Fossil
Organic remains or traces of
once living organisms preserved in rocks and minerals over time through a
variety of methods, including casts, tracks, impressions, and lithified body
parts. Real World Examples: Many
paleontologists believe that a particularly inhospitable stretch of the Gobi Desert,
near the Mongolian provincial capital of Ukhaa Tolgod, is home to the world’s
richest and most diverse deposits of dinosaur and early mammal remains from 80
mya, a critical time for life in the Cretaceous.
In the last decade or so,
paleontologists estimate that they have found 1,000 mammal skulls, which
amounts to 90 percent of all the recovered mammalian specimens from the
Cretaceous, and bones from 1,000 lizards, not to mention the fossilized remains
of many different kinds of dinosaur and their nests and eggs. For most of us
moderately educated common folk, the most famous fossils are those of the
larger dinosaurs, especially such those scare-your-wits-out carnivores like Tyrannosaurus rex.
However, many budding
geoscientists have been excited by the discovery of a giant snake, named Titanoboa cerrejonensis, by its
discoverers. The size of the snake's vertebrae suggests it weighed about 2,500
pounds and measured 42.7 feet from nose to tail tip. Geoscientists from the University of London
discovered the fossil in the Cerrejon Coal Mine in northern Colombia, South America,
in 2008. The geoscientists used the snake's size to estimate the Earth's
temperature during the time it lived in tropical South
America (somewhere between 58 to 60 million years ago).
Paleontologists have long known an age's average temperature roughly correlates
with the size of its cold-blooded animals. By their estimate, a snake of Titanoboa's size would have required an average
annual temperature of 86° to 93° F to survive. By comparison, today's average
yearly temperature of Cartagena,
Colombia, is
82.4° F.
Another fairly recent fossil
that has excited students was the 2001 discovery of the bones of a 110 million
years-old, 40-foot crocodile by researchers at Yale
University and at the University of Chicago
in the Cretaceous rocks in central Niger,
Africa, in what is part of the Tenere
Desert. It was estimated
that the crocodile, named Sarcosuchus
imperator by the researchers, weighed about 16,000 pounds. Measurements
from three adult skulls resulted in an estimate of total adult body length to
be between 39 and 42 feet long.
Fossil Assembly (Lagerstätte)
Lagerstätte is a German word
meaning “resting place” or “storage place” that recently has been borrowed by
paleontologists and applied to fossil locations of extraordinary richness or
completeness (plural: lagerstätten). A lagerstätte is a spectacular rarity and
a few dozen are scattered through the Earth and are more valuable to science
than the rarest and most precious gems. Paleontologists define
Konservat-Lagerstätten (conservation Lagerstätten) as locations known for the
exceptional preservation of fossilized organisms, including soft parts
preserved as impressions, casts, or “shadows.” Those locations are examples of
incomplete biological recycling where anoxic conditions (oxygen-free mud)
sufficiently suppressed bacterial decomposition for the initial casts of soft
body parts to be recorded.
Konzentrat-Lagerstätten
(concentration Lagerstätten) are defined as fossil deposits with concentrations
of disarticulated organic hard parts, such as a bone bed. They are less
spectacular in scale and scope than the more famous Konservat-Lagerstätten.
Deposits with a high concentration of fossils that represent an in-situ
community, such as reefs or oyster beds, are not considered Lagerstätten.
However good they may be, lagerstätten still have preservational biases, in
that certain fossils are not preserved in the sedimentary beds due to a variety
of adverse environmental conditions, especially but not only geochemical in
nature.
Real World Examples: Perhaps the best known lagerstätten for most
Americans is the Rancho La Brea Pits in Los Angeles, which has the best studied
assemblages of Pleistocene vertebrates, including over 135 species of birds and
60 species of mammal, including woolly mammoths and mastodons, grey and dire
wolves, long-horned bison, ground sloths, saber-toothed cats, and many other
recently extinct creatures that were fossilized by the hundreds in tar.
Another incredible location
is the Burgess Shale in the Canadian Rockies in Yoho National Park, British Columbia,
where the Cambrian Explosion is so beautifully documented. Even more important
with regard to its significant assemblage of Cambrian Exploxion fossils is the
Chengjiang Biota in the Maotianshan Shales of Yunnan Province, China, near the
city of Kunming.
The Chengjiang Biota is extraordinarily diverse, including many
excellently-preserved soft-bodied fossilized organisms and has been designated
by paleontologists as arguably the most significant exceptional preservation
above the Precambrian-Cambrian boundary.
