Browsing by Author "Colleary, Caitlin"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Chemical, experimental, and morphological evidence for diagenetically altered melanin in exceptionally preserved fossils
    Colleary, Caitlin; Dolocan, Andrei; Gardner, James; Singh, Suresh; Wuttke, Michael; Rabenstein, Renate; Habersetzer, Jörg; Schaal, Stephan; Feseha, Mulugeta; Clemens, Matthew; Jacobs, Bonnie F.; Currano, Ellen D.; Jacobs, Louis L.; Sylvestersen, Rene Lyng; Gabbott, Sarah E.; Vinther, Jakob (NAS, 2015-10-13)
    In living organisms, color patterns, behavior, and ecology are closely linked. Thus, detection of fossil pigments may permit inferences about important aspects of ancient animal ecology and evolution. Melanin-bearing melanosomes were suggested to preserve as organic residues in exceptionally preserved fossils, retaining distinct morphology that is associated with aspects of original color patterns. Nevertheless, these oblong and spherical structures have also been identified as fossilized bacteria. To date, chemical studies have not directly considered the effects of diagenesis on melanin preservation, and how this may influence its identification. Here we use time-of-flight secondary ion mass spectrometry to identify and chemically characterize melanin in a diverse sample of previously unstudied extant and fossil taxa, including fossils with notably different diagenetic histories and geologic ages. We document signatures consistent with melanin preservation in fossils ranging from feathers, to mammals, to amphibians. Using principal component analyses, we characterize putative mixtures of eumelanin and phaeomelanin in both fossil and extant samples. Surprisingly, both extant and fossil amphibians generally exhibit melanosomes with a mixed eumelanin/phaeomelanin composition rather than pure eumelanin, as assumed previously. We argue that experimental maturation of modern melanin samples replicates diagenetic chemical alteration of melanin observed in fossils. This refutes the hypothesis that such fossil microbodies could be bacteria, and demonstrates that melanin is widely responsible for the organic soft tissue outlines in vertebrates found at exceptional fossil localities, thus allowing for the reconstruction of certain aspects of original pigment patterns.
  • Thumbnail Image
    Is the presence of biomolecules evidence for molecular preservation in the fossil record?
    Colleary, Caitlin (Virginia Tech, 2019-05-06)
    The molecular components of life (i.e., biomolecules such as DNA, proteins, lipids) have the potential to preserve in animals that have been extinct for millions of years, offering a scale of analysis previously inaccessible from the fossil record. As new technology (e.g., high resolution mass spectrometry) has been incorporated into fossil analyses, researchers have begun to detect biomolecules in terrestrial vertebrates dating back to the Triassic Period (~230 Ma). However, these biomolecules have not been demonstrated to be the biological remains of these ancient animals and may instead be exogenous organic contaminants. Here, I developed a series of analytical techniques to detect and interpret the preservation of the degraded remains of the most common protein in bone, collagen, in terrestrial vertebrates from two time slices that represent the two ends of the preservation spectrum: a "shallow time" study of fossils <150,000 years old from different burial environments (i.e., permafrost, fluvial and hot springs) and a deep time study of dinosaurs (~212 - 66 Ma) from the same burial environment (i.e., fluvial), representing the current limit of the reported protein preservation in the fossil record. Unlike previous studies that have focused on organic extractions to detect biomolecules, I studied intact fossil bones and the rocks they were found in, to understand more about the effect of burial conditions on preservation and potential alternative sources of organic compounds. I found endogenous amino acids (the degradation products of proteins) and lipids in the mammoth bones, although they were already heavily degraded in fluvial environments, even on such short timescales. I also found that there were amino acids and lipids preserved in the dinosaur bones, however tests on the age of the amino acids and the types of lipids present, demonstrate that they are not original to the animals in this study. Therefore, fluvial environments, one of the most common depositional environments preserved in the geologic record, are not conducive to the preservation of proteins on long timescales and researchers should be cautious when using these biomolecules to make interpretations about the biology of ancient animals.
  • Thumbnail Image
    Molecular preservation in mammoth bone and variation based on burial environment
    Colleary, Caitlin; Lamadrid, Hector M.; O'Reilly, Shane S.; Dolocan, Andrei; Nesbitt, Sterling J. (2021-01-29)
    Biomolecules preserved in fossils are expanding our understanding of the biology and evolution of ancient animals. Molecular taphonomy seeks to understand how these biomolecules are preserved and how they can be interpreted. So far, few studies on molecular preservation have considered burial context to understand its impact on preservation or the potentially complementary information from multiple biomolecular classes. Here, we use mass spectrometry and other analytical techniques to detect the remains of proteins and lipids within intact fossil mammoth bones of different ages and varied depositional setting. By combining these approaches, we demonstrate that endogenous amino acids, amides and lipids can preserve well in fossil bone. Additionally, these techniques enable us to examine variation in preservation based on location within the bone, finding dense cortical bone better preserves biomolecules, both by slowing the rate of degradation and limiting the extent of exogenous contamination. Our dataset demonstrates that biomolecule loss begins early, is impacted by burial environment and temperature, and that both exogenous and endogenous molecular signals can be both present and informative in a single fossil.
  • Thumbnail Image
    Using Macro- and Microscale Preservation in Vertebrate Fossils as Predictors for Molecular Preservation in Fluvial Environments
    Colleary, Caitlin; O'Reilly, Shane; Dolocan, Andrei; Toyoda, Jason G.; Chu, Rosalie K.; Tfaily, Malak M.; Hochella, Michael F. Jr.; Nesbitt, Sterling J. (MDPI, 2022-09)
    Exceptionally preserved fossils retain soft tissues and often the biomolecules that were present in an animal during its life. The majority of terrestrial vertebrate fossils are not traditionally considered exceptionally preserved, with fossils falling on a spectrum ranging from very well-preserved to poorly preserved when considering completeness, morphology and the presence of microstructures. Within this variability of anatomical preservation, high-quality macro-scale preservation (e.g., articulated skeletons) may not be reflected in molecular-scale preservation (i.e., biomolecules). Excavation of the Hayden Quarry (HQ; Chinle Formation, Ghost Ranch, NM, USA) has resulted in the recovery of thousands of fossilized vertebrate specimens. This has contributed greatly to our knowledge of early dinosaur evolution and paleoenvironmental conditions during the Late Triassic Period (similar to 212 Ma). The number of specimens, completeness of skeletons and fidelity of osteohistological microstructures preserved in the bone all demonstrate the remarkable quality of the fossils preserved at this locality. Because the Hayden Quarry is an excellent example of good preservation in a fluvial environment, we have tested different fossil types (i.e., bone, tooth, coprolite) to examine the molecular preservation and overall taphonomy of the HQ to determine how different scales of preservation vary within a single locality. We used multiple high-resolution mass spectrometry techniques (TOF-SIMS, GC-MS, FT-ICR MS) to compare the fossils to unaltered bone from extant vertebrates, experimentally matured bone, and younger dinosaurian skeletal material from other fluvial environments. FT-ICR MS provides detailed molecular information about complex mixtures, and TOF-SIMS has high elemental spatial sensitivity. Using these techniques, we did not find convincing evidence of a molecular signal that can be confidently interpreted as endogenous, indicating that very good macro- and microscale preservation are not necessarily good predictors of molecular preservation.