite its size, Raptorex shared many of the features peculiar to the Tyrannosaurus dinosaurs, which were the dominant predators during the Late Cretaceous period, from 90 to 65 million years ago. In addition to a large head and tiny arms, Raptorex had long legs and specialized running feet, as well as large cavities in the head linked to a keen sense of smell, the researchers report.
"We see this all to our great surprise in an animal about size of a human," Sereno says.
In contrast, other dinosaurs thought to be ancestors of T. rex were lankier, with long arms, small heads and a more primitive type of foot not specialized for running.
Raptorex's features suggest to the authors that Tyrannosaurus' ancestors adapted earlier than thought to their role as runners and hunters.
With a greater need for powerful legs and a larger head with strong jaw-closing muscles, Tyrannosaurus-like dinosaurs would have had little use for forearms. Instead, the dinosaurs could have become a "running set of jaws" with puny forelimbs "along for the ride," says Sereno.
Paleontologist Thomas Holtz of the University of Maryland in College Park says the discovery of the dinosaur is strong proof that Tyrannosaurus relatives had their monstrous features long before reaching six tons. However, he says, "There's still a gap of a few tens of millions of years before we pick up the classic tyrannosaurids, and it is not clear how the body plan changed during that time.
The fact that Raptorex could have made a successful predator despite its small size implies to Sereno that a young T. rex, which has features similar to the adult, might also have been a potent killing machine. The presence of precocious youngsters could explain why T. rex was the dominant predator in Asia and North America for 25 million years.
Rare evidence has been found of dinosaurs preying on mammals. Fossilized mammal burrows that appear to have been clawed out by a predator suggests that some theropod dinosaurs dug into mammal dens to get furry morsels.
Since there were no large mammal predators 80 million years ago, the most likely candidates are dinosaurs. Making the connection even stronger is that claw marks in the burrows are a pretty good match to the claws of dinosaur fossils found in rocks nearby, though slightly later in time.
"It's pretty tight," said paleontologist Edward Simpson of Kutztown University of Pennsylvania. "We can't say whether it's a troodont or a velociraptor," because the claw bones of those found nearby have lost their nails, or cuticles. But otherwise the match is a good one, he said.
Simpson and his students have published their "trace dinosaurs fossil" discovery -- that is, fossilized evidence of animal behaviors rather than the animals themselves -- in the August issue of the journal Geology.
"To me there is almost no doubt," agreed trace fossil expert Anthony Martin of Emory University. "It's very good circumstantial evidence."
No actual mammal bones or teeth have been found, though the burrows match the complexity of those of other mouse- or shrew-like mammals of that time and their present-day counterparts. The criteria for calling something a fossilized mammal burrow were laid out a few years ago in a separate paper by Martin.
With that criteria in mind, the team feels confident that they did find a mammal's subterranean abode. The researchers could go even further to make their case.
"One of the things we could do is to take the burrows and cut them up," said Simpson. There might be mammal teeth in them, which make an even stronger case.
However, he's hesitant to do that since it's a destructive process. There is also only a very small chance they will find any mammal bones or teeth. So far Simpson and his students haven't even extracted the fossil burrow from the cliff in southern Utah in which it was found.
As for the dinosaur involved, it probably wasn't very big, judging by the claw marks in the burrows, said Martin.
Other evidence that has been reported to support the dinosaurs-bites-mammal story include the specialized jaw, teeth and skulls of some dinosaurs; mammal bones with bite marks; fossilized gut content; and feces and trackways.
This case is different in that it points directly at how the dinosaurs hunted rather than just the fact that they ate mammals.
"This is an excellent example of how trace fossils can reveal animal behavior," said Martin.
Source from Great website: http://news.discovery.com/dinosaurs/zooms/dinosaurs-claws-mammals.html
Tuesday, July 27, 2010
Join your Hot Facts Model Rachel for interesting facts about dinosaurs. What are the different names for the different types of dinosaurs? When was the Jurassic period? Was the movie Jurassic Park accurate? How big were dinosaurs? When was the first dinosaur fossil discovered? Were there flying dinosaurs? How fast were dinosaurs walking? What was the smallest species of dinosaur? Find out about dino science.
