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Supporting CT Data for: Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids

Citation

Voris, Jared et al. (2022), Supporting CT Data for: Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids, Dryad, Dataset, https://doi.org/10.5061/dryad.4mw6m90bx

Abstract

Known from dozens of specimens discovered since the early 20th century, Gorgosaurus libratus has arguably contributed more than any other taxon to our understanding of the life history of tyrannosaurids. However, juvenile material for this taxon is rare. Here, we describe two small, articulated Gorgosaurus specimens (skull lengths of ~500 mm) that help advance our knowledge of the anatomy and ontogeny of this taxon and of tyrannosaurids in general. The new specimens exhibit hallmark juvenile tyrannosaurid features, including long, low, and narrow skulls, large circular orbits, absent or incipient cranial ornamentation, ziphodont dentition, and an overall gracile skull frame. Comparison with other Gorgosaurus specimens of various ontogenetic stages allows for an examination of the timing of morphological changes that occurred through ontogeny in this taxon relative to other tyrannosaurids. Of particular note, Gorgosaurus and the larger Tyrannosaurus rex are found to have experienced similar ontogenetic transformations at similar percent skull length relative to the large known individuals for each respective taxon but at different absolute body sizes and biological ages, occurring at a larger size and older age in T. rex than in Gorgosaurus. These results suggest a dissociation between the timing of cranial development and body size in tyrannosaurids. Finally, the recognition of ontogenetically invariant characters in Gorgosaurus makes it possible to determine the taxonomic identity of previously misidentified specimens.

Methods

Data includes CT scans of the palate and medial mandible bones of juvenile Gorgosaurus specimens TMP 2009.12.14 and TMP 2016.14.1 and the alveolar region of the maxillae of TMP 1994.143.1.

CT scan information:

TMP 2016.14.1 was scanned at Mayfair Diagnostics, GE Discovery CT750 HD, 120 KVP, slice thickness 0.625mm (Z-dimension) for a total XYZ voxel dimensions of 0.841797 x 0.841797 x 0.625mm.
    TMP 2009.12.14 was scanned at Drumheller Hospital, Toshiba Aquilion, 120 KVP, slice thickness 0.5mm (Z-dimension) for a total XYZ voxel dimensions of 0.595 x 0.595 x 0.5mm.
    TMP 1994.143.1: Mayfair Diagnostics, GE Discovery CT750 HD, 120 KVP, slice thickness 0.625mm (Z-dimension) for a total XYZ voxel dimensions of 0.746094 x 0.746094 x 0.625mm.