LITERATURE REVIEW
By: Student X
Sixty-five million years ago, the Earth was a very different place. Although the
continents were most likely near their current positions, there were no polar icecaps and the
center of North America wascovered by a vast, although receding, inland sea. As for the flora,
the world of 65 million years ago was a mix of older gymnosperms (non-flowering plants) with
a growing variety of angiosperms (flowering plants), including early versions of modern
flowers, such as magnolias. The fauna, however, would be the most recognizable by modern
humans. Sixty-five million years ago, there were many animals that are still with us, such as a
variety of insects, early birds, and marsupial mammals. However, the largest creatures on the
land were a groupof reptiles known as the dinosaurs, or Latin for “terrible lizards.” Sixty-five
million years ago, the time period known as the Cretaceous was about to end, and with it its
large-sized fauna and flora.( this paragraph needs citations)
During the last age of the Late Cretaceous, the Maastrichtian, named after a city in
Holland, the dinosaurs were diverse, but their numbers, both in population and species, were
declining. In North America, the few remaining species were animals such as Triceratops
horridus(the last horned dinosaur, and also the largest) and Edmontosaurus regalis(A large
duck-billed dinosaur). Smaller herbivores included: Thescelosaurus neglectus (a primitive
herbivore)and Pachycephalosauruswyomingensis( the largest dome-headed dinosaur, also the
last). Thescelosaurus neglectus is believed by certain people to be one of the most important
finds in dinosaur history (Dr. Thomas R. Holtz, 2007). A specimen, found in Montana in the
1990’s,now displayed in a museum inNorth Carolina, has a lump of rock in its chest cavity that,
on closer examination, appears to be a four-chambered heart. If indentified as a heart, it would
support the theory that at least some dinosaurs were endotherms (warm-blooded), as all living
endotherms have a four- chambered heart, unlike ectotherms (cold-blooded), which do not.
Preying on this ragtag group of herbivores was the last, and largest member of the Tyrannosaur
line,Tyrannosaurus rex. T. rex is one of the most well-popularized dinosaurs, despite being
known from only24 specimens (Dr. Thomas R. Holtz, 2007). The Late Maastrichtian fauna of
North America is known very well from the Hell Creek and Judith River formations in Montana,
USA. Both of these formations are located in the Badlands, where late Maastrichtian rocks are
pushed to the surface, allowing easier collection of fossils from those locations. The landscape
of 65 million years ago would not have looked unlike the volcanic ash fields of modern-day
Chile. However, the dinosaurs did not have much time left 65 million years ago, as agigantic
asteroid, 6 miles wide, was approaching the Earth (Alvarez, 1997).
The last day of the Mesozoic Era, Late Cretaceous Period, Maastrichtian Era, dawned
like any other day in Earth’s history. Dinosaurs around the world went about their business,
hunting, eating, andpossibly breeding. However, if any of them had looked up into the sky, they
would have seen what looked like a second sun. The source of the light however, was not a sun
but an asteroid and on a collision course with modern-day Mexico. The asteroid grew closer
until it was just a few miles away from Chicxulub, Mexico, located on the present day Yucatan
peninsula. In the final momentsof the nearest dinosaurs, a few creatures might have looked up
from their current activities and seen a intensely bright light hit the ocean, and then their world
ended. The asteroid hit the water in a gigantic explosion, vaporizing every object, living or not,
within a 100 mile radius (Alvarez, 1997). A few milliseconds after impact, a gigantic tsunami
wave formed, spreading across the globe and drowning many coastal ecosystems. To add to the
dinosaur’s woes, the asteroid impact flung small pieces of flaming debris into the air, each piece
travelling hundreds, if not thousands, of miles and having the potential to wipe out an entire
forest. After the shock of the initial impact, the remaining dinosaurs had to cope with the fact
that any plant not killed in the global fires was choking to death. The asteroid had put up a layer
of ash and debris into the lower atmosphere, blocking off all sunlight and stopping
photosynthesis in its tracks (Erickson, 2001). The unlucky dinosaurs and several other animals
eventually died of hunger, leaving the world to the animalswe know of today.
Sixty-five million years after the dinosaur’s demise, scientists were still trying to figure
out what happened to them. But then, a man named Walter Alvarez, a geologist, made a
discoverybelieved by many to have changed the world. He was searching for the event that
made the dinosaurs go extinct and followed a large number of clues, including but not limited to:
A layer of rock from the end of the Mesozoic containing evidence of a very large tsunami, high
levels of the element iridium, rare on earth but very common in meteorites, and shocked quartz,
another object associated with extraterrestrial impacts. Eventually, he found the Chicxulub
crater. A giant crater 100 miles wide, Chicxulub was missed by so many generations of
geologists because the crater is completely buried by rock and unable to be seen without modern
technology. The age of the crater has been dated to 65 million years ago, at the very end of the
Maastrichtian era and almost without a doubt the method of dinosaur extinction.
