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Browsing by Author "Werning, Sarah"

Now showing 1 - 3 of 3
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    Are 'exceptionally' preserved skeletal fossils necessarily exceptional chemically and cytologically?
    Korneisel, Dana Elaine (Virginia Tech, 2019-09-19)
    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.
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    Osteology and relationships of Revueltosaurus callenderi (Archosauria: Suchia) from the Upper Triassic (Norian) Chinle Formation of Petrified Forest National Park, Arizona, United States
    Parker, William G.; Nesbitt, Sterling J.; Irmis, Randall B.; Martz, Jeffrey W.; Marsh, Adam D.; Brown, Matthew A.; Stocker, Michelle R.; Werning, Sarah (2021-09-29)
    Once known solely from dental material and thought to represent an early ornithischian dinosaur, the early-diverging pseudosuchian Revueltosaurus callenderi is described from a minimum of 12 skeletons from a monodominant bonebed in the upper part of the Chinle Formation of Arizona. This material includes nearly the entire skeleton and possesses a combination of plesiomorphic and derived character states that help clarify ingroup relationships within Pseudosuchia. A phylogenetic analysis recovers R. callenderi in a clade with Aetosauria and Acaenasuchus geoffreyi that is named Aetosauriformes. Key autapomorphies of R. callenderi include a skull that is longer than the femur, a complete carapace of dermal armor including paramedian and lateral rows, as well as ventral osteoderms, and a tail end sheathed in bone. Histology of the femur and associated osteoderms demonstrate that R. callenderi was slow growing and that the individuals from the bonebed were not young juveniles but had not ceased growing. A review of other material assigned to Revueltosaurus concludes that the genus cannot be adequately diagnosed based on the type materials of the three assigned species and that only R. callenderi can be confidently referred to Revueltosaurus.
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    Putative fossil blood cells reinterpreted as diagenetic structures
    Korneisel, Dana E.; Nesbitt, Sterling J.; Werning, Sarah; Xiao, Shuhai (PeerJ, 2021-12-16)
    Red to red-orange spheres in the vascular canals of fossil bone thin sections have been repeatedly reported using light microscopy. Some of these have been interpreted as the fossilized remains of blood cells or, alternatively, pyrite framboids. Here, we assess claims of blood cell preservation within bones of the therizinosauroid theropod Beipiaosaurus inexpectus from the Jehol Lagerstatte. Using Raman spectroscopy, Energy Dispersive X-ray Spectrometry, and Time of Flight Secondary Ion Mass Spectroscopy, we found evidence of high taphonomic alteration of the bone. We also found that the vascular canals in the bone, once purported to contain fossil red blood cell, are filled with a mix of clay minerals and carbonaceous compounds. The spheres could not be analyzed in isolation, but we did not find any evidence of pyrite or heme compounds in the vessels, surrounding bone, or matrix. However, we did observe similar spheres under light microscopy in petrified wood found in proximity to the dinosaur. Consequently, we conclude that the red spheres are most likely diagenetic structures replicated by the clay minerals present throughout the vascular canals.