Artistic reconstruction of Bolg amondol, depicted raiding an oviraptorosaur dinosaur nest amidst the lush Kaiparowits Formation habitat. Credit: Art by Cullen Townsend.

A new species of armoured, monstersaur lizard that lived alongside dinosaurs identified by NHM palaeontologists.

The discovery of Bolg amondol, a name inspired by JRR Tolkien’s Lord of the Rings universe, reveals the complex evolutionary history of giant Gila monster relatives.

A newly discovered raccoon-sized armoured monstersaurian lizard from Grand Staircase-Escalante National Monument in southern Utah reveals a surprising diversity of these very big lizards at the pinnacle of the Age of Dinosaurs.

Named for the goblin prince from JRR Tolkien’s The Hobbit, the new species Bolg amondol also illuminates the sometimes murky path that life travelled between ancient continents.

The collaborative research led by the Natural History Museum of Los Angeles County’s Dinosaur Institute reveals hidden treasures awaiting future palaeontologists in the bowels of museum fossil collections, and the vast potential of paleontological heritage preserved in Grand Staircase-Escalante National Monument and other public lands. 

Lead author Dr Hank Woolley, from the Dinosaur Institute, said: “I opened this jar of bones labelled ‘lizard’ at the Natural History Museum of Utah, and was like, oh wow, there’s a fragmentary skeleton here.

“We know very little about large-bodied lizards from the Kaiparowits Formation in Grand Staircase-Escalante National Monument in Utah, so I knew this was significant right away.”

Left: Publicly available rendered CT scan of Heloderma horridum (UF:Herp:153328) from morphosource.org used for comparison to Bolg amondol, with mound-like, polygonal osteoderms in green. Right: Skull of the modern monstersaur Heloderma horridum (LACM 159136), from the herpetology collection at NHMLAC, used for comparison with Bolg amondol. Credit: Dr Hank Woolley.

Hidden gems in collection drawers 

Co-author Dr Randy Irmis from the University of Utah, said: “Bolg is a great example of the importance of natural history museum collections. Although we knew the specimen was significant when it was discovered back in 2005, it took a specialist in lizard evolution like Hank to truly recognise its scientific importance, and take on the task of researching and scientifically describing this new species.”

The new species was identified from an associated skeleton of fragmentary bones: tiny pieces of the skull, vertebrae, girdles, limbs, and the bony armour called osteoderms. 

Woolley said: “What’s really interesting about this holotype specimen of Bolg is that it’s fragmentary, yes, but we have a broad sample of the skeleton preserved.

“There’s no overlapping bones – there’s not two left hip bones or anything like that. So we can be confident that these remains likely belonged to a single individual.”

Most of the fossil lizards from the Age of Dinosaurs are even more fragmented – often just single isolated bones or teeth – so despite their fragmentary nature, the parts of Bolg’s skeleton that survived contain a stunning amount of information.

Woolley said: “That means more characteristics are available for us to assess and compare to similar-looking lizards.

“Importantly, we can use those characteristics to understand this animal’s evolutionary relationships and test hypotheses about where it fits on the lizard tree of life.”

Other fossils described in the study, including remarkably armoured skull bones, demonstrate that the ancient, seasonally tropical forests of what is now southern Utah, USA hosted at least three different types of large, predatory lizards.

Co-author Dr Joe Sertich from the Smithsonian Tropical Research Institute and Colorado State University, said: “Even though these lizards were large, their skeletons are quite rare, with most of their fossil record based on single bones and teeth.

“The exceptional record of big lizards from Grand Staircase-Escalante National Monument may prove to be a normal part of dinosaur-dominated ecosystems from North America, filling key roles as smaller predators hunting down eggs and small animals in the forests of Laramidia.”

Identified bones belonging to Bolg amondol (Specimen UMNH VP 16266, Natural History Museum of Utah/ Bureau of Land Management). They are not much to look at, but they are jam-packed with valuable information on the anatomy and lifestyle of Bolg amondol. Credit: Photo by Dr Hank Woolley.

Stairway to monstersaurs

The monstersauria are characterised by their large size and distinctive features like pitted, polygonal armour attached to their skulls and sharp, spire-like teeth.

They have a roughly 100-million-year history, but their fossil record is largely incomplete, making the discovery of Bolg a big deal for understanding these charismatic lizards, and Bolg would have been a bit of a monster to our eyes.

Woolley said: “Three feet tip to tail, maybe even bigger than that, depending on the length of the tail and torso. So by modern lizard standards, a very large animal, similar in size to a Savannah monitor lizard; something that you wouldn’t want to mess around with.”

The identification of a new species of monstersaur highlights the likelihood that there were many more kinds of big lizards in the Late Cretaceous.

Additionally, this find shows that unexplored diversity is waiting to be dug up in the field and in palaeontology collections.

Bolg’s closest known relative hails from the other side of the planet in the Gobi Desert of Asia.

While dinosaurs have long been known to have travelled between the once connected continents during the Late Cretaceous Period, the discovery of Bolg reveals that smaller animals also made the trek, suggesting there were common patterns of biogeography across terrestrial vertebrates during this time.

The study is published in Royal Society Open Science.