Oklahoma's number one blog for natural and cultural history.
Some 455 million years ago, long before the wind came sweeping down the plains, Oklahoma was nothing more than a fragment of the ocean floor. A diverse array of marine life inhabited the waters above the future United States and left behind a rich prehistoric past. How do invertebrate paleontolgoists know all of this? Though these early sooners may be long gone, their skeletons remain.
Trilobites embedded in limestone
This specimen, from the invertebrate paleontology department, is one of several slabs of limestone crowded with complete skeletons of the trilobite Homotelus. Trilobites are extinct marine arthropods that disappeared roughly 250 million years ago. In case you need a refresher, arthropods are a classification of animals with segmented bodies and external skeletons, like scorpions, crabs and butterflies.
The Asian forest scorpion is an example of an arthropod.
The trilobite specimen shown above is important to scientists because it provides a snapshot into the behavior of these arthropods. Complete skeletons of trilobites are rare, as they would normally fall apart quickly after death. It is highly unusual to find hundreds of skeletons clustered together this way, as a result. Invertebrate paleontolgoists believe that the trilobites may have gathered in large numbers to spawn, much like modern horseshoe crabs along the east coast of the United States.
It’s also important to note that geography played a prominant role in the recovery of this specimen. Geological evidence indicates that the embedded trilobites were buried very quickly by mud, possibly by a storm close to shore that would have stirred up the sea floor and carried mud-laden waters offshore. After the storm waned, this mud was likely dumped on the sea bottom, burying the trilobites. Nearly 455 million years later, scientists discovered their skeletons, still intact, buried in the Ordovician rocks of the Criner Hills in southern Oklahoma.
The Criner Hills are in Carter County, Okla.
Thanks to this discovery, invertebrate paleontologists now have a unique glimpse into the life of extinct animals. They also know that the reproductive behavior of trilobites resembles modern marine arthropods. Of course, you don’t have to look 455 millions years into the past to see Oklahoma’s astounding contributions to history. In fact, next week we’ll be looking at a more recent group of Oklahomans. Can you guess who?
I’d like to share a link with you to a new web page created for identifying Oklahoma fossils, www.CommonFossilsOfOklahoma.snomnh.ou.edu.
Step one: Start with a bunch of baby Apatosaurus bones.
Our museum is fortunate to have one of the finest collections in the world of baby apatosaur bones. For years we have been hoping to mount a reconstruction of a baby as part of our “Clash of the Titans” diorama in the Hall of Ancient Life. Now at last, that plan is beginning to come to fruition.
Kyle Davies, our fossil preparator, knows a lot about dinosaurs. He has been hard at work for some weeks now, preparing drawings and designs for each of the 200+ bones that will need to be cast and assembled to build a baby apatosaur.
Designs for some of the bones are relatively easy: many of the bones that we have in our collection are well preserved and complete, or nearly complete. Others are more challenging. Several of the bones in our collection, these vertebrae, for example, are missing key parts. In some cases this is because the bones were crushed in the fossilization process, and in some cases it is because the Works Progress Administration (WPA) workers who prepared the bones in the 1930s and early ’40s did not have a clear idea of what they were looking for. Some of the finer bits of bone got chipped away in the preparation process just because the guys who were cleaning them didn’t know the difference between bone and rock. In either case, these bones have to be reconstructed a bit before they can be cast.
Kyle is doing this by making detailed scale diagrams from his initial drawings and then building up the missing parts using sculptors clay. Once the reconstructed bones are complete, he will make molds of them for later casting.
Unfortunately we don’t have ALL the necessary bones. The missing ones will have to be built from scratch. To do this, Kyle is first making drawings of baby apatosaur bones based on known adult bones. Modifications have to be made because, of course, baby bones and adult bones are different. Not only are they significantly smaller, but they are shaped quite differently, as well. Kyle studies the differences between other sets of adult and juvenile bones to get an idea of how he should modify his designs to match the shape a real baby apatosaur’s bones would probably have been in life.
Next, he makes another set of scale drawings and builds models to fit, using sculptors clay over a wood armature.
Each reconstructed bone will be cast individually before the whole thing can be assembled. Some of the bones will be cast using a traditional method – creating a rubber or latex negative from the original bone or model and then making resin casts from the mold. But new technologies now available mean that some of the bones will be cast in a completely different way.
A new tool in use here at the University of Oklahoma allows technicians to take a three-dimensional laser scan of an individual bone and then “print” a three-dimensional copy of that bone using a variety of materials: plastic, resin, plaster, even chocolate if we wanted, I suppose! (Though I don’t think a chocolate Apatosaurus would last long with the number of children who come through the museum.) Here at right, you can see a fossil bone, with its resin “print out.”
Even better, this device can scan a full scale adult bone into a computer program through which the shape of the bone can be manipulated to suit our needs: scaled down from adult to juvenile size, for example. The “print outs” of these bones can be hollow cast, to make them more lightweight – or cast in a way that will accommodate an interior steel armature without having to be cut or modified after the fact.
I find this fascinating – this mix of old and new technologies that are being combined to reconstruct an animal that lived more than 100 million years ago.
It won’t be done tomorrow, however. Needless to say, this is a time-consuming process. At present, there is not even a target date for the unveiling of Baby Patty. But I’ll keep you posted.
I went up to the vertebrate paleontology lab this morning to borrow some acetone to clean tape stick-um off my scissors, and caught them making fiberglass molds of a dinosaur fibula. I went back to the office (with my un-sticky scissors) and grabbed my camera to catch the process.
There are a number of reasons why the museum makes casts of fossils. Often casts are made for display purposes, so that the original fossils can be kept on hand in the collection area for study. Sometimes the fossils are so heavy, it’s impractical to mount the original (as in the case of the giant Apatosaurus on display in the Hall of Ancient Life. A single leg bone of that big guy weighs between 300 and 500 pounds!). Sometimes casts are used in museum educational programs, so that kids can handle the bones and examine them from all angles.
In this case, the fossil in question shows evidence of a bone disease, and a graduate student wants to do a study on it that will involve “sectioning” the bone: cutting a very thin slice to examine the structure under a microscope. The process will, of necessity, damage the original. So Kyle Davies, the museum’s fossil preparator, and his team are making a replica in order to preserve the record of the original shape and size of the bone.
Kyle and a pair of volunteers on duty explained the process to me.
fiberglassCasts are made of a number of different materials, depending on how the specific cast will be used. Most small casts are made of a pourable polyurethane. Sometimes plaster is used, if surface detail is not as important. For larger casts, where weight and/or volume becomes an issue, are often “hollow cast” in fiberglass resin: a combination of glass fibers and polyester resin that is pressed into the two halves of the mold to make a hollow finished form.
That’s the process they were doing today. They had the mold all prepared, and were alternately laying in little bits of fiberglass fabric and then painting on a layer of resin to seal it down. The resin is “catalyzed,” and causes a chemical reaction with the fiberglass that fuses the two together to make a material that is stronger than either material would be alone.
The molds themselves are made of silicone rubber… the same stuff dentists use to make molds of your teeth. A clay dam is built up around the fossil, then the rubber is poured over it to make the negative mold: first one side, then the other. Larger molds are then mounted on a fiberglass base to give them added rigidity.
After the casts are made, the two halves are glued together and the edges smoothed, then the cast is painted to mimic the coloration of the original fossil.
And voilá! Phony Bones!