I visited the British Museum.On one of the relics there was what seems to be a very accurate depiction of what looked to me like an Elasmasaurus DINOSAUR.. Can anyone tell me what this heirogyph signifies? PLEASE see also my film 'submarines and aeroplanes in ancient egypt' for more strange carvings on this artefact...If you think it's a scorpion, please post a photograph of an egyptian hieroglyph showing a scorpion. I've scoured the web and can't find one to compare with my dinosaurs
Massive creatures have once ruled the earth over 65 million years ago. Some dinosaurs were found to be tons in weight and over a hundred feet in height. How did these large creatures just disappear from the face of the earth and in such a short period of time? We have discovered that not only dinosaurs became extinct but also other organisms in the ocean and land were greatly affected. The structure of Earth has also changed where continents had moved, major ridge expansion took place, and land has sunken under sea or risen above water . Some evidences also show a "massive destabilization of the oceans and atmosphere" .A number of theories of what caused the extinction of the dinosaurs as well as other organisms developed, such as: giant meteor or comet impacts, volcanic eruptions, radiation from a nearby supernova, extreme changes in climate, diseases, and predation of dinosaur eggs by early mammals.The death of the dinosaurs is neither the most recent nor the most severe dinosaurs extinction; yet, it is a controversial debate where scientists are still trying to solve this great mystery.
Because dinosaurs were not the only organisms to become extinct the scientific theory of what caused this massive disappearance should have certain guidelines. "Clearly any successful extinction theory must explain not only why the dinosaurs became extinct; it must also explain what happened to the marine ecosystems, that so many lineages of plants and animals were wiped out. It must also explain why so many organisms were able to survive the catastrophe. It is estimated that somewhere in the range of 20% to 25% of all species extant at the beginning of the Late Cretaceous were extinct by its close" .
At the end of the Cretaceous Period over half the number of organisms disappeared leaving traces of evidences of what caused this extinction. Luis and Walter Alveraz were studying the K-T boundary in Gubbio, Italy where they found an unusual layer of clay at the boundary point which contained around thirty times the normal level of the rare element iridium . The two most common source of iridium are from outer space in the form of cosmic dust, which is constantly showering the planets and the Earth's core when there are eruptions of certain types of volcano.This evidence alluded to two different theories, The Impact Theory and the Volcanic Theory.
The volcanic theory is somewhat similar to the impact theory and is also heavily supported by a number of scientists. As mentioned before the K/T boundary was discovered to have high contents of iridium. The basaltic lava eruptions of the Deccan Traps of western India was mentioned as a possible source of the iridium found in the K/T boundary "iridium spike" (1). "It has been proposed that the out gassing, combined with possible explosive episodes, could have been sufficient of itself to have caused the same kind of a "Nuclear Winter" scenario as proposed for the giant meteor impact". Other areas in the Pacific Basin show a fairly high level of volcanic eruptions. This theory would further explain the possibility of how some organisms survived and the irregular distribution of iridium peaks in some areas.
The impact theory or the possibility that an asteroid or comet destroyed over half of the species on earth has been a strongly supported theory of why the dinosaurs became extinct. The impact of the asteroid or comet caused a chain of events beginning with the flying object becoming intensely hot and heading towards earth. This asteroid is believed to impact the ocean "ejecting massive amounts of dust and water into the atmosphere". Everything within the radius of 500 kilometers would have been instantly destroyed.Many of the groups of organisms that were hit hardest by the K/T extinction lived in the ocean.Many enormous tidal waves would be started causing even more damage as well as start a chain reaction of earthquakes and volcanic activity.The dust particles will envelop the earth covering the earth into total darkness making vegetation to dematerialize away, leave little food for the animals, and create a cold environment.Temperatures may have fluctuated below freezing point to high temperatures and photosynthesis may have ceased.At the same time large fires would have been started by the intense shock wave later creating global fires that would release large amounts of carbon dioxide increasing temperatures and cause chemical reactions forming acid rain .The impact may also have released sulfur dioxide, which may help created acid rain with a low pH causing an environment where some organism may not have been able to survive.Evidence of acid rain was found in a number of rock samples.
One of the greatest discoveries that show great support for the impact theory is a crater called the Chicxulub. Alan Hildebrand found a ring structure 180 kilometers in diameter in the Yucatan Peninsula. The Chicxulub is also believed to be 65 million years old. Alan Hildebrand wrote further explaining that the K/T boundary had two layers.The upper layer, the Fireball layer, was about 3mm thick and represented 1500 cubic kilometers of debris deposited globally with not variation in thickness. The Lower layer, the ejecta layer, was about 2mm thick .The Fireball layer contains certain traces of elements in approximately the same proportion as some meteorites .Furthermore, Tektites and micro tektites, black glassy objects produced at the time of the impact, have been found in the ejecta layer of the K-T boundary .
Evidences that further support the impact theory is the presence of soot within the clay layer. The presence of soot usually implies that a large global fire occurred as a result of temperature changes from an impact. Quartz crystals were also found physically altered within the clay layer. "This alteration only occurs under conditions of extreme temperatures and pressure".These evidences also show that a great climatic change has taken place.
