Are 'exceptionally' preserved skeletal fossils necessarily exceptional chemically and cytologically?

• Main Author: Korneisel, Dana Elaine
• Other Authors: Geosciences
• Format: Others
• Published: Virginia Tech 2019
• Subjects: taphonomy; Lagerstätte; Jehol Biota; Yixian Formation; Cretaceous
• Online Access: http://hdl.handle.net/10919/93932

At the macroscopic scale, vertebrate fossils are considered exceptional when non-biomineralized (soft) tissues are preserved. Histologically, high quality is defined by trueness to original shape of a bone, preservation of fine details (e.g. canaliculi), and presence or absence of matrix material in void spaces. Some fossils are hypothesized to preserve cells and durable organelles. Traditionally, cytological details and biomolecular remains have been sought in exceptional fossils. Durable cytological features such as melanosomes do appear to follow feather preservation, but traditionally exceptional fossils are not necessarily exceptional on a microscopic scale. Here, we analyze a feathered dinosaur specimen from the Jehol Lagerstätte to assess claims of blood cell preservation and the state of potential biomolecular preservation. Beipiaosaurus inexpectus is a fairly complete specimen with preserved feathers. Though crushed, fine details in thin section are prevalent. Using Raman spectroscopy, Energy Dispersive X-ray Spectrometry, and Time-of-Flight Secondary Ion Mass Spectroscopy we found no evidence of exceptional molecular preservation. Instead, we found evidence that the vasculature, once hypothesized to contain preserved red blood cells, is filled with clay minerals, with the purported cells chemically indistinguishable from materials of other shapes infilling the vessels. Despite yielding exceptional fossils, the preservational environment of the Jehol biota does not necessarily preserve exceptional details cytologically or biomolecularly. Consequently, we conclude that a systematic approach to biomolecular and cytological preservation studies should rely on traits other than classic exceptional preservation. === Master of Science === What makes a fossil particularly excellent? Traditionally, fossils from animals with skeletons were considered high quality when many or most of the bones from an animal are preserved. If these bones line up with one another like they would in the animal when it was alive (i.e. are articulated) the fossil is even better. To be exceptional, though, soft tissues, or parts of the animal that were not hardened with minerals while the animal lived (e.g. feathers, skin) need to be preserved. All of these traits can be observed with the naked eye. With the use of a microscope, we can see how much a skeleton has been crushed and whether the spaces in the bone for blood vessels and cells have been well preserved. Additionally, we may be able to observe preserved cells, which would be exceptional. On an even smaller scale, the molecules present in a bone might be well or poorly preserved. How much the minerals that make up the bone have changed chemically from when the animal was alive is one indicator of quality. Another might be preservation of molecules that come from the animal such as DNA and the proteins present in bone. In this study, we chose an exceptional fossil based on the traits visible to the naked eye (many of the bones are present and it has feathers) and looked for evidence of cell and unique molecule preservation. On the microscope, we saw beautiful details of the structures in the bone that held bone cells and blood vessels. We also observed red spheres which have been described by other researchers as possible blood cells in the spaces for blood vessels. Using three types of machine which can identify minerals, elements, and molecules in the bone and vessels, we did not find any evidence that the spheres represent preserved blood cells. Nor did we find any evidence of exceptional molecules. However, we did find evidence that the bone itself is not highly changed from when the animal lived, though we see elements and molecules in the vessels that probably did not come from the animal. We started this study knowing that the fossil we chose is exceptional in some ways, but what we found shows that it has a mix of excellent and poor traits visible on the microscope and it does not have any excellent traits in terms of its molecules besides the minerals in the bone itself. We conclude that fossils that are exceptional in the traditional sense are not necessarily exceptional in other ways. === What makes a fossil particularly excellent? Traditionally, fossils from animals with skeletons were considered high quality when many or most of the bones from an animal are preserved. If these bones line up with one another like they would in the animal when it was alive (i.e. are articulated) the fossil is even better. To be exceptional, though, soft tissues, or parts of the animal that were not hardened with minerals while the animal lived (e.g. feathers, skin) need to be preserved. All of these traits can be observed with the naked eye. With the use of a microscope, we can see how much a skeleton has been crushed and whether the spaces in the bone for blood vessels and cells have been well preserved. Additionally, we may be able to observe preserved cells, which would be exceptional. On an even smaller scale, the molecules present in a bone might be well or poorly preserved. How much the minerals that make up the bone have changed chemically from when the animal was alive is one indicator of quality. Another might be preservation of molecules that come from the animal such as DNA and the proteins present in bone. In this study, we chose an exceptional fossil based on the traits visible to the naked eye (many of the bones are present and it has feathers) and looked for evidence of cell and unique molecule preservation. On the microscope, we saw beautiful details of the structures in the bone that held bone cells and blood vessels. We also observed red spheres which have been described by other researchers as possible blood cells in the spaces for blood vessels. Using three types of machine which can identify minerals, elements, and molecules in the bone and vessels, we did not find any evidence that the spheres represent preserved blood cells. Nor did we find any evidence of exceptional molecules. However, we did find evidence that the bone itself is not highly changed from when the animal lived, though we see elements and molecules in the vessels that probably did not come from the animal. We started this study knowing that the fossil we chose is exceptional in some ways, but what we found shows that it has a mix of excellent and poor traits visible on the microscope and it does not have any excellent traits in terms of its molecules besides the minerals in the bone itself. We conclude that fossils that are exceptional in the traditional sense are not necessarily exceptional in other ways.