Recently discovered fossil specimens of the Monsters include new genera and species, Borguamondor, found in southern Utah’s magnificent Kaiparowitz Formation at Escalante National Monument. These specimens highlight the remarkable diversity of these large lizards during the late North American period.

Borguamondor existed in North America during the Cretaceous Campania period, approximately 72 million years ago.

These ancient reptiles represent a portion of the evolution of large-bodied lizards known as the Monsters. One of the most notable examples is the Gira monster, which still inhabits deserts where new species have been rediscovered.

“According to Monster Aurus Hank Wooley, a paleontologist at the Dinosaur Institute:

“They have a lineage spanning about 100 million years, but their fossil records remain largely incomplete. Discoveries like Borguamondor are significant in understanding these remarkable lizards, which would have appeared monstrous to us.”

“With an estimated length of about 1 m (3 feet), depending on the size of the tail and body, it may have been even larger.”

“In comparison to modern lizards, it was a large creature, akin to a monitor lizard inhabiting the savanna.

Related skeletal remains of Borguamondor, including skulls, vertebrae, girdles, limbs, and osteoderm fragments, were discovered starting in 2005 at the Kaiparowits Formation in Utah.

“Dr. Randy Ilmith, a paleontologist at the University of Utah, commented on Borguamondor:

Other fossils retrieved by the team include heavily armored skull bones, suggesting that ancient, seasonally tropical forests in southern Utah were home to at least three distinct types of large predatory lizards.

“Despite their size, the skeletal remains of these lizards are incredibly rare; most fossil records are based on isolated bones and teeth,” noted Dr. Joe Celtic, a paleontologist at the Smithsonian Tropical Research Institute and Colorado State University.

“The exceptional fossil record of large lizards from the Grand Stair Escalante National Monument may indicate that they were a typical part of the dinosaur-dominated ecosystem in North America, playing a vital role as small predators hunting for eggs and smaller animals in Lalamidia forests.”

“The identification of this new species within the Monsters category suggests the potential for undiscovered large lizards from the late Cretaceous period,” the researchers remarked.

“Moreover, this discovery underscores that there remains untapped diversity yet to be uncovered both in the field and within paleontological collections.”

“The closest known relatives of Borguamondor are found across the planet in the Asian Gobi Desert.”

“It has been widely recognized that these creatures traversed the former Cretaceous continents, which were once interconnected. The discovery of Borguamondor suggests that smaller animals also migrated, indicating a broader biogeographical pattern among terrestrial vertebrates during this era.”

Survey results will be published in the journal Royal Society Open Science.

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C. Henrik Woolley et al. 2025. New specimens of Monstaurus from the Kaiparowitz Formation in Utah reveal the unexpected diversity of ancient large lizards in late North America. R. Soc. Open SCI 12(6): 250435; doi: 10.1098/rsos.250435