18 Advances in Rocky Mountain Region Paleontology

Monday, 19 May 2025
3:45 PM - 5:30 PM
Cascade AB

INCONGRUENT PHYLOGENETIC MATRICES AND OVER-INCLUSION OF FRAGMENTARY TAXA OBSCURE TYRANNOSAUROIDEA SYSTEMATICS

Paper number: 18-3
Program: Theme Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

Tyrannosaurs were the dominant apex predators in Laramidian Cretaceous ecosystems following the rise of the Western Interior Seaway. However, the exact evolutionary history and origins of large-bodied Laramidian tyrannosaurs continues to be an epicenter of debate. While many tyrannosauroid specimens have facilitated improvement in qualitative and quantitative analyses, tyrannosauroid taxa that are fragmentary, litigious, or ontogenetically immature coupled with differing character matrices have provided varying phylogenetic hypotheses for this clade. This study conducts a phylogenetic analysis of Tyrannosauroidea by: building upon established datasets, adding additional figured tyrannosauroids not present in past datasets, and adding figured purported tyrannosauroids. We conducted strict consensus parsimony analyses using TNT v1.6 on default settings with the newly added taxa, then pruning added taxa to observe changes in tree topology and interrelationships. This study differs from others by utilizing a broader sampling of Tyrannosauroidea, multiple tests of a single character matrix, and identifying how problematic taxa can influence broader phylogenetic interrelationships and systematics.

Our findings suggest that fragmentary taxa lacking key diagnostic traits can distort phylogenetic trees via systemic polytomy, producing results that conflict with prior rigorous studies in establishing reliable taxa interrelationships. We consistently recovered from four phylogenetic trees: Nanotyrannus as intermediate between Laramidian Albertosaurinae and Asiatic Alioramini, Daspletosaurini as sister to Tyrannosaurini, Labocania spp. sister to Teratophoenini or outside Tyrannosaurinae, and Appalachian tyrannosauroids (i.e. Dryptosaurus and Appalachiosaurus) as non-monophyletic. This study ultimately presents means of testing future practices and fragmentary tyrannosauroid taxa, which can help illuminate interrelationships. This study provides evidence to elucidate evolutionary pathways within Tyrannosauroidea, which can answer further questions about ecological shifts and evolutionary history. Future work in this project will focus on Bayesian phylogenetics, time-calibrated phylogenies for mapping biogeography, and expansion of taxa sample size.

Geological Society of America Abstracts with Programs. Vol. 57, No. 5

doi: 10.1130/abs/2025RM-409871

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