Most of the evidence that was discovered points toward the impact theory. This theory explains most of the changes that occur towards the end of the Cretaceous period. Though the volcanic eruption explain some evidence that are not supported by the Impact theory, the Impact theory clearly explains the events that occurred during the period of dinosaur downfall and is more strongly supported by the evidence that was found. Temperature data shows that there was a temperature drop and later a temperature rise. The 65 million year old crater that exist on the Yucatan Peninsula shows that an asteroid did indeed collided onto Earth. Iridium, which is a common component of asteroids, was found in sediments of the Cretaceous layer. These evidences as well as other information strongly support the theory that an asteroid impacted the earth 65 million years ago and destroyed a large number of species including the massive sized dinosaurs.
A scientific whodunit unfolding at Lawrence Berkeley Laboratory (LBL) and on the UC Berkeley campus since early summer has stimulated spirited debate among geologists, paleontologists, biologists and physicists around the world.
The story revolves around a piece of pink and white limestone in whose layers are buried evidence for what paleontologists call the "great dying," the period some sixty-five million years ago when fifty percent of the earth's animals and plants were mysteriously wiped out. The rock is a sample from the sedimentary deposits near Gubbio, Italy, which were once buried beneath the sea and have since been lifted and exposed in roadcuts.
When you look closely at the rock, you see a band of brown clay at the boundary between the limestone which was laid down during the Cretaceous period sixty-five to one hundred million years ago, and the red limestone from the more recent Tertiary period. The brown clay was deposited about sixty-five million years ago, at the time of the great dinosaurs extinctions.
Looking through a magnifying glass, you see that the Cretaceous limestone is crowded with dinosaurs fossils of a tiny crustacean called Forminifera globutrucana. They are entirely absent from the clay layer. In the Tertiary limestone, a few of their relatives reappear.
Though scientists have known for more than a hundred years about the extinctions from dinosaurs fossil records like these, no one knows what event might have caused such a world-wide wipeout.
What brought the rock to LBL were conversations between physicist Luis Alvarez and his son Walter, an associate professor of geology on the UC Berkeley campus. Walter Alvarez has spent the last several years dating similar rock samples from Gubbio by a method called magnetic stratigraphy, using the reversals of the earth's magnetic field, which are recorded in the rocks, to date deposits.
Luis Alvarez wanted to know how long the forminifera extinction lasted before the species began to reestablish itself. One way to find out was to measure the sedimentary rate -- how long it took for the clay to be deposited on the ocean floor. He suggested using iridium as the yardstick.
Iridium is a stable, silver-gray metal, rare in the earth's crust because it is bound up with iron in the earth's core. But out in the rest of the solar system, it is a thousand times more abundant. It is brought to us by such solar system visitors as meteorites, which burn up or fragment and drift as fine particles through the atmosphere.
"Because we know the rate at which extraterrestrial matter rains down on the earth each year," says Alvarez, "it occurred to me that by measuring the abundance of iridium in the sedimentary deposits, we might be able to tell how long a period of time was represented by that clay layer.
"I later learned that this idea was twenty-five years old, and it had been implemented ten years ago," adds Alvarez parenthetically, but fortunately he didn't know that at the time.
The Alvarezes went to see Frank Asaro and Helen Michel, LBL nuclear chemists who have developed a technique, called neutron activation analysis (NAA), for making precise measurements of very low elemental abundances in various materials. Their NAA facility is one of only a few in the world that could undertake the difficult analytical tasks required by this problem.
Taking their samples from the clay layer and from the younger and older Tertiary and Cretaceous sediments on either side, Asaro and Michel measured iridium and thirty other elements. They discovered a sudden increase in the abundance of iridium in the clay twenty-five times more than normal, in comparison with other elements. After the initial jump in the clay layer, the iridium tapered down, more or less exponentially to the background, forming a spike. This unexpected increase, called an anomaly, coincides with the extinctions.
"The anomaly could have been caused by an increase in the amount of iridium which was deposited along with the clay," says Helen Michel, "or else the iridium might have remained constant, and the rate at which clay was deposited slowed down."
"That doesn't seem likely," she adds, because Walter Alvarez's study of the reversals of the earth's magnetic poles does not show any significant decrease in the sedimentation rate during that period."
Finding The Source
"If there was an increase in the deposition rate of iridium-rich material, a source on the earth would be unlikely, since iridium is one of the least abundant elements in the earth's crust," comments Asaro.
"If, on the other hand, the source is extraterrestrial, it would be naturally enriched in iridium and would be compatible with our measurements. So we believe the extraterrestrial hypothesis is more likely."
It wasn't the first time that an extraterrestrial source has been considered as the cause of the great dying, because a satisfactory explanation has never been proposed for such wide extinctions. No sweeping climate changes, such as the ice ages which would follow, are recorded in the rocks, and the theory that dinosaurs simply became obsolete after ruling the earth 150 million years doesn't account for the demise of so many other species. But until the discovery of the iridium anomaly at LBL, there was no direct evidence to support an extraterrestrial theory.
Once the anomaly was discovered, the problem was to find a source that would deliver the extra iridium and was capable of causing the world-wide extinctions.
