Oh how I love a good fossil hunt… All you have to do i find some sedimentary rock nearby and develop a keen eye for fossilized shells, bone, and teeth.. I like it best after a week of stormy weather so that the erosion exposes hidden fossils. When it’s early the morning after a big storm, there is an electricity in knowing you’re the first to a popular fossil site to search. I’ve found fossils of fish, ammonites, trilobites, and all manner of crinoids. To hold one in your hand is to go back in time millions of years, to the last moment of this creature’s life. It’s truly amazing that anything remains from a long lost earth.
The vast majority of fossils are found in Sedimentary rock. This type of rock generally forms in bodies of water(oceans, lakes, rivers). Imagine a clam close to shore being buried by a landslide from above. The clam dies and the “sediment” that buried it is eventually buried by even more sediment and so on.. and so on. Over time the pressure from all the layers pressing down on our clam from above creates a weak but solid mix of sand and sediment... Sedimentary rock. Over vast history of our earth the water has risen, fallen, and frozen many times over. What once was the bottom of the ocean where our clam died can become a vast desert millions of years later. If we are lucky enough to visit the rocks of these deserts, we may find our clam if the conditions are just right. Of course none of the soft parts of our crab remain, it’s only the shell. Actually, it’s not even the real shell anymore.
Like most classic fossils, this is a “Mineral Replacement Fossil.” Basically the soft parts decompose quickly and the shell does too. Our Clam shell was made largely from calcium carbonate (CaCo3) that occurs in the crystal forms as calcite. Over time the calcite can be replaced with other minerals such as silica, pyrite or hematite. These minerals “replaces” the original atoms of the shell resulting in a fossil.
As you walk past sedimentary rock it’s hard not to notice the different layers of strata. It’s like an endless layer cake with slightly different colored layers. If you rub your hand across the rock and bring it to your face, you will see powdery ancient sand. As you walk past the layers of rock you usually only need to look. A shiny white.. A dull bronze.. a tiny glimpse of shell or bone. It’s a fantastic activity and it’s free. In fact Colorado is a fantastic state to find fossils. 3 of the 4 largest dinosaur fossils ever discovered come from Colorado. Our state fossil is Stegosaurus because it was first discovered at one of the world’s most important fossil sites near Dinosaur Ridge, just west of Denver. Some of the most iconic dinosaurs were first described nearby including giants like Apatosaurus, Diplodocus, and Allosaurus. If you haven’t been…. I strongly urge you to visit the park where you can see countless dinosaur footprints and fossilized bone embedded in rock.
Perhaps the most miraculous thing about fossils is that the different species are always found in a predictable vertical order across the world.The extinct sea arthropod trilobites are always found in lower layers between 521 and 250 million years ago. They never appear in higher layers of sedimentary rock that are younger. You never find them among fossils of early mammals… ever… The order of fossils is INVARIABLE. The first amphibians are found in older layers than the first mammals. The first fish are lower than birds and so on.
That’s a powerful observation! “Not a single solitary fossil has ever been found before it could have evolved.” One of the coolest thing about the theory of evolution is how easy it would be to disprove, but it hasn’t been. Famous Geneticist John Haldane famously responded to the question of what might disprove evolution with “Fossil rabbits in the Precambrian!” J = 5 That’s all it would take, but the ordering of fossils goes from simple to complex as you move from older to younger layers of sedimentary rock.This invariable order of fossils is called Faunal Succession, and you can learn more about it at the geocache of the same name.
Not all fossils are valued the same. There are some fossils that show dramatic links between branches of our tree of life. Among the most famous is Archaeopteryx. It was discovered all the way back in 1861 in Southern Germany. The fossil is one of many from this region that show exceptional detail. It is found in strata that is ~150 million years old at the end of the jurassic period, consistent with the age of the dinosaurs. What is immediately exciting about Archaeopteryx are its wings. It has a toothed jaw and long tail like reptiles and theropod dinosaurs, but it has avian(bird) features including flight feathers, wings, a wishbone, and a partially reversed first toe. They were about the size of a Raven and could be up to 500 millimeters long(20 in).
An explosion of birds can be found in the fossil records around 130 million years ago, consistent with the rise of birds from wingless theropod dinosaurs. Archaeopteryx is a terrific example of a transition fossil, which connects the evolutionary history of two groups of organisms. Since its discovery all the way back in the late 1800s, 11 other fossils of Archaeopteryx have been found since. Additionally many new species of reptile/dinosaur/bird transition fossils have been found around the world, particularly in Eastern Asia.
The original fossil was discovered in 1861 and was apparently traded to a local german doctor in exchange for Medical service. The fossil was then sold to Museum of London in 1862 for a mere 700 pounds and it remains there today. The timing of its discovery was just two years after Charles Darwin published his world-changing book “On the Origin of Species.” In this famous text Darwin describes the theory of Natural Selection and how it could drive change within a population of all living things to better suite their constantly changing environment. Darwin discusses the very limited fossil record available at the time, and suggested that in the future “Transition Fossils” will likely be found to fill in the gaps of evolution. Sure enough one of the most important transition fossils appeared just 2 years later.
It wasn’t until the 1970’s when John Ostrom proposed that Birds evolved from Theropod dinosaurs, naming Archaeopteryx and other fossils as transitional links. In 2004, scientists used CT scanning technology to visualize of the braincase of the London Archaeopteryx specimen. They concluded that its brain was significantly larger than that of most dinosaurs, suggesting that it had a bigger brain than its Theropod ancestors. The increased brain size is necessary for flying. This can be seen today when comparing the proportionally smaller brains of reptiles compared to birds.
NAB CD.EFG W104 JK.LMN
A = How many of the largest 4 dinosaur fossils were found in Colorado?
B = John Ostrom proposed that Birds evolved from Theropod dinosaurs in the 1__70’s
C = Archaeopteryx was found in stata that is ~1_0 million years old.
D = Trilobites lived during 521 and 2_0 million years ago.
E = Archaeopteryx could be up to __00 millimeters long. That’s about 20 inches.
F = In 200__ scientists used CT scans to determine the brains of Archaeopteryx were larger than their Theropod ancestors.
G = “On the origins of species” was published in 185__
J =
K =
L = The first Archaeopteryx was discovered in 186__
M = The original Archaeopteryx fossil was traded for medical treatment then sold to a museum for __00 pounds.
N = Birds appear in the fossil record ~1__0 million years ago.
You can check your answers for this puzzle on GeoChecker.com.