The justly famous Solnhofen
Limestone beds in Bavaria, Germany, are located halfway between Nuremberg and Munich,
where the famous dinosaur-bird, Archaeopteryx, was first found in feathered and
toothful splendor. The assemblage includes sea jellies, the wings of
dragonflies, the imprints of stray feathers, and many terrestrial plants. The
range of fossils, some of which are truly spectacular, preserved in sticky
carbonate muds that trapped insects and even a few small dinosaurs, provides a
comprehensive picture of a local Jurassic ecosystem with over 600 identified
species, including 29 kinds of pterosaur ranging from the size of a sparrow to
four feet in length.
Perhaps the most famous
fossil in the world is the Solnhofen Limestone's Berlin specimen of Archaeopteryx. With its
reptilian-like teeth and tail with the feathers of a bird, it was the ideal
“missing link” Darwin’s
supporters took pride in pointing to as irrefutable proof of his theory of
evolution. The Messel Pit near Darmstadt,
Germany, is one
of the richest Konservat-Lagerstätten in the world, with more than 10,000 finds
to date from the Middle Eocene Period (Geiseltalian), about 50 mya. The Pit
provides the best preserved evidence of Geiseltalian flora and fauna ever
discovered. Many of the fossils not only feature extensive preservation of
structural integrity but also such soft body parts as feathers, fur, and
"skin shadows." In May 2009, scientists from Norway, Germany, and the
U.S. published research on what is certainly one of the most famous fossils
from the Messel Pit, a 95 percent preserved primitive primate fossil (named Darwinius masillae and nicknamed Ida,
pronounced Ee-da) that may either be an evolutionary link connecting prosimians
(lemurs) and anthropoids (apes, monkeys, and humans) or an evolutionary dead
end. Since the dust has yet to settle on that particular argument, interested
students should watch developments in the literature.
Since the 1990s, what is
perhaps the world's largest deposit of dinosaur bones has been identified
inside a 1,500-foot long, 80-foot deep ravine in the City of Zhucheng in
Shandong province on China’s eastern coast. The site contains certainly one of
the world’s greatest deposits of dinosaur fossils, at least in terms of sheer
volume, with more than 8,000 individual fossils identified as of 2012, with
many more sure to be found. Among the more significant fossils found there are Gigantoraptor, Guanlong, Incisivosaurus,
Limusaurus, Meilong, and Microraptor,
Zhuchengtyrannus
magnus.
Kinds of Fossil
The remains of plants and
animals may be preserved through a variety of natural processes including
mummification, freezing, molds and casts, impression, petrifaction, mineral
replacement, carbonization, and direct preservation of teeth, bones, and shells
in animals of relatively recent origin. Other less common kinds of fossil
include coprolites (fossilized excrement), burrows (tubes made in silt or mud
by animals such as worms), and gastroliths (stomach stones used in the stomachs
of extinct reptiles to grind food). A trace fossil, such as a mold or cast or
other evidence of life, is also known as an ichnofossil.
Real World Examples: Fossils of different Tyrannosaurus species have been
found in the Lance Formation of Eastern Wyoming; the Hell Creek Formation of
Eastern Montana, Southwestern North Dakota, and Northwestern South Dakota; the
Livingston Formation of Montana; the Javelina Formation of Big Bend Texas; the
Laramie Formation of Colorado; the McRae Formation of New Mexico; the Scollard
and Willow Creek formations of Alberta, Canada; and the Frenchman Formation of
Saskatchewan, Canada. And while you're in Canada,
you should visit Dinosaur Provincial Park,
which occupies an area of 73 square kilometers along the Red Deer River near
the center of southern Alberta.
One of the largest concentrations of dinosaur footprints known in North America
can be found in the Connecticut
Valley. Many different
types of fossil track impressions have been found in the Valley's sandstone of
the early Jurassic period (200 mya). Two thousand Eubrontes tracks (a large
three toed dinosaur that was closely related to the western genus,
Dilophosarus) were discovered on a single layer of rock. Some of the best
examples are preserved at Dinosaur State Park in Rocky Hill, a few miles south of Hartford, Connecticut.
Another type of footprint was discovered at Laetoli, Tanzania,
in 1978 by a team led by Mary Leakey that may have been made about 3.6 millions
years ago by hominids who were members of the species, Australopithecus afarensis. The track is among the longest made by
early hominids and is still among the most controversial, owing to scientific
disagreement as to which group of hominids made the footprints in what was then
loose volcanic ash. But in terms of shear numbers, probably more Americans have
visited Petrified Forest National Park in northern Arizona
than any other fossil location in the U.S., with its fascinating
fragments and even large logs of fossilized wood, which is actually a molecule
by molecule replacement of organic matter with silica.
Fossiliferous
Rock in which fossils are
profuse, for example, crinoids, brachiopods, and other marine invertebrates.