One popular theory discussed at great length in the scientific literature attributes the extinction to certain effects caused by a nearby supernova. For example, if a star exploded a light year away, the increased cosmic ray intensity could have killed the animals by giving them all an intense dose of radiation. The problem is that the probability of such a supernova explosion is only about one in a million, in the last one hundred million years. From the amount of iridium measured in the rocks, supernova explosion would have had to be a tenth of a light year away. This upped the odds to a probability of one in a billion.
In spite of the unfavorable betting odds, the supernova theory had the advantage that it could be checked experimentally in a series of delicate tests done by neutron activation analyses.
Because it is almost certain that all elements heavier than nickel and iron are synthesized in the intense neutron fluxes of a supernova, Asaro and Michel set out to find plutonium-244. This isotope, with a half-life of about eighty million years, should still be in the clay layer, if the source of the iridium had been a supernova.
Asaro and Michel brought ideal credentials to this assignment, since they were both experienced plutonium chemists before becoming NAA specialists.
From the clay sample, they separated out a few drops of acid solution which they then evaporated. If the sample contained plutonium, most of it would be found in the evaporate. Though the procedure sounds simple, Asaro and Michel in fact separated away almost all known elements, in a real "tour de force" of chemistry.
When they irradiated the evaporate in the UC Berkeley campus nuclear reactor, and looked for the gamma ray signature of plutonium-245 (into which plutonium-244 would have been converted), they came up with "no signal." They could have detected one tenth of the expected amount, if it had been present, so the results looked bad for the supernova theory of the extinction.
Since astrophysicists believe that each supernova should leave its own fingerprint in the isotope ratios of the different elements made in its oven, Asaro and Michel embarked on the difficult task of measuring the ratios of the two iridium isotopes. The tests showed that the iridium from the spike had the same isotopic ratios as solar system material, so again the evidence was against the supernova theory.
Maynard Michel, using his mass spectrometer with its supersensitive electron multiplier detector, is planning on looking further for the plutonium-244. But with two experimental strikes against it, plus the fantastically small theoretical probability, it appears the supernova just doesn't fit.
Michel and Asaro have widened the search by measuring samples from similar sedimentary deposits in Denmark. Though the Gubbio samples are from four sites over a twenty-seven kilometer area, it was important to determine if the iridium spike occurs in samples from other locations. "If we couldn't find an iridium spike in other sedimentary deposits, we would have a hard time convincing anyone, including ourselves, that we had made any observations relating to the Cretaceous-Teritiary extinctions, which we know are world-wide," says Alvarez.
In recent NAA tests on the Denmark sediments, the group found an iridium spike that is larger by a factor of between five and ten than the iridium spike in the Gubbio deposits.
"Now that the basic experiments have been done, and it seems clear that the iridium came from an extraterrestrial source within the solar system," says Alvarez, "we will spend the next few months trying to put together a satisfactory theory of the extinction. Our theory must agree with known properties of the solar system and with documented evidence from paleontology."
It is hard to imagine that one of the largest impact craters on Earth, 180-kilometers (112-mile) wide and 900-meters (3,000-feet) deep, could all but disappear from sight, but it did.
Chicxulub, located on Mexico's Yucatan peninsula, eluded detection for decades because it was hidden (and at the same time preserved) beneath a kilometer of younger rocks and sediments. Size isn't the only thing that makes Chicxulub special. Most scientists now agree it's the "smoking gun" -- evidence that a huge asteroid or comet indeed crashed into Earth's surface 65 million years ago causing the dinosaurs extinction of more than 70 percent of the living species on the planet, including the dinosaurs. This idea was first proposed by the father and son team of Luis and Walter Alvarez in 1980.
Though the buried giant can't be seen, the impact crater has left subtle clues of its existence on the surface. "When I talk to school children, I describe it like this," says Dr. Gary Kinsland, a geology professor at the University of Louisiana at Lafayette who has been doing research on Chicxulub since 1994. "Put a bowl on your bed, then throw the sheets and blankets over it. All you'll probably see of the bowl now is a subtle depression."
"There is not a big hole anymore," he continues, "but if you look at the rim of the depression on your bed, you'll see that it is still in the same position as the rim of the bowl beneath. That's how surface expression allows us to interpret something about the buried structure."
The view from space lets scientists see some of Chicxulub's surface features that are not nearly so obvious from the ground. Satellite images showing a necklace of sink holes, called cenotes, across the Yucatan's northern tip are what first caught the attention of NASA researchers Drs. Kevin Pope, Adriana Ocampo and Charles Duller in 1990. They were among the first to propose Chicxulub as the impact site linked to the mass extinctions that occurred at the end of the Cretaceous and beginning of the Tertiary geological ages, called the K/T boundary.
