One hutia jaw contained an alveolus whose interior surface was smooth rather than the rough texture typical of bone, drawing the attention of Florida Museum doctoral student Lazaro Vinola Lopez. Fossils of this hutia species are usually limited to a few isolated teeth and partial mandibles across Hispaniola, making the dense accumulation in Cueva de Mono unusual. Instead of cleaning out the sediment from the tooth sockets as usual, Vinola Lopez examined the jaw closely and noticed the smooth lining that suggested biological modification of the cavity infill.
Vinola Lopez had previously encountered insect cocoons associated with dinosaur fossils in Montana in 2014 and initially interpreted the Dominican specimens as wasp nests. He proposed a short descriptive paper on wasp nests preserved in hutia mandibles to his colleague Mitchell Riegler, also a Florida Museum doctoral student, who was focused on extinct lizards and initially hesitant to take on what he viewed as a niche side project. The material remained on hold until Riegler received a challenge from a former undergraduate adviser at the University of Texas at Austin to produce a paper within a week.
Riegler selected the putative wasp nests for the contest, expecting a simple project in which the team would scan, describe, and report the trace fossils. He and coauthor Selby Olsen joined Vinola Lopez for an intensive five-day writing session at Vinola Lopez's apartment, each drafting sections before exchanging them for revision. The group initially believed they had a concise description of wasp ichnofossils embedded in vertebrate remains and a strong entry for their rapid-writing competition.
Subsequent reading changed that interpretation. Both Vinola Lopez and Riegler independently encountered an ichnofossil study that described wasp nests made from mixtures of saliva and chewed plant material or dirt, producing rough interior and exterior surfaces. In contrast, many burrowing bees compact soil and then secrete wax from a specialized gland to coat the inside of their nests, creating a smooth, water-resistant lining. The Dominican structures matched the smooth, wax-lined pattern of bee nests rather than the rough, fibrous texture typical of wasps, revealing that the team had attributed the nests to the wrong insects.
This reassignment did not invalidate the basic observation but shifted the focus to a previously undocumented form of bee nesting behavior. Burrowing bees generally nest in open ground, and there is only one other documented case of such bees nesting in a cave. A 2001 study from a Roman necropolis reported bees that drilled into human bones to create their own burrows, but there were no prior records of bees nesting inside fossil cavities without modifying the bone itself. The Cueva de Mono bees instead occupied tooth sockets and other pre-existing voids in skeletal material already deposited in the cave.
Recognizing the novelty of the behavior, the researchers abandoned the one-week paper competition and expanded the project. They consulted entomologists who study modern bees and undertook a year-long review of literature on insect trace fossils and burrowing bee ecology. During this period, Vinola Lopez returned to Cueva de Mono to document the stratigraphy and collect additional material, as plans by a third party to build a nearby house and convert the cave into a septic tank raised concern about the site's preservation, prompting a rapid rescue excavation that recovered many more fossils.
The final study provides a detailed reconstruction of the cave's environmental history and the interactions among owls, hutias, bees, and sedimentary processes. Evidence such as owl bones and eggshells indicates that giant barn owls roosted in Cueva de Mono for many generations, repeatedly bringing hutias and other prey into the cave. In some cases the owls likely consumed their prey in the field and later regurgitated pellets in the cave, further contributing to the accumulation of fragmented bones that later became nesting sites for bees.
CT scans of the fossils revealed that individual alveoli could contain multiple generations of nests. In one hutia jaw, a single tooth socket held six nests stacked within each other, arranged like Russian dolls as bees repeatedly reused the same cavity after earlier broods emerged. Other nests were discovered in different skeletal elements, including the pulp cavity of a sloth tooth from tree sloths that once occurred in parts of the Caribbean but went extinct after humans arrived in the region, and the neural canal of a hutia vertebra through which the animal's spinal cord would have passed in life.
Field conditions around Cueva de Mono help explain why the bees nested inside the cave rather than in surface soils. The surrounding landscape is karst terrain composed of sharp, eroded limestone that has lost most of its natural soil cover, as Riegler experienced firsthand in a fall on the jagged rock. The limited soils that form on the surface are periodically washed into the island's many caves, where fine sediments accumulate in sheltered recesses and provide some of the only suitable habitat for burrowing bees in the area.
Within the cave, bees could excavate short tunnels in the accumulated fine-grained silt and then transition into ready-made cavities in fossil bones as nest cells. The study argues that the combination of scarce surface soils, cave sedimentation, long-term owl occupation, and vertebrate fossil accumulation produced an unusual setting in which bees could adopt this alternative nesting strategy. The authors note that they are continuing to analyze additional fossils from the site, which will be described in future publications at a slower, more conventional pace.
The research team reported their results in the journal Proceedings of the Royal Society B Biological Sciences. The paper documents the ichnofossils in detail, interprets the behavioral sequence that produced them, and links the trace structures to modern analogs of burrowing bee nesting. The authors emphasize that vertebrate fossils can preserve secondary traces that record interactions with other organisms long after the original animals died, expanding the behavioral information available from paleontological sites.
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Florida Museum of Natural History
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