A STATISTICAL ANALYSIS BETWEEN CLADES CONTAINING HYPERCARNIVOROUS MEGATHEROPOD SPECIES AND SIZE CLASS

The Jurassic and Cretaceous Periods saw the rise and fall of different clades of hypercarnivorous megatheropods that dominated various ecosystems. The Cretaceous Thermal Maximum acted as a catalytic event shifting the structure of predatory guilds across the globe. This macroecological shift is an area of active study and understanding the relationship between different clades and their size classes is one important aspect. We studied the relationship of size class between five clades containing hypercarnivorous megatheropods (Theropods >1000 kg) across six bins spanning the Jurassic-Cretaceous Periods. Climatic events or period/stage boundaries defined these time bins. We modified a matrix provided by one author. Selected valid species were assigned specific metrics including a temporal and spatial value, time bin, mass estimates, and size class per Holtz (2021). We used a non-parametric Kruskal-Wallis test on the size class data with Wilcoxon and Bonferroni post hoc tests. Additionally, data from Holtz (2021) pertaining to the number of missing size classes in ecosystems dominated by different apex predators was analyzed using a One-way ANOVA coupled with a Kruskal-Wallis test and subsequent post hoc tests.

We found a p-value = 1.392e-05 for the Kruskal-Wallis test for size class vs clades. Furthermore, between the two post hoc methods, four pairs were tentatively found to be significant: Ceratosauria-Megalosauroidea, Ceratosauria-Allosauroidea, Allosauroidea-Megaraptora, and Allosauroidea-Tyrannosauroidea. For the Holtz data, we returned a p-value of 0.00231 with One-Way ANOVA. Two post hoc methods indicated tyrannosauroid-allosauroid/megalosauroid was the only significant pair. We found a p-value of 0.006772 from a Kruskal-Wallis test for this dataset; using two post hoc methods, the only significant comparison pair was tyrannosauroid-allosauroid/megalosauroid. Statistical results for the missing size class data were confirmed using PAST 4.15 (2023). The results indicate potential ecological relationships between certain clades based on a significant correlation between their size classes. Differences in allosauroid/megalosauroid vs tyrannosauroid-dominated ecosystems also illustrate shifts in the structure of predatory guilds following the Cretaceous Thermal Maximum.