"We were ignorant of the existence of a crater," says Pope, now an independent geologist, "We were working on a project on surface water and Mayan archaeology when we saw this perfect semi-circular structure in images from the Landsat Thematic Mapper. "We were fascinated and got the magnetic and gravity data from the area collected earlier by the Mexican petroleum company, who had been looking for oil. Their data showed a large, remarkably circular structure that they had identified as an impact crater." Pope and his colleagues reasoned that the cenotes resulted from fractures in the buried crater's rim and that the area within the cenote ring corresponded with the crater's floor.
Further studies by other researchers of the magnetic and gravity data plus analysis of rocks and ocean sediments published in 1991 helped convince the scientific world that Chicxulub was the site of the impact that sent life on Earth in a new direction, from the age of dinosaurs to the age of mammals.
Scientists continue to comb through the clues the impact has left behind, some of which show up best from space. "The classic spaceborne synoptic view," says Pope, "is what you need to see a large structure like this." Maps of the region's wetlands, produced by the spaceborne imaging radar-C (SIR-C) mission in 1994, identified zones of groundwater discharge that correlate with the crater's structure.
Now researchers are getting their first look at detailed, three-dimensional topographical data from the Shuttle Radar Topography Mission. "This new image gives us both corroboration of what we expected and also shows up things we haven't seen before," says Kinsland. "We'll be working to get as much out of the data as possible. Anything we learn at the surface tells us more about the buried crater."
Much about Chicxulub remains mysterious. "We don't know exactly how the impact caused the mass extinctions," says Pope. "We believe it did, but we don't know what the "kill mechanism" was. One theory is that the impact threw up so much dust into the atmosphere than it obscured the Sun and stopped plants from growing. Another is that the sulfur released by the impact lead to global sulfuric acid clouds that also blocked the Sun and fell as acid rain. Global wild fires triggered by the atmospheric reentry of red-hot debris from the impact are another possibility.
Also unresolved is whether Chicxulub is the result of a collision with a comet or an asteroid. "There are arguments on both sides," says JPL's Dr. Don Yeomans, who manages NASA's Near-Earth Object Program Office. "There are far more asteroids in Earth's orbital vicinity than comets," says Yeomans, "but most are much smaller than the 10-kilometer size (6.2-mile) of the one that hit Chicxulub. When you get to that size range, then comets are about as prevalent. Most people say it was an asteroid, but it is still not altogether clear. Whatever it was, once you're hit with something that large, it's horrendous."
Monday, July 26, 2010
What is a fossil?
A fossil is the remains, trace, or imprint of a plant or animal that has been preserved in the earth's crust since some past geologic time [adapted from AGI's "Glossary of Geology"].
Types of Kentucky Fossils
The Ordovician, Silurian, Devonian, Mississippian, and some of the Pennsylvanian rocks of Kentucky began as sediments laid down in shallow tropical seas; consequently, the fossils found in them are types of marine shellfish (invertebrates). The most common types include corals, moss animals (bryozoans), lampshells (brachiopods), trilobites, clams (pelecypods), snails (gastropods), shell-bearing squid-like animals (cephalopods), and sea-lily animals (crinoids). The famous Devonian fossil coral beds at the Falls of the Ohio near Louisville are an example of marine fossils. Some of the Pennsylvanian rocks were laid down as river, delta, and swamp deposits on land and, accordingly, contain abundant plant fossils. The numerous coal beds in Kentucky are essentially fossil swamp peats (deposits of plant material). The Cretaceous and Tertiary rocks were laid down as shallow marine and terrestrial deposits, and in some places contain plant fossils. The Quaternary sediments in some parts of Kentucky, such as at Big Bone Lick State Park near Cincinnati, contain mammal fossils, including the extinct mammoth, mastodon, and giant ground sloth.
* Types of fossils
* Did I find a fossil bone
* Fossil Fact Sheets
The Study of Fossils
The study of fossils is called paleontology; it is not to be confused with archaeology, which is the study of human artifacts. Paleontology is closely associated with geology, which is the study of the physical nature and history of the earth.
Fossil Bearing Rocks
Fossils are most commonly found in sedimentary rocks. Sedimentary rocks result from the consolidation of loose sediment that has accumulated in layers. Almost all of Kentucky's rocks at the surface (but below the soil) are of sedimentary origin, and almost all bear fossils. Consequently, Kentucky is an excellent place to collect fossils.
The common sedimentary rocks in Kentucky are limestone, shale, and sandstone. Limestones began as limey muds and sands that were deposited under shallow tropical seas in a setting similar to the modern Bahamas platform. During burial, the sediment grains became cemented together and they became limestone. Shales and sandstones began as deposits of non-limey mud and sand, respectively. Deposits of mud and sand formed in seas and on land. Again, cementation of the muds and sands transformed the sediment into rocks; this process is called consolidation or cementation. Plant and animal remains trapped in the original deposit became fossils.
