POSTER: CT-Imaging and Virtual Endocast Reconstruction in Carnivoramorpha (Mammalia) Spaulding, M., J. Flynn, E.M.Hughes, N. Pilla. Society of Vertebrate Paleontology 75th Meeting, Dallas, TX. October 14 – October 17, 2015.
ABSTRACT The evolution of the large mammalian brain is one of the classical hallmarks of our class of vertebrates, and this organ has convergently expanded even further within many mammalian orders. Recent work focusing on the evolution of the carnivoran brain revealed that neocortex expansion began not at the base of Carnivoramorpha (the total group of taxa that are more closely related to Carnivora than to other mammalian crown clades or to extinct creodonts within Ferae), as previously hypothesized, but rather within a more restricted subclade-the Carnivoraformes. Viverravidae (the basalmost group within Carnivoramorpha) possess little neocortex expansion relative to carnivoramorphan outgroups, displaying smooth cerebral hemispheres, and no expansion of the cerebrum (posteriorly over the midbrain, anteriorly toward the olfactory bulbs, laterally to expand the forebrain, or dorsally). However, these previous studies on the brains of Viverravidae had been based on either partially damaged natural endocasts or solely on the digital endocast of one of the smallest known members of the clade, Viverravus minutus, complicating matters as it is known very small carnivorans have less cerebral sulci than their larger relatives; therefore, these observations could have been evolutionary reversals. Here we confirm the majority of these previous observations via highresolution micro-computerized tomography (CT) scans that have yielded a digitally extracted endocast for the much larger viverravid Didymictis protenus (YPM PU 14917), from the Wasatch Formation of Wyoming, USA. This specimen is roughly equivalent in size to a modern coyote, and its endocast shows no evidence of cranial sulci or anterior, posterior, or lateral expansion of the cerebrum (although minor dorsal expansion is present). This confirms that the Viverravidae (across a range of body sizes) do not have the same degree of cranial expansion observed in Carnivoraformes, documenting that increased encephalization within Carnivoramorpha began after initial diversification of the clade.
In addition to these findings, we detail our methodology for reconstructing digital endocasts, starting with processing of the slices generated from the source CT scans through formatting the resulting products for 3D-printing (for research and education/outreach uses) on a wide variety of rapid prototyping machines. We highlight how manageable, and quick, working with CT data has become with the growing availability of high-resolution CT scans and increasingly affordable computing power.
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POSTER: The Brain and Internal Cranial Anatomy of Viverravus minutus (Mammalia: Carnivoramorpha) Spaulding, M., E.M.Hughes, J. Flynn. Society of Vertebrate Paleontology 73rd Meeting, Los Angeles, CA. October 30 – November 02, 2013.
The clade Viverravidae repeatedly has been found to be the most basal monophyletic clade within Carnivoramorpha. Viverravids predominately occur in the Paleocene, but several species extend into the early Eocene, including Viverravus minutus, one of the smallest known carnivoramorphans. Here we present a digitally constructed endocast produced from a high-resolution computerized tomography (CT) scan generated by the American Museum of Natural History’s Microscopy and Imaging Facility of an almost undistorted skull, AMNH 12621, recovered from the Bridger Formation of Wyoming, USA. This is not only the first virtual endocast of a viverravid but also the first non-distorted endocast known for any member of this clade. When the endocast of Viverravus is compared to taxa in their sister clade Carnivoraformes, the viverravid is found to display a much more limited cerebral expansion. The midbrain is almost completely exposed, there is no contact between the frontal poles and olfactory bulbs, and the dorsal profile of the cerebrum forms almost a straight line, rather than the sharply convex shape occurring in contemporaneous carnivoraforms such as Oodectes. No traces of the major cranial neocortical sulci are seen on the cerebrum, and the presence of a distinct rhinal fissure as well as traces of the paths of the sagittal and transverse sinuses indicate that these neocortical sulci were truly absent, rather than simply not preserved on the wall of the braincase. This confirms observations of the complete absence of these sulci described previously in a badly damaged endocast of the larger-bodied viverravid Didymictis. These features together indicate that the expansion and greater development of the cerebral cortex seen in modern Carnivora began at the base of Carnivoraformes within Carnivoramorpha. The new CT scan data also permit examination of the internal cranial anatomy of Viverravus minutus. There is no ossified tentorium, contra the condition known for Oodectes and carnivorans. As some degree of tentorium ossification is seen in both pangolin and creodont outgroups to Carnivoramorpha, we conclude this classical carnivoran synapomorphy was lost in the Viverravidae, and may represent a synapomorphy at a higher taxonomic level (Ferae or Ostentoria).
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