Discovery of New Large Lizards in Cretaceous North America Enhances Paleontological Understanding

Recent findings from the Kaiparowits Formation in southern Utah have unveiled significant insights into the diversity of large-bodied lizards that coexisted with dinosaurs during the Late Cretaceous period. Researchers have identified a new genus and species, named Bolg amondol, which lived approximately 72 million years ago. This discovery is pivotal in enhancing our understanding of the ecosystems that existed in North America during the Campanian age.

According to Dr. Henrik Woolley, a paleontologist with the Dinosaur Institute, the identification of Bolg amondol sheds light on the evolutionary lineage of a group of large-bodied lizards known as monstersaurs, which includes the modern-day Gila monsters. "Monstersauria are characterized by their sizeable dimensions and distinct features, such as pitted, polygonal armor and spire-like teeth," Dr. Woolley stated, emphasizing the importance of this finding in understanding the ecological roles these reptiles played.

The fossil remains of Bolg amondol include an associated skeleton comprising skull fragments, vertebrae, girdles, limbs, and osteoderms—bony armor pieces. These specimens were collected in 2005 and were part of a larger paleontological excavation that aimed to explore the rich fossil record of the Grand Staircase-Escalante National Monument.

Dr. Randy Irmis, a paleontologist at the University of Utah, remarked on the significance of natural history museum collections in facilitating such discoveries. He noted that while large lizards are relatively rare in the fossil record, the Kaiparowits Formation has provided a unique opportunity to study these ancient creatures, suggesting a previously underestimated diversity of large lizards in prehistoric ecosystems.

In addition to Bolg amondol, the research team, which includes Dr. Joe Sertich from the Smithsonian Tropical Research Institute and Colorado State University, has documented various other remarkably armored lizards that indicate the presence of at least three distinct types of large predatory lizards in the region. Dr. Sertich pointed out that the exceptional fossil record from this area could reflect a common ecological dynamic in dinosaur-dominated landscapes, where large lizards likely occupied significant ecological niches as predators.

The evolutionary implications of Bolg amondol extend beyond mere anatomical characteristics. The findings suggest that there were likely numerous other species within the monstersaur lineage, indicating a rich diversity that remains to be explored. Furthermore, the geographic connections between North America and Asia during the Late Cretaceous suggest that not only dinosaurs but also smaller vertebrates traversed these landscapes, pointing to broader patterns of biogeography during this era.

The research was published in the journal Royal Society Open Science on June 18, 2025, marking a significant contribution to the field of paleontology. The study underscores the importance of continued exploration of fossil sites, as many undiscovered species may still await classification. As the field of paleontology evolves, it becomes increasingly clear that the ecosystems of the Late Cretaceous were far more complex and diverse than previously understood, and discoveries like Bolg amondol are vital for reconstructing the biological narratives of our planet’s distant past.