Age of Kentucky Fossils :
Most of Kentucky's fossils are very ancient, and most are much older than the dinosaurs. Fossils are the same age as the sedimentary rocks that contain them, and the sedimentary rocks at Kentucky's surface are 505 to 438 million years old (putting them in the Ordovician Period), 438 to 408 million years old (Silurian Period), 408 to 360 million years old (Devonian Period), 360 to 320 million years ago (Mississippian Period), 320 to 285 million years old (Pennsylvanian Period), 144 to 65 million years old (Cretaceous Period), 65 to 1.6 million years old (Tertiary Period), and less than 1.6 million years old (Quaternary Period). A geologic map of Kentucky shows the distribution of these different age rocks. Not all ages are found in Kentucky.
* Geologic time in Kentucky
* Geologic map of Kentucky
Collecting Fossils in Kentucky :
Part of the fun of collecting is finding your own sites by learning to use the geologic quadrangle maps for your area (see below). We do not have published lists of fossil-collecting localities. The laws governing fossil collecting in Kentucky are the same as in most states: you need to get permission from the landowner before you enter and collect. Native American artifacts are protected by the Kentucky Antiquities Law. Contact the Kentucky Paleontological Society about fossil collecting trips in and near Kentucky.
Further Information :
For more information on Kentucky fossils, see "Guide to Progression of Life," published by the Kentucky Geological Survey. In addition, geologic quadrangle maps (GQ's) contain an abundance of information useful to the collector. These and several other paleontological publications are listed in the Survey's List of Publications. For further information, contact Dr. Stephen Greb at the Kentucky Geological Survey, (606) 257-5500.
You may also want to contact: Kentucky Paleontological Society, Inc.: They have regularly scheduled monthly meetings with presentations and have monthly fossil-collecting field trips. This organization is for all ages. Their address is: Kentucky Paleontological Society, Inc., 365 Cromwell Way, Lexington, KY 40503 (606-277-3148).
The theropod (meaning "beast-footed") dinosaurs are a diverse group of bipedal saurischian dinosaurs. They include the largest terrestrial carnivores ever to have made the earth tremble. What most people think of as theropods (e.g., T. rex, Deinonychus) are extinct today, but recent studies have conclusively shown that birds are actually the descendants of small nonflying theropods. Thus when people say that dinosaurs are extinct, they are technically not correct. Still it's not as exciting seeing a sparrow at your birdfeeder as it would be to see a Tyrannosaurus rex there.
Our knowledge of the evolutionary history of the Theropoda is constantly under revision stimulated by new, exciting fossil finds every year or so such as Mononykus olecranus, a very bird-like theropod found recently in the Mongolian desert, or Giganotosaurus carolinii, a giant theropod probably rivaling the size of T.rex., found recently in Argentina. In fact, the 1960's discovery and study of the remains of Deinonychus antirrhopus helped to revise paleontology's old vision of all dinosaurs as slow, stupid reptiles, and was a key factor in the onset of the controversial hot-blooded/cold-blooded debate. Currently, there are two or three main groups of theropods, depending on whom you ask; we have yet to fully understand their origin. Why is this so? The main reason is the lack of good specimens; theropod remains are fairly rare and more often than not, fragmentary — theropods have a poor fossil record compared to most of the ornithischian dinosaurs. Fossils of small theropods are especially rare, since small bones are harder to find and are weathered away easily. Without well-preserved, complete specimens, it is hard to tell who is most closely related to whom using cladistics.
Fragments of hollow theropod bones
Several characters that typify a theropod: hollow, thin-walled bones are diagnostic of theropod dinosaurs. A jumbled box containing theropod bones (from the UCMP collections) is shown at right. The hollow nature of the bones is certainly more obvious in 3D, but you should at least be able to make out the general tubular structure of the dinosaurs bones. Other theropod characters include modifications of the hands and feet: three main fingers on the manus (hand); the fourth and fifth digits are reduced; and three main (weight-bearing) toes on the pes (foot); the first and fifth digits are reduced. Most theropods had sharp, recurved teeth useful for eating flesh, and claws were present on the ends of all of the fingers and toes. Note that some of these characters are lost or changed later in theropod evolution, depending on the group in question.
Theropod classification :
The Herrerasauridae are an early group represented by Herrerasaurus, which was discovered in a wonderful middle-late Triassic period fossil locality (the famous Ischigualasto Formation) in Argentina in the 1970s. Another herrerasaur is Staurikosaurus, which has been known since the 1960s from remains found in Brazil. More recently (in 1993), another herrerasaur-like fossil was found in the same general area and named Eoraptor, or "dawn thief." It appears to be closely related to the herrerasaurs, but smaller in size and slightly older. Both Eoraptor and the herrerasaurs seem to have been small to medium-sized carnivores. These curious animals have some basic theropod characteristics, but lack others; in fact, they lack some dinosaurian characteristics as well. The Herrerasauridae and Eoraptor may be the earliest group of theropods, or it is quite possible that they are not even theropods at all, but rather non-dinosaurs (dinosauromorphs) closely related to the ancestor of dinosaurs. The fact is, we don't know for sure. Experts in dinosaur systematics are currently embroiled in a controversy over the exact relationships of the Herrerasauridae to theropods and other dinosaurs.
