Supplemental data from: Intraspecific facial bite marks in tyrannosaurids provide insight into sexual maturity and evolution of bird-like intersexual display

Intraspecific aggression, or agonism, is a widespread intrasexual
selective behavior important to understanding animal behavioral ecology
and reproductive systems. Such behavior can be studied either by direct
observation or inferred from wound/scar frequency in extant species, but
is difficult to document in extinct taxa, limiting understanding of its
evolution. Among extant archosaurs, crocodylians display extensive
intrasexual aggression, whereas birds show extreme visual/vocal
intersexual display. The evolutionary origin of this behavioral
divergence, and pattern in non-avian dinosaurs, is unknown. Here we
document the morphology, frequency, and ontogeny of intraspecific facial
bite lesions (324 lesions) in a large sample of tyrannosaurids (202
specimens, 528 elements) to infer patterns of intraspecific aggression in
non-avian theropods. Facial scars are consistent in position and
orientation across tyrannosaurid species, suggesting bites were inflicted
due to repeated/postured behavior. Facial scars are absent in young
tyrannosaurids, first appear in immature animals (~50% adult skull
length), are present in ~60% of the adult-sized specimens, and show
aggressor:victim size isometry. The ontogenetic distribution of bite scars
suggests agonistic behavior is associated with the onset of sexual
maturity, and scar presence in approximately half the specimens may relate
to a sexual pattern. Considered in a phylogenetic context, intraspecific
bite marks are consistent and widely distributed in fossil and extant
crocodyliforms and non-maniraptoriform theropods, suggesting a potential
plesiomorphic behavior in archosaurs. Their absence in maniraptoriform
theropods, including birds, may reflect a transition from boney cranial
ornamentation and crocodylian-like intrasexual aggression to avian-like
intersexual display with the evolution of pennaceous feathers.