The asteroid that killed the dinosaurs did not only kill off the dinosaurs. Other victims
included: The plesiosaurs, graceful, long-necked sea reptiles; the mosasaurs, large carnivores
from the oceanrelated to snakes; the pterosaurs; flying reptile which had ruled the skies for most
of the Mesozoic Era; the ammonites, coiled shellfish that looked like the modern-day nautilus,
most of the bird species, and many plant species. In fact, over 60 percent off all species on the
planet perished in the inferno that ended the Mesozoic.
The age of reptiles may have ended, but the dinosaurs may still be with us. In 1861,
German miners found the fossil of an animal known as Archaeopteryx litographica.
Archaeopteryx looked like a bird crossed between a reptile and was for many years considered a
bird. However, just recently, a fossil from China that was confirmed as a dinosaur has been
directly traced back to A.litographica, meaning that what was thought of as the earliest bird, was
actually a dinosaur (Viegas, 2011). This combined with other evidence, proves that the birds of
today are not just mere descendants of the “terrible lizards,” but are in fact living, breathing
members of the class Dinosauria, therefore suggesting that the dinosaurs are not extinct, but still
living among us in the forms of pigeons, bald eagles, and any other bird ever to exist on the
earth, living or extinct.
In the asteroid impact, plants were particularly hard-hit. After the initial impact, it is
likely that almost microscopic particles of molten rock were flung into the atmosphere, to land in
global forests which would, in turn, create massive forest fires. However, this theory is hotly
debated among scientists. Several scientists point out a layer of soot at the same time of the
Chicxulub impact as proof of global wildfires, while others argue that it is just soot from the
initial fireball cooled and spread out throughout the globe (Rincon, 2003). After the supposed
wildfire, a thick cover of ash, soot, and other microscopic particles sat in Earth’s atmosphere
. This blocked the plants’ ability to reach sunlight and photosynthesize. This resulted in most
major concentrations of plants dying out, leaving small colonies of different species scattered
across the globe. However, in the earliest part of the Cenozoic era, the age of mammals, there is
a very noticeable spike in ferns, a major source of food for the past 300 million years and also
one of the first plants to recover after a major disaster (Viji Vajda, 2001). This spike can almost
confirm, along with other research, that a major catastrophe wiped out the already declining
dinosaurs. Any herbivorous dinosaur lucky enough to survive the asteroid strike and its after
effects would find a world full of food, but no other animals to breed with, meaning that its genes
would have died with it. The “polar winter” that preceded this fern spike would have
turned the earth into a world full of dead and dying organisms, with no scavengers left to clean
up the corpses. Also, the absence of large groupings of plants would have deeply affected the
earth’s oxygen production, meaning that large animals would not be able to breathe often and
possibly die of asphyxiation. While deeply-buried seedswould have survived the catastrophe,
many genuses of plants went extinct along with their movingcounterparts, the dinosaurs.
Works Cited
- Alvarez, W. (1997). T. Rex and the Crater of Doom. Princeton, New Jersey, USA: Princeton University Press.
- Bigelow, P. (n.d.). Cretaceous "Hell Creek Faunal Facies"; Late Maastrichtian. Retrieved September 25, 2011, from Paleo Ring:
- Cretaceous Period: Life. (n.d.). Retrieved September 25, 2011, from University of California Museum of Paleontology:
- Dr. Thomas R. Holtz, J. (2007). Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages. New York: Random House, Inc.
- Erickson, J. (2001). Lost Creatures of the Earth. New York: Facts on File, Inc.
- McLoughlin, V. V. (2004). Fungal Proliferation at the Cretaceous-Tertiary Boundry. Science , 1489.
- Rincon, P. (2003, December 9). No fiery extinction for dinosaurs. Retrieved September 26, 2011, from BBC News:
- Viegas, J. (2011, July 27). Ancient Bird Was Actually a Dinosaur. Retrieved September 25, 2011, from Discovery News:
- Viji Vajda, J. I. (2001). Indication of Global Deforestation at the Cretaceous-Tertiary Boundry by New Zealand Fern Spike. Science , 1700-1702.
- Ward, P. D. (2006). Out of Thin Air. Washington, DC: Joseph Henry Press.