A second group of theropods is the Ceratosauria, a more morphologically modified and diverse group which includes the UCMP's very own Dilophosaurus, one of the stars of the novel and movie Jurassic Park. Segisaurus is a small, mysterious theropod known from only one specimen, which is housed in the collections of the UCMP. Recent discoveries have revealed that ceratosaurs formed a more diverse group than was previously expected....
The last, and by far the largest group of theropods is the Tetanurae, consisting of two major clades (sister taxa), the Carnosauria and the Coelurosauria. Some early tetanurines such as Megalosaurus fall outside of this dichotomy, but most are poorly known.
The carnosaurs were the huge, fierce predators such as Allosaurus (shown at the top of this page chasing Dryosaurus, an ornithischian dinosaur), and recent headline-makers like the gigantic Carcharodontosaurus and Giganotosaurus, both of which seemed to have reached or exceeded the size of T. rex, making them the largest terrestrial bipeds ever to have terrorized the terrestrial realm.
Velociraptor and Protoceratops
The Coelurosauria were generally smaller in stature, but more diverse, including such famous creatures as Velociraptor (shown at right grasping Protoceratops, a ceratopsian dinosaur) and our feathered friends the birds. Recent studies have agreed that T. rex and the tyrannosaurs belong with the coelurosaurs, not with the carnosaurs as was originally believed. Such is the ever-changing nature of theropod phylogeny; new finds and analyses are frequently overturning old ideas. This area of dinosaur paleontology is in a major state of flux.
Enjoy your visit with the fearsome and amazing theropods! You can learn more about theropod groups by either selecting links from the above text, or by clicking on a box in the cladogram pictured above.
Take an "audio tour" and hear about the discovery and reconstruction of Dilophosaurus from the discoverer himself, the late Sam Welles.
Dinosaurs inhabited Maryland through much of their 160 million-year history. While dinosaurs were not as abundant or diverse in this area as other regions in the U.S., the Maryland population included a interesting range of species. At least twelve species of "terrible lizards" roamed the ancient Maryland landscape from the Late Triassic (228 million years ago) to the Late Cretaceous (70 mya). Maryland's climate and topography during this 158 million year period varied widely, from a tropical, volcanic lowland to a shallow, warm, sea teaming with life.
These conditions were perfect for the deposition and preservation of animal remains which would eventually become dinosaurs fossils. The bones, shells and other decay-resistant body parts of land and sea creatures, and even plants, were rapidly buried in alluvial sediments that were washed into these low-lying areas. If the remains were not destroyed by scavengers, bacteria or erosion, they eventually became fossilized. The sediments which surrounded these remains eventually turned to rock through the process of lithification. The animal remains within the sediments became petrified as the sediments turned to rock.. While not all fossils are petrified, dinosaurs fossils in Maryland are. These fossils have remained in place for millions of year until erosion, or humans, uncover them.
Dr. Christopher Johnston was the first to record dinosaur fossils in Maryland. The fossils, reported in 1859, consisted of teeth recovered from a Bladensburg iron mine. See Astrodon johnstoni: the Maryland State Dinosaur for more information on this species. Since that first report of dinosaur fossils, hundreds of bones, teeth, footprints and other remains have been found in Maryland, mostly by amateur paleontologists and bone hunters.
Dinosaur fossils are found in rocks in central Maryland. These rocks are from the Mesozoic era, between the Triassic and Cretaceous periods. Most of the specimens are found in the Arundel Clay (Lower Cretaceous), the Severn and Mt. Laurel Formations (Upper Cretaceous), and the Gettysburg Shale (Upper Triassic). Rocks from the Jurassic period are either not exposed or missing in Maryland.
Australian Dinosaurs :
* Make a geological time line showing the major periods of the Earth's history. Try to make your time line to scale (1 cm = 5 million years?) Illustrate your time scale with drawings of appropriate fossils.
* Australia's fossil record includes invertebrate fossils (e.g. trilobites, ammonites, graptolites), and fossils of extinct marsupials from the last ice age (e.g. Diprotodon and Procoptodon). Visit Prehistoric Life and choose one fossil family to research.
Dinosaurs have been found in a number of places in Australia, but compared to countries like China and USA, discoveries have been few and far between.
* Make a list of Australian dinosaurs. Start by obtaining copies of the recent Australia Post stamp series.
