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Grallator Tracks as a Window to Growth Strategies of Small-Bodied Early Theropods

Year: 2023

Presenter Name: Karrah Spendlove

Fossil tracks are far more abundant than skeletal remains and record both locomotory information and impressions of the soft tissues that covered the feet. Thus, they have large sample sizes and can act as proxies for determining growth regimes among living dinosaur feet. The St. George Dinosaur Discovery Site at Johnson Farm (SGDS) in St. George, Utah, USA, has a wealth of tridactyl Grallator tracks, likely made by early, small theropods, preserved on closely-spaced bedding planes. Therefore, the site is as close to population sampling as possible. Tracks were measured using eleven linear metrics, which were used to determine whether these early theropods experienced allometric or isometric growth of their feet. Analysis of track metrics using bivariate plots and regressions suggests weak, negative allometric linear relationships between the width of the track and the length of digits III and IV. Photographs of tracks were utilized in 2D geometric morphometrics, which removes the effect of size by establishing common landmarks on specimen photographs and normalizing all specimens to a single size. This increases understanding of possible allometric growth in ways traditional linear measurements cannot. Both linear measurements and geometric morphometrics suggest a single continuous sample, suggesting the tracks were likely made by a single species or closely related species having similar foot morphologies. These data suggest that as early small theropods increased in size, growth in toe length was slower than growth in foot width. This could indicate that growth progressed to convey larger theropods greater stability to support their increased mass.
University / Institution: University of Utah
Type: Oral
Format: In Person
SESSION B (10:45AM-12:15PM)
Area of Research: Science & Technology
Faculty Mentor: Randall Irmis
Location: Union Building, PANORAMA EAST (11:25am)