* Research dinosaur discoveries in parts of Australia other than Victoria-particularly Queensland. Start with Minmi, Muttaburrasaurus and Rhoetosaurus. The dinosaur trackway (footprints) at Lark Quarry near Winton in Queensland, and the discovery, excavation and export to Boston, USA of the Queensland Kronosaur are of particular interest. Ref. Long, J. A. 1991, Dinosaurs of Australia, Reed Books, Balgowlah, N.S.W.
* The dinosaurs that have been found at Dinosaur Cove in Victoria were alive about 100 million years ago. Think of some ways of conceptualising 100 million. (10 Grand Final crowds; 1,000,000mm = 1 kilometre)
* On a map of Victoria, shade the areas where rocks of the right age for dinosaurs (Cretaceous Period) are found (Otway and Strezlecki Ranges). Mark the places where dinosaurs have been found-particularly Dinosaur Cove and Inverloch.
* Leallynasaura and other dinosaurs found in southern Victoria probably had big eyes for seeing in the semi-darkness of the polar winter. Explain why polar regions have long periods of darkness in winter.
* Research the names of dinosaurs. Most are derived from Ancient Greek and Latin, and may incorporate the name of the place where they were first discovered (e.g. Muttaburrasaurus, found at Muttaburra in Queensland).
* Research a few 'dinosaur bloopers' from the past, e.g. Brontosaurus (renamed Apatosaurus) was exhibited with the skull of another dinosaur for several decades. The spike on Tsintaosaurus' nose was probably not there, and the spike which was once thought to have been on Iguanadon's nose is now thought to have been a 'thumb'.
* Make your own dinosaur dictionary using words which you come across while studying dinosaurs.
* Replicate dinosaur footprints by placing a handprint in a tray of mud. Place a retaining collar of cardboard around the handprint and pour in a mixture of plaster of paris. When dry, remove the mould. This can then be used to make casts-coat the mould with petroleum jelly, surround it with the cardboard collar, and pour in plaster of paris as before. When dry, separate the cast from the mould.
N.B. Dental plaster sets in about 20 minutes and isn't expensive to buy.
* Fossils are normally found in sedimentary rock which has been exposed by erosion (wind or water, e.g. ocean cliffs), uplift (e.g. in an earthquake) or in a mine, quarry or road cutting. Write a story about finding and extracting a dinosaur fossil.
* Compare a diagram of the human skeleton with that of a dinosaur. What are the similarities and differences?
* How do we know that T-rex(type of dinosaurs) was a carnivore?
* Choose one of the dinosaurs which were herbivores (95% of all dinosaurs). What features show that it was a herbivore?
Sunday, July 25, 2010
It was at this time when something happened that caused dinosaurs to become extinct. While there are several ideas, one that many scientists believe is that a huge comet or asteroid 6 to 12 miles wide slammed into the region that is now part of the eastern coast of Mexico, but at that time was under water.
The impact of this object is believed to have caused darkness over the entire earth for many months, due to the huge amounts of dust that were thrown into the atmosphere. A global wildfire would have destroyed over half of all living things. Water would have been poisoned in most places, and the earth would have sunk into a deep freeze while the dust was in the air.
Even through all this, some plants and animals survived, including some insects, fishes, frogs, crocodiles, turtles, birds, and mammoths.
This may have just been part of a series of changes that caused the extinction of the dinosaurs. Before the asteroid/comet hit the earth, massive eruptions of volcanoes had caused earth's climate to be changed. At about the same time, sea levels dropped dramatically, opening new land bridges, changing ocean currents, and affecting the climate. These changes in climate likely reduced the ability of the dinosaurs to adapt, and the impact from the asteroid/comet was the last straw.
The creatures that were able to survive all these changes came to dominate the landscape. Mammals grew larger, and moved into new areas, taking over locations that had previously been the habitat of dinosaurs.
Changes in sea levels, ocean currents, and other events were also bringing in a new climatic cycle to the earth. Huge ice sheets would begin to cover large areas of the earth on a periodic basis. These swings in climate would have a major effect on animal habitats.
65 million years ago a comet or asteroid impacted the earth and brought the age of the dinosaurs to an end. But, was that reall what happened? Profs. Gerta Keller and Wolfgang Stinnesbeck deconstruct the evidence to find out what really killed the dinosaurs, tonight on The Urban Mystic Show.
The asteroid collision theory, which was brought to wide attention in 1980 by Walter Alvarez and colleagues, links the dinosaurs extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez et al.
Proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact. The bulk of the evidence now suggests that a 5 to 15 kilometer (3 to 9 mi) wide bolide hit in the vicinity of the Yucatán Peninsula, creating the 170 kilometers (110 mi) wide Chicxulub Crater and triggering the mass extinction.
Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave.
Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).